feat(code): CodeSession + agent loop + Matrix room bridge

phase 2 server core:
- CodeSession: create/resume sessions, Matrix room per project,
  Mistral conversation lifecycle, tool dispatch loop
- agent loop: user input → Mistral → tool calls → route (client
  via gRPC / server via ToolRegistry) → collect results → respond
- Matrix bridge: all messages posted to project room, accessible
  from any Matrix client
- code_sessions SQLite table (Postgres-compatible schema)
- coding mode context injection (project path, git info, prompt.md)

src/persistence.rs

@@ -83,6 +83,19 @@ impl Store {
                 PRIMARY KEY (localpart, service)
             );
 
+            CREATE TABLE IF NOT EXISTS code_sessions (
+                session_id      TEXT PRIMARY KEY,
+                user_id         TEXT NOT NULL,
+                room_id         TEXT NOT NULL,
+                conversation_id TEXT,
+                project_path    TEXT NOT NULL,
+                project_name    TEXT NOT NULL,
+                model           TEXT NOT NULL,
+                status          TEXT NOT NULL DEFAULT 'active',
+                created_at      TEXT NOT NULL DEFAULT (datetime('now')),
+                last_active     TEXT NOT NULL DEFAULT (datetime('now'))
+            );
+
             CREATE TABLE IF NOT EXISTS research_sessions (
                 session_id    TEXT PRIMARY KEY,
                 room_id       TEXT NOT NULL,
@@ -244,6 +257,120 @@ impl Store {
         }
     }
 
+    // =========================================================================
+    // Code Sessions (sunbeam code)
+    // =========================================================================
+
+    /// Find an active code session for a user + project.
+    pub fn find_code_session(
+        &self,
+        user_id: &str,
+        project_name: &str,
+    ) -> Option<(String, String, String)> {
+        let conn = self.conn.lock().unwrap();
+        conn.query_row(
+            "SELECT session_id, room_id, conversation_id FROM code_sessions
+             WHERE user_id = ?1 AND project_name = ?2 AND status = 'active'
+             ORDER BY last_active DESC LIMIT 1",
+            params![user_id, project_name],
+            |row| Ok((
+                row.get::<_, String>(0)?,
+                row.get::<_, String>(1)?,
+                row.get::<_, String>(2)?,
+            )),
+        )
+        .ok()
+    }
+
+    /// Create a new code session.
+    pub fn create_code_session(
+        &self,
+        session_id: &str,
+        user_id: &str,
+        room_id: &str,
+        project_path: &str,
+        project_name: &str,
+        model: &str,
+    ) {
+        let conn = self.conn.lock().unwrap();
+        if let Err(e) = conn.execute(
+            "INSERT INTO code_sessions (session_id, user_id, room_id, project_path, project_name, model)
+             VALUES (?1, ?2, ?3, ?4, ?5, ?6)",
+            params![session_id, user_id, room_id, project_path, project_name, model],
+        ) {
+            warn!("Failed to create code session: {e}");
+        }
+    }
+
+    /// Update the conversation_id for a code session.
+    pub fn set_code_session_conversation(
+        &self,
+        session_id: &str,
+        conversation_id: &str,
+    ) {
+        let conn = self.conn.lock().unwrap();
+        if let Err(e) = conn.execute(
+            "UPDATE code_sessions SET conversation_id = ?1, last_active = datetime('now')
+             WHERE session_id = ?2",
+            params![conversation_id, session_id],
+        ) {
+            warn!("Failed to update code session conversation: {e}");
+        }
+    }
+
+    /// Touch the last_active timestamp.
+    pub fn touch_code_session(&self, session_id: &str) {
+        let conn = self.conn.lock().unwrap();
+        if let Err(e) = conn.execute(
+            "UPDATE code_sessions SET last_active = datetime('now') WHERE session_id = ?1",
+            params![session_id],
+        ) {
+            warn!("Failed to touch code session: {e}");
+        }
+    }
+
+    /// End a code session.
+    pub fn end_code_session(&self, session_id: &str) {
+        let conn = self.conn.lock().unwrap();
+        if let Err(e) = conn.execute(
+            "UPDATE code_sessions SET status = 'ended' WHERE session_id = ?1",
+            params![session_id],
+        ) {
+            warn!("Failed to end code session: {e}");
+        }
+    }
+
+    /// Check if a room is a code session room.
+    pub fn is_code_room(&self, room_id: &str) -> bool {
+        let conn = self.conn.lock().unwrap();
+        conn.query_row(
+            "SELECT 1 FROM code_sessions WHERE room_id = ?1 AND status = 'active' LIMIT 1",
+            params![room_id],
+            |_| Ok(()),
+        )
+        .is_ok()
+    }
+
+    /// Get project context for a code room.
+    pub fn get_code_room_context(
+        &self,
+        room_id: &str,
+    ) -> Option<(String, String, String)> {
+        let conn = self.conn.lock().unwrap();
+        conn.query_row(
+            "SELECT project_name, project_path, model FROM code_sessions
+             WHERE room_id = ?1 AND status = 'active'
+             ORDER BY last_active DESC LIMIT 1",
+            params![room_id],
+            |row| Ok((
+                row.get::<_, String>(0)?,
+                row.get::<_, String>(1)?,
+                row.get::<_, String>(2)?,
+            )),
+        )
+        .ok()
+    }
+
     // =========================================================================
     // Service Users (OIDC → service username mapping)
     // =========================================================================