Add test coverage for error mapping and tsjs helpers

[ChristianPavilonis]

Summary

• add exhaustive unit coverage for TrustedServerError::status_code() so each public variant is pinned to its expected HTTP response
• add direct tsjs formatting tests for unified and deferred script URL/tag helpers using computed hashes
• cover invalid UTF-8 cookie-header handling and simplify duplicate callback serde rename tests

Changes

File	Change
crates/trusted-server-core/src/error.rs	Added a table-driven test covering HTTP status code mapping for every TrustedServerError variant.
crates/trusted-server-core/src/tsjs.rs	Added direct unit tests for unified and deferred TS/JS script URL and tag helpers.
crates/trusted-server-core/src/cookies.rs	Added a unit test for invalid UTF-8 Cookie header handling in handle_request_cookies().
crates/trusted-server-core/src/models.rs	Consolidated duplicate callback serde rename tests into one focused test.

Closes

Closes #448
Closes #450
Closes #454
Closes #456

Test plan

• cargo test --workspace
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• cargo fmt --all -- --check
• JS tests: cd crates/js/lib && npx vitest run
• JS format: cd crates/js/lib && npm run format
• Docs format: cd docs && npm run format
• WASM build: cargo build --package trusted-server-adapter-fastly --release --target wasm32-wasip1
• Manual testing via fastly compute serve
• Other:

Checklist

• Changes follow CLAUDE.md conventions
• No unwrap() in production code — use expect("should ...")
• Uses tracing macros (not println!)
• New code has tests
• No secrets or credentials committed

[aram356]

Summary

Pure test additions/consolidation — no production code changes. Tests pass on wasm32-wasip1, clippy is clean, and CI is fully green. The substantive concerns below are about test design — what these tests would catch on regression — rather than correctness of what was added. Requesting changes primarily on the exhaustiveness and tautology issues; the rest are non-blocking.

Blocking

♻️ refactor

• Status code mapping test is not exhaustive at compile time — error.rs:144-247. Hand-maintained cases array means a new variant added to TrustedServerError won't fail this test. A non-exhaustive match guard would force exhaustive coverage. See inline comment.
• tsjs hash assertions are tautological — tsjs.rs:75-116. expected_hash is derived by calling the same concatenated_hash the production code calls. If concatenated_hash regressed, both sides would change in lockstep. Suggest asserting hash structure (64 hex chars) and that different module sets yield different URLs. See inline comment.
• Redundant import in tsjs test module — tsjs.rs:70. Duplicates the top-of-file import; use super::* at line 72 is sufficient (verified locally).

Non-blocking

🤔 thinking

• tsjs_deferred_script_src_uses_empty_hash_for_unknown_module locks in silent failure — tsjs.rs:137-143. Empty hash produces a 404-bound URL with no logging. Capturing this as "expected" makes future improvements look like regressions.

🌱 seedling

• Production unwrap_or_default() for unknown deferred modules is invisible — tsjs.rs:44 (unchanged in this PR, so noted in the body). single_module_hash(module_id).unwrap_or_default() silently produces a 404-bound URL with no logging when the module isn't registered. Worth a follow-up issue to add log::warn! for unregistered module IDs.

📝 note

• Issue #454 wording vs implementation — cookies.rs:353-372. Issue says "returning None" but production returns Err. Test correctly verifies current implementation; issue text is stale.

⛏ nitpick

• ["core", "creative"] redundantly includes core — tsjs.rs:76, 88. concatenate_modules always prepends core; could be simplified to ["creative"].
• HeaderValue::from_bytes expect message is slightly misleading — cookies.rs:358. Reads like a property of handle_request_cookies but is about HeaderValue::from_bytes.

CI Status

• fmt: PASS
• clippy: PASS
• rust tests: PASS (verified locally on wasm32-wasip1)
• vitest: PASS
• format-typescript / format-docs: PASS
• browser & integration tests: PASS