feat(tui): add usage overlay and sidebar for displaying usage statistics and tasks

feat(tui): implement status bar with connection and turn state indicators
feat(tui): create workflow panel for agent status and progress visualization
feat(web): introduce web frontend interface with static file serving
feat(ws): add WebSocket interface for real-time communication and session management

apps/infrastructure/src/subagent/spawn.rs

@@ -0,0 +1,37 @@
+//! Subagent spawning — launch a subagent on a background OS thread.
+//!
+//! Flow: creates a new tokio runtime on a dedicated OS thread, then
+//! `block_on` the engine's `run_agent` future. Returns a
+//! `JoinHandle<Result<String>>` the caller can `.join()`.
+
+use std::thread;
+
+use anyhow::Result;
+use tracing::info;
+
+use crate::subagent::context::SubagentContext;
+use crate::subagent::division::AccessTier;
+use crate::subagent::engine::run_agent;
+use crate::tools::ToolCtx;
+
+/// Spawn a subagent on a background OS thread.
+///
+/// The subagent runs inside its own tokio runtime so it can make async calls
+/// without blocking the calling thread's runtime.
+///
+/// Flow: `thread::spawn` → create `tokio::runtime::Runtime` →
+/// `runtime.block_on(run_agent(...))` → return.
+///
+/// Returns a `JoinHandle` the caller can `join()` to await the result.
+pub fn spawn_subagent(
+    ctx: SubagentContext,
+    directive: String,
+    access: AccessTier,
+    tool_ctx: ToolCtx,
+) -> thread::JoinHandle<Result<String>> {
+    info!("Spawning subagent: {directive}");
+    thread::spawn(move || {
+        let rt = tokio::runtime::Runtime::new()?;
+        rt.block_on(run_agent(ctx, &directive, access, tool_ctx))
+    })
+}