feat(booth): asks — a multiple-choice question a session poses in a booth, answered by the operator as a radio form + notes, written back as an answer sidecar

- booth/asks.py (stdlib): <stem>.ask.json question / <stem>.answer.json answer; normalise+validate, atomic write, list with answer folded in, broken asks surfaced not hidden
- POST /b/<name>/answer: validates choice against the ask (400), unknown stem 404, re-answer overwrites
- booth.html asks panel above the gallery; amber open / green answered; JS-off form POST; index card + booth header badge for open asks
- CLI: booth ask / asks / answer [--wait [SECS]]; remote sessions poll <stem>.answer.json over HTTP
- ask/answer files excluded from gallery items and item counts; 23 tests; v0.1.9

services/booth/README.md

@@ -88,6 +88,60 @@ Deliberately **not** a database. The board is a markdown file — editable with
 any editor, greppable, and trivially prunable by hand, which is the whole point
 of the Booth's filesystem-is-the-state model.
 
+## Asks — let the operator pick one of N, and read the pick back
+
+The one **interactive** primitive. A session needs a human decision — which
+render wins, which plan, go/no-go — and wants to act on it without a chat
+round-trip. Drop a question in a booth; the page renders it as a radio form
+with a notes field; the operator's submit writes an **answer sidecar** the
+session reads. Filesystem is still the state:
+
+```
+<booth>/<stem>.ask.json      the question   (a session writes it)
+<booth>/<stem>.answer.json   the answer     (the web UI writes it, atomically)
+```
+
+```bash
+# On nh3-dev — pose, then block until answered (default 1h), then act on it:
+booth ask r18-ab winner "Which render wins?" "A — baseline" "B — cudaMallocAsync"
+booth answer r18-ab winner --wait            # prints the answer JSON when it lands
+booth answer r18-ab winner                   # non-blocking: exit 1 while unanswered
+booth asks   r18-ab                          # list a booth's asks + state
+
+# Options can carry an id + detail line instead of a bare label — write the
+# JSON yourself (booth.asks.write_ask validates the same way):
+cat > ~/booth-data/r18-ab/plan.ask.json <<'EOF'
+{"prompt": "Ship which?",
+ "options": [{"id": "a", "label": "Plan A", "detail": "smaller diff, no migration"},
+             {"id": "b", "label": "Plan B", "detail": "cleaner, needs the DB change"}],
+ "notes": true, "notes_label": "why / conditions"}
+EOF
+
+# From another host: rsync the ask in, then poll the sidecar over HTTP:
+curl -sf http://10.100.10.50:8090/b/r18-ab/winner.answer.json   # 404 until answered
+```
+
+The answer: `{"stem", "prompt", "choice", "choice_index", "label", "notes",
+"answered_at", "answered_by"}` — `choice` is the option id (the label itself
+for string options), `choice_index` its 0-based position, `answered_by` the
+client address. `POST /b/<name>/answer` (form fields `ask`, `choice`, `notes`)
+is what the form submits; a bad choice is a 400, an unknown stem a 404.
+
+Rules of the primitive:
+
+- **Radio, one pick.** ≥ 2 options, ≤ 40. No multi-select (not yet asked for).
+- **Re-answering overwrites.** The sidecar is the *current* answer, not a log.
+  The page shows the recorded answer with a collapsed *change answer* form.
+- **Open asks are flagged** — an amber `? N asks` badge on the index card and in
+  the booth header — so a waiting question is visible from the front page.
+- **A broken ask is shown as broken**, not hidden: if the JSON does not
+  validate, the page says why, so a session never thinks it posted a question
+  the operator cannot see.
+- Ask/answer files are not gallery items and do not count toward the booth's
+  item count; they render as the panel above the gallery. Answering bumps the
+  booth's mtime, so it lives another TTL — the session has 24h to read it.
+- Works with JavaScript off (plain form POST). No auth, same as everything here.
+
 ## Upload for pickup
 
 The reverse direction — put files in through the web, pick them up by id:
@@ -136,6 +190,7 @@ to a safe basename (no path traversal).
 | `GET /b/<name>/` | A booth (its `index.html`, else auto-gallery) |
 | `GET /b/<name>/<file>` | Serve a file out of the booth |
 | `POST /upload` | Upload files → new pickup booth; 303-redirects to `/b/<id>/` (id in `Location`) |
+| `POST /b/<name>/answer` | Answer an ask (form fields `ask` = stem, `choice` = option id, `notes`); writes `<stem>.answer.json`, 303 back to the booth |
 | `POST /b/<name>/delete` | Wipe a booth (the UI's "Wipe now" button) |
 | `POST /b/<name>/keep` | Pin a booth — exempt from the sweep |
 | `POST /b/<name>/unkeep` | Release the pin (the UI's "release" button on kept cards) |