Rename /__ts/page-bids to /_ts/page-bids

[prk-Jr]

Summary

• /__ts/page-bids was the only internal Trusted Server route using a double-underscore prefix; every other internal path lives under /_ts/. This moves the SPA re-auction endpoint to /_ts/page-bids and switches the tsjs client fetch to match.
• A browser runs whichever tsjs bundle it was already served, so pages loaded before the rename — and cached bundles — keep requesting the old path. On a SPA that path is what delivers ads for in-session navigations, so /__ts/page-bids stays registered to the same handler as a transition alias. Removal is tracked by Remove the deprecated /__ts/page-bids transition alias #970.
• Route coverage was missing for the page-bids GET registrations on Cloudflare and Spin. Mutation testing confirmed a broken registration previously passed every suite; that gap is now closed.

Changes

File	Change
crates/trusted-server-core/src/publisher.rs	Add PAGE_BIDS_PATH / PAGE_BIDS_LEGACY_PATH as the single source of truth; log an info line when the alias serves a gate-passed request; add deprecated_alias_response_matches_canonical_path; split make_page_bids_request_on out of make_page_bids_request; update doc comments
crates/trusted-server-adapter-fastly/src/app.rs	Register both paths via NAMED_ROUTES; add page_bids_serves_canonical_path_and_deprecated_alias, pinning the consts to their literal values
crates/trusted-server-adapter-axum/src/app.rs	Register both paths; named_routes() widens to [NamedRoute; 13]
crates/trusted-server-adapter-cloudflare/src/app.rs	Collapse four near-identical registrations into a loop over both paths, matching the existing legacy_admin_deny pattern
crates/trusted-server-adapter-spin/src/app.rs	Register both paths; named_fallback_paths() widens to 13 so non-primary methods still reach the publisher fallback
crates/trusted-server-adapter-axum/tests/routes.rs	Pin GET/OPTIONS on both paths in all_explicit_routes_are_registered
crates/trusted-server-adapter-cloudflare/tests/routes.rs	Same route-table assertions
crates/trusted-server-adapter-spin/tests/routes.rs	Add page_bids_get_is_routed_on_canonical_path_and_alias (Spin has no route-list test)
crates/trusted-server-integration-tests/tests/parity.rs	Preflight-denial parity now loops both paths
crates/trusted-server-js/lib/src/integrations/gpt/index.ts	SPA hook fetches /_ts/page-bids
crates/trusted-server-js/lib/test/integrations/gpt/spa_hook.test.ts	Update three fetch assertions
crates/trusted-server-core/src/auction/{endpoints,orchestrator,telemetry}.rs, integrations/gpt.rs	Doc-comment path updates

Closes

Closes #942

Test plan

• cargo test-fastly && cargo test-axum — also cargo test-cloudflare && cargo test-spin
• cargo clippy-fastly && cargo clippy-axum — also clippy-cloudflare, clippy-cloudflare-wasm, clippy-spin-native, clippy-spin-wasm
• cargo fmt --all -- --check
• JS tests: cd crates/trusted-server-js/lib && npx vitest run (411 passed)
• JS format: cd crates/trusted-server-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: parity suite (--test parity, 13 passed); mutation testing of all 8 registrations

Mutation testing

Because the alias exists precisely to avoid a silent ad-serving gap, each registration was deliberately broken to confirm a test fails. All 8 are caught (Fastly / Axum / Cloudflare / Spin × canonical / alias). Before this PR's added coverage, breaking the Cloudflare GET registration — canonical or alias — passed every suite.

Verified the built bundle rather than assuming: dist/ is gitignored and regenerated by build.rs; the rebuilt tsjs-gpt.js contains /_ts/page-bids once and /__ts/ zero times. The separately-shipped external Prebid bundle takes only prebid/index.ts and does not embed this path, so there is no half-ship risk.

Also confirmed the namespace move does not change behaviour: every handler regex in the repo is ^/_ts/admin, which does not match /_ts/page-bids, so the route is not pulled behind basic auth. No starts_with("/_ts") special-casing exists; integration path filters are all under /integrations/; cache and privacy logic key on headers, never path.

Notes

The docs/superpowers/ plan and spec files still reference /__ts/page-bids. They are dated point-in-time design records that also describe code shapes since changed, so they were left as history rather than rewritten. Happy to sweep them if reviewers prefer.

Not applicable: no config-derived regex or pattern compilation is touched.

Checklist

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