Add auction endpoint request handling coverage

[ChristianPavilonis]

Summary

• Add route-level coverage for /auction request handling
• Return 400 Bad Request for malformed auction JSON payloads
• Cover semantic validation failures, orchestration failures, and a stable no-network success path
• Note /auction now returns 502 Bad Gateway when every configured provider is skipped, disabled, or fails to launch instead of returning 200 with an empty seatbid.

Closes #452

Testing

• cargo test -p trusted-server-adapter-fastly route_tests -- --nocapture
• cargo test -p trusted-server-core auction:: -- --nocapture
• cargo fmt --all -- --check
• cargo test --workspace
• cargo clippy --workspace --all-targets --all-features -- -D warnings

[prk-Jr]

Summary

The route coverage is useful, but one new test now codifies a configuration typo as a request-time 502 instead of a startup/configuration failure.

Blocking

🔧 wrench

• Missing auction provider should fail startup, not become request-time 502: auction.providers = ["missing-provider"] currently builds the route stack and only fails when /auction is called. Invalid enabled providers should fail during startup/registration so deployments do not start with a mistyped provider list.

CI Status

• cargo fmt / clippy: PASS
• rust tests: PASS
• js tests: PASS
• integration tests: PASS

[aram356]

Summary

The endpoint change correctly fixes a real bug — malformed /auction JSON now returns 400 instead of 502 — and the three accompanying tests for that path are solid. The contentious piece (already flagged by @prk-Jr) is the fourth test, which codifies a configuration typo (providers = ["missing-provider"]) as a request-time 502. That conflicts with the project rule in CLAUDE.md and locks in disputed behavior with an asserting test ahead of the #669 follow-up. Inline notes cover the blocking item, two thinking notes, two refactor suggestions, and one seedling.

Blocking

🔧 wrench

• Test codifies a config typo as request-time 502, conflicting with the project rule (crates/trusted-server-adapter-fastly/src/route_tests.rs:389-400). See inline comment for the two suggested resolutions (validate at startup, or drop just this test pending #669).

Non-blocking

🤔 thinking

• Orchestrator guard behavior change is broader than the typo case (crates/trusted-server-core/src/auction/orchestrator.rs:365-369). Inline.
• Test name "no_providers" is ambiguous (crates/trusted-server-adapter-fastly/src/route_tests.rs:377). Inline.

♻️ refactor

• Error message lacks diagnostic info (crates/trusted-server-core/src/auction/orchestrator.rs:367). Inline alongside the thinking note.
• TOML duplication between test settings helpers (crates/trusted-server-adapter-fastly/src/route_tests.rs:166-196). Inline.

🌱 seedling

• Add a unit-level test for the new orchestrator guard. The existing TODO at orchestrator.rs:765-778 already notes the gap. A fake AuctionProvider whose request_bids returns Err would cover the "registered-but-failed-to-launch" path that the route-level test doesn't reach. Could land with the #669 follow-up.

CI Status

• cargo fmt: PASS
• cargo clippy: PASS
• cargo test (Rust): PASS
• vitest (JS): PASS
• format-typescript / format-docs: PASS
• integration tests + browser integration tests: PASS
• CodeQL / Analyze: PASS

[aram356]

Summary

Adds route- and orchestrator-level coverage for /auction, reclassifies malformed-body parsing as 400, fails the auction with 502 when no provider request launches, and validates configured provider/mediator names at startup. The changes are correct, well-tested, and convention-aligned. Verified locally: cargo fmt --check, cargo clippy --all-targets --all-features -D warnings, and the affected auction:: / route_tests suites all pass. No blocking issues — approving with a few non-blocking observations.

Non-blocking

🤔 thinking

• Whole-service blast radius for an auction config typo — build_orchestrator runs in the per-request entrypoint (main.rs:85) before routing, so the new validate_configured_provider_names makes an unregistered/typo'd provider return a Configuration error (500) for every route, not just /auction. This matches the pre-existing fail-closed posture of build_orchestrator (a bad server_url already does this) and aligns with the "don't silently disable invalid providers" convention — but it's the opposite philosophy from the adjacent consent-store handling, which deliberately scopes failures to consent routes (enshrined by configured_missing_consent_store_only_breaks_consent_routes). Worth a conscious maintainer thumbs-up that taking the whole service down on an [auction].providers typo is the intended tradeoff. (crates/trusted-server-core/src/auction/orchestrator.rs:56, crates/trusted-server-adapter-fastly/src/main.rs:85)
• Empty-provider route test covers the old guard, not the new branch — see inline comment on route_tests.rs:383.

🌱 seedling / ⛏ nitpick

• Validation message wording — see inline comment on orchestrator.rs:72.
• Irrelevant bids in valid_banner_ad_unit_body — see inline comment on route_tests.rs:248.

CI Status

• fmt: PASS (local)
• clippy: PASS (local, core + adapter, -D warnings)
• rust tests: PASS (local — auction:: 29 passed, route_tests 4 passed)
• js tests: N/A (no JS changes)
• CodeQL (GitHub): PASS

[aram356]

🤔 thinking — This test uses providers = [], which hits the pre-existing "No providers configured" guard in orchestrator.rs (run_providers_parallel, ~line 284), not the new pending_requests.is_empty() branch (~line 391) this PR adds. Both return TrustedServerError::Auction → 502, so the route-level mapping is verified — but the new branch's end-to-end route mapping isn't covered here (only the LaunchFailingProvider orchestrator unit test exercises it).

Consider a route test with a registered-but-disabled provider so the request reaches the new branch end-to-end.

[aram356]

🌱 seedling — The message "configured but not registered" leans on internal vocabulary. The most common real cause is a disabled (or absent) integration, which "not registered" doesn't hint at. A more actionable phrasing, e.g.:

message: format!(
    "Auction provider `{provider_name}` is listed in [auction] but no enabled integration provides it"
),

would point an operator straight at the fix (enable the integration / fix the name).

[aram356]

⛏ nitpick — This bids array references bidder "missing-provider" that is never asserted on, and the only caller runs with providers = [], so it's irrelevant to the assertion. For a helper named valid_banner_ad_unit_body it's a bit confusing — dropping the bids block would read cleaner.