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/comms/mod.rs

@@ -0,0 +1,33 @@
+use anyhow::Result;
+use serde::{Deserialize, Serialize};
+
+use crate::session::store::StateStore;
+
+/// Message types for inter-agent communication.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub enum MessageType {
+    /// Task handoff from one agent to another
+    TaskHandoff { task: String, context: String },
+    /// Agent requesting information from another
+    Query { question: String },
+    /// Response to a query
+    Response { answer: String },
+    /// Notification of completion
+    Completed { summary: String, files_changed: Vec<String> },
+    /// Conflict detected (e.g., two agents editing the same file)
+    Conflict { file: String, description: String },
+}
+
+/// Send a structured message between sessions.
+pub fn send(db: &StateStore, from: &str, to: &str, msg: &MessageType) -> Result<()> {
+    let content = serde_json::to_string(msg)?;
+    let msg_type = match msg {
+        MessageType::TaskHandoff { .. } => "task_handoff",
+        MessageType::Query { .. } => "query",
+        MessageType::Response { .. } => "response",
+        MessageType::Completed { .. } => "completed",
+        MessageType::Conflict { .. } => "conflict",
+    };
+    db.send_message(from, to, &content, msg_type)?;
+    Ok(())
+}