fix(sidecars): bound streamed response bytes

[luvs01]

Summary

• Bound raw Responses SSE consumed by web-search and vision sidecars to 64 KiB before decoded and authoritative/delta copies can accumulate.
• Preserve complete events accepted up to the cap, keep current data: parsing and malformed-frame behavior, and cancel upstream without letting a rejecting or stalled cancel fail the partial result.
• Add exact-boundary, no-space data, partial-event, truncated UTF-8, and cancellation-rejection regressions.
• Keep the Sources-header linear-scan stress cases substantial while fitting below the new transport ceiling.

Verification

• Bun 1.3.14: bun test tests/web-search-parse.test.ts — 36 passed.
• bun run typecheck — passed.
• bun run privacy:scan — passed.
• git diff --check HEAD^ HEAD — passed.

Checklist

• Scope stays focused and avoids unrelated cleanup.
• Comments for both sidecar callers document the shared response ceiling.
• The branch is based on the latest dev.

Review readiness checklist

• All CI tests are green on my local testing.

• I pushed my PR to the latest dev commit.

• I resolved all correct Codex and CodeRabbit findings.

• My PR is ready for review.

Summary by CodeRabbit

• Bug Fixes

  • Limited streamed search and vision responses to 64 KiB to prevent excessively large responses.
  • Preserved complete events and partial output when responses are truncated.
  • Improved handling of cancelled or interrupted streams, including malformed UTF-8 data.

• Tests

  • Added coverage for response limits, cancellation behavior, partial events, and truncated data.

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✅ Deterministic PR hygiene checks passed.

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✅ READY

• all PR quality gates passed; the review readiness checklist is complete.

Review readiness checklist

• ✅ All CI tests are green on my local testing.
• ✅ I pushed my PR to the latest dev commit.
• ✅ I resolved all correct Codex and CodeRabbit findings.
• ✅ My PR is ready for review.

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Maintainers: @lidge-jun @Ingwannu @Wibias

[Wibias]

Please rebase this PR onto the latest dev (e8ce2b93dd3ef8074d96dee407704c5dc06e2699) before merge, then rerun the exact-head CI checks.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 2eb93497-fcb6-413e-807e-5e8d9ad87263

📥 Commits

Reviewing files that changed from the base of the PR and between d517161 and 30adf56.

📒 Files selected for processing (4)

• src/vision/describe.ts
• src/web-search/executor.ts
• src/web-search/parse.ts
• tests/web-search-parse.test.ts

---

📝 Walkthrough

Walkthrough

The sidecar SSE parser now limits streamed input to 64 KiB, processes complete accepted events, discards truncated data, and cancels the reader without waiting. Tests cover byte boundaries, UTF-8 truncation, cancellation failures, and header parsing. Comments document the limit.

Changes

Sidecar SSE response limits

Layer / File(s)	Summary
Bounded parser and cancellation src/web-search/parse.ts:32-35, src/web-search/parse.ts:182-190, src/web-search/parse.ts:204, src/web-search/parse.ts:259-275, src/vision/describe.ts:83-84, src/web-search/executor.ts:65-66	parseSidecarSSE enforces a 64 KiB accepted-byte limit, processes complete SSE data, discards truncated decoder state, and cancels the reader without waiting. Related comments document the raw-byte limit and downstream display clamp.
Parser limit validation tests/web-search-parse.test.ts:2-18, tests/web-search-parse.test.ts:27-115, tests/web-search-parse.test.ts:231-238	Tests cover exact-cap responses, incomplete events, truncated UTF-8 sequences, rejected cancellation promises, and reduced long Sources-header fixtures.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant SidecarStream
  participant parseSidecarSSE
  participant TextDecoder
  participant Reader
  SidecarStream->>parseSidecarSSE: provide streamed response chunks
  parseSidecarSSE->>TextDecoder: decode bytes below 64 KiB
  TextDecoder-->>parseSidecarSSE: return complete SSE data
  parseSidecarSSE->>Reader: cancel without waiting at byte limit
  parseSidecarSSE-->>SidecarStream: return bounded parsed output

Loading

Possibly related PRs

• lidge-jun/opencodex#1114: Adds byte-bounded SSE parsing safeguards in another parser.
• lidge-jun/opencodex#1133: Adds byte-bounded handling to relay SSE inspection.
• lidge-jun/opencodex#1155: Modifies web-search streaming limits, cancellation, and buffering behavior.

Suggested reviewers: lidge-jun, ingwannu, wibias

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 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: bounding streamed sidecar response bytes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

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[luvs01]

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[Wibias]

Thanks @luvs01 — strong bounded-stream hardening here. Capping raw sidecar SSE before decoded/authoritative copies accumulate, while preserving complete events and cancellation semantics, closes the memory-growth path cleanly. 🙏