diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 1b04006f..48c534df 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -13,6 +13,7 @@ concurrency:
   cancel-in-progress: true
 
 env:
+  RUSTUP_TOOLCHAIN: stable
   RUSTFLAGS: -Dwarnings
   RUST_BACKTRACE: 1
   rust_min: "1.90.0"
@@ -114,6 +115,8 @@ jobs:
     name: MSRV
     runs-on: ubuntu-latest
     needs: [basics]
+    env:
+      RUSTUP_TOOLCHAIN: "1.90.0"
     steps:
       - uses: actions/checkout@v6
       - uses: dtolnay/rust-toolchain@master
@@ -158,6 +161,9 @@ jobs:
         if: contains(matrix.generator, 'rust-')
       - uses: Swatinem/rust-cache@v2
         if: contains(matrix.generator, 'rust-')
+        with:
+          key: golden-${{ matrix.generator }}
+          workspaces: . -> target/golden-build/${{ matrix.generator }}
       - uses: actions/setup-node@v6
         if: contains(matrix.generator, 'typescript-fetch')
         with:
@@ -180,11 +186,44 @@ jobs:
         if: contains(matrix.generator, 'java-') || contains(matrix.generator, 'kotlin-')
         with:
           distribution: 'temurin'
-          java-version: '17'
+          java-version: '27'
       - uses: gradle/actions/setup-gradle@v6
         if: contains(matrix.generator, 'java-') || contains(matrix.generator, 'kotlin-')
+        with:
+          gradle-version: current
       - run: ${{ matrix.cmd }}
 
+  script-checks:
+    name: Validation Scripts
+    runs-on: ubuntu-latest
+    needs: [basics]
+    steps:
+      - uses: actions/checkout@v6
+      - uses: taiki-e/install-action@just
+      - run: just script-check
+
+  jvm-client-tests:
+    name: JVM Client Tests (${{ matrix.backend }})
+    runs-on: ubuntu-latest
+    needs: [basics]
+    strategy:
+      fail-fast: false
+      matrix:
+        backend: [java, kotlin]
+    steps:
+      - uses: actions/checkout@v6
+      - uses: dtolnay/rust-toolchain@stable
+      - uses: taiki-e/install-action@just
+      - uses: Swatinem/rust-cache@v2
+      - uses: actions/setup-java@v5
+        with:
+          distribution: 'temurin'
+          java-version: '27'
+      - uses: gradle/actions/setup-gradle@v6
+        with:
+          gradle-version: current
+      - run: just golden-jvm::test-${{ matrix.backend }}
+
   rust-client-tests:
     name: Rust Client Tests (${{ matrix.backend }})
     runs-on: ubuntu-latest
@@ -211,6 +250,8 @@ jobs:
     runs-on: ${{ matrix.os }}
     needs: [basics]
     if: github.event_name == 'push' && github.ref == 'refs/heads/main'
+    env:
+      RUSTUP_TOOLCHAIN: "1.90"
     strategy:
       fail-fast: false
       matrix:
diff --git a/.gitignore b/.gitignore
index 244aaf65..420ad9cf 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,6 +8,9 @@ test-output/
 examples/*/generated/
 examples/*/target/
 tests/generated-clients/rust/*/generated/
+tests/generated-clients/jvm/*/generated/
+tests/generated-clients/jvm/**/.gradle/
+tests/generated-clients/jvm/**/build/
 
 # mdbook build output
 docs/book/
diff --git a/Justfile b/Justfile
index 5ba0c759..b7921bf5 100644
--- a/Justfile
+++ b/Justfile
@@ -8,6 +8,7 @@ mod golden-rust 'just/golden-rust.just'
 mod golden-python 'just/golden-python.just'
 mod golden-java 'just/golden-java.just'
 mod golden-kotlin 'just/golden-kotlin.just'
+mod golden-jvm 'just/golden-jvm.just'
 
 # ---------- Build ----------
 
@@ -63,6 +64,10 @@ test-doc:
 # Run all tests (nextest + doctests)
 test-all: test test-doc
 
+# Lint native validation entrypoints
+script-check:
+    shellcheck scripts/golden-build-*.sh scripts/generate-*-client-fixtures.sh
+
 # Run a specific test by name
 test-specific TEST_NAME:
     cargo test {{ TEST_NAME }}
@@ -164,4 +169,4 @@ publish:
 # ---------- CI (run everything locally) ----------
 
 # Run the full CI pipeline locally
-ci: fmt-check clippy doc-check book msrv test-all coverage-lcov golden-check golden-rust::test
+ci: fmt-check clippy doc-check book msrv script-check test-all coverage-lcov golden-build-all golden-rust::test golden-jvm::test
diff --git a/build.rs b/build.rs
index c3d50484..25032029 100644
--- a/build.rs
+++ b/build.rs
@@ -1,161 +1,28 @@
-//! Build script: discover OpenAPI Generator fixtures and generate one `#[test]` per file.
-//! Emits `generated_fixture_tests.rs` into OUT_DIR for inclusion under `#[cfg(test)]`.
+//! Register upstream fixtures with Cargo's native test runner.
 
-use std::collections::HashSet;
-use std::env;
-use std::fs;
-use std::path::{Path, PathBuf};
+use std::{env, fs, path::PathBuf};
 
-const FIXTURES_SUBDIR: &str = "tests/openapi-generator-fixtures";
-const OAS30_PREFIX: &str = "oas30/";
-const OAS31_PREFIX: &str = "oas31/";
-const OAS32_PREFIX: &str = "oas32/";
-const SUPPORTED_EXTENSIONS: &[&str] = &["yaml", "yml", "json"];
-const SKIP_SUFFIX: &str = "tags.json";
-const TEST_FN_PREFIX: &str = "test_oag_fixture_";
-
-/// Load skip paths from `test_fixture_skip_paths.txt` (one path per line; # and blank lines ignored).
-fn load_skip_paths(manifest_dir: &Path) -> Vec<String> {
-    let path = manifest_dir.join("test_fixture_skip_paths.txt");
-    let content = match fs::read_to_string(&path) {
-        Ok(c) => c,
-        Err(_) => return Vec::new(),
-    };
-    content
-        .lines()
-        .map(|line| line.trim())
-        .filter(|line| !line.is_empty() && !line.starts_with('#'))
-        .map(String::from)
-        .collect()
-}
-
-fn is_skip_path(rel: &str, skip_paths: &[String]) -> bool {
-    if rel.ends_with(SKIP_SUFFIX) {
-        return true;
-    }
-    skip_paths.iter().any(|s| s == rel)
-}
-
-fn collect_fixture_paths(
-    dir: &Path,
-    base: &Path,
-    prefix: &str,
-    skip_paths: &[String],
-    out: &mut Vec<String>,
-) {
-    if !dir.exists() {
-        return;
-    }
-    let Ok(entries) = fs::read_dir(dir) else {
-        return;
-    };
-    for e in entries.flatten() {
-        let path = e.path();
-        if path.is_dir() {
-            let name = path.file_name().unwrap().to_string_lossy();
-            collect_fixture_paths(
-                &path,
-                base,
-                &format!("{}{}/", prefix, name),
-                skip_paths,
-                out,
-            );
-        } else if path.is_file() {
-            let rel = path.strip_prefix(base).unwrap_or(&path);
-            let rel_str = rel.to_string_lossy().replace('\\', "/");
-            let full_path = format!("{}{}", prefix, rel_str);
-            let ext_ok = rel
-                .extension()
-                .and_then(|e| e.to_str())
-                .map(|e| SUPPORTED_EXTENSIONS.contains(&e))
-                .unwrap_or(false);
-            if ext_ok && !is_skip_path(&full_path, skip_paths) {
-                out.push(full_path);
-            }
-        }
-    }
-}
-
-/// Sanitize relative path to a valid Rust test function name (alphanumeric and `_` only).
-fn path_to_test_name(rel: &str) -> String {
-    let s: String = rel
-        .chars()
-        .map(|c| match c {
-            '/' | '.' | '-' => '_',
-            c if c.is_ascii_alphanumeric() || c == '_' => c,
-            _ => '_',
-        })
-        .collect();
-    s.trim_matches('_')
-        .split("__")
-        .filter(|p| !p.is_empty())
-        .collect::<Vec<_>>()
-        .join("_")
-}
-
-fn unique_test_name(base_name: &str, taken: &mut HashSet<String>) -> String {
-    let mut name = base_name.to_string();
-    let mut counter = 0u32;
-    while !taken.insert(name.clone()) {
-        counter += 1;
-        name = format!("{}_{}", base_name, counter);
-    }
-    name
-}
+#[path = "build_support/fixture_tests.rs"]
+mod fixture_tests;
 
 fn main() {
-    let out_dir = env::var("OUT_DIR").expect("OUT_DIR");
-    let manifest_dir = env::var("CARGO_MANIFEST_DIR").expect("CARGO_MANIFEST_DIR");
-    let manifest_dir = PathBuf::from(&manifest_dir);
-    let fixtures_base = manifest_dir.join(FIXTURES_SUBDIR);
-
-    println!("cargo::rerun-if-changed={}", fixtures_base.display());
-    println!(
-        "cargo::rerun-if-changed={}",
-        manifest_dir.join("test_fixture_skip_paths.txt").display()
-    );
-
-    let skip_paths = load_skip_paths(&manifest_dir);
-
-    let oas30 = fixtures_base.join("oas30");
-    let oas31 = fixtures_base.join("oas31");
-    let oas32 = fixtures_base.join("oas32");
-    let mut rel_paths = Vec::new();
-    if oas30.exists() {
-        collect_fixture_paths(&oas30, &oas30, OAS30_PREFIX, &skip_paths, &mut rel_paths);
+    let manifest_dir =
+        PathBuf::from(env::var_os("CARGO_MANIFEST_DIR").expect("CARGO_MANIFEST_DIR"));
+    let out_dir = PathBuf::from(env::var_os("OUT_DIR").expect("OUT_DIR"));
+    for input in [
+        "build_support/fixture_tests.rs",
+        "tests/openapi-generator-fixtures",
+        "test_fixture_skip_paths.txt",
+        "test_fixture_rejections.txt",
+    ] {
+        println!(
+            "cargo::rerun-if-changed={}",
+            manifest_dir.join(input).display()
+        );
     }
-    if oas31.exists() {
-        collect_fixture_paths(&oas31, &oas31, OAS31_PREFIX, &skip_paths, &mut rel_paths);
-    }
-    if oas32.exists() {
-        collect_fixture_paths(&oas32, &oas32, OAS32_PREFIX, &skip_paths, &mut rel_paths);
-    }
-    rel_paths.sort();
-
-    let mut test_names = HashSet::new();
-    let lines: Vec<String> = rel_paths
-        .iter()
-        .map(|rel| {
-            let base_name = format!("{}{}", TEST_FN_PREFIX, path_to_test_name(rel));
-            let unique_name = unique_test_name(&base_name, &mut test_names);
-            let rel_escaped = rel.replace('\\', "/").replace('"', r#"\""#);
-            format!(
-                r#"#[test]
-fn {}() {{ super::run_fixture_test("{}"); }}"#,
-                unique_name, rel_escaped
-            )
-        })
-        .collect();
-
-    let content = if lines.is_empty() {
-        r#"// No fixtures found (run scripts/sync-openapi-generator-fixtures.sh).
-#[test]
-fn test_oag_fixture_no_fixtures_placeholder() {}"#
-            .to_string()
-    } else {
-        lines.join("\n\n")
-    };
-
-    let out_path = Path::new(&out_dir).join("generated_fixture_tests.rs");
-    fs::write(out_path, content).expect("write generated_fixture_tests.rs");
+    fs::write(
+        out_dir.join("generated_fixture_tests.rs"),
+        fixture_tests::generate_fixture_tests(&manifest_dir),
+    )
+    .expect("write generated_fixture_tests.rs");
 }
diff --git a/build_support/fixture_tests.rs b/build_support/fixture_tests.rs
new file mode 100644
index 00000000..7b8ce168
--- /dev/null
+++ b/build_support/fixture_tests.rs
@@ -0,0 +1,153 @@
+//! Shared fixture discovery and Cargo test registration used by the build script.
+
+use std::collections::HashSet;
+use std::fs;
+use std::path::Path;
+
+const FIXTURES_SUBDIR: &str = "tests/openapi-generator-fixtures";
+const OAS30_PREFIX: &str = "oas30/";
+const OAS31_PREFIX: &str = "oas31/";
+const OAS32_PREFIX: &str = "oas32/";
+const SUPPORTED_EXTENSIONS: &[&str] = &["yaml", "yml", "json"];
+const SKIP_SUFFIX: &str = "tags.json";
+const TEST_FN_PREFIX: &str = "test_oag_fixture_";
+
+/// Load fixture expectation paths (one per line; # and blank lines ignored).
+fn load_paths(manifest_dir: &Path, filename: &str) -> Vec<String> {
+    let path = manifest_dir.join(filename);
+    let content = match fs::read_to_string(&path) {
+        Ok(c) => c,
+        Err(error) if error.kind() == std::io::ErrorKind::NotFound => return Vec::new(),
+        Err(error) => panic!("cannot read {}: {error}", path.display()),
+    };
+    content
+        .lines()
+        .map(|line| line.trim())
+        .filter(|line| !line.is_empty() && !line.starts_with('#'))
+        .map(String::from)
+        .collect()
+}
+
+fn is_skip_path(rel: &str, skip_paths: &[String]) -> bool {
+    if rel.ends_with(SKIP_SUFFIX) {
+        return true;
+    }
+    skip_paths.iter().any(|s| s == rel)
+}
+
+fn collect_fixture_paths(
+    dir: &Path,
+    base: &Path,
+    prefix: &str,
+    skip_paths: &[String],
+    out: &mut Vec<String>,
+) {
+    let entries = fs::read_dir(dir)
+        .unwrap_or_else(|error| panic!("cannot discover fixtures in {}: {error}", dir.display()));
+    for e in entries {
+        let e = e.expect("fixture directory entry is readable");
+        let path = e.path();
+        if path.is_dir() {
+            collect_fixture_paths(&path, base, prefix, skip_paths, out);
+        } else if path.is_file() {
+            let rel = path.strip_prefix(base).unwrap_or(&path);
+            let rel_str = rel.to_string_lossy().replace('\\', "/");
+            let full_path = format!("{}{}", prefix, rel_str);
+            let ext_ok = rel
+                .extension()
+                .and_then(|e| e.to_str())
+                .map(|e| SUPPORTED_EXTENSIONS.contains(&e))
+                .unwrap_or(false);
+            if ext_ok && !is_skip_path(&full_path, skip_paths) {
+                out.push(full_path);
+            }
+        }
+    }
+}
+
+/// Sanitize relative path to a valid Rust test function name (alphanumeric and `_` only).
+fn path_to_test_name(rel: &str) -> String {
+    let s: String = rel
+        .chars()
+        .map(|c| match c {
+            '/' | '.' | '-' => '_',
+            c if c.is_ascii_alphanumeric() || c == '_' => c,
+            _ => '_',
+        })
+        .collect();
+    s.trim_matches('_')
+        .split("__")
+        .filter(|p| !p.is_empty())
+        .collect::<Vec<_>>()
+        .join("_")
+}
+
+fn unique_test_name(base_name: &str, taken: &mut HashSet<String>) -> String {
+    let mut name = base_name.to_string();
+    let mut counter = 0u32;
+    while !taken.insert(name.clone()) {
+        counter += 1;
+        name = format!("{}_{}", base_name, counter);
+    }
+    name
+}
+
+/// Discover the corpus and emit registrations for Cargo's native test runner.
+pub fn generate_fixture_tests(manifest_dir: &Path) -> String {
+    let fixtures_base = manifest_dir.join(FIXTURES_SUBDIR);
+    let skip_paths = load_paths(manifest_dir, "test_fixture_skip_paths.txt");
+    let rejections = load_paths(manifest_dir, "test_fixture_rejections.txt");
+
+    let oas30 = fixtures_base.join("oas30");
+    let oas31 = fixtures_base.join("oas31");
+    let oas32 = fixtures_base.join("oas32");
+    let mut rel_paths = Vec::new();
+    if oas30.exists() {
+        collect_fixture_paths(&oas30, &oas30, OAS30_PREFIX, &skip_paths, &mut rel_paths);
+    }
+    if oas31.exists() {
+        collect_fixture_paths(&oas31, &oas31, OAS31_PREFIX, &skip_paths, &mut rel_paths);
+    }
+    if oas32.exists() {
+        collect_fixture_paths(&oas32, &oas32, OAS32_PREFIX, &skip_paths, &mut rel_paths);
+    }
+    rel_paths.sort();
+
+    for rejection in &rejections {
+        assert!(
+            rel_paths.binary_search(rejection).is_ok(),
+            "rejection fixture not registered: {rejection} (missing or excluded)"
+        );
+    }
+
+    let mut test_names = HashSet::new();
+    let lines: Vec<String> = rel_paths
+        .iter()
+        .map(|rel| {
+            let base_name = format!("{}{}", TEST_FN_PREFIX, path_to_test_name(rel));
+            let unique_name = unique_test_name(&base_name, &mut test_names);
+            let rel_escaped = rel.replace('\\', "/").replace('"', r#"\""#);
+            let expectation = if rejections.contains(rel) {
+                "#[should_panic(expected = \"parse oas\")]\n"
+            } else {
+                ""
+            };
+            format!(
+                r#"#[test]
+{}fn {}() {{ super::run_fixture_test("{}"); }}"#,
+                expectation, unique_name, rel_escaped
+            )
+        })
+        .collect();
+
+    if lines.is_empty() {
+        r#"// No fixtures found (run scripts/sync-openapi-generator-fixtures.sh).
+#[test]
+fn test_oag_fixture_requires_nonempty_selection() {
+    panic!("no OpenAPI fixtures discovered; run scripts/sync-openapi-generator-fixtures.sh");
+}"#
+        .to_string()
+    } else {
+        lines.join("\n\n")
+    }
+}
diff --git a/docs/src/golden_testing.md b/docs/src/golden_testing.md
index 382b2a26..76771bde 100644
--- a/docs/src/golden_testing.md
+++ b/docs/src/golden_testing.md
@@ -140,6 +140,49 @@ rather than replace, snapshot comparison and the all-golden compile checks.
 See [the consumer test README](https://github.com/rust-codegen-group/openapi-nexus/tree/main/tests/generated-clients/rust)
 for direct Cargo/IDE use and the retained coverage per fixture.
 
+## JVM Client Runtime Tests
+
+Java and Kotlin runtime checks are standalone Gradle consumer builds under
+`tests/generated-clients/jvm/`. `just golden-jvm::test` prepares fresh generated
+dependencies and runs normal JUnit tests, one Gradle invocation per backend.
+Generated manifests are never patched. Each fixture has an isolated consumer
+classpath, and both backends assert union precedence and complete payload
+round-trips, not only wrapper identity or discriminator substrings.
+
+There are no JVM build subprocesses or global directory locks in the Rust test
+suite. The independent JVM Client Tests CI matrix and `just ci` run these checks.
+
+## Validation Contracts and Toolchains
+
+- Missing fixture files fail their parser tests. Nested fixture paths are relative
+  to the fixture tree exactly once; an empty discovery produces a failing test,
+  not a green placeholder. Known malformed upstream documents are executed as
+  explicit expected parse failures in `test_fixture_rejections.txt`. Missing
+  files or read errors cannot satisfy those rejection expectations.
+- Every golden directory must have its build manifest. Native validators reject
+  empty selections and missing manifests instead of reporting `0/0 passed`.
+- Rust golden builds retain their cache under `target/golden-build/rust-<backend>`
+  or the explicitly configured `CARGO_TARGET_DIR`. CI caches the same directory.
+- Python prepares dependencies and resolves pyright once per backend, sharing
+  that environment across its fixtures. `PYTHON` selects the install interpreter;
+  the active `pyright` is used when available, otherwise npm resolves it once.
+- Development and ordinary CI validation select current Rust `stable` (locally
+  validated with Rust 1.99.0). MSRV checks explicitly select Rust 1.90.0; they do
+  not substitute for stable validation.
+- Current local JVM validation uses Homebrew JDK 27 with Gradle 9.8.1, respecting
+  `JAVA_HOME` or the active JVM. CI validates on JDK 27. Generated libraries may
+  still declare a Java 17 compile target, independently of the consumer test JVM.
+
+Fixture discovery is tested in-process through the same build-support module
+used by `build.rs`. Cargo compiles and executes the registered parser tests
+normally; no test harness launches a compiler, build tool, or validation script.
+`just script-check` lints the native build entrypoints. Tool orchestration belongs
+to just/CI, which directly run the golden builds and ordinary consumer projects.
+
+`just ci` includes generator tests and coverage, all nine generators' native
+golden builds, and Rust/JVM consumer tests. Golden comparison is already included
+in `test-all`, so the full recipe does not repeat it as another standalone step.
+
 ## Extra File Detection
 
 The test harness detects when a generator produces files that have no corresponding `.golden` file. This prevents regressions where new output silently goes untested. If a generator adds a new file, the test will fail with a clear message listing the unmatched files and instructing you to run `UPDATE_GOLDEN=1`.
diff --git a/docs/src/ir_reference.md b/docs/src/ir_reference.md
index ccfa3f07..f0eb059a 100644
--- a/docs/src/ir_reference.md
+++ b/docs/src/ir_reference.md
@@ -132,6 +132,12 @@ For object properties, the outer nullable wrapper is recorded in
 container does not make its contents nullable, and nullability is independent
 of whether a property is required.
 
+OpenAPI 3.0 boolean `exclusiveMinimum` / `exclusiveMaximum` flags retain both
+`true` and `false` in validation metadata. The public 3.0 `ObjectSchema` fields
+use `ExclusiveBound` to preserve those booleans as well as the legacy numeric
+form already accepted by the parser. The numeric form retains its previous
+lowering behavior; OpenAPI 3.1/3.2 numeric-bound handling is unchanged.
+
 ## Operations
 
 Each `IrOperation` represents one HTTP method + path:
diff --git a/just/golden-jvm.just b/just/golden-jvm.just
new file mode 100644
index 00000000..87b6c268
--- /dev/null
+++ b/just/golden-jvm.just
@@ -0,0 +1,13 @@
+# Native consumer tests for freshly generated Java and Kotlin clients.
+set working-directory := '..'
+
+test: test-java test-kotlin
+
+@prepare BACKEND:
+    bash ./scripts/generate-jvm-client-fixtures.sh {{ BACKEND }}
+
+@test-java: (prepare "java")
+    gradle --no-daemon --max-workers=2 -p tests/generated-clients/jvm/java test
+
+@test-kotlin: (prepare "kotlin")
+    gradle --no-daemon --max-workers=2 -p tests/generated-clients/jvm/kotlin test
diff --git a/rust-toolchain.toml b/rust-toolchain.toml
index 8cf9c187..73cb934d 100644
--- a/rust-toolchain.toml
+++ b/rust-toolchain.toml
@@ -1,3 +1,3 @@
 [toolchain]
-channel = "1.90"
+channel = "stable"
 components = ["rustfmt", "clippy"]
diff --git a/scripts/generate-jvm-client-fixtures.sh b/scripts/generate-jvm-client-fixtures.sh
new file mode 100644
index 00000000..78e557df
--- /dev/null
+++ b/scripts/generate-jvm-client-fixtures.sh
@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+backend="${1:?Usage: generate-jvm-client-fixtures.sh <java|kotlin>}"
+case "$backend" in
+  java|kotlin) ;;
+  *) echo "unsupported JVM backend: $backend" >&2; exit 1 ;;
+esac
+root="$(cd "$(dirname "$0")/.." && pwd)"
+project="$root/tests/generated-clients/jvm/$backend"
+
+while read -r name fixture; do
+  case "$name" in
+    ""|\#*) continue ;;
+    *[!a-zA-Z0-9_-]*) echo "invalid fixture name: $name" >&2; exit 1 ;;
+  esac
+  output="$project/generated/$name"
+  # Only these fixed, ignored fixture output directories are disposable.
+  rm -rf "$output"
+  cargo run --quiet --manifest-path "$root/Cargo.toml" --bin openapi-nexus -- generate \
+    --config "$root/tests/generated-clients/config.toml" \
+    --input "$root/tests/fixtures/$fixture" --output "$output" --generators "$backend-okhttp"
+done < "$root/tests/generated-clients/jvm/fixtures.txt"
diff --git a/scripts/generate-rust-client-fixtures.sh b/scripts/generate-rust-client-fixtures.sh
index ba5927e9..12a690cf 100644
--- a/scripts/generate-rust-client-fixtures.sh
+++ b/scripts/generate-rust-client-fixtures.sh
@@ -16,7 +16,7 @@ for fixture in typed-error-responses rust-error-payload-shapes nested-nullable;
   # Remove stale source files so a deleted declaration cannot pass unnoticed.
   rm -rf "$output"
   cargo run --quiet --manifest-path "$root/Cargo.toml" --bin openapi-nexus -- generate \
-    --config "$root/tests/generated-clients/rust/config.toml" \
+    --config "$root/tests/generated-clients/config.toml" \
     --input "$root/tests/fixtures/valid/$fixture.yaml" \
     --output "$output" \
     --generators "rust-$backend"
diff --git a/scripts/golden-build-common.sh b/scripts/golden-build-common.sh
new file mode 100644
index 00000000..f58cbd8a
--- /dev/null
+++ b/scripts/golden-build-common.sh
@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+# Shared input contracts for every native golden validator.
+
+golden_require_projects() {
+  local directory="$1" marker="$2" project count=0
+  if [ ! -d "$directory" ]; then
+    echo "error: golden dir not found: $directory" >&2
+    return 1
+  fi
+  for project in "$directory"/*/; do
+    [ -d "$project" ] || continue
+    if [ ! -f "$project/$marker" ]; then
+      echo "error: missing $marker in $project" >&2
+      return 1
+    fi
+    count=$((count + 1))
+  done
+  golden_require_selection "$count"
+}
+
+golden_require_selection() {
+  if [ "$1" -eq 0 ]; then
+    echo "error: no golden projects selected; no compilation was performed" >&2
+    return 1
+  fi
+}
diff --git a/scripts/golden-build-go.sh b/scripts/golden-build-go.sh
index c1ac1094..91b33dae 100755
--- a/scripts/golden-build-go.sh
+++ b/scripts/golden-build-go.sh
@@ -4,10 +4,9 @@ set -euo pipefail
 root="$(cd "$(dirname "$0")/.." && pwd)"
 golden="$root/tests/golden/go/go-http"
 
-if [ ! -d "$golden" ]; then
-  echo "error: golden dir not found: $golden" >&2
-  exit 1
-fi
+# shellcheck source=./scripts/golden-build-common.sh
+source "$root/scripts/golden-build-common.sh"
+golden_require_projects "$golden" go.mod.golden
 
 total=0; passed=0; failed=0; fails=()
 
@@ -43,6 +42,7 @@ for test_dir in "$golden"/*/; do
 done
 
 echo
+golden_require_selection "$total"
 echo "Go: $passed/$total passed"
 if [ "$failed" -gt 0 ]; then
   echo "failed:"
diff --git a/scripts/golden-build-java.sh b/scripts/golden-build-java.sh
index 67258c8a..de08b94b 100755
--- a/scripts/golden-build-java.sh
+++ b/scripts/golden-build-java.sh
@@ -4,10 +4,9 @@ set -euo pipefail
 root="$(cd "$(dirname "$0")/.." && pwd)"
 golden="$root/tests/golden/java/java-okhttp"
 
-if [ ! -d "$golden" ]; then
-  echo "error: golden dir not found: $golden" >&2
-  exit 1
-fi
+# shellcheck source=./scripts/golden-build-common.sh
+source "$root/scripts/golden-build-common.sh"
+golden_require_projects "$golden" build.gradle.golden
 
 tmp=$(mktemp -d)
 log=$(mktemp)
@@ -45,10 +44,7 @@ SETTINGS
 done
 
 echo
-if [ "$total" -eq 0 ]; then
-  echo "Java: 0/0 passed"
-  exit 0
-fi
+golden_require_selection "$total"
 
 echo "Java: compiling $total golden projects"
 if (cd "$tmp" && gradle --no-daemon --quiet --parallel --continue "${tasks[@]}") >"$log" 2>&1; then
diff --git a/scripts/golden-build-kotlin.sh b/scripts/golden-build-kotlin.sh
index 328cebcd..042f3adf 100755
--- a/scripts/golden-build-kotlin.sh
+++ b/scripts/golden-build-kotlin.sh
@@ -4,10 +4,9 @@ set -euo pipefail
 root="$(cd "$(dirname "$0")/.." && pwd)"
 golden="$root/tests/golden/kotlin/kotlin-okhttp"
 
-if [ ! -d "$golden" ]; then
-  echo "error: golden dir not found: $golden" >&2
-  exit 1
-fi
+# shellcheck source=./scripts/golden-build-common.sh
+source "$root/scripts/golden-build-common.sh"
+golden_require_projects "$golden" build.gradle.kts.golden
 
 tmp=$(mktemp -d)
 log=$(mktemp)
@@ -45,10 +44,7 @@ SETTINGS
 done
 
 echo
-if [ "$total" -eq 0 ]; then
-  echo "Kotlin: 0/0 passed"
-  exit 0
-fi
+golden_require_selection "$total"
 
 echo "Kotlin: compiling $total golden projects"
 if (cd "$tmp" && gradle --no-daemon --quiet --parallel --continue "${tasks[@]}") >"$log" 2>&1; then
diff --git a/scripts/golden-build-python.sh b/scripts/golden-build-python.sh
index 2af8f89c..7a135b46 100755
--- a/scripts/golden-build-python.sh
+++ b/scripts/golden-build-python.sh
@@ -6,9 +6,24 @@ backend="${1:?Usage: golden-build-python.sh <httpx|requests>}"
 root="$(cd "$(dirname "$0")/.." && pwd)"
 golden="$root/tests/golden/python/python-$backend"
 
-if [ ! -d "$golden" ]; then
-  echo "error: golden dir not found: $golden" >&2
-  exit 1
+# shellcheck source=./scripts/golden-build-common.sh
+source "$root/scripts/golden-build-common.sh"
+golden_require_projects "$golden" pyproject.toml.golden
+
+# One dependency installation and checker resolution per backend, not per fixture.
+deps=$(mktemp -d)
+tmp=""; log=""
+cleanup() {
+  rm -rf "$deps"
+  [ -z "$tmp" ] || rm -rf "$tmp"
+  [ -z "$log" ] || rm -f "$log"
+}
+trap cleanup EXIT
+"${PYTHON:-python3}" -m pip install "$backend" --quiet --target "$deps"
+if command -v pyright >/dev/null 2>&1; then
+  checker=$(command -v pyright)
+else
+  checker=$(npm exec --yes --package pyright -- which pyright)
 fi
 
 total=0; passed=0; failed=0; fails=()
@@ -20,7 +35,6 @@ for test_dir in "$golden"/*/; do
   printf "[%d] %s... " "$total" "$name"
 
   tmp=$(mktemp -d)
-  trap 'rm -rf "$tmp"' EXIT
 
   while IFS= read -r -d '' f; do
     rel="${f#"$test_dir"}"
@@ -29,19 +43,17 @@ for test_dir in "$golden"/*/; do
     cp "$f" "$dst"
   done < <(find "$test_dir" -type f -name '*.golden' -print0)
 
-  pip3 install "$backend" --quiet --target "$tmp/.deps" 2>/dev/null
-
   cat > "$tmp/pyrightconfig.json" <<PYRIGHT
 {
     "pythonVersion": "3.12",
     "typeCheckingMode": "strict",
-    "extraPaths": [".deps"],
+    "extraPaths": ["$deps"],
     "reportUnnecessaryIsInstance": "none"
 }
 PYRIGHT
 
   log=$(mktemp)
-  if (cd "$tmp" && npx pyright) >"$log" 2>&1; then
+  if (cd "$tmp" && "$checker") >"$log" 2>&1; then
     echo "ok"
     passed=$((passed + 1))
   else
@@ -52,10 +64,11 @@ PYRIGHT
   fi
 
   rm -rf "$tmp" "$log"
-  trap - EXIT
+  tmp=""; log=""
 done
 
 echo
+golden_require_selection "$total"
 echo "Python-$backend: $passed/$total passed"
 if [ "$failed" -gt 0 ]; then
   echo "failed:"
diff --git a/scripts/golden-build-rust.sh b/scripts/golden-build-rust.sh
index e92ee8e8..4bcda893 100755
--- a/scripts/golden-build-rust.sh
+++ b/scripts/golden-build-rust.sh
@@ -6,12 +6,16 @@ backend="${1:?Usage: golden-build-rust.sh <reqwest|ureq|aioduct>}"
 root="$(cd "$(dirname "$0")/.." && pwd)"
 golden="$root/tests/golden/rust/rust-$backend"
 
-if [ ! -d "$golden" ]; then
-  echo "error: golden dir not found: $golden" >&2
-  exit 1
-fi
-
-shared_target=$(mktemp -d)
+# shellcheck source=./scripts/golden-build-common.sh
+source "$root/scripts/golden-build-common.sh"
+golden_require_projects "$golden" Cargo.toml.golden
+
+shared_target="${CARGO_TARGET_DIR:-$root/target/golden-build/rust-$backend}"
+case "$shared_target" in
+  /*) ;;
+  *) shared_target="$PWD/$shared_target" ;;
+esac
+mkdir -p "$shared_target"
 total=0; passed=0; failed=0; fails=()
 
 for test_dir in "$golden"/*/; do
@@ -45,7 +49,7 @@ for test_dir in "$golden"/*/; do
   trap - EXIT
 done
 
-rm -rf "$shared_target"
+golden_require_selection "$total"
 
 echo
 echo "Rust-$backend: $passed/$total passed"
diff --git a/scripts/golden-build-typescript.sh b/scripts/golden-build-typescript.sh
index b65cd2fc..786f3115 100755
--- a/scripts/golden-build-typescript.sh
+++ b/scripts/golden-build-typescript.sh
@@ -4,10 +4,9 @@ set -euo pipefail
 root="$(cd "$(dirname "$0")/.." && pwd)"
 golden="$root/tests/golden/typescript/typescript-fetch"
 
-if [ ! -d "$golden" ]; then
-  echo "error: golden dir not found: $golden" >&2
-  exit 1
-fi
+# shellcheck source=./scripts/golden-build-common.sh
+source "$root/scripts/golden-build-common.sh"
+golden_require_projects "$golden" tsconfig.json.golden
 
 toolchain="${1:-}"
 if [ "$toolchain" != "tsc" ] && [ "$toolchain" != "vp" ]; then
@@ -73,6 +72,7 @@ for test_dir in "$golden"/*/; do
 done
 
 echo
+golden_require_selection "$total"
 echo "TypeScript ($toolchain): $passed/$total passed"
 if [ "$failed" -gt 0 ]; then
   echo "failed:"
diff --git a/src/ir/lower/v30.rs b/src/ir/lower/v30.rs
index d9e41ed7..40b90535 100644
--- a/src/ir/lower/v30.rs
+++ b/src/ir/lower/v30.rs
@@ -1291,9 +1291,15 @@ fn extract_validation(obj: &ObjectSchema) -> Option<IrValidation> {
         min_length: obj.min_length,
         pattern: obj.pattern.clone(),
         maximum: obj.maximum.as_ref().and_then(|n| n.as_f64()),
-        exclusive_maximum: obj.exclusive_maximum.as_ref().map(|_| true),
+        exclusive_maximum: obj
+            .exclusive_maximum
+            .as_ref()
+            .map(|bound| bound.is_exclusive()),
         minimum: obj.minimum.as_ref().and_then(|n| n.as_f64()),
-        exclusive_minimum: obj.exclusive_minimum.as_ref().map(|_| true),
+        exclusive_minimum: obj
+            .exclusive_minimum
+            .as_ref()
+            .map(|bound| bound.is_exclusive()),
         multiple_of: obj.multiple_of.as_ref().and_then(|n| n.as_f64()),
         max_items: obj.max_items,
         min_items: obj.min_items,
diff --git a/src/spec/oas30/spec/schema.rs b/src/spec/oas30/spec/schema.rs
index 7cd55160..c3b3dd98 100644
--- a/src/spec/oas30/spec/schema.rs
+++ b/src/spec/oas30/spec/schema.rs
@@ -32,6 +32,24 @@ pub enum AdditionalProperties {
     Schema(Box<Schema>),
 }
 
+/// OpenAPI 3.0 uses boolean exclusivity flags. Retain the previously accepted
+/// numeric representation for compatibility with generated specifications.
+#[derive(Debug, Clone, PartialEq, Deserialize, Serialize)]
+#[serde(untagged)]
+pub enum ExclusiveBound {
+    Boolean(bool),
+    Number(serde_json::Number),
+}
+
+impl ExclusiveBound {
+    pub fn is_exclusive(&self) -> bool {
+        match self {
+            Self::Boolean(value) => *value,
+            Self::Number(_) => true,
+        }
+    }
+}
+
 /// A schema object allows the definition of input and output data types.
 /// OAS 3.0 uses a single `type` string and optional `nullable` boolean.
 #[derive(Debug, Clone, PartialEq, Default, Deserialize, Serialize)]
@@ -71,13 +89,13 @@ pub struct ObjectSchema {
     pub maximum: Option<serde_json::Number>,
 
     #[serde(rename = "exclusiveMaximum", skip_serializing_if = "Option::is_none")]
-    pub exclusive_maximum: Option<serde_json::Number>,
+    pub exclusive_maximum: Option<ExclusiveBound>,
 
     #[serde(skip_serializing_if = "Option::is_none")]
     pub minimum: Option<serde_json::Number>,
 
     #[serde(rename = "exclusiveMinimum", skip_serializing_if = "Option::is_none")]
-    pub exclusive_minimum: Option<serde_json::Number>,
+    pub exclusive_minimum: Option<ExclusiveBound>,
 
     #[serde(rename = "maxLength", skip_serializing_if = "Option::is_none")]
     pub max_length: Option<u64>,
diff --git a/src/spec/test_utils.rs b/src/spec/test_utils.rs
index b7113991..29226931 100644
--- a/src/spec/test_utils.rs
+++ b/src/spec/test_utils.rs
@@ -1,6 +1,5 @@
 //! Test-only utilities for fixture-based spec parsing tests.
 
-use std::env;
 use std::fs;
 use std::path::Path;
 use std::path::PathBuf;
@@ -11,34 +10,12 @@ const FIXTURES_SUBDIR: &str = "tests/openapi-generator-fixtures";
 const OAS30_PREFIX: &str = "oas30/";
 const OAS31_PREFIX: &str = "oas31/";
 
-/// Candidate base directories for the fixtures tree (order matters: first found wins).
-fn fixture_base_candidates() -> Vec<PathBuf> {
-    let mut candidates = Vec::new();
-    if let Ok(manifest_dir) = env::var("CARGO_MANIFEST_DIR") {
-        candidates.push(
-            Path::new(&manifest_dir)
-                .join("..")
-                .join("..")
-                .join(FIXTURES_SUBDIR),
-        );
-        candidates.push(Path::new(&manifest_dir).join("..").join(FIXTURES_SUBDIR));
-    }
-    candidates.extend([
-        Path::new(FIXTURES_SUBDIR).to_path_buf(),
-        Path::new("../").join(FIXTURES_SUBDIR),
-        Path::new("../../").join(FIXTURES_SUBDIR),
-        Path::new("../../../").join(FIXTURES_SUBDIR),
-    ]);
-    candidates
-}
-
-/// Resolve `rel_path` to an absolute path under one of the candidate fixture bases.
-/// Returns `None` if the path does not exist under any candidate (e.g. stale generated test).
+/// Resolve a fixture under this checkout, independent of the test's working directory.
 fn resolve_fixture_path(rel_path: &str) -> Option<PathBuf> {
-    fixture_base_candidates().into_iter().find_map(|base| {
-        let p = base.join(rel_path);
-        if p.exists() { Some(p) } else { None }
-    })
+    let path = Path::new(env!("CARGO_MANIFEST_DIR"))
+        .join(FIXTURES_SUBDIR)
+        .join(rel_path);
+    path.is_file().then_some(path)
 }
 
 /// Parse fixture content as OAS 3.0 or 3.1 spec based on `rel_path` prefix.
@@ -61,14 +38,20 @@ fn parse_fixture(content: &str, ext: &str, rel_path: &str) {
 }
 
 /// Load fixture at `rel_path`, parse as OAS 3.0 or 3.1, and panic on error.
-/// Skips (passes) if the path does not exist under any candidate (stale generated test).
 pub fn run_fixture_test(rel_path: &str) {
-    let path = match resolve_fixture_path(rel_path) {
-        Some(p) => p,
-        None => return, // path missing, e.g. stale generated test; skip
-    };
+    let path =
+        resolve_fixture_path(rel_path).unwrap_or_else(|| panic!("fixture not found: {rel_path}"));
     let content =
         fs::read_to_string(&path).unwrap_or_else(|e| panic!("read {}: {}", path.display(), e));
     let ext = path.extension().and_then(|e| e.to_str()).unwrap_or("");
     parse_fixture(&content, ext, rel_path);
 }
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    #[should_panic(expected = "fixture not found")]
+    fn missing_fixture_is_a_failure_not_a_passing_parser_test() {
+        super::run_fixture_test("oas30/__missing_fixture_regression__.yaml");
+    }
+}
diff --git a/test_fixture_rejections.txt b/test_fixture_rejections.txt
new file mode 100644
index 00000000..626510d4
--- /dev/null
+++ b/test_fixture_rejections.txt
@@ -0,0 +1,28 @@
+# Explicit rejection cases: these files are exercised, not silently skipped.
+# Each registered test must fail during spec parsing, not file loading.
+
+# Swagger 2 documents placed in the upstream oas30 tree (no openapi field).
+oas30/cpp-ue4/petstore.yaml
+oas30/spring/petstore-with-spring-provide-args.yaml
+# Schema fragment without required document-level info/paths.
+oas30/csharp/composed-enum.yaml
+# Invalid string values `required: optional` where OpenAPI requires booleans.
+oas30/dart/petstore-with-fake-endpoints-models-for-testing.yaml
+oas30/elixir/petstore-with-fake-endpoints-models-for-testing.yaml
+oas30/javascript/petstore-with-fake-endpoints-models-for-testing.yaml
+oas30/jaxrs-spec/petstore-with-fake-endpoints-models-for-testing.yaml
+oas30/k6/petstore-with-fake-endpoints-models-for-testing.yaml
+oas30/perl/petstore-with-fake-endpoints-models-for-testing.yaml
+oas30/php-nextgen/petstore-with-fake-endpoints-models-for-testing.yaml
+oas30/php/petstore-with-fake-endpoints-models-for-testing.yaml
+oas30/python/petstore-with-fake-endpoints-models-for-testing.yaml
+oas30/ruby/petstore-with-fake-endpoints-models-for-testing.yaml
+oas30/spring/petstore-with-fake-endpoints-models-for-testing-x-implements.yaml
+# Empty/null response objects rather than Response Objects.
+oas30/kotlin/issue21238_queryParam_validation.yaml
+# Schema.required is a boolean, not a list of required property names.
+oas30/kotlin/petstore-with-tags.yaml
+# Unquoted YAML null key where a string property name is required.
+oas30/kotlin/reserved_words.yaml
+# Numeric YAML parameter names where OpenAPI requires string names.
+oas30/python/petstore-with-fake-endpoints-models-for-testing-with-http-signature.yaml
diff --git a/test_fixture_skip_paths.txt b/test_fixture_skip_paths.txt
index 60321285..d1465237 100644
--- a/test_fixture_skip_paths.txt
+++ b/test_fixture_skip_paths.txt
@@ -27,14 +27,7 @@ oas30/v1beta3.yaml
 oas30/validation.yaml
 oas31/exclusive-min-max.yaml
 #
-# Stale / wrong spec (e.g. cpp-ue4/petstore is Swagger 2.0)
-oas30/cpp-ue4/cpp-ue4/petstore.yaml
-oas30/csharp/csharp/composed-enum.yaml
-oas30/csharp/csharp/composed_enum.yaml
-#
-# asciidoc (and stale duplicated-path variants if present)
-oas30/asciidoc/asciidoc/api-docs.json
-oas30/asciidoc/generated-snippets/rest/project/GET/asciidoc/generated-snippets/rest/project/GET/GET.json
+# asciidoc fragments (malformed complete documents are in test_fixture_rejections.txt)
 oas30/asciidoc/api-docs.json
 oas30/asciidoc/generated-snippets/rest/project/GET/GET.json
 #
diff --git a/tests/fixture_discovery.rs b/tests/fixture_discovery.rs
new file mode 100644
index 00000000..8eb23fe7
--- /dev/null
+++ b/tests/fixture_discovery.rs
@@ -0,0 +1,60 @@
+//! Exercise the actual build-support logic in-process, without compiling a harness.
+
+use std::{fs, path::Path};
+
+#[path = "../build_support/fixture_tests.rs"]
+mod fixture_tests;
+
+#[test]
+fn nested_fixture_paths_resolve_once_under_the_corpus() {
+    let root = Path::new(env!("CARGO_MANIFEST_DIR"));
+    let registrations = fixture_tests::generate_fixture_tests(root);
+    assert!(registrations.contains("super::run_fixture_test(\"oas30/ada/petstore.yaml\")"));
+
+    let paths: Vec<_> = registrations
+        .lines()
+        .filter_map(|line| line.split_once("super::run_fixture_test(\""))
+        .map(|(_, rest)| rest.split_once('"').expect("registered path ends").0)
+        .collect();
+    assert!(!paths.is_empty(), "the corpus must register real fixtures");
+    for relative in paths {
+        let path = root.join("tests/openapi-generator-fixtures").join(relative);
+        fs::read_to_string(&path)
+            .unwrap_or_else(|error| panic!("registered fixture {}: {error}", path.display()));
+    }
+}
+
+#[test]
+fn empty_discovery_registers_a_failure_instead_of_a_passing_placeholder() {
+    // This checked-in directory has no upstream corpus or expectation manifests.
+    let root = Path::new(env!("CARGO_MANIFEST_DIR")).join("tests/fixtures/valid");
+    assert!(root.is_dir());
+    assert_eq!(
+        fixture_tests::generate_fixture_tests(&root),
+        r#"// No fixtures found (run scripts/sync-openapi-generator-fixtures.sh).
+#[test]
+fn test_oag_fixture_requires_nonempty_selection() {
+    panic!("no OpenAPI fixtures discovered; run scripts/sync-openapi-generator-fixtures.sh");
+}"#
+    );
+}
+
+#[test]
+#[should_panic(expected = "rejection fixture not registered: oas30/missing.yaml")]
+fn missing_rejection_fixture_fails_even_when_other_fixtures_are_registered() {
+    let root =
+        Path::new(env!("CARGO_MANIFEST_DIR")).join("tests/fixtures/discovery/missing-rejection");
+    fixture_tests::generate_fixture_tests(&root);
+}
+
+#[test]
+#[should_panic(expected = "rejection fixture not registered: oas30/rejected.yaml")]
+fn excluded_rejection_fixture_fails_even_when_its_file_exists() {
+    let root =
+        Path::new(env!("CARGO_MANIFEST_DIR")).join("tests/fixtures/discovery/excluded-rejection");
+    assert!(
+        root.join("tests/openapi-generator-fixtures/oas30/rejected.yaml")
+            .is_file()
+    );
+    fixture_tests::generate_fixture_tests(&root);
+}
diff --git a/tests/fixtures/discovery/excluded-rejection/test_fixture_rejections.txt b/tests/fixtures/discovery/excluded-rejection/test_fixture_rejections.txt
new file mode 100644
index 00000000..b3cad356
--- /dev/null
+++ b/tests/fixtures/discovery/excluded-rejection/test_fixture_rejections.txt
@@ -0,0 +1 @@
+oas30/rejected.yaml
diff --git a/tests/fixtures/discovery/excluded-rejection/test_fixture_skip_paths.txt b/tests/fixtures/discovery/excluded-rejection/test_fixture_skip_paths.txt
new file mode 100644
index 00000000..b3cad356
--- /dev/null
+++ b/tests/fixtures/discovery/excluded-rejection/test_fixture_skip_paths.txt
@@ -0,0 +1 @@
+oas30/rejected.yaml
diff --git a/tests/fixtures/discovery/excluded-rejection/tests/openapi-generator-fixtures/oas30/present.yaml b/tests/fixtures/discovery/excluded-rejection/tests/openapi-generator-fixtures/oas30/present.yaml
new file mode 100644
index 00000000..56b93dd3
--- /dev/null
+++ b/tests/fixtures/discovery/excluded-rejection/tests/openapi-generator-fixtures/oas30/present.yaml
@@ -0,0 +1,5 @@
+openapi: 3.0.3
+info:
+  title: Present fixture
+  version: '1'
+paths: {}
diff --git a/tests/fixtures/discovery/excluded-rejection/tests/openapi-generator-fixtures/oas30/rejected.yaml b/tests/fixtures/discovery/excluded-rejection/tests/openapi-generator-fixtures/oas30/rejected.yaml
new file mode 100644
index 00000000..1577e224
--- /dev/null
+++ b/tests/fixtures/discovery/excluded-rejection/tests/openapi-generator-fixtures/oas30/rejected.yaml
@@ -0,0 +1,5 @@
+swagger: '2.0'
+info:
+  title: Rejected fixture
+  version: '1'
+paths: {}
diff --git a/tests/fixtures/discovery/missing-rejection/test_fixture_rejections.txt b/tests/fixtures/discovery/missing-rejection/test_fixture_rejections.txt
new file mode 100644
index 00000000..e838e90a
--- /dev/null
+++ b/tests/fixtures/discovery/missing-rejection/test_fixture_rejections.txt
@@ -0,0 +1 @@
+oas30/missing.yaml
diff --git a/tests/fixtures/discovery/missing-rejection/tests/openapi-generator-fixtures/oas30/present.yaml b/tests/fixtures/discovery/missing-rejection/tests/openapi-generator-fixtures/oas30/present.yaml
new file mode 100644
index 00000000..56b93dd3
--- /dev/null
+++ b/tests/fixtures/discovery/missing-rejection/tests/openapi-generator-fixtures/oas30/present.yaml
@@ -0,0 +1,5 @@
+openapi: 3.0.3
+info:
+  title: Present fixture
+  version: '1'
+paths: {}
diff --git a/tests/generated-clients/rust/config.toml b/tests/generated-clients/config.toml
similarity index 100%
rename from tests/generated-clients/rust/config.toml
rename to tests/generated-clients/config.toml
diff --git a/tests/generated-clients/jvm/README.md b/tests/generated-clients/jvm/README.md
new file mode 100644
index 00000000..415af281
--- /dev/null
+++ b/tests/generated-clients/jvm/README.md
@@ -0,0 +1,45 @@
+# JVM generated-client tests
+
+Java and Kotlin each have an independent Gradle consumer build. The public CLI
+generates the six inputs in `fixtures.txt` into ignored `generated/` directories.
+Generated manifests and source are used unchanged. Each fixture has a separate
+consumer subproject, so identically named SDK classes do not share a classpath.
+
+```bash
+just golden-jvm::test
+just golden-jvm::test-java
+just golden-jvm::test-kotlin
+
+# Prepare once, then run a normal Gradle test directly or from an IDE.
+just golden-jvm::prepare java
+gradle -p tests/generated-clients/jvm/java test
+gradle -p tests/generated-clients/jvm/java :cases:any-union:test
+```
+
+Test sources and dependency lockfiles are checked in under each build's `cases/`
+tree. Update locks intentionally with
+`gradle -p tests/generated-clients/jvm/java test --write-locks` (and the
+corresponding Kotlin command). A single Gradle build runs all fixtures for a
+backend and retains normal Gradle caches; Rust tests no longer write JVM programs, patch Gradle files,
+launch Gradle, or acquire global directory locks. Interrupted processes therefore
+cannot leave the previous harness's lock directories behind.
+
+The cases retain charset/header decoding, union dispatch, explicit nulls, and
+tagged/untagged shapes. They additionally verify that string/number alternatives
+win before `Any`, that fallback payloads are preserved, and that discriminator,
+adjacent, and external round-trips retain complete JSON and decoded payloads.
+
+The runner respects `JAVA_HOME` or Gradle's active JVM. Current local validation
+uses Homebrew JDK 27 and Gradle 9.8.1; CI also runs the JVM validation on JDK 27.
+Generated libraries keep their declared Java 17 compilation target. The Foojay
+resolver supplies that compiler where needed, without forcing the consumer tests
+to run on an older JVM. No patch-versioned JDK installation path is baked into
+the tests.
+
+On JDK 27, the generated Kotlin clients' Gson 2.11.0 emits final-field reflection
+warnings; Kotlin's Gradle plugin also reports Gradle 10 deprecations. Tests do
+not suppress either warning or rewrite generated dependencies to hide them.
+
+Run this matrix separately from generator coverage. `just ci` and the CI JVM
+Client Tests matrix include it. Regenerate after any generator or fixture change;
+do not edit generated dependencies to make a test pass.
diff --git a/tests/generated-clients/jvm/build-common.gradle b/tests/generated-clients/jvm/build-common.gradle
new file mode 100644
index 00000000..b6e3aa95
--- /dev/null
+++ b/tests/generated-clients/jvm/build-common.gradle
@@ -0,0 +1,28 @@
+apply plugin: "java"
+
+subprojects {
+    if (path.startsWith(":cases:")) {
+        apply plugin: "java"
+        if (fileTree("src/test/java").matching { include "**/*Test.java" }.isEmpty()) {
+            throw new GradleException("No consumer tests found in ${projectDir}")
+        }
+        repositories { mavenCentral() }
+        dependencyLocking { lockAllConfigurations() }
+        dependencies {
+            testImplementation project(":clients:${project.name}")
+            testImplementation platform("org.junit:junit-bom:5.12.2")
+            testImplementation "org.junit.jupiter:junit-jupiter"
+            testRuntimeOnly "org.junit.platform:junit-platform-launcher"
+            testImplementation "com.google.code.gson:gson:2.11.0"
+            testImplementation "com.squareup.okhttp3:okhttp:4.12.0"
+        }
+        tasks.named("test") {
+            useJUnitPlatform()
+            testLogging { events "passed", "skipped", "failed" }
+        }
+    }
+}
+
+tasks.named("test") {
+    dependsOn subprojects.findAll { it.path.startsWith(":cases:") }.collect { "${it.path}:test" }
+}
diff --git a/tests/generated-clients/jvm/fixtures.txt b/tests/generated-clients/jvm/fixtures.txt
new file mode 100644
index 00000000..b3cd81ab
--- /dev/null
+++ b/tests/generated-clients/jvm/fixtures.txt
@@ -0,0 +1,7 @@
+# Consumer project name and input under tests/fixtures/.
+typed-error-responses valid/typed-error-responses.yaml
+closed-sum valid/type-aliases/closed-sum-payload-shapes.yaml
+object-union valid/comprehensive-schemas.yaml
+any-union valid/type-aliases/union-with-any.yaml
+tagged-union valid/type-aliases/discriminated-union-mixed-unit-and-allof.yaml
+tagged-shapes valid/enum-repr/enum-repr.yaml
diff --git a/tests/generated-clients/jvm/java/build.gradle b/tests/generated-clients/jvm/java/build.gradle
new file mode 100644
index 00000000..40528512
--- /dev/null
+++ b/tests/generated-clients/jvm/java/build.gradle
@@ -0,0 +1 @@
+apply from: file("../build-common.gradle")
diff --git a/tests/generated-clients/jvm/java/cases/any-union/gradle.lockfile b/tests/generated-clients/jvm/java/cases/any-union/gradle.lockfile
new file mode 100644
index 00000000..ee58d791
--- /dev/null
+++ b/tests/generated-clients/jvm/java/cases/any-union/gradle.lockfile
@@ -0,0 +1,25 @@
+# This is a Gradle generated file for dependency locking.
+# Manual edits can break the build and are not advised.
+# This file is expected to be part of source control.
+# To regenerate this file, run: ./gradlew :cases:any-union:dependencies --write-locks
+com.google.code.gson:gson:2.11.0=testCompileClasspath,testRuntimeClasspath
+com.google.errorprone:error_prone_annotations:2.27.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okhttp3:okhttp:4.12.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio-jvm:3.6.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio:3.6.0=testCompileClasspath,testRuntimeClasspath
+org.apiguardian:apiguardian-api:1.1.2=testCompileClasspath
+org.jetbrains.kotlin:kotlin-stdlib-common:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains:annotations:13.0=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-api:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-engine:5.12.2=testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-params:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-commons:1.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-engine:1.12.2=testRuntimeClasspath
+org.junit.platform:junit-platform-launcher:1.12.2=testRuntimeClasspath
+org.junit:junit-bom:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.opentest4j:opentest4j:1.3.0=testCompileClasspath,testRuntimeClasspath
+empty=testAnnotationProcessor
diff --git a/tests/generated-clients/jvm/java/cases/any-union/src/test/java/AnyUnionTest.java b/tests/generated-clients/jvm/java/cases/any-union/src/test/java/AnyUnionTest.java
new file mode 100644
index 00000000..9ae9bbc1
--- /dev/null
+++ b/tests/generated-clients/jvm/java/cases/any-union/src/test/java/AnyUnionTest.java
@@ -0,0 +1,29 @@
+import com.example.sdk.models.Config;
+import com.google.gson.Gson;
+import com.google.gson.JsonParser;
+import static org.junit.jupiter.api.Assertions.*;
+
+public final class AnyUnionTest {
+    private final Gson gson = new Gson();
+
+    @org.junit.jupiter.api.Test
+    void stringPrefersItsSpecificVariantOverAny() {
+        Config.VariantString value = assertInstanceOf(Config.VariantString.class, gson.fromJson("\"specific\"", Config.class));
+        assertEquals("specific", value.value0());
+    }
+
+    @org.junit.jupiter.api.Test
+    void numberPrefersItsSpecificVariantOverAny() {
+        Config.VariantNumber value = assertInstanceOf(Config.VariantNumber.class, gson.fromJson("7.5", Config.class));
+        assertEquals(7.5, value.value0());
+    }
+
+    @org.junit.jupiter.api.Test
+    void unmatchedValuesUseAnyWithoutLosingTheirPayload() {
+        for (String json : new String[] {"true", "{\"key\":1}"}) {
+            Config.VariantAny value = assertInstanceOf(Config.VariantAny.class, gson.fromJson(json, Config.class));
+            assertEquals(JsonParser.parseString(json), value.value0());
+            assertEquals(JsonParser.parseString(json), JsonParser.parseString(gson.toJson(value, Config.class)));
+        }
+    }
+}
diff --git a/tests/generated-clients/jvm/java/cases/closed-sum/gradle.lockfile b/tests/generated-clients/jvm/java/cases/closed-sum/gradle.lockfile
new file mode 100644
index 00000000..f8918557
--- /dev/null
+++ b/tests/generated-clients/jvm/java/cases/closed-sum/gradle.lockfile
@@ -0,0 +1,25 @@
+# This is a Gradle generated file for dependency locking.
+# Manual edits can break the build and are not advised.
+# This file is expected to be part of source control.
+# To regenerate this file, run: ./gradlew :cases:closed-sum:dependencies --write-locks
+com.google.code.gson:gson:2.11.0=testCompileClasspath,testRuntimeClasspath
+com.google.errorprone:error_prone_annotations:2.27.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okhttp3:okhttp:4.12.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio-jvm:3.6.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio:3.6.0=testCompileClasspath,testRuntimeClasspath
+org.apiguardian:apiguardian-api:1.1.2=testCompileClasspath
+org.jetbrains.kotlin:kotlin-stdlib-common:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains:annotations:13.0=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-api:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-engine:5.12.2=testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-params:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-commons:1.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-engine:1.12.2=testRuntimeClasspath
+org.junit.platform:junit-platform-launcher:1.12.2=testRuntimeClasspath
+org.junit:junit-bom:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.opentest4j:opentest4j:1.3.0=testCompileClasspath,testRuntimeClasspath
+empty=testAnnotationProcessor
diff --git a/tests/generated-clients/jvm/java/cases/closed-sum/src/test/java/ClosedSumTest.java b/tests/generated-clients/jvm/java/cases/closed-sum/src/test/java/ClosedSumTest.java
new file mode 100644
index 00000000..211e5711
--- /dev/null
+++ b/tests/generated-clients/jvm/java/cases/closed-sum/src/test/java/ClosedSumTest.java
@@ -0,0 +1,15 @@
+import com.example.sdk.models.Choice;
+import com.google.gson.Gson;
+import static org.junit.jupiter.api.Assertions.*;
+
+public final class ClosedSumTest {
+    @org.junit.jupiter.api.Test
+    void preservesArraysPrimitivesAndNull() {
+        Gson gson = new Gson();
+        Choice.VariantArray array = assertInstanceOf(Choice.VariantArray.class, gson.fromJson("[1,2]", Choice.class));
+        assertEquals(java.util.List.of(1, 2), array.value0());
+        assertEquals("\"ok\"", gson.toJson(new Choice.VariantString("ok"), Choice.class));
+        assertInstanceOf(Choice.VariantNull.class, gson.fromJson("null", Choice.class));
+        assertEquals("null", gson.toJson(Choice.VariantNull.INSTANCE, Choice.class));
+    }
+}
diff --git a/tests/generated-clients/jvm/java/cases/object-union/gradle.lockfile b/tests/generated-clients/jvm/java/cases/object-union/gradle.lockfile
new file mode 100644
index 00000000..7d392e6f
--- /dev/null
+++ b/tests/generated-clients/jvm/java/cases/object-union/gradle.lockfile
@@ -0,0 +1,25 @@
+# This is a Gradle generated file for dependency locking.
+# Manual edits can break the build and are not advised.
+# This file is expected to be part of source control.
+# To regenerate this file, run: ./gradlew :cases:object-union:dependencies --write-locks
+com.google.code.gson:gson:2.11.0=testCompileClasspath,testRuntimeClasspath
+com.google.errorprone:error_prone_annotations:2.27.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okhttp3:okhttp:4.12.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio-jvm:3.6.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio:3.6.0=testCompileClasspath,testRuntimeClasspath
+org.apiguardian:apiguardian-api:1.1.2=testCompileClasspath
+org.jetbrains.kotlin:kotlin-stdlib-common:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains:annotations:13.0=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-api:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-engine:5.12.2=testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-params:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-commons:1.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-engine:1.12.2=testRuntimeClasspath
+org.junit.platform:junit-platform-launcher:1.12.2=testRuntimeClasspath
+org.junit:junit-bom:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.opentest4j:opentest4j:1.3.0=testCompileClasspath,testRuntimeClasspath
+empty=testAnnotationProcessor
diff --git a/tests/generated-clients/jvm/java/cases/object-union/src/test/java/ObjectUnionTest.java b/tests/generated-clients/jvm/java/cases/object-union/src/test/java/ObjectUnionTest.java
new file mode 100644
index 00000000..21997ad9
--- /dev/null
+++ b/tests/generated-clients/jvm/java/cases/object-union/src/test/java/ObjectUnionTest.java
@@ -0,0 +1,12 @@
+import com.example.sdk.models.OneOfObjects;
+import com.google.gson.Gson;
+import static org.junit.jupiter.api.Assertions.*;
+
+public final class ObjectUnionTest {
+    @org.junit.jupiter.api.Test
+    void selectsMatchingRequiredFields() {
+        Gson gson = new Gson();
+        OneOfObjects value = gson.fromJson("{\"user\":{\"id\":1}}", OneOfObjects.class);
+        assertInstanceOf(OneOfObjects.VariantNestedObject.class, value);
+    }
+}
diff --git a/tests/generated-clients/jvm/java/cases/tagged-shapes/gradle.lockfile b/tests/generated-clients/jvm/java/cases/tagged-shapes/gradle.lockfile
new file mode 100644
index 00000000..33a0e553
--- /dev/null
+++ b/tests/generated-clients/jvm/java/cases/tagged-shapes/gradle.lockfile
@@ -0,0 +1,25 @@
+# This is a Gradle generated file for dependency locking.
+# Manual edits can break the build and are not advised.
+# This file is expected to be part of source control.
+# To regenerate this file, run: ./gradlew :cases:tagged-shapes:dependencies --write-locks
+com.google.code.gson:gson:2.11.0=testCompileClasspath,testRuntimeClasspath
+com.google.errorprone:error_prone_annotations:2.27.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okhttp3:okhttp:4.12.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio-jvm:3.6.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio:3.6.0=testCompileClasspath,testRuntimeClasspath
+org.apiguardian:apiguardian-api:1.1.2=testCompileClasspath
+org.jetbrains.kotlin:kotlin-stdlib-common:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains:annotations:13.0=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-api:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-engine:5.12.2=testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-params:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-commons:1.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-engine:1.12.2=testRuntimeClasspath
+org.junit.platform:junit-platform-launcher:1.12.2=testRuntimeClasspath
+org.junit:junit-bom:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.opentest4j:opentest4j:1.3.0=testCompileClasspath,testRuntimeClasspath
+empty=testAnnotationProcessor
diff --git a/tests/generated-clients/jvm/java/cases/tagged-shapes/src/test/java/TaggedShapesTest.java b/tests/generated-clients/jvm/java/cases/tagged-shapes/src/test/java/TaggedShapesTest.java
new file mode 100644
index 00000000..e1f4f22e
--- /dev/null
+++ b/tests/generated-clients/jvm/java/cases/tagged-shapes/src/test/java/TaggedShapesTest.java
@@ -0,0 +1,31 @@
+import com.example.sdk.models.AdjacentlyTaggedEnum;
+import com.example.sdk.models.ExternallyTaggedEnum;
+import com.example.sdk.models.VariantA;
+import com.google.gson.Gson;
+import com.google.gson.JsonParser;
+import static org.junit.jupiter.api.Assertions.*;
+
+public final class TaggedShapesTest {
+    @org.junit.jupiter.api.Test
+    void adjacentRoundTripRetainsTheCompletePayload() {
+        Gson gson = new Gson();
+        VariantA payload = new VariantA("value", 7);
+        AdjacentlyTaggedEnum value = new AdjacentlyTaggedEnum.VariantAdjacentlyTaggedEnumVariantA(payload);
+        String json = gson.toJson(value, AdjacentlyTaggedEnum.class);
+        assertEquals(JsonParser.parseString("{\"ty\":\"ADJACENTLY_TAGGED_ENUM_VARIANT_A\",\"data\":{\"field1\":\"value\",\"field2\":7}}"), JsonParser.parseString(json));
+        var decoded = assertInstanceOf(AdjacentlyTaggedEnum.VariantAdjacentlyTaggedEnumVariantA.class, gson.fromJson(json, AdjacentlyTaggedEnum.class));
+        assertEquals("value", decoded.value0().getField1());
+        assertEquals(7, decoded.value0().getField2());
+    }
+
+    @org.junit.jupiter.api.Test
+    void externalRoundTripRetainsTheCompletePayload() {
+        Gson gson = new Gson();
+        ExternallyTaggedEnum value = new ExternallyTaggedEnum.VariantExternallyTaggedEnumVariantA(new VariantA("value", 7));
+        String json = gson.toJson(value, ExternallyTaggedEnum.class);
+        assertEquals(JsonParser.parseString("{\"EXTERNALLY_TAGGED_ENUM_VARIANT_A\":{\"field1\":\"value\",\"field2\":7}}"), JsonParser.parseString(json));
+        var decoded = assertInstanceOf(ExternallyTaggedEnum.VariantExternallyTaggedEnumVariantA.class, gson.fromJson(json, ExternallyTaggedEnum.class));
+        assertEquals("value", decoded.value0().getField1());
+        assertEquals(7, decoded.value0().getField2());
+    }
+}
diff --git a/tests/generated-clients/jvm/java/cases/tagged-union/gradle.lockfile b/tests/generated-clients/jvm/java/cases/tagged-union/gradle.lockfile
new file mode 100644
index 00000000..703457fd
--- /dev/null
+++ b/tests/generated-clients/jvm/java/cases/tagged-union/gradle.lockfile
@@ -0,0 +1,25 @@
+# This is a Gradle generated file for dependency locking.
+# Manual edits can break the build and are not advised.
+# This file is expected to be part of source control.
+# To regenerate this file, run: ./gradlew :cases:tagged-union:dependencies --write-locks
+com.google.code.gson:gson:2.11.0=testCompileClasspath,testRuntimeClasspath
+com.google.errorprone:error_prone_annotations:2.27.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okhttp3:okhttp:4.12.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio-jvm:3.6.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio:3.6.0=testCompileClasspath,testRuntimeClasspath
+org.apiguardian:apiguardian-api:1.1.2=testCompileClasspath
+org.jetbrains.kotlin:kotlin-stdlib-common:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains:annotations:13.0=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-api:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-engine:5.12.2=testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-params:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-commons:1.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-engine:1.12.2=testRuntimeClasspath
+org.junit.platform:junit-platform-launcher:1.12.2=testRuntimeClasspath
+org.junit:junit-bom:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.opentest4j:opentest4j:1.3.0=testCompileClasspath,testRuntimeClasspath
+empty=testAnnotationProcessor
diff --git a/tests/generated-clients/jvm/java/cases/tagged-union/src/test/java/TaggedUnionTest.java b/tests/generated-clients/jvm/java/cases/tagged-union/src/test/java/TaggedUnionTest.java
new file mode 100644
index 00000000..e81594a1
--- /dev/null
+++ b/tests/generated-clients/jvm/java/cases/tagged-union/src/test/java/TaggedUnionTest.java
@@ -0,0 +1,16 @@
+import com.example.sdk.models.Setup;
+import com.google.gson.Gson;
+import com.google.gson.JsonParser;
+import static org.junit.jupiter.api.Assertions.*;
+
+public final class TaggedUnionTest {
+    @org.junit.jupiter.api.Test
+    void preservesDiscriminatorAndBusinessFields() {
+        Gson gson = new Gson();
+        String json = "{\"kind\":\"SETUP_QUICK\",\"name\":\"x\",\"engine\":\"e\"}";
+        Setup.VariantSetupQuick setup = assertInstanceOf(Setup.VariantSetupQuick.class, gson.fromJson(json, Setup.class));
+        assertEquals("x", setup.value0().getName());
+        assertEquals("e", setup.value0().getEngine());
+        assertEquals(JsonParser.parseString(json), JsonParser.parseString(gson.toJson(setup, Setup.class)));
+    }
+}
diff --git a/tests/generated-clients/jvm/java/cases/typed-error-responses/gradle.lockfile b/tests/generated-clients/jvm/java/cases/typed-error-responses/gradle.lockfile
new file mode 100644
index 00000000..cbe4a336
--- /dev/null
+++ b/tests/generated-clients/jvm/java/cases/typed-error-responses/gradle.lockfile
@@ -0,0 +1,25 @@
+# This is a Gradle generated file for dependency locking.
+# Manual edits can break the build and are not advised.
+# This file is expected to be part of source control.
+# To regenerate this file, run: ./gradlew :cases:typed-error-responses:dependencies --write-locks
+com.google.code.gson:gson:2.11.0=testCompileClasspath,testRuntimeClasspath
+com.google.errorprone:error_prone_annotations:2.27.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okhttp3:okhttp:4.12.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio-jvm:3.6.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio:3.6.0=testCompileClasspath,testRuntimeClasspath
+org.apiguardian:apiguardian-api:1.1.2=testCompileClasspath
+org.jetbrains.kotlin:kotlin-stdlib-common:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains:annotations:13.0=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-api:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-engine:5.12.2=testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-params:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-commons:1.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-engine:1.12.2=testRuntimeClasspath
+org.junit.platform:junit-platform-launcher:1.12.2=testRuntimeClasspath
+org.junit:junit-bom:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.opentest4j:opentest4j:1.3.0=testCompileClasspath,testRuntimeClasspath
+empty=testAnnotationProcessor
diff --git a/tests/generated-clients/jvm/java/cases/typed-error-responses/src/test/java/CharsetTest.java b/tests/generated-clients/jvm/java/cases/typed-error-responses/src/test/java/CharsetTest.java
new file mode 100644
index 00000000..59a77512
--- /dev/null
+++ b/tests/generated-clients/jvm/java/cases/typed-error-responses/src/test/java/CharsetTest.java
@@ -0,0 +1,21 @@
+import com.example.sdk.apis.CreateResourceServerError;
+import com.example.sdk.apis.CreateResourceException;
+import java.nio.charset.StandardCharsets;
+import okhttp3.Headers;
+
+public final class CharsetTest {
+    @org.junit.jupiter.api.Test
+    void preservesCharsetAndHeaders() {
+        byte[] raw = "{\"message\":\"caf\u00e9\",\"retryable\":true}".getBytes(StandardCharsets.ISO_8859_1);
+        Headers headers = Headers.of("Content-Type", "application/json; charset=iso-8859-1", "Retry-After", "120");
+        CreateResourceServerError detail = new CreateResourceServerError(503, headers, raw);
+        String message = detail.body().getMessage();
+        if (!"caf\u00e9".equals(message)) {
+            throw new AssertionError("expected charset-aware message, got: " + message);
+        }
+        CreateResourceException error = new CreateResourceException(503, "Service Unavailable", message, headers, raw, detail);
+        if (!"120".equals(error.getRetryAfterHeader())) {
+            throw new AssertionError("expected Retry-After header");
+        }
+    }
+}
diff --git a/tests/generated-clients/jvm/java/settings.gradle b/tests/generated-clients/jvm/java/settings.gradle
new file mode 100644
index 00000000..289dfe4d
--- /dev/null
+++ b/tests/generated-clients/jvm/java/settings.gradle
@@ -0,0 +1,4 @@
+plugins {
+    id("org.gradle.toolchains.foojay-resolver-convention") version "1.0.0"
+}
+apply from: file("../settings-common.gradle")
diff --git a/tests/generated-clients/jvm/kotlin/build.gradle b/tests/generated-clients/jvm/kotlin/build.gradle
new file mode 100644
index 00000000..40528512
--- /dev/null
+++ b/tests/generated-clients/jvm/kotlin/build.gradle
@@ -0,0 +1 @@
+apply from: file("../build-common.gradle")
diff --git a/tests/generated-clients/jvm/kotlin/cases/any-union/gradle.lockfile b/tests/generated-clients/jvm/kotlin/cases/any-union/gradle.lockfile
new file mode 100644
index 00000000..7db3fa1e
--- /dev/null
+++ b/tests/generated-clients/jvm/kotlin/cases/any-union/gradle.lockfile
@@ -0,0 +1,25 @@
+# This is a Gradle generated file for dependency locking.
+# Manual edits can break the build and are not advised.
+# This file is expected to be part of source control.
+# To regenerate this file, run: ./gradlew :cases:any-union:dependencies --write-locks
+com.google.code.gson:gson:2.11.0=testCompileClasspath,testRuntimeClasspath
+com.google.errorprone:error_prone_annotations:2.27.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okhttp3:okhttp:4.12.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio-jvm:3.6.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio:3.6.0=testCompileClasspath,testRuntimeClasspath
+org.apiguardian:apiguardian-api:1.1.2=testCompileClasspath
+org.jetbrains.kotlin:kotlin-stdlib-common:2.2.21=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib:2.2.21=testCompileClasspath,testRuntimeClasspath
+org.jetbrains:annotations:13.0=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-api:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-engine:5.12.2=testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-params:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-commons:1.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-engine:1.12.2=testRuntimeClasspath
+org.junit.platform:junit-platform-launcher:1.12.2=testRuntimeClasspath
+org.junit:junit-bom:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.opentest4j:opentest4j:1.3.0=testCompileClasspath,testRuntimeClasspath
+empty=testAnnotationProcessor
diff --git a/tests/generated-clients/jvm/kotlin/cases/any-union/src/test/java/AnyUnionTest.java b/tests/generated-clients/jvm/kotlin/cases/any-union/src/test/java/AnyUnionTest.java
new file mode 100644
index 00000000..c2ef7260
--- /dev/null
+++ b/tests/generated-clients/jvm/kotlin/cases/any-union/src/test/java/AnyUnionTest.java
@@ -0,0 +1,29 @@
+import com.example.sdk.models.Config;
+import com.google.gson.Gson;
+import com.google.gson.JsonParser;
+import static org.junit.jupiter.api.Assertions.*;
+
+public final class AnyUnionTest {
+    private final Gson gson = new Gson();
+
+    @org.junit.jupiter.api.Test
+    void stringPrefersItsSpecificVariantOverAny() {
+        Config.VariantString value = assertInstanceOf(Config.VariantString.class, gson.fromJson("\"specific\"", Config.class));
+        assertEquals("specific", value.getValue0());
+    }
+
+    @org.junit.jupiter.api.Test
+    void numberPrefersItsSpecificVariantOverAny() {
+        Config.VariantNumber value = assertInstanceOf(Config.VariantNumber.class, gson.fromJson("7.5", Config.class));
+        assertEquals(7.5, value.getValue0());
+    }
+
+    @org.junit.jupiter.api.Test
+    void unmatchedValuesUseAnyWithoutLosingTheirPayload() {
+        for (String json : new String[] {"true", "{\"key\":1}"}) {
+            Config.VariantAny value = assertInstanceOf(Config.VariantAny.class, gson.fromJson(json, Config.class));
+            assertEquals(JsonParser.parseString(json), value.getValue0());
+            assertEquals(JsonParser.parseString(json), JsonParser.parseString(gson.toJson(value, Config.class)));
+        }
+    }
+}
diff --git a/tests/generated-clients/jvm/kotlin/cases/closed-sum/gradle.lockfile b/tests/generated-clients/jvm/kotlin/cases/closed-sum/gradle.lockfile
new file mode 100644
index 00000000..07c29e30
--- /dev/null
+++ b/tests/generated-clients/jvm/kotlin/cases/closed-sum/gradle.lockfile
@@ -0,0 +1,25 @@
+# This is a Gradle generated file for dependency locking.
+# Manual edits can break the build and are not advised.
+# This file is expected to be part of source control.
+# To regenerate this file, run: ./gradlew :cases:closed-sum:dependencies --write-locks
+com.google.code.gson:gson:2.11.0=testCompileClasspath,testRuntimeClasspath
+com.google.errorprone:error_prone_annotations:2.27.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okhttp3:okhttp:4.12.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio-jvm:3.6.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio:3.6.0=testCompileClasspath,testRuntimeClasspath
+org.apiguardian:apiguardian-api:1.1.2=testCompileClasspath
+org.jetbrains.kotlin:kotlin-stdlib-common:2.2.21=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib:2.2.21=testCompileClasspath,testRuntimeClasspath
+org.jetbrains:annotations:13.0=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-api:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-engine:5.12.2=testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-params:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-commons:1.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-engine:1.12.2=testRuntimeClasspath
+org.junit.platform:junit-platform-launcher:1.12.2=testRuntimeClasspath
+org.junit:junit-bom:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.opentest4j:opentest4j:1.3.0=testCompileClasspath,testRuntimeClasspath
+empty=testAnnotationProcessor
diff --git a/tests/generated-clients/jvm/kotlin/cases/closed-sum/src/test/java/ClosedSumTest.java b/tests/generated-clients/jvm/kotlin/cases/closed-sum/src/test/java/ClosedSumTest.java
new file mode 100644
index 00000000..e29b9033
--- /dev/null
+++ b/tests/generated-clients/jvm/kotlin/cases/closed-sum/src/test/java/ClosedSumTest.java
@@ -0,0 +1,15 @@
+import com.example.sdk.models.Choice;
+import com.google.gson.Gson;
+import static org.junit.jupiter.api.Assertions.*;
+
+public final class ClosedSumTest {
+    @org.junit.jupiter.api.Test
+    void preservesArraysPrimitivesAndNull() {
+        Gson gson = new Gson();
+        Choice.VariantArray array = assertInstanceOf(Choice.VariantArray.class, gson.fromJson("[1,2]", Choice.class));
+        assertEquals(java.util.List.of(1, 2), array.getValue0());
+        assertEquals("\"ok\"", gson.toJson(new Choice.VariantString("ok"), Choice.class));
+        assertInstanceOf(Choice.VariantNull.class, gson.fromJson("null", Choice.class));
+        assertEquals("null", gson.toJson(Choice.VariantNull.INSTANCE, Choice.class));
+    }
+}
diff --git a/tests/generated-clients/jvm/kotlin/cases/object-union/gradle.lockfile b/tests/generated-clients/jvm/kotlin/cases/object-union/gradle.lockfile
new file mode 100644
index 00000000..4df87064
--- /dev/null
+++ b/tests/generated-clients/jvm/kotlin/cases/object-union/gradle.lockfile
@@ -0,0 +1,25 @@
+# This is a Gradle generated file for dependency locking.
+# Manual edits can break the build and are not advised.
+# This file is expected to be part of source control.
+# To regenerate this file, run: ./gradlew :cases:object-union:dependencies --write-locks
+com.google.code.gson:gson:2.11.0=testCompileClasspath,testRuntimeClasspath
+com.google.errorprone:error_prone_annotations:2.27.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okhttp3:okhttp:4.12.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio-jvm:3.6.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio:3.6.0=testCompileClasspath,testRuntimeClasspath
+org.apiguardian:apiguardian-api:1.1.2=testCompileClasspath
+org.jetbrains.kotlin:kotlin-stdlib-common:2.2.21=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib:2.2.21=testCompileClasspath,testRuntimeClasspath
+org.jetbrains:annotations:13.0=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-api:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-engine:5.12.2=testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-params:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-commons:1.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-engine:1.12.2=testRuntimeClasspath
+org.junit.platform:junit-platform-launcher:1.12.2=testRuntimeClasspath
+org.junit:junit-bom:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.opentest4j:opentest4j:1.3.0=testCompileClasspath,testRuntimeClasspath
+empty=testAnnotationProcessor
diff --git a/tests/generated-clients/jvm/kotlin/cases/object-union/src/test/java/ObjectUnionTest.java b/tests/generated-clients/jvm/kotlin/cases/object-union/src/test/java/ObjectUnionTest.java
new file mode 100644
index 00000000..21997ad9
--- /dev/null
+++ b/tests/generated-clients/jvm/kotlin/cases/object-union/src/test/java/ObjectUnionTest.java
@@ -0,0 +1,12 @@
+import com.example.sdk.models.OneOfObjects;
+import com.google.gson.Gson;
+import static org.junit.jupiter.api.Assertions.*;
+
+public final class ObjectUnionTest {
+    @org.junit.jupiter.api.Test
+    void selectsMatchingRequiredFields() {
+        Gson gson = new Gson();
+        OneOfObjects value = gson.fromJson("{\"user\":{\"id\":1}}", OneOfObjects.class);
+        assertInstanceOf(OneOfObjects.VariantNestedObject.class, value);
+    }
+}
diff --git a/tests/generated-clients/jvm/kotlin/cases/tagged-shapes/gradle.lockfile b/tests/generated-clients/jvm/kotlin/cases/tagged-shapes/gradle.lockfile
new file mode 100644
index 00000000..5ef15d73
--- /dev/null
+++ b/tests/generated-clients/jvm/kotlin/cases/tagged-shapes/gradle.lockfile
@@ -0,0 +1,25 @@
+# This is a Gradle generated file for dependency locking.
+# Manual edits can break the build and are not advised.
+# This file is expected to be part of source control.
+# To regenerate this file, run: ./gradlew :cases:tagged-shapes:dependencies --write-locks
+com.google.code.gson:gson:2.11.0=testCompileClasspath,testRuntimeClasspath
+com.google.errorprone:error_prone_annotations:2.27.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okhttp3:okhttp:4.12.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio-jvm:3.6.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio:3.6.0=testCompileClasspath,testRuntimeClasspath
+org.apiguardian:apiguardian-api:1.1.2=testCompileClasspath
+org.jetbrains.kotlin:kotlin-stdlib-common:2.2.21=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib:2.2.21=testCompileClasspath,testRuntimeClasspath
+org.jetbrains:annotations:13.0=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-api:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-engine:5.12.2=testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-params:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-commons:1.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-engine:1.12.2=testRuntimeClasspath
+org.junit.platform:junit-platform-launcher:1.12.2=testRuntimeClasspath
+org.junit:junit-bom:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.opentest4j:opentest4j:1.3.0=testCompileClasspath,testRuntimeClasspath
+empty=testAnnotationProcessor
diff --git a/tests/generated-clients/jvm/kotlin/cases/tagged-shapes/src/test/java/TaggedShapesTest.java b/tests/generated-clients/jvm/kotlin/cases/tagged-shapes/src/test/java/TaggedShapesTest.java
new file mode 100644
index 00000000..427f9bdc
--- /dev/null
+++ b/tests/generated-clients/jvm/kotlin/cases/tagged-shapes/src/test/java/TaggedShapesTest.java
@@ -0,0 +1,31 @@
+import com.example.sdk.models.AdjacentlyTaggedEnum;
+import com.example.sdk.models.ExternallyTaggedEnum;
+import com.example.sdk.models.VariantA;
+import com.google.gson.Gson;
+import com.google.gson.JsonParser;
+import static org.junit.jupiter.api.Assertions.*;
+
+public final class TaggedShapesTest {
+    @org.junit.jupiter.api.Test
+    void adjacentRoundTripRetainsTheCompletePayload() {
+        Gson gson = new Gson();
+        VariantA payload = new VariantA("value", 7);
+        AdjacentlyTaggedEnum value = new AdjacentlyTaggedEnum.VariantAdjacentlyTaggedEnumVariantA(payload);
+        String json = gson.toJson(value, AdjacentlyTaggedEnum.class);
+        assertEquals(JsonParser.parseString("{\"ty\":\"ADJACENTLY_TAGGED_ENUM_VARIANT_A\",\"data\":{\"field1\":\"value\",\"field2\":7}}"), JsonParser.parseString(json));
+        var decoded = assertInstanceOf(AdjacentlyTaggedEnum.VariantAdjacentlyTaggedEnumVariantA.class, gson.fromJson(json, AdjacentlyTaggedEnum.class));
+        assertEquals("value", decoded.getValue0().getField1());
+        assertEquals(7, decoded.getValue0().getField2());
+    }
+
+    @org.junit.jupiter.api.Test
+    void externalRoundTripRetainsTheCompletePayload() {
+        Gson gson = new Gson();
+        ExternallyTaggedEnum value = new ExternallyTaggedEnum.VariantExternallyTaggedEnumVariantA(new VariantA("value", 7));
+        String json = gson.toJson(value, ExternallyTaggedEnum.class);
+        assertEquals(JsonParser.parseString("{\"EXTERNALLY_TAGGED_ENUM_VARIANT_A\":{\"field1\":\"value\",\"field2\":7}}"), JsonParser.parseString(json));
+        var decoded = assertInstanceOf(ExternallyTaggedEnum.VariantExternallyTaggedEnumVariantA.class, gson.fromJson(json, ExternallyTaggedEnum.class));
+        assertEquals("value", decoded.getValue0().getField1());
+        assertEquals(7, decoded.getValue0().getField2());
+    }
+}
diff --git a/tests/generated-clients/jvm/kotlin/cases/tagged-union/gradle.lockfile b/tests/generated-clients/jvm/kotlin/cases/tagged-union/gradle.lockfile
new file mode 100644
index 00000000..9731ffb3
--- /dev/null
+++ b/tests/generated-clients/jvm/kotlin/cases/tagged-union/gradle.lockfile
@@ -0,0 +1,25 @@
+# This is a Gradle generated file for dependency locking.
+# Manual edits can break the build and are not advised.
+# This file is expected to be part of source control.
+# To regenerate this file, run: ./gradlew :cases:tagged-union:dependencies --write-locks
+com.google.code.gson:gson:2.11.0=testCompileClasspath,testRuntimeClasspath
+com.google.errorprone:error_prone_annotations:2.27.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okhttp3:okhttp:4.12.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio-jvm:3.6.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio:3.6.0=testCompileClasspath,testRuntimeClasspath
+org.apiguardian:apiguardian-api:1.1.2=testCompileClasspath
+org.jetbrains.kotlin:kotlin-stdlib-common:2.2.21=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib:2.2.21=testCompileClasspath,testRuntimeClasspath
+org.jetbrains:annotations:13.0=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-api:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-engine:5.12.2=testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-params:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-commons:1.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-engine:1.12.2=testRuntimeClasspath
+org.junit.platform:junit-platform-launcher:1.12.2=testRuntimeClasspath
+org.junit:junit-bom:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.opentest4j:opentest4j:1.3.0=testCompileClasspath,testRuntimeClasspath
+empty=testAnnotationProcessor
diff --git a/tests/generated-clients/jvm/kotlin/cases/tagged-union/src/test/java/TaggedUnionTest.java b/tests/generated-clients/jvm/kotlin/cases/tagged-union/src/test/java/TaggedUnionTest.java
new file mode 100644
index 00000000..d7c959de
--- /dev/null
+++ b/tests/generated-clients/jvm/kotlin/cases/tagged-union/src/test/java/TaggedUnionTest.java
@@ -0,0 +1,16 @@
+import com.example.sdk.models.Setup;
+import com.google.gson.Gson;
+import com.google.gson.JsonParser;
+import static org.junit.jupiter.api.Assertions.*;
+
+public final class TaggedUnionTest {
+    @org.junit.jupiter.api.Test
+    void preservesDiscriminatorAndBusinessFields() {
+        Gson gson = new Gson();
+        String json = "{\"kind\":\"SETUP_QUICK\",\"name\":\"x\",\"engine\":\"e\"}";
+        Setup.VariantSetupQuick setup = assertInstanceOf(Setup.VariantSetupQuick.class, gson.fromJson(json, Setup.class));
+        assertEquals("x", setup.getValue0().getName());
+        assertEquals("e", setup.getValue0().getEngine());
+        assertEquals(JsonParser.parseString(json), JsonParser.parseString(gson.toJson(setup, Setup.class)));
+    }
+}
diff --git a/tests/generated-clients/jvm/kotlin/cases/typed-error-responses/gradle.lockfile b/tests/generated-clients/jvm/kotlin/cases/typed-error-responses/gradle.lockfile
new file mode 100644
index 00000000..e1b7652c
--- /dev/null
+++ b/tests/generated-clients/jvm/kotlin/cases/typed-error-responses/gradle.lockfile
@@ -0,0 +1,25 @@
+# This is a Gradle generated file for dependency locking.
+# Manual edits can break the build and are not advised.
+# This file is expected to be part of source control.
+# To regenerate this file, run: ./gradlew :cases:typed-error-responses:dependencies --write-locks
+com.google.code.gson:gson:2.11.0=testCompileClasspath,testRuntimeClasspath
+com.google.errorprone:error_prone_annotations:2.27.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okhttp3:okhttp:4.12.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio-jvm:3.6.0=testCompileClasspath,testRuntimeClasspath
+com.squareup.okio:okio:3.6.0=testCompileClasspath,testRuntimeClasspath
+org.apiguardian:apiguardian-api:1.1.2=testCompileClasspath
+org.jetbrains.kotlin:kotlin-stdlib-common:2.2.21=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.9.10=testCompileClasspath,testRuntimeClasspath
+org.jetbrains.kotlin:kotlin-stdlib:2.2.21=testCompileClasspath,testRuntimeClasspath
+org.jetbrains:annotations:13.0=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-api:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-engine:5.12.2=testRuntimeClasspath
+org.junit.jupiter:junit-jupiter-params:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.jupiter:junit-jupiter:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-commons:1.12.2=testCompileClasspath,testRuntimeClasspath
+org.junit.platform:junit-platform-engine:1.12.2=testRuntimeClasspath
+org.junit.platform:junit-platform-launcher:1.12.2=testRuntimeClasspath
+org.junit:junit-bom:5.12.2=testCompileClasspath,testRuntimeClasspath
+org.opentest4j:opentest4j:1.3.0=testCompileClasspath,testRuntimeClasspath
+empty=testAnnotationProcessor
diff --git a/tests/generated-clients/jvm/kotlin/cases/typed-error-responses/src/test/java/CharsetTest.java b/tests/generated-clients/jvm/kotlin/cases/typed-error-responses/src/test/java/CharsetTest.java
new file mode 100644
index 00000000..944db9ff
--- /dev/null
+++ b/tests/generated-clients/jvm/kotlin/cases/typed-error-responses/src/test/java/CharsetTest.java
@@ -0,0 +1,21 @@
+import com.example.sdk.apis.CreateResourceException;
+import com.example.sdk.apis.CreateResourceServerError;
+import java.nio.charset.StandardCharsets;
+import okhttp3.Headers;
+
+public final class CharsetTest {
+    @org.junit.jupiter.api.Test
+    void preservesCharsetAndHeaders() {
+        byte[] raw = "{\"message\":\"caf\u00e9\",\"retryable\":true}".getBytes(StandardCharsets.ISO_8859_1);
+        Headers headers = Headers.of("Content-Type", "application/json; charset=iso-8859-1", "Retry-After", "120");
+        CreateResourceServerError detail = new CreateResourceServerError(503, headers, raw);
+        String message = detail.body().getMessage();
+        if (!"caf\u00e9".equals(message)) {
+            throw new AssertionError("expected charset-aware message, got: " + message);
+        }
+        CreateResourceException error = new CreateResourceException(detail, 503, "Service Unavailable", message, headers, raw);
+        if (!"120".equals(error.retryAfterHeader())) {
+            throw new AssertionError("expected Retry-After header");
+        }
+    }
+}
diff --git a/tests/generated-clients/jvm/kotlin/settings.gradle b/tests/generated-clients/jvm/kotlin/settings.gradle
new file mode 100644
index 00000000..289dfe4d
--- /dev/null
+++ b/tests/generated-clients/jvm/kotlin/settings.gradle
@@ -0,0 +1,4 @@
+plugins {
+    id("org.gradle.toolchains.foojay-resolver-convention") version "1.0.0"
+}
+apply from: file("../settings-common.gradle")
diff --git a/tests/generated-clients/jvm/settings-common.gradle b/tests/generated-clients/jvm/settings-common.gradle
new file mode 100644
index 00000000..51ceaeba
--- /dev/null
+++ b/tests/generated-clients/jvm/settings-common.gradle
@@ -0,0 +1,11 @@
+rootProject.name = "${settingsDir.name}-client-tests"
+include(":clients")
+project(":clients").projectDir = new File(settingsDir, "generated")
+new File(settingsDir, "../fixtures.txt").eachLine { line ->
+    if (line.trim() && !line.startsWith("#")) {
+        def name = line.tokenize()[0]
+        include(":clients:${name}", ":cases:${name}")
+        project(":clients:${name}").projectDir = new File(settingsDir, "generated/${name}")
+        project(":cases:${name}").projectDir = new File(settingsDir, "cases/${name}")
+    }
+}
diff --git a/tests/generated-clients/rust/README.md b/tests/generated-clients/rust/README.md
index 206a69e3..4e2d97de 100644
--- a/tests/generated-clients/rust/README.md
+++ b/tests/generated-clients/rust/README.md
@@ -47,4 +47,5 @@ errors, thiserror, and Snafu; ureq retains its synchronous propagation check.
 The root `just test-all` and `just coverage-lcov` cover the generator workspace,
 not these projects. CI runs a separate Rust Client Tests matrix, and `just ci`
 includes `just golden-rust::test`. Golden comparison and all-golden compilation
-remain separate checks. JVM runtime tests are unchanged by this separation.
+remain separate checks. JVM consumer tests have their own Gradle projects under
+`tests/generated-clients/jvm/` and run through `just golden-jvm::test`.
diff --git a/tests/jvm_http_error_runtime.rs b/tests/jvm_http_error_runtime.rs
deleted file mode 100644
index b37b191a..00000000
--- a/tests/jvm_http_error_runtime.rs
+++ /dev/null
@@ -1,690 +0,0 @@
-use std::collections::HashMap;
-use std::fs;
-use std::io::ErrorKind;
-use std::path::{Path, PathBuf};
-use std::process::Command;
-use std::thread;
-use std::time::{Duration, Instant, SystemTime, UNIX_EPOCH};
-
-use openapi_nexus::generators::java::okhttp::JavaOkhttpCodeGenerator;
-use openapi_nexus::generators::kotlin::okhttp::KotlinOkhttpCodeGenerator;
-use openapi_nexus::test_utils::{generate_files, read_fixture};
-
-fn empty_config() -> toml::value::Table {
-    toml::value::Table::new()
-}
-
-struct TempDir {
-    path: PathBuf,
-}
-
-impl TempDir {
-    fn new(name: &str) -> Self {
-        let nanos = SystemTime::now()
-            .duration_since(UNIX_EPOCH)
-            .expect("system clock should be after UNIX_EPOCH")
-            .as_nanos();
-        let path = std::env::temp_dir().join(format!(
-            "openapi-nexus-{name}-{}-{nanos}",
-            std::process::id()
-        ));
-        fs::create_dir_all(&path).expect("temporary project directory should be created");
-        Self { path }
-    }
-}
-
-impl Drop for TempDir {
-    fn drop(&mut self) {
-        let _ = fs::remove_dir_all(&self.path);
-    }
-}
-
-struct LockDir {
-    path: PathBuf,
-}
-
-impl LockDir {
-    fn acquire(name: &str) -> Self {
-        let path = std::env::temp_dir().join(format!("openapi-nexus-{name}.lock"));
-        let deadline = Instant::now() + Duration::from_secs(300);
-        loop {
-            match fs::create_dir(&path) {
-                Ok(()) => return Self { path },
-                Err(err) if err.kind() == ErrorKind::AlreadyExists && Instant::now() < deadline => {
-                    thread::sleep(Duration::from_millis(250));
-                }
-                Err(err) => panic!("failed to acquire {name} lock at {}: {err}", path.display()),
-            }
-        }
-    }
-}
-
-impl Drop for LockDir {
-    fn drop(&mut self) {
-        let _ = fs::remove_dir_all(&self.path);
-    }
-}
-
-fn write_generated_project(files: &HashMap<String, String>, root: &Path) {
-    for (relative_path, contents) in files {
-        let path = root.join(relative_path);
-        if let Some(parent) = path.parent() {
-            fs::create_dir_all(parent).expect("generated parent directory should be created");
-        }
-        fs::write(path, contents).expect("generated file should be written");
-    }
-}
-
-const CHARSET_SMOKE_JAVA: &str = r#"
-import com.example.sdk.apis.CreateResourceServerError;
-import com.example.sdk.apis.CreateResourceException;
-import java.nio.charset.StandardCharsets;
-import okhttp3.Headers;
-
-public final class CharsetSmoke {
-    public static void main(String[] args) {
-        byte[] raw = "{\"message\":\"caf\u00e9\",\"retryable\":true}".getBytes(StandardCharsets.ISO_8859_1);
-        Headers headers = Headers.of(
-            "Content-Type", "application/json; charset=iso-8859-1",
-            "Retry-After", "120"
-        );
-        CreateResourceServerError detail = new CreateResourceServerError(503, headers, raw);
-        String message = detail.body().getMessage();
-        if (!"caf\u00e9".equals(message)) {
-            throw new AssertionError("expected charset-aware message, got: " + message);
-        }
-        CreateResourceException error = new CreateResourceException(
-            503, "Service Unavailable", message, headers, raw, detail
-        );
-        if (!"120".equals(error.getRetryAfterHeader())) {
-            throw new AssertionError("expected Retry-After header");
-        }
-    }
-}
-"#;
-
-const CHARSET_SMOKE_KOTLIN_JAVA: &str = r#"
-import com.example.sdk.apis.CreateResourceException;
-import com.example.sdk.apis.CreateResourceServerError;
-import java.nio.charset.StandardCharsets;
-import okhttp3.Headers;
-
-public final class CharsetSmoke {
-    public static void main(String[] args) {
-        byte[] raw = "{\"message\":\"caf\u00e9\",\"retryable\":true}".getBytes(StandardCharsets.ISO_8859_1);
-        Headers headers = Headers.of(
-            "Content-Type", "application/json; charset=iso-8859-1",
-            "Retry-After", "120"
-        );
-        CreateResourceServerError detail = new CreateResourceServerError(503, headers, raw);
-        String message = detail.body().getMessage();
-        if (!"caf\u00e9".equals(message)) {
-            throw new AssertionError("expected charset-aware message, got: " + message);
-        }
-        CreateResourceException error = new CreateResourceException(
-            detail, 503, "Service Unavailable", message, headers, raw
-        );
-        if (!"120".equals(error.retryAfterHeader())) {
-            throw new AssertionError("expected Retry-After header");
-        }
-    }
-}
-"#;
-
-const CLOSED_SUM_SMOKE: &str = r#"
-import com.example.sdk.models.Choice;
-import com.google.gson.Gson;
-
-public final class ClosedSumSmoke {
-    public static void main(String[] args) {
-        Gson gson = new Gson();
-        Choice choice = gson.fromJson("[1,2]", Choice.class);
-        if (!(choice instanceof Choice.VariantArray array) || array.value0().size() != 2) {
-            throw new AssertionError("expected typed array union case");
-        }
-        String choiceJson = gson.toJson(new Choice.VariantString("ok"), Choice.class);
-        if (!"\"ok\"".equals(choiceJson)) {
-            throw new AssertionError("expected typed primitive union serialization, got " + choiceJson);
-        }
-
-        Choice nullChoice = gson.fromJson("null", Choice.class);
-        if (!(nullChoice instanceof Choice.VariantNull)) {
-            throw new AssertionError("expected typed null union case");
-        }
-        String nullJson = gson.toJson(Choice.VariantNull.INSTANCE, Choice.class);
-        if (!"null".equals(nullJson)) {
-            throw new AssertionError("expected typed null union serialization, got " + nullJson);
-        }
-
-    }
-}
-"#;
-
-const OBJECT_UNION_SMOKE: &str = r#"
-import com.example.sdk.models.OneOfObjects;
-import com.google.gson.Gson;
-
-public final class ObjectUnionSmoke {
-    public static void main(String[] args) {
-        Gson gson = new Gson();
-        OneOfObjects value = gson.fromJson("{\"user\":{\"id\":1}}", OneOfObjects.class);
-        if (!(value instanceof OneOfObjects.VariantNestedObject)) {
-            throw new AssertionError("expected nested object union case");
-        }
-    }
-}
-"#;
-
-const ANY_UNION_SMOKE: &str = r#"
-import com.example.sdk.models.Config;
-import com.google.gson.Gson;
-
-public final class AnyUnionSmoke {
-    public static void main(String[] args) {
-        Gson gson = new Gson();
-        Config booleanValue = gson.fromJson("true", Config.class);
-        if (!(booleanValue instanceof Config.VariantAny)) {
-            throw new AssertionError("expected Any union case for boolean");
-        }
-        Config objectValue = gson.fromJson("{\"key\":1}", Config.class);
-        if (!(objectValue instanceof Config.VariantAny)) {
-            throw new AssertionError("expected Any union case for object");
-        }
-    }
-}
-"#;
-
-const TAGGED_SUM_SMOKE: &str = r#"
-import com.example.sdk.models.Setup;
-import com.google.gson.Gson;
-
-public final class TaggedSumSmoke {
-    public static void main(String[] args) {
-        Gson gson = new Gson();
-        Setup setup = gson.fromJson(
-            "{\"kind\":\"SETUP_QUICK\",\"name\":\"x\",\"engine\":\"e\"}",
-            Setup.class
-        );
-        if (!(setup instanceof Setup.VariantSetupQuick)) {
-            throw new AssertionError("expected typed discriminator case");
-        }
-        String setupJson = gson.toJson(setup, Setup.class);
-        if (!setupJson.contains("\"kind\":\"SETUP_QUICK\"")) {
-            throw new AssertionError("expected discriminator serialization, got " + setupJson);
-        }
-    }
-}
-"#;
-
-const TAGGED_SHAPES_SMOKE: &str = r#"
-import com.example.sdk.models.AdjacentlyTaggedEnum;
-import com.example.sdk.models.ExternallyTaggedEnum;
-import com.example.sdk.models.VariantA;
-import com.google.gson.Gson;
-
-public final class TaggedShapesSmoke {
-    public static void main(String[] args) {
-        Gson gson = new Gson();
-        VariantA payload = new VariantA("value", 7);
-
-        AdjacentlyTaggedEnum adjacent =
-            new AdjacentlyTaggedEnum.VariantAdjacentlyTaggedEnumVariantA(payload);
-        String adjacentJson = gson.toJson(adjacent, AdjacentlyTaggedEnum.class);
-        if (!adjacentJson.contains("\"ty\":\"ADJACENTLY_TAGGED_ENUM_VARIANT_A\"")
-            || !adjacentJson.contains("\"data\"")) {
-            throw new AssertionError("expected adjacent wire shape, got " + adjacentJson);
-        }
-        if (!(gson.fromJson(adjacentJson, AdjacentlyTaggedEnum.class)
-            instanceof AdjacentlyTaggedEnum.VariantAdjacentlyTaggedEnumVariantA)) {
-            throw new AssertionError("expected adjacent union case");
-        }
-
-        ExternallyTaggedEnum external =
-            new ExternallyTaggedEnum.VariantExternallyTaggedEnumVariantA(payload);
-        String externalJson = gson.toJson(external, ExternallyTaggedEnum.class);
-        if (!externalJson.contains("\"EXTERNALLY_TAGGED_ENUM_VARIANT_A\"")) {
-            throw new AssertionError("expected external wire shape, got " + externalJson);
-        }
-        if (!(gson.fromJson(externalJson, ExternallyTaggedEnum.class)
-            instanceof ExternallyTaggedEnum.VariantExternallyTaggedEnumVariantA)) {
-            throw new AssertionError("expected external union case");
-        }
-    }
-}
-"#;
-
-fn add_java_charset_smoke(root: &Path) {
-    let smoke_dir = root.join("smoke");
-    fs::create_dir_all(&smoke_dir).expect("smoke source directory should be created");
-    fs::write(smoke_dir.join("CharsetSmoke.java"), CHARSET_SMOKE_JAVA)
-        .expect("Java smoke test should be written");
-
-    let build_gradle = root.join("build.gradle");
-    let mut build = fs::read_to_string(&build_gradle).expect("build.gradle should be readable");
-    build.push_str(
-        r#"
-
-sourceSets {
-    smoke {
-        java {
-            srcDirs("smoke")
-        }
-        compileClasspath += sourceSets.main.output + sourceSets.main.compileClasspath
-        runtimeClasspath += output + compileClasspath
-    }
-}
-
-tasks.register("charsetSmoke", JavaExec) {
-    dependsOn("compileSmokeJava")
-    classpath = sourceSets.smoke.runtimeClasspath
-    mainClass = "CharsetSmoke"
-}
-"#,
-    );
-    fs::write(build_gradle, build).expect("build.gradle should be updated");
-}
-
-fn add_kotlin_charset_smoke(root: &Path) {
-    let smoke_dir = root.join("smoke");
-    fs::create_dir_all(&smoke_dir).expect("smoke source directory should be created");
-    fs::write(
-        smoke_dir.join("CharsetSmoke.java"),
-        CHARSET_SMOKE_KOTLIN_JAVA,
-    )
-    .expect("Kotlin smoke test should be written");
-
-    let build_gradle = root.join("build.gradle.kts");
-    let mut build = fs::read_to_string(&build_gradle).expect("build.gradle.kts should be readable");
-    build.push_str(
-        r#"
-
-sourceSets {
-    create("smoke") {
-        java.srcDirs("smoke")
-        compileClasspath += sourceSets["main"].output + sourceSets["main"].compileClasspath
-        runtimeClasspath += output + compileClasspath
-    }
-}
-
-tasks.register<JavaExec>("charsetSmoke") {
-    dependsOn("compileSmokeJava")
-    classpath = sourceSets["smoke"].runtimeClasspath
-    mainClass.set("CharsetSmoke")
-}
-"#,
-    );
-    fs::write(build_gradle, build).expect("build.gradle.kts should be updated");
-}
-
-fn add_java_closed_sum_smoke(root: &Path, source: &str, class_name: &str, task_name: &str) {
-    let smoke_dir = root.join("smoke");
-    fs::create_dir_all(&smoke_dir).expect("smoke source directory should be created");
-    fs::write(smoke_dir.join(format!("{class_name}.java")), source)
-        .expect("closed-sum Java smoke test should be written");
-
-    let build_gradle = root.join("build.gradle");
-    let mut build = fs::read_to_string(&build_gradle).expect("build.gradle should be readable");
-    let gradle = r#"
-
-sourceSets {
-    smoke {
-        java {
-            srcDirs("smoke")
-        }
-        compileClasspath += sourceSets.main.output + sourceSets.main.compileClasspath
-        runtimeClasspath += output + compileClasspath
-    }
-}
-
-    tasks.register("{task_name}", JavaExec) {
-        dependsOn("compileSmokeJava")
-        classpath = sourceSets.smoke.runtimeClasspath
-        mainClass = "{class_name}"
-}
-"#
-    .replace("{task_name}", task_name)
-    .replace("{class_name}", class_name);
-    build.push_str(&gradle);
-    fs::write(build_gradle, build).expect("build.gradle should be updated");
-}
-
-fn add_kotlin_closed_sum_smoke(root: &Path, source: &str, class_name: &str, task_name: &str) {
-    let smoke_dir = root.join("smoke");
-    fs::create_dir_all(&smoke_dir).expect("smoke source directory should be created");
-    let source = source.replace(".value0()", ".getValue0()");
-    fs::write(smoke_dir.join(format!("{class_name}.java")), source)
-        .expect("closed-sum Kotlin smoke test should be written");
-
-    let build_gradle = root.join("build.gradle.kts");
-    let mut build = fs::read_to_string(&build_gradle).expect("build.gradle.kts should be readable");
-    let gradle = r#"
-
-sourceSets {
-    create("smoke") {
-        java.srcDirs("smoke")
-        compileClasspath += sourceSets["main"].output + sourceSets["main"].compileClasspath
-        runtimeClasspath += output + compileClasspath
-    }
-}
-
-    tasks.register<JavaExec>("{task_name}") {
-        dependsOn("compileSmokeJava")
-        classpath = sourceSets["smoke"].runtimeClasspath
-        mainClass.set("{class_name}")
-}
-"#
-    .replace("{task_name}", task_name)
-    .replace("{class_name}", class_name);
-    build.push_str(&gradle);
-    fs::write(build_gradle, build).expect("build.gradle.kts should be updated");
-}
-
-fn gradle_charset_smoke(root: &Path) -> std::process::Output {
-    let _lock = LockDir::acquire("gradle-charset-smoke");
-    let mut cmd = Command::new("gradle");
-    if let Some(java_home) = std::env::var_os("JAVA_HOME") {
-        cmd.env("JAVA_HOME", java_home);
-    }
-    cmd.arg("--no-daemon")
-        .arg("--max-workers=1")
-        .arg("--quiet")
-        .arg("charsetSmoke")
-        .env("GRADLE_OPTS", "-Dorg.gradle.daemon=false")
-        .current_dir(root)
-        .output()
-        .expect("generated JVM charset smoke should run")
-}
-
-fn gradle_closed_sum_smoke(root: &Path, task_name: &str) -> std::process::Output {
-    let _lock = LockDir::acquire("gradle-closed-sum-smoke");
-    let mut cmd = Command::new("gradle");
-    if let Some(java_home) = std::env::var_os("JAVA_HOME") {
-        cmd.env("JAVA_HOME", java_home);
-    }
-    cmd.arg("--no-daemon")
-        .arg("--max-workers=1")
-        .arg("--quiet")
-        .arg(task_name)
-        .env("GRADLE_OPTS", "-Dorg.gradle.daemon=false")
-        .current_dir(root)
-        .output()
-        .expect("generated JVM closed-sum smoke should run")
-}
-
-#[test]
-fn java_error_detail_body_honors_response_charset() {
-    let fixture = read_fixture("valid/typed-error-responses.yaml");
-    let files = generate_files(&JavaOkhttpCodeGenerator::new(empty_config()), &fixture)
-        .expect("typed error fixture should generate Java");
-    let temp = TempDir::new("typed-http-error-java");
-    write_generated_project(&files, &temp.path);
-    add_java_charset_smoke(&temp.path);
-
-    let output = gradle_charset_smoke(&temp.path);
-    assert!(
-        output.status.success(),
-        "generated Java charset smoke failed\nstatus: {}\nstdout:\n{}\nstderr:\n{}",
-        output.status,
-        String::from_utf8_lossy(&output.stdout),
-        String::from_utf8_lossy(&output.stderr)
-    );
-}
-
-#[test]
-fn kotlin_error_detail_body_honors_response_charset() {
-    let fixture = read_fixture("valid/typed-error-responses.yaml");
-    let files = generate_files(&KotlinOkhttpCodeGenerator::new(empty_config()), &fixture)
-        .expect("typed error fixture should generate Kotlin");
-    let temp = TempDir::new("typed-http-error-kotlin");
-    write_generated_project(&files, &temp.path);
-    add_kotlin_charset_smoke(&temp.path);
-
-    let output = gradle_charset_smoke(&temp.path);
-    assert!(
-        output.status.success(),
-        "generated Kotlin charset smoke failed\nstatus: {}\nstdout:\n{}\nstderr:\n{}",
-        output.status,
-        String::from_utf8_lossy(&output.stdout),
-        String::from_utf8_lossy(&output.stderr)
-    );
-}
-
-#[test]
-fn java_closed_sum_round_trip_preserves_union_shapes() {
-    let fixture = read_fixture("valid/type-aliases/closed-sum-payload-shapes.yaml");
-    let files = generate_files(&JavaOkhttpCodeGenerator::new(empty_config()), &fixture)
-        .expect("closed-sum fixture should generate Java");
-    let temp = TempDir::new("closed-sum-java");
-    write_generated_project(&files, &temp.path);
-    add_java_closed_sum_smoke(
-        &temp.path,
-        CLOSED_SUM_SMOKE,
-        "ClosedSumSmoke",
-        "closedSumSmoke",
-    );
-
-    let output = gradle_closed_sum_smoke(&temp.path, "closedSumSmoke");
-    assert!(
-        output.status.success(),
-        "generated Java closed-sum smoke failed\nstatus: {}\nstdout:\n{}\nstderr:\n{}",
-        output.status,
-        String::from_utf8_lossy(&output.stdout),
-        String::from_utf8_lossy(&output.stderr)
-    );
-}
-
-#[test]
-fn kotlin_closed_sum_round_trip_preserves_union_shapes() {
-    let fixture = read_fixture("valid/type-aliases/closed-sum-payload-shapes.yaml");
-    let files = generate_files(&KotlinOkhttpCodeGenerator::new(empty_config()), &fixture)
-        .expect("closed-sum fixture should generate Kotlin");
-    let temp = TempDir::new("closed-sum-kotlin");
-    write_generated_project(&files, &temp.path);
-    add_kotlin_closed_sum_smoke(
-        &temp.path,
-        CLOSED_SUM_SMOKE,
-        "ClosedSumSmoke",
-        "closedSumSmoke",
-    );
-
-    let output = gradle_closed_sum_smoke(&temp.path, "closedSumSmoke");
-    assert!(
-        output.status.success(),
-        "generated Kotlin closed-sum smoke failed\nstatus: {}\nstdout:\n{}\nstderr:\n{}",
-        output.status,
-        String::from_utf8_lossy(&output.stdout),
-        String::from_utf8_lossy(&output.stderr)
-    );
-}
-
-#[test]
-fn java_untagged_object_union_selects_matching_required_fields() {
-    let fixture = read_fixture("valid/comprehensive-schemas.yaml");
-    let files = generate_files(&JavaOkhttpCodeGenerator::new(empty_config()), &fixture)
-        .expect("comprehensive fixture should generate Java");
-    let temp = TempDir::new("object-union-java");
-    write_generated_project(&files, &temp.path);
-    add_java_closed_sum_smoke(
-        &temp.path,
-        OBJECT_UNION_SMOKE,
-        "ObjectUnionSmoke",
-        "objectUnionSmoke",
-    );
-
-    let output = gradle_closed_sum_smoke(&temp.path, "objectUnionSmoke");
-    assert!(
-        output.status.success(),
-        "generated Java object-union smoke failed\nstatus: {}\nstdout:\n{}\nstderr:\n{}",
-        output.status,
-        String::from_utf8_lossy(&output.stdout),
-        String::from_utf8_lossy(&output.stderr)
-    );
-}
-
-#[test]
-fn kotlin_untagged_object_union_selects_matching_required_fields() {
-    let fixture = read_fixture("valid/comprehensive-schemas.yaml");
-    let files = generate_files(&KotlinOkhttpCodeGenerator::new(empty_config()), &fixture)
-        .expect("comprehensive fixture should generate Kotlin");
-    let temp = TempDir::new("object-union-kotlin");
-    write_generated_project(&files, &temp.path);
-    add_kotlin_closed_sum_smoke(
-        &temp.path,
-        OBJECT_UNION_SMOKE,
-        "ObjectUnionSmoke",
-        "objectUnionSmoke",
-    );
-
-    let output = gradle_closed_sum_smoke(&temp.path, "objectUnionSmoke");
-    assert!(
-        output.status.success(),
-        "generated Kotlin object-union smoke failed\nstatus: {}\nstdout:\n{}\nstderr:\n{}",
-        output.status,
-        String::from_utf8_lossy(&output.stdout),
-        String::from_utf8_lossy(&output.stderr)
-    );
-}
-
-#[test]
-fn java_any_union_is_a_last_resort_case() {
-    let fixture = read_fixture("valid/type-aliases/union-with-any.yaml");
-    let files = generate_files(&JavaOkhttpCodeGenerator::new(empty_config()), &fixture)
-        .expect("Any union fixture should generate Java");
-    let temp = TempDir::new("any-union-java");
-    write_generated_project(&files, &temp.path);
-    add_java_closed_sum_smoke(
-        &temp.path,
-        ANY_UNION_SMOKE,
-        "AnyUnionSmoke",
-        "anyUnionSmoke",
-    );
-
-    let output = gradle_closed_sum_smoke(&temp.path, "anyUnionSmoke");
-    assert!(
-        output.status.success(),
-        "generated Java Any-union smoke failed\nstatus: {}\nstdout:\n{}\nstderr:\n{}",
-        output.status,
-        String::from_utf8_lossy(&output.stdout),
-        String::from_utf8_lossy(&output.stderr)
-    );
-}
-
-#[test]
-fn kotlin_any_union_is_a_last_resort_case() {
-    let fixture = read_fixture("valid/type-aliases/union-with-any.yaml");
-    let files = generate_files(&KotlinOkhttpCodeGenerator::new(empty_config()), &fixture)
-        .expect("Any union fixture should generate Kotlin");
-    let temp = TempDir::new("any-union-kotlin");
-    write_generated_project(&files, &temp.path);
-    add_kotlin_closed_sum_smoke(
-        &temp.path,
-        ANY_UNION_SMOKE,
-        "AnyUnionSmoke",
-        "anyUnionSmoke",
-    );
-
-    let output = gradle_closed_sum_smoke(&temp.path, "anyUnionSmoke");
-    assert!(
-        output.status.success(),
-        "generated Kotlin Any-union smoke failed\nstatus: {}\nstdout:\n{}\nstderr:\n{}",
-        output.status,
-        String::from_utf8_lossy(&output.stdout),
-        String::from_utf8_lossy(&output.stderr)
-    );
-}
-
-#[test]
-fn java_tagged_closed_sum_round_trip_preserves_discriminator() {
-    let fixture = read_fixture("valid/type-aliases/discriminated-union-mixed-unit-and-allof.yaml");
-    let files = generate_files(&JavaOkhttpCodeGenerator::new(empty_config()), &fixture)
-        .expect("tagged closed-sum fixture should generate Java");
-    let temp = TempDir::new("tagged-closed-sum-java");
-    write_generated_project(&files, &temp.path);
-    add_java_closed_sum_smoke(
-        &temp.path,
-        TAGGED_SUM_SMOKE,
-        "TaggedSumSmoke",
-        "taggedSumSmoke",
-    );
-
-    let output = gradle_closed_sum_smoke(&temp.path, "taggedSumSmoke");
-    assert!(
-        output.status.success(),
-        "generated Java tagged closed-sum smoke failed\nstatus: {}\nstdout:\n{}\nstderr:\n{}",
-        output.status,
-        String::from_utf8_lossy(&output.stdout),
-        String::from_utf8_lossy(&output.stderr)
-    );
-}
-
-#[test]
-fn kotlin_tagged_closed_sum_round_trip_preserves_discriminator() {
-    let fixture = read_fixture("valid/type-aliases/discriminated-union-mixed-unit-and-allof.yaml");
-    let files = generate_files(&KotlinOkhttpCodeGenerator::new(empty_config()), &fixture)
-        .expect("tagged closed-sum fixture should generate Kotlin");
-    let temp = TempDir::new("tagged-closed-sum-kotlin");
-    write_generated_project(&files, &temp.path);
-    add_kotlin_closed_sum_smoke(
-        &temp.path,
-        TAGGED_SUM_SMOKE,
-        "TaggedSumSmoke",
-        "taggedSumSmoke",
-    );
-
-    let output = gradle_closed_sum_smoke(&temp.path, "taggedSumSmoke");
-    assert!(
-        output.status.success(),
-        "generated Kotlin tagged closed-sum smoke failed\nstatus: {}\nstdout:\n{}\nstderr:\n{}",
-        output.status,
-        String::from_utf8_lossy(&output.stdout),
-        String::from_utf8_lossy(&output.stderr)
-    );
-}
-
-#[test]
-fn java_tagged_shapes_round_trip_through_gson() {
-    let fixture = read_fixture("valid/enum-repr/enum-repr.yaml");
-    let files = generate_files(&JavaOkhttpCodeGenerator::new(empty_config()), &fixture)
-        .expect("enum representation fixture should generate Java");
-    let temp = TempDir::new("tagged-shapes-java");
-    write_generated_project(&files, &temp.path);
-    add_java_closed_sum_smoke(
-        &temp.path,
-        TAGGED_SHAPES_SMOKE,
-        "TaggedShapesSmoke",
-        "taggedShapesSmoke",
-    );
-
-    let output = gradle_closed_sum_smoke(&temp.path, "taggedShapesSmoke");
-    assert!(
-        output.status.success(),
-        "generated Java tagged-shapes smoke failed\nstatus: {}\nstdout:\n{}\nstderr:\n{}",
-        output.status,
-        String::from_utf8_lossy(&output.stdout),
-        String::from_utf8_lossy(&output.stderr)
-    );
-}
-
-#[test]
-fn kotlin_tagged_shapes_round_trip_through_gson() {
-    let fixture = read_fixture("valid/enum-repr/enum-repr.yaml");
-    let files = generate_files(&KotlinOkhttpCodeGenerator::new(empty_config()), &fixture)
-        .expect("enum representation fixture should generate Kotlin");
-    let temp = TempDir::new("tagged-shapes-kotlin");
-    write_generated_project(&files, &temp.path);
-    add_kotlin_closed_sum_smoke(
-        &temp.path,
-        TAGGED_SHAPES_SMOKE,
-        "TaggedShapesSmoke",
-        "taggedShapesSmoke",
-    );
-
-    let output = gradle_closed_sum_smoke(&temp.path, "taggedShapesSmoke");
-    assert!(
-        output.status.success(),
-        "generated Kotlin tagged-shapes smoke failed\nstatus: {}\nstdout:\n{}\nstderr:\n{}",
-        output.status,
-        String::from_utf8_lossy(&output.stdout),
-        String::from_utf8_lossy(&output.stderr)
-    );
-}
diff --git a/tests/schema_exclusive_bounds.rs b/tests/schema_exclusive_bounds.rs
new file mode 100644
index 00000000..68d4687a
--- /dev/null
+++ b/tests/schema_exclusive_bounds.rs
@@ -0,0 +1,20 @@
+use openapi_nexus::ir::types::IrSchemaKind;
+
+#[test]
+fn oas30_boolean_exclusive_bounds_retain_true_and_false() {
+    for (literal, expected) in [("true", true), ("false", false), ("1", true)] {
+        let yaml = format!(
+            "openapi: 3.0.3\ninfo:\n  title: Bounds\n  version: '1'\npaths: {{}}\ncomponents:\n  schemas:\n    Bounds:\n      type: object\n      properties:\n        value:\n          type: number\n          minimum: 0\n          maximum: 10\n          exclusiveMinimum: {literal}\n          exclusiveMaximum: {literal}\n"
+        );
+        let parsed = openapi_nexus::parser::parse_content_yaml(&yaml).expect("bound schema parses");
+        let ir = openapi_nexus::ir::lower::lower(parsed).expect("bound schema lowers");
+        let IrSchemaKind::Object(object) = &ir.schemas["Bounds"].kind else {
+            panic!("expected object");
+        };
+        let validation = object.properties["value"].validation.as_ref().unwrap();
+        assert_eq!(validation.minimum, Some(0.0));
+        assert_eq!(validation.maximum, Some(10.0));
+        assert_eq!(validation.exclusive_minimum, Some(expected));
+        assert_eq!(validation.exclusive_maximum, Some(expected));
+    }
+}