feat(compaction): explicit native protocol capabilities for Responses gateways

[fliaping]

Summary

• Add independent opt-ins for native Responses v2 compaction_trigger and v1 /responses/compact. Custom gateways retain portable summaries by default. Generation capability does not imply ciphertext replay, OpenAI identity or permission to forward caller credentials.
• Custom native v1 reuses normal Responses URL/header construction for key/local/forward routes and ordinary replay sanitization: explicit plaintext/metadata preservation, null-channel omission, drop-reasoning and strict adjacency policy. Generic OAuth retains routed compaction with its existing credential selection/refresh/dispatch fence; native v2 remains independent.
• Validate successful nonempty native v1 replacement history before committing serving/replay provenance. Failed/empty/malformed HTTP 200 bodies preserve the prior identity. Cross-provider overrides and v1 fallback remain portable; canonical transport retains its existing policy. Update provider/configuration/protocol documentation and wire-level regressions.

Verification

• Pushed head: b93c76f936fa6a2c8c2ab928d2dca60d521b61ee; contained/current dev: 7af092ca4f78828238b425bf351d5989e237f89f. Original contributor commit 61afaab15b5302dc10a954725bd2e14c69cee34e remains an ancestor. Normal push to the existing contributor branch; no force push/rebase.
• OCX_TEST_NO_QUEUE=1 bun run scripts/test.ts --parallel=2 tests/responses/native-compaction-oauth.test.ts tests/responses/native-compaction-provenance.test.ts tests/responses/native-compaction-gateway.test.ts tests/responses/native-compaction-gateway-policy.test.ts tests/responses/responses-compaction.test.ts tests/responses/responses-compaction-routing.test.ts tests/responses/responses-compaction-policy-identity.test.ts tests/responses/responses-compaction-override.test.ts tests/responses/responses-compaction-recovery.test.ts tests/responses/responses-compaction-recovery-policy.test.ts tests/responses/responses-canonical-only-top-level-fields.test.ts tests/responses/responses-opaque-blob-recovery.test.ts tests/responses/opaque-blob-wrapped-rejection.test.ts tests/adapters/reasoning-replay-identity.test.ts tests/adapters/reasoning-replay-robustness.test.ts tests/lib/reasoning-replay-scope-source.test.ts tests/providers/deepseek-reasoning-replay.test.ts: 636 pass / 0 fail, 17 files.
• New OAuth real-handler fixture: 6 pass / 0 fail, true/false/unset authenticated routed sends and missing-login zero inference; account/snapshot spies restore after each case. Removing only the OAuth direct-v1 guard produced 4 pass / 2 fail, then the guard was restored. Native v2 declaration remains enabled in these controls.
• Earlier provenance mutation red proof 19 pass / 50 fail became 69 green new cases; earlier strict plaintext proof 86 pass / 2 fail became 88 green policy cases. These regressions are included in the final 636-case batch.
• bun run typecheck, bun run structure:check, bun run privacy:scan: exit 0. Layout/tooling/ratchet/Lab guard batch initially 52 pass / 1 fail only for new seed classification. Corrected both seed regexes; final layout/tooling 19 pass / 0 fail. Ratchet 9 and Lab 25 passed before the seed-only correction; caps unchanged and both inventories registered.
• Final bun run --cwd docs-site build: exit 0, 569 pages / 79,338 internal links. No dependency declarations/lockfiles changed.
• Fresh independent gpt-6.1-sol full-diff and explicit security review PASS at b93c76f936fa6a2c8c2ab928d2dca60d521b61ee against dev 7af092ca4f78828238b425bf351d5989e237f89f: all 30 changed files reviewed, no concrete P0–P2 findings; 168 pure in-memory checks passed with zero network sends. Explicit maintainer security/merge disposition remains with the coordinator.
• Concurrent-resource exception: full local and unfiltered changed-suite execution omitted. The changed graph selected 1,782 files with zero executed cases under a no-match selection probe, which is not a correctness pass. Focused coverage above exercises the changed contracts; full-suite, live upstream, required hosted and cross-platform CI remain with the coordinator's final integration.
• PR remains draft. No merge, hosted dispatch/approval/wait, label or readiness change performed by this lane.

Checklist

• Scope stays focused and avoids unrelated cleanup.
• Docs or release notes were updated when needed.
• Security-sensitive changes were reviewed for secrets, auth, and unsafe defaults.

Review readiness checklist

• Required local validation passed; commands, results, and any full-suite exception are documented.
• I pushed my PR to a recent dev commit (at most 10 behind; a maintainer may still ask for the exact tip before merge).
• I resolved all correct Codex and CodeRabbit findings.
• My PR is ready for review.

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[github-actions]

⚠️ Deterministic hygiene checks failed.

• unsponsored_surface — This changes an authentication, workflow, release-automation, or dependency surface. MAINTAINERS.md requires security review for these; ask a maintainer to apply maintainer-sponsored once they have reviewed it. Paths: src/server/auth-cors.ts.

[github-actions]

⏳ DRAFT

• hygiene: unsponsored_surface.

What to do

• Fix unsponsored_surface — This changes an authentication, workflow, release-automation, or dependency surface. MAINTAINERS.md requires security review for these; ask a maintainer to apply maintainer-sponsored once they have reviewed it. Paths: src/server/auth-cors.ts.
• Tick all four boxes in the PR description once you're done (currently 2/4).

Review readiness checklist

• ✅ Required local validation passed; commands, results, and any full-suite exception are documented.
• ✅ I pushed my PR to a recent dev commit (at most 10 behind; a maintainer may still ask for the exact tip before merge).
• ⬜ I resolved all correct Codex and CodeRabbit findings.
• ⬜ My PR is ready for review.

2/4 boxes ticked.

This pull request was already a draft. Its draft status will be preserved after every issue above is resolved.
@fliaping Tick the boxes once required local validation has passed with commands, results, and any full-suite exception documented, your branch is on the latest dev commit, and every correct Codex and CodeRabbit finding is resolved.

[fliaping]

@lidge-jun This draft is blocked by unsponsored_surface on src/server/auth-cors.ts. Could a maintainer review the security boundary and, if satisfied, apply maintainer-sponsored? That file adds the two new capability fields at the existing editor policy level beside decodesNativeCompactionBlobs; it does not grant canonical identity or caller credential forwarding. The shared transport and compact-v1 metadata/replay handling were also independently reviewed, with no remaining security or logic findings after the regression fixes. Head: 61afaab15b5302dc10a954725bd2e14c69cee34e. Local focused validation and the full-suite resource exception are documented in the description. Required upstream CI has not passed, and CodeRabbit skipped this draft; I am keeping it in draft rather than marking it ready or applying an approval label myself. Live sub2api evidence supports v2 generation plus replay only; its native v1 endpoint is explicitly documented as unsupported in that deployment.

@Ingwannu Both failed checks (hygiene and enforce-target) report the same unsponsored_surface requirement, not a compile/test failure. Could either maintainer perform the required security review and apply maintainer-sponsored if approved? The fork author cannot submit a formal reviewer request (GitHub returned a permission error), so this comment is the review request. The label should trigger both gates to reevaluate; no source or workflow changes are needed to hide or bypass the requirement.

[Ingwannu]

For the explicit review request: I confirmed head 61afaab15b5302dc10a954725bd2e14c69cee34e and the current unsponsored_surface hold. The schema/editor mapping and the transport/replay contract require their own explicit boundary review; author-reported or model-reported validation is not that sign-off. I have not completed that review in this pass and am not adding maintainer-sponsored as a gate workaround.

Cross-platform CI 37765275217 and React Doctor 37765275223 remain action_required, not compile/test failures or passing execution. Keep Draft and retain the documented v2-generation/replay versus unsupported native-v1 distinction. No workflow execution, scan or sponsorship label was authorized here.