fix(server): add sanitized hints for common VCS command failures

[jaikhuranna]

What Changed

VCS command failures now explain themselves. When a git/provider-CLI process exits non-zero, we pattern-match stderr against a small set of known failure modes and emit a fixed, sanitized hint in the error message instead of the generic "Process exited with a non-zero status."

Examples:

VCS process failed in GitVcsDriver.initRepository: git (/path/to/project) exited with 128
- Permission denied. Check that the directory is owned by your user account and writable.

- SSH authentication failed. Check that your SSH key is set up for this host, or use an HTTPS URL.

- The directory is owned by a different user, which git refuses to trust. Fix the directory ownership or add it to git's safe.directory list.

• packages/contracts: VcsProcessExitFailure gains an optional failureDetail consumed by the command-failed branch of VcsProcessExitError.fromProcessExit. Wire schema unchanged.
• apps/server: new resolveCommandFailureHint in VcsProcess (hints: SSH Permission denied (publickey), git dubious ownership, Permission denied, not a git repository), wired into the non-zero-exit path and both GitCommandError sites in GitVcsDriverCore. Op-specific fallbackErrorDetail keeps priority.
• Tests: 4 hint cases in VcsProcess.test.ts (including multi-method SSH stderr like Permission denied (publickey,password)) and a GitVcsDriverCore.test.ts case covering the GitCommandError path — each asserting the hint appears and raw stderr never does.

Why

VCS process stderr is deliberately not retained in error messages (CLIs like gh can print tokens), which leaves users with "exited with 128" and no way to self-diagnose. Real case: git init failing on a root-owned project directory surfaced nothing actionable. This keeps the no-raw-stderr security posture but recovers the reason for the most common failure modes with fixed, secret-free text. Hints only apply where no operation-specific fallbackErrorDetail exists, and unknown failures keep the previous generic message.

UI Changes

N/A — error strings only; they render in the existing error surfaces on web/desktop/mobile via the current error serialization.

Checklist

• This PR is small and focused
• I explained what changed and why
• N/A — no UI changes (before/after screenshots not applicable)
• N/A — no animation/interaction changes

Verification: full src/vcs suite 93/94 (the one failure, preserves newline characters in worktree paths when listing refs, fails identically on pristine main — pre-existing/environmental); tsc --noEmit clean for the server package. Includes tests for the multi-method SSH stderr variant and the GitCommandError hint path.

Done with GLM (fireworks-ai/glm-flash-latest) via the OpenCode harness in T3 Code.

Summary by CodeRabbit

• Bug Fixes
  • Git command failures now provide clearer, user-friendly guidance for common issues, including SSH authentication, permission problems, unsafe repository ownership, and non-repository directories.
  • Error messages use sanitized hints instead of exposing raw command output, reducing the risk of sensitive details appearing in user-facing failures.
  • Generic failures now provide more specific details when available, while authentication, rate-limit, and not-found error handling remains unchanged.

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Reviewing files that changed from the base of the PR and between 6f00d38 and 826c878.

📒 Files selected for processing (5)

• apps/server/src/vcs/GitVcsDriverCore.test.ts
• apps/server/src/vcs/GitVcsDriverCore.ts
• apps/server/src/vcs/VcsProcess.test.ts
• apps/server/src/vcs/VcsProcess.ts
• packages/contracts/src/vcs.ts

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📝 Walkthrough

Walkthrough

Git failures now derive sanitized hints from selected stderr patterns. The hints flow through VCS exit errors and Git driver paths. Tests cover permission-denied, dubious-ownership, and SSH authentication failures without exposing raw stderr.

Changes

Git failure hints

Layer / File(s)	Summary
Failure detail contract packages/contracts/src/vcs.ts	VcsProcessExitFailure now accepts optional failureDetail, which VcsProcessExitError uses for generic command failures.
Failure hint resolution apps/server/src/vcs/VcsProcess.ts	VcsProcess matches selected Git stderr patterns and attaches fixed, secret-free hints only to command-failed errors.
Git driver integration and validation apps/server/src/vcs/GitVcsDriverCore.ts, apps/server/src/vcs/GitVcsDriverCore.test.ts, apps/server/src/vcs/VcsProcess.test.ts	Git command paths consult resolved hints. Tests verify permission, ownership, and SSH failure details without raw stderr in the error message.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~15 minutes

Change: Bug fix

Suggested reviewers: bil0000

Merge Risk: ⚪ Minimal · up to 826c8

The sanitized failure-hint paths have no unresolved merge-blocking risk in this change.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: adding sanitized hints for common server-side VCS command failures.
Description check	✅ Passed	The description includes complete What Changed and Why sections, explains the security rationale and scope, documents that UI changes are not applicable, completes the checklist, and reports verificat…
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 5…
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.

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• 🪄 Fix CodeRabbit comments on this PR

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Inline comments:
In `@apps/server/src/vcs/GitVcsDriverCore.ts`:
- Around line 841-849: Add direct GitVcsDriverCore coverage using recognized
stderr failure patterns, exercising both runGitCommand’s resolved stderr.text
path and executeGit’s resolved result.stderr path. Assert that each non-zero
exit produces the exact sanitized GitCommandError.detail from
resolveCommandFailureHint, while preserving the existing secret-redaction
coverage.

In `@apps/server/src/vcs/VcsProcess.ts`:
- Line 112: Update the SSH authentication error pattern in VcsProcess to match
comma-separated combinations of publickey, password, and keyboard-interactive
methods, while preserving matching for a single method and ensuring it is
evaluated before the generic permission-denied matcher.

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📒 Files selected for processing (4)

• apps/server/src/vcs/GitVcsDriverCore.ts
• apps/server/src/vcs/VcsProcess.test.ts
• apps/server/src/vcs/VcsProcess.ts
• packages/contracts/src/vcs.ts

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[jaikhuranna]

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