fix(cursor): preserve internal agent errors without transport labels

[shivamhwp]

Cursor can return an internal agent-loop error as its assistant answer. T3 currently calls every RetriableError a transport failure, including [internal] Failed to run step, exceeded max retries. Preserve internal diagnostics as returned text instead of replacing their meaning with a transport label.

Refs #10480. This fixes the classification issue identified in maintainer triage; it does not repair Cursor ACP or add retries.

Validation: 42 focused parser/adapter tests pass. Both new internal-error regressions fail on the parent, including a stack trace. Targeted lint, formatting and diff checks pass. No live Cursor ACP/model request was tested. Internal Fable refinement pending.

Rebased onto main; only the diagnostic parser and its tests change.

Model and harness: GPT-6 through Codex.

Rebased on main 20363c32c9bfdbf49c2716ef11d1f18483fcc01b. Scoped validation rerun after rebasing; existing native and human review limits remain.

Summary by CodeRabbit

• Bug Fixes
  • Improved error handling so internal retryable step-failure messages are preserved as readable error details instead of being incorrectly classified as terminal transport failures.
  • Continued recognizing genuine retryable and connection-related transport errors as expected.

[macroscopeapp]

Approvability

Verdict: Approved at 6611910

Macroscope's review found this PR approvable — This is a narrowly scoped Cursor error-classification fix with regression tests. It preserves internal agent diagnostics without changing transport-error handling, product defaults, schemas, deployment, or static-analysis configuration.

Notes:

• Diff unchanged. Approvability was decided on eligibility alone.

No code changes detected at 13ba4c7. Prior analysis still applies.

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[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.5 KiB	13.6 KiB	+10 B (+0.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.0 KiB	7.0 KiB	−5 B (−0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.5 KiB	+15 B (+0.2%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.0 KiB	57.0 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	8	8	0 (0.0%)	21	✅
Claude	Total thread wire	13.6 KiB	13.6 KiB	−39 B (−0.3%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.1 KiB	7.1 KiB	−3 B (−0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.6 KiB	6.5 KiB	−36 B (−0.5%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.9 KiB	57.8 KiB	−44 B (−0.1%)	66.4 KiB	✅
Claude	Live turn messages	10	9	−1 (−10.0%)	21	✅

Baseline: e628683 · PR result: 13ba4c7 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 113.9 KiB
• Claude decoded thread snapshot: 114.6 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

[greatitself]

Independent validation of 3ab5724370bb4e7430ee9eabefa4998dd577a987 (merge-base 050e2cafb144).

Checked the internal-error diagnostic at every possible two-chunk stream split, with LF/CRLF and optional stack trace: 354 cases. This revision preserved the diagnostic in every case; the merge-base classified every case as a transport failure. Unavailable, aborted, and deadline-exceeded transport diagnostics still classified as failures. Assertions were made after the complete diagnostic arrived.

Reproduction scripts and recorded results — first.mjs; the numbered metadata file pins this PR’s tested revisions.

Model: GPT-6. Harness: Codex.

Dismissing prior approval to re-evaluate 6611910

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Advanced

Run ID: a6b87bab-6106-4970-94b0-176662026de9

📥 Commits

Reviewing files that changed from the base of the PR and between 20363c3 and 6611910.

📒 Files selected for processing (2)

• apps/server/src/provider/acp/CursorTransportFailure.test.ts
• apps/server/src/provider/acp/CursorTransportFailure.ts

Limit details: You’ve used all 10 included reviews currently available.

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📝 Walkthrough

Walkthrough

The transport-error matcher now excludes RetriableError diagnostics containing [internal]. Regression tests cover internal failures with and without stack traces.

Changes

Cursor transport classification

Layer / File(s)	Summary
Exclude internal retriable failures apps/server/src/provider/acp/CursorTransportFailure.ts, apps/server/src/provider/acp/CursorTransportFailure.test.ts	The matcher rejects RetriableError diagnostics containing [internal]. Tests verify this behavior with and without stack traces while preserving other transport-error classifications.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~5 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 13ba4

Internal agent-loop diagnostics retain their diagnostic text, and no concrete current-head merge-blocking risk is identified.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 2…
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.
Title check	✅ Passed	The title clearly and concisely describes the main change: preserving Cursor internal agent errors without classifying them as transport failures.
Description check	✅ Passed	The description explains what changed, why it changed, scope limits, validation results, and testing limitations. It does not include the template headings or checklist, but the required information i…

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/cursor-internal-error-classification

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