[adamcavendish]

Summary

Use structured sigil-stitch fragments for TypeScript Fetch response-status dispatch, lazy error payloads, and named/array JSON conversion callbacks. Keep types and imports semantic through final rendering.

Problem

Response dispatch and error throws still assembled dynamic source with formatted strings. That bypassed structured code composition and made import tracking and emission failures harder to preserve.

Behavior

Surface	Result
Response selection	Exact statuses precede wildcards, then the existing fallback.
Error payloads	JSON, text, blob, and void decoding stay lazy and cached.
camelCase JSON responses	Named and array conversion callbacks retain semantic imports.
Emission failures	Invalid lowered types retain API context and original errors.
Source layout	Long-type continuations use structural branch indentation.
JVM output expectations	Closed-sum snapshots reflect normalized nested code composition.

Compatibility and boundaries

• No generated-client API or wire-behavior change is intended. The new fixture covers exact, wildcard, default-only, success-only, and error-only response combinations in ordinary and camelCase configurations.
• Existing TypeScript golden changes are limited to continuation indentation in three projects. The 50 changed JVM golden files and two adapter-render expectations differ only in whitespace; JVM generator logic and strict assertions are unchanged.
• This PR does not change Cargo.toml or Cargo.lock, add dependency patches, or include any machine-local Cargo configuration.
• Dependency prerequisite: these emissions and expectations require the upstream sigil-stitch code-composition fixes (d87abd2 and 455acfe), which are not in the currently published and locked 0.7.3 release. Without that fix, exact-render and golden checks fail. The released dependency prerequisite must be resolved before merging; fixed-checkout results must not be treated as validation of the unchanged published dependency.