fix(api): check tool names on every chat route and report an upstream refusal as a 400

[krisztian-gajdar]

Summary

Three fixes to chat on remote-backed models and to tool validation.

1. Single-node remote chat checks tool calls. The queued route and the single-node locally rendered path already check an upstream chat answer against the request's tools with _check_tools. The single-node route that forwards to the upstream's chat endpoint did not, so an answer that called an undeclared function was served with 200, streamed and buffered. That route now runs the same checks on every streamed event and on the buffered answer: a call to an undeclared function, any call under tool_choice: "none", a call to a function other than the named one, several calls under parallel_tool_calls: false, and no call under "required" or a named function. A violation is reported as each route reports every other upstream failure: before output, 502 upstream_error on a single node and 500 inference_error through the gateway, and an error event once a stream has started. A streamed name is checked as OpenAI clients assemble it, by concatenating the fragments of each call index. A fragment is delivered while the name so far begins a permitted name, so a stream can deliver the start of a name (for example read) before the call fails. _check_tools treats an explicit "tools": null as no tools, so such a request is served on every chat route, including the locally rendered path, which raised a 500 on it before.
2. Tool names follow the OpenAI pattern at the edge. The gateway's chat validation and the single-node chat validation refuse a tools[i].function.name outside ^[a-zA-Z0-9_-]{1,64}$ with 400 and type: "invalid_request_error", naming the field (param: "tools[i].function.name"). The code is each surface's code for every other chat validation refusal: invalid_request from the gateway and INVALID_INPUT from a single node. Before, a local profile accepted such a name and an OpenAI-compatible upstream refused it, so the same request succeeded or failed depending on which backend served it.
3. An upstream 400 or 422 on a generation call is the caller's 400. Chat, completions and native generation, streamed or buffered, and chat that the server renders through the model's template, send the upstream the caller's messages or prompt and sampling, together with defaults the model configures (sampling defaults, stop sequences, chat template arguments). All of them go through open_stream. There, a 400 or 422 without a known SIE error code (how an OpenAI-compatible API answers, for example, a prompt longer than its context) now raises InvalidInputError, as the coded INVALID_INPUT answer already did. The caller receives 400 invalid_request with fixed text that repeats nothing the upstream sent and does not name it, on the single-node and queued routes. Before, it was 502 upstream_error on a single node and 500 inference_error in a cluster. An upstream that refuses a configured default answers the same way, so open_stream logs every refused generation request at WARNING with the upstream's name and the status, and an operator sees a refused default as a refusal of every request. Encode, score and extraction keep reporting that answer as a server error through send_bounded. 401, 403, 404, 413, and a 400 or 422 with another known SIE code stay server errors. 429 and 5xx stay retryable.

REMOTE_BACKENDS.md documents the refusal mapping, the log line, the tool checks with each route's status, and the name rule with each route's code, in "Controls and failure behavior".

Behavior changes

• Tool names. A chat request whose tool name contains . or another character outside [a-zA-Z0-9_-], or is longer than 64 characters, now receives 400 on every chat route, including local GPU profiles that accepted it before. OpenAI and OpenAI-compatible APIs already refuse such names, so a caller that sends them must rename its tools (for example math.factorial to math_factorial). No test, fixture or example in this repository sends such a name through a chat route. The one dotted name, a.b+c in test_tool_call_grammar.py, drives the grammar builder directly and is unaffected.
• Repeated tool-call names. On a single node, a stream whose upstream repeats function.name on every tool-call delta is now cut with an upstream_error event after the first delta, because the concatenated name (read_fileread_file) is not declared. The queued route already did this. OpenAI's streaming format sends a name once, and a client that concatenates fragments would assemble the same undeclared name.
• Upstream refusals. A remote generation request that an upstream refuses with an uncoded 400 or 422 now answers 400 instead of a server error, and the server logs upstream '<name>' refused a generation request: the upstream refused the input (<status>) at WARNING. Under single-node fallback, such a failed remote attempt now reports X-SIE-Fallback-Error: INVALID_INPUT instead of INFERENCE_ERROR.

Tests

• tests/api/test_remote_chat.py drives the real single-node routes against a scripted upstream, for both upstream kinds:
  • six answers outside the requested tools, streamed and buffered, are refused;
  • six answers within them are served unchanged;
  • streamed names are accumulated per call index: a name split across events and a second call that arrives in a later event are served, and a name repeated on every delta is cut after the first delta;
  • an explicit "tools": null is served, streamed and buffered, on the forwarded route and on the locally rendered path;
  • an uncoded 400 or 422 gives 400 with code invalid_request, without the upstream's text, name or X-SIE-Upstream, and with exactly one WARNING line, on native generation, chat and completions (streamed and buffered) and responses. On chat, 401, 403 and 404 stay 502;
  • invalid tool names never dispatch and get the same code as the route's other tool refusals, and valid ones, including a 64-character name, reach the upstream;
  • native streamed generation answers an uncoded upstream 400 with 400 before the stream starts.
• tests/processors/test_remote_chat.py drives the queued StreamingProcessor against the scripted upstream. An uncoded 400 or 422 gives invalid_request. A 400 with MODEL_NOT_FOUND, a 413, 401, 403 and 404 give inference_error. The existing single-attempt test now expects invalid_request for an uncoded 400.
• The gateway test chat_tool_names_outside_the_openai_pattern_are_refused_before_routing drives proxy_chat. Invalid names get 400 invalid_request on tools[1].function.name before routing. Valid names pass validation and reach the model's tool-capability gate.
• tests/adapters/test_remote_openai_adapter.py::test_an_upstream_refusal_is_a_server_error_that_repeats_nothing_it_sent is unchanged and still passes: encode keeps 500 for an uncoded upstream 400 or 422.

Mutation checks (each mutation applied alone, then reverted):

Mutation	Tests that fail
Drop the streamed tool check in _remote_chat_events	14 streamed cases: 12 refusals and 2 repeated names
Drop the buffered tool check	12 buffered refusal cases
Ignore the streamed call index (index = position)	2 second-call-in-a-later-event cases
Assign each streamed name fragment instead of concatenating	4 name-split-across-events and name-repeated-per-delta cases
body.get("tools", []) in _check_tools	8 explicit-null-tools cases, forwarded and rendered
Drop the server name check, or use match instead of fullmatch	10 invalid-name cases
Server pattern {1,65}, or allow .	the 65-character and dotted-name cases
open_stream without caller_request=True	44 uncoded 400/422 cases on every generation surface and the queued route
Drop the refusal log line	28 cases across native, chat, completions and responses
Treat any known code as the caller's refusal	the queued 400 MODEL_NOT_FOUND case
Treat every 4xx as the caller's refusal	22 401/403/404/413 cases
Default caller_request to True (encode included)	the existing encode refusal test
Gateway: drop the name check, allow ., or allow 65 characters	chat_tool_names_outside_the_openai_pattern_are_refused_before_routing

Validation

• mise run lint, mise run typecheck: pass, after merging origin/main.
• tests/api, tests/processors and tests/adapters under packages/sie_server/tests: 7,019 passed, 76 skipped. After merging origin/main, tests/api, the remote chat processor suites and the remote OpenAI adapter suite: 1,547 passed.
• mise run gateway-test (with NATS): 1,738 passed, and 1,749 with cloud-storage. mise run gateway-clippy and mise run gateway-fmt -- --check: pass. The gateway is unchanged since that run.
• tools/ci/check_public_tree.py: pass.

Summary by CodeRabbit

• New Features
  • Chat tool names must now contain 1–64 ASCII letters, numbers, underscores, or hyphens.
  • Responses are checked against the tools and call constraints in the request, including during streaming. Invalid tool calls are rejected.
• Bug Fixes
  • Upstream generation refusals without a recognized error code now return a caller-facing error. Other upstream failures are classified separately, and refusal details are not exposed in responses.
  • Chat requests with an explicit tools: null are handled correctly.

[coderabbitai]

📝 Walkthrough

The change updates upstream refusal classification for caller-originated generation requests. It also validates chat tool names and checks buffered and streamed remote tool calls against request constraints.

Changes: Upstream Refusal Classification

Layer / File(s)	Summary
Map upstream refusals packages/sie_server/src/sie_server/adapters/remote/_http.py, packages/sie_server/tests/api/test_remote_chat.py, packages/sie_server/tests/processors/test_remote_chat.py, packages/sie_server/REMOTE_BACKENDS.md	Generation requests that forward caller input classify uncoded upstream 400 and 422 responses as input errors. The changes log refused input and preserve distinct mappings for other status and error-code combinations. Tests cover sanitized responses and refusal details. The guide documents the mappings.

Chat Tool Validation

Layer / File(s)	Summary
Validate tool function names packages/sie_gateway/src/handlers/proxy.rs, packages/sie_server/src/sie_server/api/openai_local.py, packages/sie_server/tests/api/test_remote_chat.py, packages/sie_server/REMOTE_BACKENDS.md	Gateway and local chat routes accept tool function names matching ^[a-zA-Z0-9_-]{1,64}$ and reject other names. Tests cover accepted and rejected names.
Check remote tool-call responses packages/sie_server/src/sie_server/api/openai_local.py, packages/sie_server/src/sie_server/processors/remote_chat.py, packages/sie_server/tests/api/test_remote_chat.py, packages/sie_server/REMOTE_BACKENDS.md	The local chat route checks buffered and streamed remote tool calls against the request’s tool policy. Tests cover undeclared calls, choice and parallel-call constraints, required calls, and permitted responses. Explicit tools: null is handled as an empty tool list.

Sequence Diagram(s)

sequenceDiagram
  participant Client
  participant OpenAIChatRoute
  participant UpstreamBackend
  Client->>OpenAIChatRoute: submit chat request and tool policy
  OpenAIChatRoute->>UpstreamBackend: dispatch chat request
  UpstreamBackend-->>OpenAIChatRoute: return buffered response or stream chunks
  OpenAIChatRoute->>OpenAIChatRoute: accumulate streamed tool names and check tool policy
  OpenAIChatRoute-->>Client: return response or upstream error

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Suggested reviewers: svonava

Priority: ➖ Normal

Merge Risk: 🔵 Low · up to 92c48

Malformed upstream tool output may produce an unexpected chat error. The risk is bounded, but the response boundary should be hardened or adapter validation confirmed.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 6.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 30 functions across 5 files. (1 skipped: 1…	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

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Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly summarizes the two main changes: chat tool-name validation across routes and mapping upstream refusals to a 400 response.

Full details: Docstring Coverage

Explanation

Docstring coverage is 6.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 30 functions across 5 files. (1 skipped: 1 unsupported.)

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[krisztian-gajdar]

Review round, head 92c48101. An independent review of 9ce2eeb2 raised six gaps and five risks. Each one is fixed with a test or answered below.

Fixed

• Explicit "tools": null crashed with a plain 500. _check_tools read body.get("tools", []), which is None for an explicit null. It now reads body.get("tools") or []. That also fixes the locally rendered path, which on main already raised the same TypeError at the end of any answer to such a request. Tests: test_direct_remote_chat_serves_explicit_null_tools (streamed and buffered, both upstream kinds) and a null-tools case of test_onboarded_direct_chat_uses_raw_template_without_chat_dispatch. Reverting the fix fails all 8.
• Per-index name accumulation was untested. test_direct_remote_chat_accumulates_each_streamed_tool_name_by_call_index covers three streams: a name split across events (read + _file), a second call that arrives in a later event (index 1), and a name repeated on every delta. It also checks which names reach the caller. index = position fails the 2 later-event cases. Assigning each fragment instead of concatenating fails the 4 split and repeated cases.
• Item 3 evidence was incomplete. test_uncoded_upstream_refusal_is_a_logged_callers_400_on_every_generation_surface sends an uncoded 400 and 422 on native generation, chat and completions (each streamed and buffered) and on responses, for both upstream kinds. Each case checks 400, code invalid_request, no upstream text, no upstream name, no X-SIE-Upstream, and one request.
• A configured default the upstream refuses looked like a client error, and nothing was logged. open_stream now logs every refused generation request at WARNING: upstream '<name>' refused a generation request: the upstream refused the input (<status>). The line carries the status and nothing the upstream sent. The surface test above asserts that exact line. Dropping it fails all 28 cases. The caller's answer is unchanged. The log goes to the operator, who sees a refused default as a refusal of every request. This does not overlap the route-level RemoteUpstreamError logging proposed in feat(examples): run the OpenCode example on self-hosted SIE with an OpenRouter upstream #735, which does not catch InvalidInputError.
• Documentation accuracy.
  • REMOTE_BACKENDS.md now says a generation request carries the caller's messages or prompt and sampling, together with configured sampling defaults, stop sequences or chat template arguments. It includes the rendered chat path and documents the log line.
  • It drops the "build every upstream body themselves" rationale for encode, score and extraction and states only their behaviour.
  • It states the tool-violation statuses: 502 upstream_error on a single node and 500 inference_error through the gateway before output, and an error event after.
  • It states that a fragment that begins a permitted name is delivered before a later fragment can fail the call, and that a name repeated on every delta fails.
  • The _http.py module and open_stream docstrings now cover buffered chat too.
• The repeated-name behaviour change was undisclosed. It is now in the PR body's behaviour changes and in REMOTE_BACKENDS.md, and the name-repeated-per-delta case pins it. The queued route already cut such a stream. The OpenAI streaming format sends a name once, and a client that concatenates fragments assembles the same undeclared name.

Answered, not changed

• Tool violations answer 502 upstream_error on a single node, not the queued route's 500 inference_error. _check_tools raises the same RemoteUpstreamError, with the same text, on both routes. Each route then gives that exception the answer it gives every other upstream contract failure. The single-node remote chat route's except RemoteUpstreamError returns _upstream_error_response() (502) for usage over the token bound, an oversized answer and an invalid chat answer alike. The queued route publishes every RemoteUpstreamError as inference_error, which the gateway returns as 500. Giving tool violations alone a 500 on a single node would give one route two answers for the same failure class. The difference is a property of the two routes and predates this PR. REMOTE_BACKENDS.md now states both.
• The single-node name refusal has code INVALID_INPUT, and the gateway's has invalid_request. Status 400, type: "invalid_request_error" and param: "tools[i].function.name" agree. The codes follow each surface's convention for every chat validation refusal. _bad_request defaults to INVALID_INPUT for every single-node chat validation, and the gateway's validate_chat_tools uses oai_code::INVALID_REQUEST for every one. A local and a remote profile behind the same surface get the same answer, which is what the edge check is for. Giving this one check a different code would split the single-node validator. test_tool_names_outside_the_openai_pattern_never_dispatch now pins the name refusal's code as equal to a sibling refusal's (a tool with no name). The doc states both codes. Aligning the two surfaces' codes would touch every chat validation and belongs in its own change.
• The rendered chat path maps an uncoded 400 to the caller's 400. Its upstream body is the caller's messages rendered through the model's template, plus the caller's sampling and the configured defaults. That is the same content as the forwarded route in another shape. prepare_rendered_chat bounds the prompt only by bytes and counts no tokens, so the most likely uncoded 400 there is a prompt longer than the upstream's context, which is the caller's input. A refused configured default is visible in the new log line on this path too.

Validation: mise run lint and mise run typecheck pass. Before the merge, tests/api, tests/processors and tests/adapters pass (7,019 passed, 76 skipped). After merging origin/main (#736), tests/api, the two remote chat processor suites and the remote OpenAI adapter suite pass (1,547 passed). The gateway is unchanged in this round.

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Review comments at @packages/sie_server/src/sie_server/api/openai_local.py:
- Line 1283: Validate each tool-call fragment before updating names: ensure tool
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RemoteUpstreamError for invalid shapes before concatenation. Preserve the
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• packages/sie_server/src/sie_server/processors/remote_chat.py
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