fix(CF-352): Auto-create session in sessionCommitLink to prevent FK constraint error

- Check if session exists before inserting commit link
- Auto-create minimal session record if missing (status=active, no project)
- Prevents FK constraint violation when cache/DB drift occurs
- Return message indicates if session was auto-created for monitoring
- Handles edge cases: concurrent calls, missing committed_at, NULL project

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/tools/sessions.ts

@@ -407,6 +407,24 @@ export async function sessionCommitLink(
   commit_message: string | null,
   committed_at: string | null
 ): Promise<string> {
+  // Check if session exists
+  const sessionExists = await queryOne<{ exists: boolean }>(
+    'SELECT EXISTS(SELECT 1 FROM sessions WHERE id = $1) as exists',
+    [session_id]
+  );
+
+  // Auto-create session if missing (prevents FK constraint error)
+  if (!sessionExists?.exists) {
+    const timestamp = committed_at || new Date().toISOString();
+    await execute(
+      `INSERT INTO sessions (id, started_at, status)
+       VALUES ($1, $2, 'active')
+       ON CONFLICT (id) DO NOTHING`,
+      [session_id, timestamp]
+    );
+  }
+
+  // Now safely insert commit link
   await execute(
     `INSERT INTO session_commits (session_id, commit_sha, repo, commit_message, committed_at)
      VALUES ($1, $2, $3, $4, $5)
@@ -414,5 +432,6 @@ export async function sessionCommitLink(
     [session_id, commit_sha, repo, commit_message, committed_at]
   );
 
-  return `Linked commit ${commit_sha.substring(0, 7)} to session ${session_id}`;
+  const prefix = sessionExists?.exists ? '' : '[auto-created session] ';
+  return `${prefix}Linked commit ${commit_sha.substring(0, 7)} to session ${session_id}`;
 }