fix(compaction): keep compaction_trigger as final input item

[ImogeneOctaviap794]

What happened

Codex Responses requests can carry a compaction_trigger before a later input item. This showed up repeatedly with the Codex VS Code client build 26.814.41407 and was rejected upstream with:

The 'compaction_trigger' item must be the final input item.

Fix

• Normalize direct compaction_trigger items after response-context expansion.
• Keep one trigger and move it to the end of input while preserving all other items in order.
• Apply the same check at the final Codex HTTP/WS and OpenAI Responses relay send boundaries.
• Leave nested objects in tool output untouched.
• Preserve object and string input when the legacy compact endpoint is rewritten.

Tests

• Added request-body, response-cache continuation, Codex WebSocket, Codex HTTP, and OpenAI Responses relay coverage.
• go test ./...
• go vet ./...
• frontend build, tests, typecheck, and audit gate

Summary by CodeRabbit

• Bug Fixes

  • Ensured compaction triggers are unique and consistently placed at the end of request input.
  • Improved handling of string and object-form inputs while preserving valid request data.
  • Ignored nested tool-output values when detecting existing triggers.
  • Applied consistent behavior across HTTP, WebSocket, cached-history, Codex, and OpenAI Responses requests.

• Tests

  • Added coverage for trigger ordering, deduplication, input preservation, and cached histories.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 01fcedf7-a4bd-4988-85c5-fff6ccb46a0d

📥 Commits

Reviewing files that changed from the base of the PR and between 89cd930 and 8a6a2d3.

📒 Files selected for processing (7)

• proxy/compact_via_responses.go
• proxy/compact_via_responses_test.go
• proxy/executor.go
• proxy/executor_test.go
• proxy/response_cache_handler_test.go
• proxy/translator.go
• proxy/translator_test.go

Included review availability: Your plan includes up to 4 reviews per rolling hour; 3 remain after this review.

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📝 Walkthrough

Walkthrough

The change normalizes Responses request bodies so direct compaction_trigger items are unique and final. Codex and OpenAI preparation paths, cached histories, WebSocket execution, and HTTP execution now apply this ordering. Tests cover duplicate, nested, object-form, preparation, cache, and transport cases.

Changes

Compaction trigger finalization

Layer / File(s)	Summary
Trigger normalization proxy/compact_via_responses.go, proxy/compact_via_responses_test.go	Normalization removes direct duplicate triggers, preserves non-trigger items, handles string and object inputs, and appends one final trigger when required.
Response-body preparation proxy/translator.go, proxy/translator_test.go	Codex and OpenAI Responses preparation moves the trigger to the final input position. Cached previous-response histories retain the normalized trigger in prepared and expanded input output.
Transport enforcement proxy/executor.go, proxy/executor_test.go, proxy/response_cache_handler_test.go	WebSocket and HTTP execution normalize forwarded request bodies. Tests verify final trigger placement in transport and compaction fallback requests.

Estimated code review effort: 4 (Complex) | ~45 minutes

Merge Risk: ⚪ Minimal · up to 8a6a2

The change normalizes compaction triggers at request boundaries while preserving other input items and legacy input forms. No actionable merge-blocking risk remains beyond normal checks and review.

Sequence Diagram(s)

sequenceDiagram
  participant Client
  participant PrepareResponsesBody
  participant normalizeCompactionTriggerFinal
  participant ResponsesExecutor
  participant UpstreamResponsesAPI
  Client->>PrepareResponsesBody: prepare Responses request body
  PrepareResponsesBody->>normalizeCompactionTriggerFinal: normalize input items
  normalizeCompactionTriggerFinal-->>PrepareResponsesBody: one final compaction_trigger
  PrepareResponsesBody->>ResponsesExecutor: forward prepared body
  ResponsesExecutor->>normalizeCompactionTriggerFinal: enforce final trigger ordering
  normalizeCompactionTriggerFinal-->>ResponsesExecutor: normalized request body
  ResponsesExecutor->>UpstreamResponsesAPI: send normalized request

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🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 14.29% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 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: keeping compaction_trigger as the final input item.
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

🧪 Generate unit tests (beta)

• Create PR with unit tests

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