fix(runtime): name ripgrep when Grep cannot run it

[Totoro-qaq]

Summary

Without ripgrep, every Grep call on the local path failed with a bare spawn rg ENOENT, and the filesystem worker said only "Grep is unavailable in this runtime." Both paths now fail with grep_unavailable and a message that names ripgrep, gives a platform install command and the official install page. The local path looks rg up on every call, so it says to retry; the worker resolves ripgrep once when the runtime starts, so it says to restart Maka.

Two cases needed more than new copy:

• Node reports a missing spawn cwd exactly like a missing executable (spawn rg ENOENT both ways). The local path only blames ripgrep after confirming the cwd still exists; a deleted session directory keeps its original error.
• The worker pins ripgrep's realpath at startup. If that file disappears later, for example when brew upgrade removes the old keg, the spawn ENOENT was normalized to not_found ("The requested path was not found.", marked recoverable), which reads as a missing search path. The worker runs rg from the filesystem root, so that ENOENT now maps to grep_unavailable with the stale path and a restart hint.

Exit code 1 still means no matches, and EACCES, timeouts and other spawn errors keep their current handling. The Windows sandbox refusal is unchanged. Shipping ripgrep with the product (Phase 2 in the issue) is out of scope.

Fixes #5167

Thanks to @colaforniaw for the analysis and the phased plan in the issue.

Verification

Local macOS arm64, Node 22.23.1, dependencies installed with npm 11.19.0:

• Runtime suite (test:dist): 3,411 tests, 3,398 passed, 13 skipped, 0 failed.
• Five new tests in workspace-executor.test.ts and filesystem-worker.test.ts. On main the three conversion tests fail (ENOENT, not_found, and the old copy). The two guards, missing cwd keeps ENOENT and a non-executable rg keeps EACCES, pass on both; removing the cwd check makes the missing-cwd guard fail.
• The pre-push checks from CONTRIBUTING pass: npm run lint, npm run format:check, npm run build (all workspaces), npm run typecheck, and knip for apps/desktop and packages/ui. The ASF header check and git diff --check pass too.

Local path with no rg on PATH:

RipgrepUnavailableError [grep_unavailable]: Grep requires ripgrep (`rg`), which was not found on PATH. Install it with `brew install ripgrep`, or see https://github.com/BurntSushi/ripgrep#installation. Then retry.

Not run locally: Linux, Windows, and the suites of the workspaces downstream of runtime. CI covers them for this diff: scripts/ci-test-plan.mjs selects the runtime, eval, computer-use, cli, desktop and runtime-host suites plus the Linux sandbox smoke, and the filesystem-worker/** path filter triggers the Windows sandbox workflow. The packaged desktop app was not exercised.

AI use

• No generative tool made a substantive contribution
• Generative tooling made a substantive contribution

Tool(s) and scope: Claude Code investigated the defect, authored the implementation and regression tests, ran local verification, and prepared the contribution drafts. Submitted with contributor approval.

Checklist

• Tests cover the change and fail without it
• Lint, format, typecheck and the affected suites pass locally

Does this PR entail a change in behavior?

• Yes — described under Summary above
• No

🤖 Generated with Claude Code