fix(server): say why threads without a project are unavailable#32342

Problem

T3 Code turns off threads without a project ("No project") when the T3 home directory sits inside a Git work tree, so scratch folders don't pick up that repository's status and checkpoints. That rule is intended, but nothing explains it. The UI just hides every "No project" entry, the server logs nothing, and agents that start a thread with scratch: true get "Threads without a project are not available on this environment." In the report, the home directory was an accidental empty git init, and nothing pointed at it.

Reproduced on main (33f85846be) with the dev server and fresh databases (T3CODE_DEV_SEED=0):

• T3 home inside an empty git init repo (the reporter's case): no "or start without a project" line on the new-thread screen, and no log line about scratch.
• T3 home at the worktree's own .t3 (inside the checkout): the same.
• T3 home outside any repository (control): the line is there.

Change

• The probe that decides scratch availability now keeps the enclosing repository's root. It reads it from the detection it already ran (GitWorkflowService.isRepository becomes repositoryRoot), so no extra git process is spawned.
• When the T3 home is inside a repository, ScratchUnavailableError names the T3 home and the repository root. It then says what to do: if the repository was created by mistake, move its .git out of the way; otherwise point T3CODE_HOME (or --base-dir) at a folder outside it, then restart.
• Agents (the MCP thread launch with scratch: true) and the projectsEnsureScratch RPC already pass this message through, so they get the reason. Mobile's "Triage an issue" calls that RPC and shows the message in its "Could not start triage" alert, so that alert now carries the reason too. Web hides its scratch entry points in this state and never makes the call.
• The server logs the same text once as a warning. The probe stays cached for the server's lifetime, so the warning appears once per start.
• Other probe failures keep the old generic message.
• No contract, setting or UI code change.
• The span name GitWorkflowService.isRepository becomes GitWorkflowService.repositoryRoot, because the operation now returns the root. The probe was its only caller.

Scope and approval

Fixes pingdotgg/t3code#32339

Verification

• vp test run apps/server/src/project/ManagedProjectFolders.test.ts: 12 passed. The existing case "offers nothing, and says why once, when the data dir sits inside a Git checkout" now also checks that the error names the T3 home and the repository root, and that two ensureScratchProject calls log exactly one warning. With main's ManagedProjectFolders.ts and GitWorkflowService.ts it fails with expected 'Threads without a project are not ava…' to include '/tmp/t3-scratch-repo-…/.t3'.
• vp run check:changed at b8e9296a49 (main merged at cfb7cae2b9): format, lint, knip, graphql, typecheck (3 packages) and the tests beside the changed files pass.
• Other probe failures and an interrupted probe are unchanged, and were not re-captured.
• Not checked: macOS and Windows path formatting in the message, read from the code only (git reports /private/var/... on macOS and forward slashes on Windows). Android palette navigation: the capture opened the palette through its mounted callback, then tapped the real "Triage an issue" item.

Evidence

Captured all required rows (R1–R5) of the fixture matrix for #32342, before 7389423507 → after 82d8f232de. R6 (other probe failures) and R7 (interrupted probe) are unchanged behaviour and were not captured.

Environment: Linux x86_64 VM fs-45, Node v26.12.1; separate real dev servers and fresh synthetic databases with T3CODE_DEV_SEED=0. Same Simlock Pixel 9 x86_64 emulator, Android 16/API 36, React Native 0.88.1, 1080×2424 physical pixels, DPR 2.625 (420 dpi), font scale 1.0, light theme. Status bars normalized to 9:41. Native-client fingerprint matched on both revisions; each mobile JavaScript bundle came from its own checkout. Before environment · After environment.

Full stills: before · after. The crop pair comes from crop-diffs.sh. At 0% the full-frame diff (526,586 px) is 526,015 px inside the crop and 571 px above it, all in the background thread-age label (12m → 15m, capture timing). Nothing changed below the crop.

R4 trigger caveat: Android's native keyboard handler at these revisions has no command-palette shortcut. Through Metro CDP, the driver invoked the existing mounted T3KeyboardCommands.onCommand("commandPalette") callback, then AgentDevice tapped the actual Triage an issue item. This ran the normal openScratch RPC and native alert path, with no source changes or injected errors. Triage capability is enabled by default; no capability override was needed. Before trigger record · After trigger record. Ordinary Android navigation into the palette remains unverified; the alert render and real RPC failure path are captured.

Each retained still passed a pair of pixel-identical screenshots taken with a 500 ms pause after the first screenshot completed. Every selected image and diff was opened and visually inspected. The complete message and both buttons fit without clipping or a stale keyboard/spinner overlay. Before stability · After stability.

Full-frame diff masks and metrics: Diff0 · DiffT · metrics.

What else changed:

• The generic message becomes the home/root diagnostic with remediation and restart advice; the CLI fallback remains and wraps after the longer message.
• The alert grows vertically: its top moves up, bottom moves down, title moves up, and the two buttons move down. Text wrapping and the white card footprint change accordingly.
• The dimmed background thread age changes from 12m to 15m. No other pixels outside the alert/its text and this age label differ at zero threshold.

Transport checks: Decoded transport equality, warning counts, filesystem controls.

Drivers (all scratch files; none committed):

• start-runtime.py
• stop-runtime.py
• runtime-driver.mjs
• pair-mobile.py
• metro-runtime.py
• capture-alert.py
• make-diffs.py
• mobile-runtime.mjs
• mobile-environment.mjs
• inspect-runtime.js
• open-command-palette.js
• finalize-evidence.py