Address GHCP review: stash race, signal ordering, a11y, outcome schema, error handling

- extension.mjs: serialize stash read-modify-write behind a per-desk mutex;
  order signals by explicit ISO timestamp (clone-safe) not mtime; keep desks
  with malformed latest signal as 'awaiting'; gate calibration badge on a real
  gap value; add prefers-reduced-motion CSS; toast aria-live region; rename
  open_desk -> get_desk_path (returns path, no session); handle server.listen errors.
- signal-write/SKILL.md: document timestamp + run_id, ordering guidance, and the
  outcome (calibration) signal schema.
- workshop-ta.agent.md: a desk is a persistent workstream picked up by independent
  sessions, not one long-running process.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 26faf13e-639c-4a21-ac05-c0dc2bff7c62

skills/signal-write/SKILL.md

@@ -52,6 +52,8 @@ Create `desks/<desk-name>/.signals/<timestamp>.json`:
 {
   "signal_type": "execution",
   "subtype": "checkpoint",
+  "timestamp": "2026-07-19T21:30:00Z",
+  "run_id": "<optional; set to pair this with an outcome signal>",
   "agent_name": "<desk-name>",
   "self_assessment": {
     "intent": 4,
@@ -91,6 +93,11 @@ dashboard consumers. `signal_type` controls sort priority
 > consuming signals in your own tooling, prefer `subtype` for the
 > specific state.
 
+> **Ordering:** include a `timestamp` (ISO 8601 UTC). The dashboard
+> orders signals by it and falls back to file mtime only when it's
+> absent — a git clone/checkout resets mtimes, so mtime alone is not a
+> dependable clock.
+
 ### 2. Note the signal in the journal
 
 Also append a short marker to the desk's journal for persistence:
@@ -103,6 +110,38 @@ Also append a short marker to the desk's journal for persistence:
 The journal note is the trail marker. The JSON file is the
 machine-readable signal.
 
+## Outcome signals (calibration)
+
+The signals-dashboard can pair a desk's self-assessment with an
+*outcome* — an independent rating of the realized result — and show
+the **honesty gap** (how far the desk's confidence was from the
+delivered quality). Outcome signals are optional and are usually
+emitted by a reviewer/evaluator, not the desk itself.
+
+Write them to the **same** `.signals/` directory:
+
+```json
+{
+  "signal_type": "outcome",
+  "run_id": "<same run_id as the signal it rates>",
+  "agent_name": "<reviewer name>",
+  "quality_rating": 4,
+  "effort_to_merge": "minimal",
+  "issues_found": ["optional short strings"],
+  "timestamp": "2026-07-19T22:00:00Z"
+}
+```
+
+- **`run_id`** correlates an outcome with the execution/partnership
+  signal it rates — set the same `run_id` on both. If it's absent, the
+  dashboard falls back to the nearest outcome emitted shortly after the
+  latest signal.
+- **`quality_rating`** (0–5) is the realized quality; the dashboard
+  compares it to the desk's self-assessed `confidence` to compute the
+  honesty gap.
+- **`effort_to_merge`** — `"minimal"`, `"moderate"`, or `"significant"`.
+- **`issues_found`** — optional array of short strings.
+
 ## Principles
 
 - Signals are structured, not chatty. Short, factual, actionable.