fix: report command start failures instead of phantom exit 0

[matheusht]

Summary

verify.ExecRunner.Run swallowed command start failures. When a command's binary does not exist (bad path, permission denied), cmd.Run() returns an error but cmd.ProcessState is nil, so the function returned (0, "", "", nil). Evidence gates then saw a phantom exit: 0 and passed checks that never actually ran.

That meant a misconfigured check/merge node (e.g. a typo'd binary name, or a tool missing on the worker) would silently pass corral's proof gates — directly undermining the "proof, not promises" guarantee.

Fix

• ExecRunner.Run now returns the real error when the command never started (err != nil && cmd.ProcessState == nil). Legit non-zero exits and timeouts are unchanged (they set ProcessState).
• startCheck / startMerge (scheduler) now surface a start failure through their evidence gates (exit 1 with the real error as stderr feedback) instead of returning an error that would bubble up and kill the run loop.

Tests

All four new regression tests fail on the previous code and pass with the fix:

• TestExecRunnerReportsStartFailure — missing binary returns a real error, never a clean exit 0.
• TestCommandGateDoesNotPassOnMissingBinary — command gate fails when the binary is absent.
• TestCheckNodeFailsGateOnMissingBinary — scheduler check node lands failed (run settles, no phantom pass).
• TestMergeFailsOnMissingVerificationBinary — scheduler merge node lands failed (run settles).

Verification

• make test — all packages pass
• go test -race — all packages pass
• go vet ./... + gofmt — clean

Summary by CodeRabbit

• Bug Fixes

  • Verification commands that cannot start now fail cleanly instead of being treated as successful.
  • Failed checks and merges are recorded accurately, including failed attempts and diagnostic details.
  • Runs continue through normal verification handling and settle without unexpected scheduler errors.

• Tests

  • Added coverage for missing verification executables in checks, merges, and direct command verification.

[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: 24055c49-1625-46c4-aadb-aafa174325f6

📥 Commits

Reviewing files that changed from the base of the PR and between 7d4acb5 and 399a680.

📒 Files selected for processing (5)

• internal/sched/gates_test.go
• internal/sched/sched.go
• internal/sched/worktree_test.go
• internal/verify/verify.go
• internal/verify/verify_test.go

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📝 Walkthrough

Walkthrough

Command startup failures now return execution errors from verification. Check and merge scheduler gates convert those failures into recorded failed results, allowing runs to settle. Regression tests cover missing binaries for direct verification, check nodes, and merge verification.

Changes

Verification and scheduling failure handling

Layer / File(s)	Summary
Command-start error contract internal/verify/verify.go, internal/verify/verify_test.go	ExecRunner.Run returns command-start errors with exit code 0. Verification tests confirm missing executables do not pass.
Scheduler gate failure handling internal/sched/sched.go, internal/sched/gates_test.go, internal/sched/worktree_test.go	Check and merge launch failures become failed gate results with diagnostic stderr and exit code 1. Scheduler tests confirm runs settle with failed nodes and failed attempts.

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

Suggested reviewers: thiago-ss

🚥 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: reporting command start failures instead of treating them as successful exit 0 results.
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

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[matheusht]

i like it