feat(pi): opt-in Pi extension loading via WARDEN_PI_EXTENSION_PATHS

packages/docs/src/content/docs/config/models.mdx

@@ -58,6 +58,20 @@ Warden mirrors these to the native `{PROVIDER}_API_KEY` expected by each SDK at
 If you already have a native provider key set (e.g. `OPENAI_API_KEY`), Warden will use it
 directly and the `WARDEN_`-prefixed form is not required.
 
+### Pi Extensions
+
+By default the Pi runtime loads **no** [Pi extensions](https://pi.dev/docs/extensions),
+neither project-local nor global ones, so runs are hermetic. To load specific extension
+files (for example an LLM proxy router or a tracing hook), set
+`WARDEN_PI_EXTENSION_PATHS` to a comma-separated list of extension file paths:
+
+```yaml title="GitHub Actions"
+env:
+  WARDEN_PI_EXTENSION_PATHS: /home/runner/warden-extensions/tracing.ts
+```
+
+Only the listed files are loaded; extension auto-discovery stays disabled.
+
 ## Claude Runtime Models
 
 When `runtime = "claude"`, use the model IDs accepted by Claude Code:

packages/warden/src/sdk/runtimes/pi.test.ts

@@ -219,6 +219,27 @@ describe('piRuntime.runSkill', () => {
     });
   });
 
+  it('loads no Pi extensions by default', async () => {
+    await piRuntime.runSkill(baseSkillRequest());
+
+    expect(piMocks.resourceLoaderOptions[0]).toEqual(expect.objectContaining({ noExtensions: true }));
+    expect(piMocks.resourceLoaderOptions[0]).not.toHaveProperty('additionalExtensionPaths');
+  });
+
+  it('threads WARDEN_PI_EXTENSION_PATHS into the resource loader', async () => {
+    vi.stubEnv('WARDEN_PI_EXTENSION_PATHS', '/ext/tracing.ts, /ext/routing.ts,');
+    try {
+      await piRuntime.runSkill(baseSkillRequest());
+    } finally {
+      vi.unstubAllEnvs();
+    }
+
+    expect(piMocks.resourceLoaderOptions[0]).toEqual(expect.objectContaining({
+      noExtensions: true,
+      additionalExtensionPaths: ['/ext/tracing.ts', '/ext/routing.ts'],
+    }));
+  });
+
   it('records Pi tool execution spans when trace capture is active', async () => {
     const toolResult = {
       role: 'toolResult',

packages/warden/src/sdk/runtimes/pi.ts

@@ -343,18 +343,27 @@ async function promptWithTimeout(
   }
 }
 
+function piExtensionPathsFromEnv(env: NodeJS.ProcessEnv = process.env): string[] {
+  return (env['WARDEN_PI_EXTENSION_PATHS'] ?? '')
+    .split(',')
+    .map((path) => path.trim())
+    .filter((path) => path.length > 0);
+}
+
 async function runPiPrompt(options: PiPromptOptions): Promise<PiPromptResult> {
   const warnings: string[] = [];
   bridgeWardenProviderApiKeyEnv();
   const modelRuntime = await createModelRuntime(options.model, options.legacyAnthropicApiKey);
   const model = resolvePiModel(options.model, modelRuntime);
   const settingsManager = buildSettingsManager(options.timeout, options.maxRetries);
   const agentDir = getAgentDir();
+  const additionalExtensionPaths = piExtensionPathsFromEnv();
   const resourceLoader = new DefaultResourceLoader({
     cwd: options.cwd,
     agentDir,
     settingsManager,
     noExtensions: true,
+    ...(additionalExtensionPaths.length > 0 ? { additionalExtensionPaths } : {}),
     noSkills: true,
     noPromptTemplates: true,
     noThemes: true,