feat(routing): engage modes + sender scope + accumulate/drop + per-agent fan-out

Replaces the opaque trigger_rules JSON + response_scope enum on
messaging_group_agents with four explicit orthogonal columns:

    engage_mode            'pattern' | 'mention' | 'mention-sticky'
    engage_pattern         regex source; required when mode='pattern';
                           '.' is the "always" sentinel
    sender_scope           'all' | 'known'
    ignored_message_policy 'drop' | 'accumulate'

Inbound routing becomes a fan-out — every wired agent is evaluated
independently. A match gets its own session + container wake. A miss
with accumulate keeps the message as context-only (trigger=0) in that
agent's session, so when the agent does eventually engage it sees the
prior chatter.

## Schema

- Migration 010 (`engage-modes`): adds the 4 new columns, backfills
  from trigger_rules.pattern + requiresTrigger + response_scope, drops
  the legacy columns.
- messages_in gains `trigger INTEGER NOT NULL DEFAULT 1` (session DB
  schema + `migrateMessagesInTable` forward-compat).
- countDueMessages gates waking on `trigger = 1`.

## Routing

- `pickAgent` (returns one) → loop over all wired agents. Per agent:
  evaluate engage_mode; run access gate + sender-scope gate; on full
  match → resolveSession + writeSessionMessage(trigger=1) + wake. On
  miss with accumulate → writeSessionMessage(trigger=0), no wake. On
  miss with drop → skip.
- New `findSessionForAgent(agentGroupId, mgId, threadId)` scopes
  session lookup by agent so fan-out doesn't cross sessions.
- `messageIdForAgent` namespaces inbound message ids by agent_group_id
  so PRIMARY KEY doesn't collide across per-agent session DBs.

## Adapter layer

- `ConversationConfig` replaces `triggerPattern` + `requiresTrigger`
  with `engageMode` + `engagePattern`.
- Chat SDK bridge stores `Map<platformId, ConversationConfig[]>` (multi-
  agent per conversation) and applies union gating pre-onInbound:
    * onSubscribedMessage: engage if any wiring keeps firing in
      subscribed state (mention-sticky or pattern)
    * onNewMention: engage on mention; only subscribes the thread if
      at least one wiring is `mention-sticky`
    * onDirectMessage: engage per mode; sticky follows same rule
- Bridge no longer unconditionally calls `thread.subscribe()`.

## Sender scope

- Permissions module registers a second hook `setSenderScopeGate` that
  runs per-wiring after the existing access gate. `sender_scope='known'`
  requires canAccessAgentGroup(); `'all'` is a no-op. Not installed →
  no-op everywhere (default allow).

## Container side

- Host passes `NANOCLAW_MAX_MESSAGES_PER_PROMPT` (reuses existing
  MAX_MESSAGES_PER_PROMPT config; was dead code from v1).
- `getPendingMessages` queries `ORDER BY seq DESC LIMIT N`, reverses to
  chronological order for the prompt — accumulated context rides along
  with trigger rows up to the cap.
- `MessageInRow` gains `trigger: number` so the container can tell them
  apart in downstream code (container still processes both; only the
  host uses `trigger=0` for don't-wake).

## Defaults (per ACTION-ITEMS item 1 decision)

- DM (is_group=0): `engage_mode='pattern'`, `engage_pattern='.'` (always)
- Threaded group: `engage_mode='mention-sticky'` (seed-discord)
- Non-threaded group / CLI: pattern '.' in bootstrap scripts

## Tests

- src/host-core.test.ts: 3 new cases — fan-out (2 agents, 2 sessions,
  2 wakes), accumulate (trigger=0 + no wake), drop (no session created).
- Existing 10 host-core tests still pass.
- Migration 010 runs on an empty DB in 0-row path — verified.

Closes: ACTION-ITEMS items 1, 4.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/session-manager.ts

@@ -17,7 +17,14 @@ import path from 'path';
 import type { OutboundFile } from './channels/adapter.js';
 import { DATA_DIR } from './config.js';
 import { getMessagingGroup } from './db/messaging-groups.js';
-import { createSession, findSession, findSessionByAgentGroup, getSession, updateSession } from './db/sessions.js';
+import {
+  createSession,
+  findSession,
+  findSessionByAgentGroup,
+  findSessionForAgent,
+  getSession,
+  updateSession,
+} from './db/sessions.js';
 import {
   ensureSchema,
   openInboundDb as openInboundDbRaw,
@@ -89,7 +96,9 @@ export function resolveSession(
     }
   } else if (messagingGroupId) {
     const lookupThreadId = sessionMode === 'shared' ? null : threadId;
-    const existing = findSession(messagingGroupId, lookupThreadId);
+    // Scope lookup by agent_group_id so fan-out to multiple agents in the
+    // same chat doesn't accidentally deliver to the wrong agent's session.
+    const existing = findSessionForAgent(agentGroupId, messagingGroupId, lookupThreadId);
     if (existing) {
       return { session: existing, created: false };
     }
@@ -187,6 +196,13 @@ export function writeSessionMessage(
     content: string;
     processAfter?: string | null;
     recurrence?: string | null;
+    /**
+     * 1 = this message should wake the agent (the default); 0 = accumulate
+     * as context only, don't wake. Host's countDueMessages gates on this
+     * column; the container still reads all prior messages as context when
+     * a trigger-1 message does arrive.
+     */
+    trigger?: 0 | 1;
   },
 ): void {
   // Extract base64 attachment data, save to inbox, replace with file paths
@@ -204,6 +220,7 @@ export function writeSessionMessage(
       content,
       processAfter: message.processAfter ?? null,
       recurrence: message.recurrence ?? null,
+      trigger: message.trigger ?? 1,
     });
   } finally {
     db.close();