Spike 3: Sub-agent infrastructure fixes for multi-agent coordination

- Fix CLAUDECODE env var blocking nested Claude Code sessions
- Add drain-based event_log for reliable get_agent_output polling
- Add non-SSE get_agent_output fallback (critical for MCP tool calls)
- Preserve worktrees on agent stop instead of destroying work
- Reap zombie processes with child.wait() after kill
- Increase broadcast buffer from 256 to 1024
- Engineer supervisor and coder prompts in project.toml
- Point .mcp.json to test port 3002

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/worktree.rs

@@ -3,6 +3,7 @@ use std::path::{Path, PathBuf};
 use std::process::Command;
 
 #[derive(Debug, Clone)]
+#[allow(dead_code)]
 pub struct WorktreeInfo {
     pub path: PathBuf,
     pub branch: String,
@@ -104,6 +105,7 @@ fn create_worktree_sync(
 }
 
 /// Remove a git worktree and its branch.
+#[allow(dead_code)]
 pub async fn remove_worktree(
     project_root: &Path,
     info: &WorktreeInfo,
@@ -120,6 +122,7 @@ pub async fn remove_worktree(
         .map_err(|e| format!("spawn_blocking: {e}"))?
 }
 
+#[allow(dead_code)]
 fn remove_worktree_sync(
     project_root: &Path,
     wt_path: &Path,
@@ -161,6 +164,7 @@ async fn run_setup_commands(wt_path: &Path, config: &ProjectConfig) -> Result<()
     Ok(())
 }
 
+#[allow(dead_code)]
 async fn run_teardown_commands(wt_path: &Path, config: &ProjectConfig) -> Result<(), String> {
     for component in &config.component {
         let cmd_dir = wt_path.join(&component.path);