fix: support pi extensions from ~/.pi/agent/extensions/ (#51)

Update buildResourceLoader to include ~/.pi/agent/extensions/ in
additionalExtensionPaths, allowing GSD to discover and use extensions
installed in pi's default location.

This resolves extension loading issues when users have extensions
installed in ~/.pi/agent/extensions/ instead of ~/.gsd/agent/extensions/.

- resource-loader.ts: add piExtensionsDir to additionalExtensionPaths
- app-smoke.test.ts: add test verifying the source includes .pi path

src/resource-loader.ts

@@ -1,4 +1,5 @@
 import { DefaultResourceLoader } from '@mariozechner/pi-coding-agent'
+import { homedir } from 'node:os'
 import { cpSync, existsSync, mkdirSync, readFileSync, writeFileSync } from 'node:fs'
 import { dirname, join, resolve } from 'node:path'
 import { fileURLToPath } from 'node:url'
@@ -52,10 +53,16 @@ export function initResources(agentDir: string): void {
 }
 
 /**
- * Constructs a DefaultResourceLoader with no additionalExtensionPaths.
- * Extensions are synced to agentDir by initResources() and pi auto-discovers
- * them from ~/.gsd/agent/extensions/ via its normal agentDir scan.
+ * Constructs a DefaultResourceLoader that loads extensions from both
+ * ~/.gsd/agent/extensions/ (GSD's default) and ~/.pi/agent/extensions/ (pi's default).
+ * This allows users to use extensions from either location.
  */
 export function buildResourceLoader(agentDir: string): DefaultResourceLoader {
-  return new DefaultResourceLoader({ agentDir })
+  const piAgentDir = join(homedir(), '.pi', 'agent')
+  const piExtensionsDir = join(piAgentDir, 'extensions')
+  
+  return new DefaultResourceLoader({
+    agentDir,
+    additionalExtensionPaths: [piExtensionsDir],
+  })
 }

src/tests/app-smoke.test.ts

@@ -366,3 +366,33 @@ test("gsd launches and loads extensions without errors", async () => {
     "no ERR_MODULE_NOT_FOUND",
   );
 });
+/**
+ * 9. buildResourceLoader includes ~/.pi/agent/extensions in additionalExtensionPaths
+ */
+test("buildResourceLoader source includes ~/.pi/agent/extensions path", async () => {
+  const { join } = await import("node:path");
+  
+  // Verify the source code includes the pi extensions path
+  const loaderSrc = readFileSync(join(projectRoot, "src", "resource-loader.ts"), "utf-8");
+  
+  // Check that buildResourceLoader references ~/.pi/agent
+  assert.ok(
+    loaderSrc.includes(".pi"),
+    "resource-loader.ts references .pi directory"
+  );
+  assert.ok(
+    loaderSrc.includes("additionalExtensionPaths"),
+    "resource-loader.ts uses additionalExtensionPaths"
+  );
+  assert.ok(
+    loaderSrc.includes("homedir()"),
+    "resource-loader.ts uses homedir() to construct paths"
+  );
+  
+  // Verify the function constructs the correct path
+  assert.match(
+    loaderSrc,
+    /join\(homedir\(\),\s*['"]\.pi['"],\s*['"]agent['"]\)/,
+    "buildResourceLoader constructs ~/.pi/agent path"
+  );
+});