fix(server): check project directory on location boot

[opencode-agent]

Stacked review of #51171

This PR is based on an exact mirror of OpeOginni:folder-access-errors at eb15a9b so the Changes tab shows only the follow-up. GitHub App permissions do not allow us to create a PR against the contributor’s fork directly. This base branch is for review only; merging this PR into the mirror will not update #51171 or v2. After review, the commits can be cherry-picked onto the contributor branch or the final fix.

• Move the directory check into the per-location graph build, so it runs on boot/reload rather than every HTTP request.
• Keep failed boots retryable and return the existing typed 400/403 errors at the HTTP boundary. Skip the local check for workspace-backed locations.
• Remove the directoryCheck option at Brendan’s request for review. The probe now runs whenever the map has FSUtil and the location is bare.
• Add regression coverage for repeated requests and reload.

Review caveat: FSUtil is also present in workerd (for temporary filesystem use) and simulation. This change removes their explicit opt-outs, so a bare location in either environment now attempts a host realPath probe. Existing workerd coverage only tests /api/info, not location boot. Do not treat the passing tests as proof that those environments support this behavior; resolve this concern before merging into a runtime branch.

Verification: server tests (17 passed), core location/node-build tests (30 passed), scoped typechecks for core/server/client/protocol (4 passed), and oxlint (0 errors). Full bun run check is blocked by this host’s Node 18: Astro requires Node >=22.12 for @opencode/www.

Requested by: @Brendonovich (Brendan via Slack)