refactor(v2): extract session DB operations into src/db/session-db.ts

Move all raw SQL out of session-manager, delivery, and host-sweep into
a dedicated DB module. Make session schemas idempotent (IF NOT EXISTS)
so initSessionFolder always applies them. Revert the markdown
plain-text retry from 4c477ac.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/session-manager.ts

@@ -10,7 +10,7 @@
  *   3. One writer per file — DELETE-mode journal-unlink isn't atomic across
  *      the mount; concurrent writers corrupt the DB.
  */
-import Database from 'better-sqlite3';
+import type Database from 'better-sqlite3';
 import fs from 'fs';
 import path from 'path';
 
@@ -19,8 +19,16 @@ import { getAgentGroup } from './db/agent-groups.js';
 import { getDestinations } from './db/agent-destinations.js';
 import { getMessagingGroup } from './db/messaging-groups.js';
 import { createSession, findSession, findSessionByAgentGroup, getSession, updateSession } from './db/sessions.js';
+import {
+  ensureSchema,
+  openInboundDb as openInboundDbRaw,
+  openOutboundDb as openOutboundDbRaw,
+  upsertSessionRouting,
+  replaceDestinations,
+  insertMessage,
+  type DestinationRow,
+} from './db/session-db.js';
 import { log } from './log.js';
-import { INBOUND_SCHEMA, OUTBOUND_SCHEMA } from './db/schema.js';
 import type { Session } from './types.js';
 
 /** Root directory for all session data. */
@@ -116,23 +124,8 @@ export function initSessionFolder(agentGroupId: string, sessionId: string): void
   fs.mkdirSync(dir, { recursive: true });
   fs.mkdirSync(path.join(dir, 'outbox'), { recursive: true });
 
-  const inPath = inboundDbPath(agentGroupId, sessionId);
-  if (!fs.existsSync(inPath)) {
-    const db = new Database(inPath);
-    db.pragma('journal_mode = DELETE');
-    db.exec(INBOUND_SCHEMA);
-    db.close();
-    log.debug('Inbound DB created', { dbPath: inPath });
-  }
-
-  const outPath = outboundDbPath(agentGroupId, sessionId);
-  if (!fs.existsSync(outPath)) {
-    const db = new Database(outPath);
-    db.pragma('journal_mode = DELETE');
-    db.exec(OUTBOUND_SCHEMA);
-    db.close();
-    log.debug('Outbound DB created', { dbPath: outPath });
-  }
+  ensureSchema(inboundDbPath(agentGroupId, sessionId), 'inbound');
+  ensureSchema(outboundDbPath(agentGroupId, sessionId), 'outbound');
 }
 
 /**
@@ -172,18 +165,9 @@ export function writeSessionRouting(agentGroupId: string, sessionId: string): vo
     }
   }
 
-  const db = new Database(dbPath);
-  db.pragma('journal_mode = DELETE');
-  db.pragma('busy_timeout = 5000');
+  const db = openInboundDb(agentGroupId, sessionId);
   try {
-    db.prepare(
-      `INSERT INTO session_routing (id, channel_type, platform_id, thread_id)
-       VALUES (1, @channel_type, @platform_id, @thread_id)
-       ON CONFLICT(id) DO UPDATE SET
-         channel_type = excluded.channel_type,
-         platform_id  = excluded.platform_id,
-         thread_id    = excluded.thread_id`,
-    ).run({
+    upsertSessionRouting(db, {
       channel_type: channelType,
       platform_id: platformId,
       thread_id: session.thread_id,
@@ -199,15 +183,7 @@ export function writeDestinations(agentGroupId: string, sessionId: string): void
   if (!fs.existsSync(dbPath)) return;
 
   const rows = getDestinations(agentGroupId);
-  type DestRow = {
-    name: string;
-    display_name: string | null;
-    type: 'channel' | 'agent';
-    channel_type: string | null;
-    platform_id: string | null;
-    agent_group_id: string | null;
-  };
-  const resolved: DestRow[] = [];
+  const resolved: DestinationRow[] = [];
 
   for (const row of rows) {
     if (row.target_type === 'channel') {
@@ -235,19 +211,9 @@ export function writeDestinations(agentGroupId: string, sessionId: string): void
     }
   }
 
-  const db = new Database(dbPath);
-  db.pragma('journal_mode = DELETE');
-  db.pragma('busy_timeout = 5000');
+  const db = openInboundDb(agentGroupId, sessionId);
   try {
-    const tx = db.transaction((entries: DestRow[]) => {
-      db.prepare('DELETE FROM destinations').run();
-      const stmt = db.prepare(
-        `INSERT INTO destinations (name, display_name, type, channel_type, platform_id, agent_group_id)
-         VALUES (@name, @display_name, @type, @channel_type, @platform_id, @agent_group_id)`,
-      );
-      for (const e of entries) stmt.run(e);
-    });
-    tx(resolved);
+    replaceDestinations(db, resolved);
   } finally {
     db.close();
   }
@@ -279,28 +245,10 @@ export function writeSessionMessage(
   // Extract base64 attachment data, save to inbox, replace with file paths
   const content = extractAttachmentFiles(agentGroupId, sessionId, message.id, message.content);
 
-  const dbPath = inboundDbPath(agentGroupId, sessionId);
-  const db = new Database(dbPath);
-  db.pragma('journal_mode = DELETE');
-  db.pragma('busy_timeout = 5000');
-
+  const db = openInboundDb(agentGroupId, sessionId);
   try {
-    // Host uses even seq, container uses odd. This is not just collision
-    // avoidance between the two DB files — the seq is the agent-facing
-    // message ID returned by send_message and accepted by edit_message /
-    // add_reaction, and those tools look up by seq across BOTH tables
-    // (see container/agent-runner/src/db/messages-out.ts:getMessageIdBySeq).
-    // So the {messages_in.seq, messages_out.seq} namespace MUST be disjoint,
-    // or the agent's "edit message #5" could resolve to the wrong row.
-    const maxSeq = (db.prepare('SELECT COALESCE(MAX(seq), 0) AS m FROM messages_in').get() as { m: number }).m;
-    const nextSeq = maxSeq < 2 ? 2 : maxSeq + 2 - (maxSeq % 2); // next even
-
-    db.prepare(
-      `INSERT INTO messages_in (id, seq, kind, timestamp, status, platform_id, channel_type, thread_id, content, process_after, recurrence)
-       VALUES (@id, @seq, @kind, @timestamp, 'pending', @platformId, @channelType, @threadId, @content, @processAfter, @recurrence)`,
-    ).run({
+    insertMessage(db, {
       id: message.id,
-      seq: nextSeq,
       kind: message.kind,
       timestamp: message.timestamp,
       platformId: message.platformId ?? null,
@@ -357,19 +305,12 @@ function extractAttachmentFiles(
 
 /** Open the inbound DB for a session (host reads/writes). */
 export function openInboundDb(agentGroupId: string, sessionId: string): Database.Database {
-  const dbPath = inboundDbPath(agentGroupId, sessionId);
-  const db = new Database(dbPath);
-  db.pragma('journal_mode = DELETE');
-  db.pragma('busy_timeout = 5000');
-  return db;
+  return openInboundDbRaw(inboundDbPath(agentGroupId, sessionId));
 }
 
 /** Open the outbound DB for a session (host reads only). */
 export function openOutboundDb(agentGroupId: string, sessionId: string): Database.Database {
-  const dbPath = outboundDbPath(agentGroupId, sessionId);
-  const db = new Database(dbPath, { readonly: true });
-  db.pragma('busy_timeout = 5000');
-  return db;
+  return openOutboundDbRaw(outboundDbPath(agentGroupId, sessionId));
 }
 
 /**