fix(server): distinguish missing cwd from missing binary in codex version check

[sachssem]

What Changed

assertSupportedCodexCliVersion now disambiguates ENOENT errors before blaming the binary. When spawnSync
fails with an ENOENT-class error, the handler checks whether the working directory is accessible. If the cwd is
the problem, the error message reports "Working directory '…' does not exist or is not accessible" instead
of "Codex CLI (codex) is not installed or not executable".

The check runs only in the error path (not as a preflight), so there is no TOCTOU race.

Single-file production change in codexAppServerManager.ts. One regression test added.

Why

assertSupportedCodexCliVersion passes the project directory as cwd to spawnSync. When that directory has
been deleted or moved, Node emits ENOENT. The existing error handler treats any ENOENT as a missing binary,
producing the misleading message "Codex CLI (codex) is not installed or not executable" — even when the CLI
is installed and on PATH.

This is confusing for users who see a "not installed" banner after simply moving a project folder.

Fixes #975, fixes #1932

Before / After

Before:

After:

Validation

• bun fmt — clean
• bun lint — clean
• 38/38 codexAppServerManager tests pass (1 new)

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes

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Note

Low Risk
Low risk: change is limited to the Codex CLI version-check error path and adds a single regression test; main behavior only differs when spawnSync fails with ENOENT-like errors.

Overview
Improves assertSupportedCodexCliVersion to disambiguate ENOENT-style failures by checking cwd accessibility before reporting a missing/unexecutable Codex CLI binary, surfacing a clearer “working directory does not exist or is not accessible” error when appropriate.

Adds a regression test in codexAppServerManager.test.ts to ensure startSession emits session/startFailed and throws the new cwd-specific error when the provided cwd is missing.

^{Reviewed by Cursor Bugbot for commit 2d0d25b. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Fix assertSupportedCodexCliVersion to distinguish missing working directory from missing binary

When the Codex CLI version check fails with an ENOENT-like error, it was not clear whether the binary or the working directory was missing. Now, codexAppServerManager.ts checks cwd accessibility via fs.accessSync before concluding the binary is absent, throwing a specific 'Working directory ... does not exist or is not accessible.' error when the directory is the problem. A corresponding test case is added in codexAppServerManager.test.ts.

^{Macroscope summarized 2d0d25b.}

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[macroscopeapp]

Approvability

Verdict: Approved

Straightforward bug fix that improves error message accuracy when a working directory doesn't exist during codex version check. The change is limited to an error handling path, doesn't affect normal runtime behavior, and includes a test to verify the new behavior.

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