fix(pi-runner): allow host-side extension path override for task runs

Task-run pi launches hardcoded the container path /app/extensions/tavily-search.mjs;
on the no-docker host sidecar every squad/dialogue task run failed at spawn with
ENOENT/extension-load errors. Add PI_AGENT_EXTENSION override and export the
managed pi-dir extension path from the sidecar start script.

deploy/pi-agent-sidecar/start.sh

@@ -76,6 +76,7 @@ cat > "${PI_DIR}/settings.json" <<EOF
 EOF
 
 export PORT DATA_DIR PI_CODING_AGENT_DIR="$PI_DIR"
+export PI_AGENT_EXTENSION="${PI_DIR}/extensions/tavily-search.mjs"
 export PATH="${PATH}:/home/linuxbrew/.linuxbrew/bin"
 
 echo "================================================================="

deploy/pi-agent/runner.mjs

@@ -299,6 +299,10 @@ async function handleRun(body) {
 
   // 2. Build pi arguments. Unknown profiles fail closed before spawn.
   const piBin = process.env.PI_AGENT_BIN || "pi";
+  // Extension path: container default is /app/extensions/...; the host
+  // sidecar overrides via PI_AGENT_EXTENSION (deploy/pi-agent-sidecar/start.sh
+  // exports the managed pi-dir path).
+  const extensionPath = process.env.PI_AGENT_EXTENSION || "/app/extensions/tavily-search.mjs";
   const sysPromptFile = resolve(workspace, "INSTRUCTIONS.md");
   let args;
   try {
@@ -307,7 +311,7 @@ async function handleRun(body) {
       provider,
       model,
       systemPromptFile: existsSync(sysPromptFile) ? "INSTRUCTIONS.md" : "",
-      extension: "/app/extensions/tavily-search.mjs",
+      extension: extensionPath,
       workspaceTools: "read,write,edit,tavily_search,web_search",
     });
   } catch (e) {