perf(responses): reuse measured entry strings for the state snapshot

[lidge-jun]

Summary

Carries the snapshot half of #4732 by @chilung-cgu onto current dev.

writeBoundedSnapshot already serializes every candidate entry once in selectSnapshotEntries to measure its UTF-8 size, then serialized the whole selection a second time to build the payload. The selector now keeps the measured entry strings and the payload is assembled by joining them, so a snapshot write does one JSON.stringify pass over the entries instead of two. The output is byte-identical.

The router half of #4732 (static PROVIDER_REGISTRY lookup maps) is not carried: dev has since reshaped the snapshot code into selectSnapshotEntries, and a direct measurement showed no measurable routeModel change from the registry cache, so it would add state without a benefit.

Measured with a standalone script (not committed) that runs the previous dev selector verbatim against the new one on a 1,200-entry state map that produces a 23.98 MiB payload, asserting identical output before timing (30 runs after 5 warmups, two rounds):

	median	p90
previous dev	29.0–30.3 ms	32.8–36.8 ms
this change	17.6–18.0 ms	19.7–22.0 ms

Closes #4732 as carried.

Co-authored-by: WU, CHI-LUNG chilung-cgu@users.noreply.github.com

Verification

• Local test suite and typecheck were not run, on maintainer instruction; verification is the hosted CI on this exact head.
• New regression test tests/responses/responses-state-snapshot-select.test.ts pins the exact snapshot bytes across stub and resident entries, multibyte text, escapes, and both byte budgets; it is registered in scripts/test-layout/layout.json and tests/fixtures/test-layout-expected.json.
• Standalone benchmark above, with the old and new payloads compared for equality before timing.

Checklist

• Scope stays focused and avoids unrelated cleanup.
• Docs or release notes were updated when needed. (No user-visible behavior change.)
• Security-sensitive changes were reviewed for secrets, auth, and unsafe defaults. (No auth, credential, or dependency surface touched.)

Summary by CodeRabbit

• Improvements
  • Response-state snapshots continue to follow the existing entry selection and size limits, including for entries containing multibyte text.
  • Snapshot output remains consistent across different storage budgets, with an appropriate empty-state format when there are no entries.
  • These changes do not alter which entries are selected for snapshots.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-01T07:24:13.053488Z	a0d9da3	PR opened

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📚 Code guidelines (2)

scripts/AGENTS.md — auto-discovered
src/AGENTS.md — auto-discovered

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📥 Commits

Reviewing files that changed from the base of the PR and between 6429463 and a0d9da3.

📒 Files selected for processing (5)

• scripts/test-layout/layout.json
• src/responses/state.ts
• src/responses/state/snapshot-select.ts
• tests/fixtures/test-layout-expected.json
• tests/responses/responses-state-snapshot-select.test.ts

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📝 Walkthrough

Walkthrough

Snapshot selection now returns serialized entries, which the snapshot writer uses to build the version-2 payload. Tests cover serialized output, byte budgets, and the empty-store payload.

Changes

Snapshot serialization

Layer / File(s)	Summary
Select entries and build snapshot payload src/responses/state/snapshot-select.ts, src/responses/state.ts, tests/responses/responses-state-snapshot-select.test.ts, scripts/test-layout/layout.json, tests/fixtures/test-layout-expected.json	selectSnapshotEntries returns serialized entry strings and measures their UTF-8 byte lengths. snapshotPayload assembles the version-2 body, and writeBoundedSnapshot delegates payload construction to it. Tests cover exact output, budget-limited selections, and the empty-store payload. The test-layout mappings include the new test.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Refactor

Merge Risk: ⚪ Minimal · up to a0d9d

The change reuses serialized snapshot entries while preserving the existing format and selection behavior. No concrete merge-blocking issue is identified; normal CI checks should pass before merging.

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Linked Issues check	⚠️ Warning	Issue [#4732] has two coding objectives. The snapshot objective is implemented: src/responses/state/snapshot-select.ts now serializes each selected entry once, measures UTF-8 bytes, and exposes `sna…	Implement the [#4732] router objective in src/router.ts: add the required static registry lookup maps, replace the repeated PROVIDER_REGISTRY.find(...) and related Object.keys() scans in knownModelIdsForProvider, `routedProviderConf…
Docstring Coverage	⚠️ Warning	Docstring coverage is 40.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 3 files. (2 skipped: 2…	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: reusing measured serialized entry strings when building the responses state snapshot.
Out of Scope Changes check	✅ Passed	The changed files stay within the snapshot portion of [#4732]. src/responses/state/snapshot-select.ts reuses serialized entries and builds the version-2 payload. src/responses/state.ts adopts that…

Full details: Linked Issues check

Explanation

Issue [#4732] has two coding objectives. The snapshot objective is implemented: src/responses/state/snapshot-select.ts now serializes each selected entry once, measures UTF-8 bytes, and exposes snapshotPayload; src/responses/state.ts uses that payload builder. tests/responses/responses-state-snapshot-select.test.ts covers exact output, multibyte text, escapes, entry types, and byte budgets. The router objective is not implemented. The reviewed src/router.ts still uses PROVIDER_REGISTRY.find(...) in captureRouteStaticPolicy, knownModelIdsForProvider, and routedProviderConfig, and the repository evidence does not show the required static lookup maps or their routing tests. The issue remains open, so its router requirements apply.

Resolution

Implement the [#4732] router objective in src/router.ts: add the required static registry lookup maps, replace the repeated PROVIDER_REGISTRY.find(...) and related Object.keys() scans in knownModelIdsForProvider, routedProviderConfig, and routeModelInternal with map lookups, and add automated routing tests that verify lookup integrity and behavior. Alternatively, link this PR only to a snapshot-scoped issue if the router work is intentionally excluded.

Full details: Docstring Coverage

Explanation

Docstring coverage is 40.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 3 files. (2 skipped: 2 unsupported.)

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