feat: scaffold ECC 2.0 Rust TUI — agentic IDE control plane

Initial scaffold for ECC 2.0, a terminal-native agentic IDE built with
Ratatui. Compiles to a 3.4MB single binary.

Core modules:
- Session manager with SQLite-backed state store
- TUI dashboard with split-pane layout (sessions, output, metrics)
- Worktree orchestration (auto-create per agent session)
- Observability with tool call risk scoring
- Inter-agent communication via SQLite mailbox
- Background daemon with heartbeat monitoring
- CLI with start/stop/sessions/status/daemon subcommands

Tech stack: Rust + Ratatui + Crossterm + Tokio + rusqlite + git2 + clap

ecc2/src/session/daemon.rs

@@ -0,0 +1,46 @@
+use anyhow::Result;
+use std::time::Duration;
+use tokio::time;
+
+use super::store::StateStore;
+use super::SessionState;
+use crate::config::Config;
+
+/// Background daemon that monitors sessions, handles heartbeats,
+/// and cleans up stale resources.
+pub async fn run(db: StateStore, cfg: Config) -> Result<()> {
+    tracing::info!("ECC daemon started");
+
+    let heartbeat_interval = Duration::from_secs(cfg.heartbeat_interval_secs);
+    let timeout = Duration::from_secs(cfg.session_timeout_secs);
+
+    loop {
+        if let Err(e) = check_sessions(&db, timeout) {
+            tracing::error!("Session check failed: {e}");
+        }
+
+        time::sleep(heartbeat_interval).await;
+    }
+}
+
+fn check_sessions(db: &StateStore, timeout: Duration) -> Result<()> {
+    let sessions = db.list_sessions()?;
+
+    for session in sessions {
+        if session.state != SessionState::Running {
+            continue;
+        }
+
+        let elapsed = chrono::Utc::now()
+            .signed_duration_since(session.updated_at)
+            .to_std()
+            .unwrap_or(Duration::ZERO);
+
+        if elapsed > timeout {
+            tracing::warn!("Session {} timed out after {:?}", session.id, elapsed);
+            db.update_state(&session.id, &SessionState::Failed)?;
+        }
+    }
+
+    Ok(())
+}