Participants report taking the room into work (join)

- POST /api/rooms/:id/join + rendezvous_join MCP tool; creator auto-joined
- joined_at shown to agents, observer (invite not confirmed yet) and used by
  the turn indicator; what_you_should_do_next starts with joining
- fix: participant list order is now stable (insertion order)

packages/core/src/advice.ts

@@ -30,6 +30,19 @@ export function computeAdvice(input: AdviceInput): string {
     return 'The contract is agreed by all participants and the room is finalized. Download the final artifact with GET /api/rooms/{room_id}/final.md (Authorization: Bearer <your token>) while the room still exists.';
   }
 
+  if (!you.joined_at) {
+    return (
+      'You have opened your invite but not reported taking the room into work yet. ' +
+      'First POST /api/rooms/{room_id}/join (Authorization: Bearer <your token>) so the other side knows the task has been picked up, then read the room state again.'
+    );
+  }
+
+  const notJoined = input.participants.filter((p) => p.id !== you.id && !p.joined_at);
+  const joinNote =
+    notJoined.length > 0
+      ? `Note: ${notJoined.map((p) => p.role).join(', ')} has not joined yet (invite not confirmed) — you can state your facts now, but do not expect answers until they join. `
+      : '';
+
   const addressedToYou = openQuestions.filter(
     (q) => q.addressed_to === null || q.addressed_to === you.id,
   );
@@ -41,6 +54,7 @@ export function computeAdvice(input: AdviceInput): string {
   if (blockingToYou.length > 0) {
     const first = blockingToYou[0];
     return (
+      joinNote +
       `There ${blockingToYou.length === 1 ? 'is 1 blocking question' : `are ${blockingToYou.length} blocking questions`} waiting for you. ` +
       `First: "${first.question}" (asked by ${first.author_role}${first.addressed_to_role ? ` specifically of ${first.addressed_to_role}` : ''}). ` +
       'Verify the relevant facts on your side, post your answer as a message, then resolve the question with POST /api/rooms/{room_id}/questions/{question_id}/resolve including the verified facts in the resolution.'
@@ -49,6 +63,7 @@ export function computeAdvice(input: AdviceInput): string {
 
   if (blockingFromYou.length > 0) {
     return (
+      joinNote +
       `You have ${blockingFromYou.length === 1 ? 'an open blocking question' : `${blockingFromYou.length} open blocking questions`} that ${others(input.participants, you.id)} must answer. ` +
       'While waiting, verify the facts you already claimed, keep your answers ready, and do not finalize until these are resolved.'
     );
@@ -99,7 +114,7 @@ export function computeAdvice(input: AdviceInput): string {
  */
 export function computeTurn(
   status: string,
-  participants: { id: string; role: string }[],
+  participants: { id: string; role: string; joined_at: string | null }[],
   openQuestions: { addressed_to: string | null; participant_id: string; blocking: boolean; question: string }[],
   contract: { version: number; agreements: { participant_id: string; version: number }[] } | null,
 ): { text: string; waiting_for: string[] } {
@@ -108,6 +123,13 @@ export function computeTurn(
     return { text: 'Done: contract agreed by everyone. Fetch final.md before the room expires.', waiting_for: [] };
 
   const roleOf = (id: string) => participants.find((p) => p.id === id)?.role ?? 'unknown';
+  const notJoined = participants.filter((p) => !p.joined_at);
+  if (notJoined.length > 0) {
+    return {
+      text: `Waiting for ${notJoined.map((p) => p.role).join(', ')} to open their invite and report they have taken the room into work.`,
+      waiting_for: notJoined.map((p) => p.role),
+    };
+  }
   const blocking = openQuestions.filter((q) => q.blocking);
   if (blocking.length > 0) {
     const q = blocking[0];
@@ -142,6 +164,7 @@ export function availableActions(status: string): string[] {
     return ['GET /api/rooms/{room_id} (read)', 'GET /api/rooms/{room_id}/final.md (download artifact)'];
   }
   return [
+    'POST /api/rooms/{room_id}/join — report you have taken the room into work (once, first)',
     'POST /api/rooms/{room_id}/messages — post a message',
     'POST /api/rooms/{room_id}/questions — open a question {question, blocking, addressed_to_participant_id?}',
     'POST /api/rooms/{room_id}/questions/{question_id}/resolve — answer/resolve a question {resolution}',

packages/core/src/markdown.ts

@@ -11,7 +11,12 @@ export function renderObserverMarkdown(o: ObserverView, baseUrl: string): string
   parts.push(`**Whose turn:** ${o.turn}`);
   if (o.turn_waiting_for.length) parts.push(`**Waiting on:** ${o.turn_waiting_for.map((r) => `**${r}**`).join(', ')}`);
   parts.push('');
-  parts.push(`Participants: ${o.participants.map((p) => p.role).join(', ')}`);
+  parts.push(
+    'Participants: ' +
+      o.participants
+        .map((p) => (p.joined_at ? `${p.role} (✅ joined ${p.joined_at})` : `${p.role} (⏳ invite not confirmed)`))
+        .join(', '),
+  );
   parts.push('');
   parts.push('## Open questions');
   if (o.open_questions.length === 0) parts.push('(none)');
@@ -66,6 +71,8 @@ export function renderRoomMarkdown(i: MarkdownInput): string {
   parts.push('');
   parts.push('You are a participant in an AI Rendezvous room — a temporary neutral meeting place for existing AI sessions on different machines, harnesses and providers. The server is transport-only state coordination; it never calls any model. Negotiate by exchanging messages and open questions, verify facts on your side, converge on the Agreed Contract. The room is deleted automatically.');
   parts.push('');
+  parts.push('**First action:** if the Participants list below marks you as "has NOT reported" — POST /api/rooms/{room_id}/join (Authorization: Bearer your token) to announce you have taken the room into work. The other side sees it.');
+  parts.push('');
   parts.push(`- **Goal:** ${i.goal || '(not set)'}`);
   if (i.brief) parts.push(`- **Brief:** ${i.brief}`);
   parts.push(`- **Status:** ${i.status}`);
@@ -74,7 +81,10 @@ export function renderRoomMarkdown(i: MarkdownInput): string {
 
   parts.push('## Participants');
   for (const p of i.participants) {
-    parts.push(`### ${p.role}${p.display_name && p.display_name !== p.role ? ` (${p.display_name})` : ''}`);
+    const joined = p.joined_at
+      ? `✅ joined ${p.joined_at}`
+      : '⏳ has NOT reported taking this room into work yet';
+    parts.push(`### ${p.role}${p.display_name && p.display_name !== p.role ? ` (${p.display_name})` : ''} — ${joined}`);
     if (p.knows.length) parts.push(`- **knows:** ${p.knows.join('; ')}`);
     if (p.needs_to_determine.length) parts.push(`- **needs to determine:** ${p.needs_to_determine.join('; ')}`);
     if (p.instructions) parts.push(`- **instructions:** ${p.instructions}`);
@@ -120,6 +130,7 @@ export function renderRoomMarkdown(i: MarkdownInput): string {
   parts.push('## Available API actions');
   parts.push(`Base URL: ${i.baseUrl}. Authenticate with \`Authorization: Bearer <your invite token>\` or \`?token=<token>\`.`);
   parts.push('- `GET /api/rooms/' + i.roomId + '` — full room state as JSON (your_role, room_goal, conversation, open_questions, current_contract, room_status, what_you_should_do_next)');
+  parts.push('- `POST /api/rooms/' + i.roomId + '/join` — report that you have taken the room into work (do this first, once)');
   parts.push('- `POST /api/rooms/' + i.roomId + '/messages` — {"content": "..."}');
   parts.push('- `POST /api/rooms/' + i.roomId + '/questions` — {"question": "...", "blocking": true, "addressed_to_participant_id": "..."}');
   parts.push('- `POST /api/rooms/' + i.roomId + '/questions/{question_id}/resolve` — {"resolution": "verified facts..."}');

packages/core/src/service.ts

@@ -84,8 +84,8 @@ export class RendezvousService {
       `INSERT INTO rooms (id, title, brief, goal, status, created_at, expires_at, observer_token) VALUES (?, ?, ?, ?, 'open', ?, ?, ?)`,
     );
     const insertParticipant = this.db.prepare(
-      `INSERT INTO participants (id, room_id, role, display_name, token, knows, needs_to_determine, instructions, created_at)
-       VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)`,
+      `INSERT INTO participants (id, room_id, role, display_name, token, knows, needs_to_determine, instructions, joined_at, created_at)
+       VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`,
     );
 
     const observerToken = newToken();
@@ -104,6 +104,7 @@ export class RendezvousService {
           JSON.stringify((p.knows ?? []).slice(0, 50).map((s) => String(s).slice(0, 1000))),
           JSON.stringify((p.needs_to_determine ?? []).slice(0, 50).map((s) => String(s).slice(0, 1000))),
           (p.instructions ?? '').slice(0, 20000),
+          created.length === 0 ? createdAt : null, // creator is present from the start
           createdAt,
         );
         created.push({ id: pid, role: p.role.trim(), token });
@@ -166,7 +167,7 @@ export class RendezvousService {
 
   listParticipants(roomId: string): ParticipantView[] {
     return (this.db
-      .prepare('SELECT * FROM participants WHERE room_id = ? ORDER BY created_at, id')
+      .prepare('SELECT rowid AS _rowid, * FROM participants WHERE room_id = ? ORDER BY rowid')
       .all(roomId) as unknown as ParticipantRow[]).map((p) => this.toParticipantView(p));
   }
 
@@ -178,6 +179,7 @@ export class RendezvousService {
       knows: JSON.parse(p.knows) as string[],
       needs_to_determine: JSON.parse(p.needs_to_determine) as string[],
       instructions: p.instructions,
+      joined_at: p.joined_at,
     };
   }
 
@@ -340,6 +342,22 @@ export class RendezvousService {
     };
   }
 
+  /**
+   * Report that this participant has taken the room into work. Idempotent:
+   * the first timestamp is kept. Lets the other side (and the human) see the
+   * task has been picked up.
+   */
+  join(roomId: string, token: string): { participants: ParticipantView[] } {
+    const { room, participant } = this.authenticate(roomId, token);
+    this.ensureOpen(room);
+    if (!participant.joined_at) {
+      this.db
+        .prepare('UPDATE participants SET joined_at = ? WHERE id = ? AND joined_at IS NULL')
+        .run(nowIso(), participant.id);
+    }
+    return { participants: this.listParticipants(roomId) };
+  }
+
   // ---------- writes ----------
 
   postMessage(roomId: string, token: string, content: string): MessageView {

packages/core/src/store.ts

@@ -24,6 +24,7 @@ export interface ParticipantRow {
   knows: string; // JSON array
   needs_to_determine: string; // JSON array
   instructions: string;
+  joined_at: string | null;
   created_at: string;
 }
 
@@ -88,6 +89,7 @@ CREATE TABLE IF NOT EXISTS participants (
   knows TEXT NOT NULL DEFAULT '[]',
   needs_to_determine TEXT NOT NULL DEFAULT '[]',
   instructions TEXT NOT NULL DEFAULT '',
+  joined_at TEXT,
   created_at TEXT NOT NULL
 );
 CREATE TABLE IF NOT EXISTS messages (
@@ -146,6 +148,10 @@ export class Store {
     if (!cols.some((c) => c.name === 'observer_token')) {
       this.db.exec('ALTER TABLE rooms ADD COLUMN observer_token TEXT');
     }
+    const pcols = this.db.prepare('PRAGMA table_info(participants)').all() as { name: string }[];
+    if (!pcols.some((c) => c.name === 'joined_at')) {
+      this.db.exec('ALTER TABLE participants ADD COLUMN joined_at TEXT');
+    }
     // Backfill: every room, including pre-observer-token ones, gets one.
     const update = this.db.prepare('UPDATE rooms SET observer_token = ? WHERE id = ?');
     for (const r of this.db.prepare('SELECT id FROM rooms WHERE observer_token IS NULL').all() as { id: string }[]) {

packages/core/src/types.ts

@@ -26,6 +26,8 @@ export interface ParticipantView {
   knows: string[];
   needs_to_determine: string[];
   instructions: string;
+  /** When this participant reported taking the room into work (null = invite not opened yet). */
+  joined_at: string | null;
 }
 
 export interface MessageView {

packages/core/test/core.test.ts

@@ -165,6 +165,27 @@ test('destroyRoom: allowed for participant and observer, rejected for strangers'
   assert.throws(() => svc.getRoomView(c2.room_id, c2.participants[0].token), RendezvousError);
 });
 
+test('join: creator auto-joined, invitee reports once and idempotently', () => {
+  const { svc } = makeService();
+  const created = createTwoPartyRoom(svc);
+  const [, tokenB] = created.participants.map((p) => p.token);
+
+  const viewA = svc.getRoomView(created.room_id, created.participants[0].token);
+  assert.ok(viewA.participants[0].joined_at, 'creator is joined from the start');
+  assert.equal(viewA.participants[1].joined_at, null);
+
+  // B's advice tells it to join first
+  const viewB = svc.getRoomView(created.room_id, tokenB);
+  assert.match(viewB.what_you_should_do_next, /join/);
+
+  const first = svc.join(created.room_id, tokenB).participants.find((p) => p.role === 'application')!;
+  const ts = first.joined_at!;
+  assert.ok(ts);
+  // idempotent: timestamp does not change
+  const again = svc.join(created.room_id, tokenB).participants.find((p) => p.role === 'application')!;
+  assert.equal(again.joined_at, ts);
+});
+
 test('only addressee or author can resolve a question', () => {
   const { svc } = makeService();
   const created = createTwoPartyRoom(svc);