feat(harness): expose native Pi runtime

.github/workflows/build.yml

@@ -77,6 +77,9 @@ jobs:
       - name: Build enricher
         run: pnpm --filter @posthog/enricher build
 
+      - name: Build harness
+        run: pnpm --filter @posthog/harness build
+
       - name: Build agent
         run: pnpm --filter agent build
 

.github/workflows/code-build-test.yml

@@ -88,6 +88,7 @@ jobs:
           pnpm --filter @posthog/shared run build
           pnpm --filter @posthog/git run build
           pnpm --filter @posthog/enricher run build
+          pnpm --filter @posthog/harness run build
           pnpm --filter @posthog/agent run build
 
       # build/Assets.car is gitignored; regenerate it so the packaged app ships
@@ -205,6 +206,7 @@ jobs:
           pnpm --filter @posthog/shared run build
           pnpm --filter @posthog/git run build
           pnpm --filter @posthog/enricher run build
+          pnpm --filter @posthog/harness run build
           pnpm --filter @posthog/agent run build
 
       - name: Build app
@@ -275,6 +277,7 @@ jobs:
           pnpm --filter @posthog/shared run build
           pnpm --filter @posthog/git run build
           pnpm --filter @posthog/enricher run build
+          pnpm --filter @posthog/harness run build
           pnpm --filter @posthog/agent run build
 
       - name: Build app

.github/workflows/code-release.yml

@@ -140,6 +140,9 @@ jobs:
       - name: Build enricher package
         run: pnpm --filter @posthog/enricher run build
 
+      - name: Build harness package
+        run: pnpm --filter @posthog/harness run build
+
       - name: Build agent package
         run: pnpm --filter @posthog/agent run build
 
@@ -331,6 +334,9 @@ jobs:
       - name: Build enricher package
         run: pnpm --filter @posthog/enricher run build
 
+      - name: Build harness package
+        run: pnpm --filter @posthog/harness run build
+
       - name: Build agent package
         run: pnpm --filter @posthog/agent run build
 
@@ -457,6 +463,9 @@ jobs:
       - name: Build enricher package
         run: pnpm --filter @posthog/enricher run build
 
+      - name: Build harness package
+        run: pnpm --filter @posthog/harness run build
+
       - name: Build agent package
         run: pnpm --filter @posthog/agent run build
 

.github/workflows/code-storybook.yml

@@ -149,16 +149,20 @@ jobs:
           pid2=$!
           wait_all "$pid1" "$pid2"
 
-          # @posthog/agent imports @posthog/git's dist, so git must finish
-          # before the last group starts.
-          pnpm --filter @posthog/git build
-
-          pnpm --filter @posthog/enricher build &
+          # @posthog/agent imports the dist of @posthog/git and
+          # @posthog/harness, so both must finish before the last group starts.
+          pnpm --filter @posthog/git build &
           pid3=$!
-          pnpm --filter @posthog/agent build &
+          pnpm --filter @posthog/harness build &
           pid4=$!
           wait_all "$pid3" "$pid4"
 
+          pnpm --filter @posthog/enricher build &
+          pid5=$!
+          pnpm --filter @posthog/agent build &
+          pid6=$!
+          wait_all "$pid5" "$pid6"
+
       - name: Build Storybook
         working-directory: apps/code
         run: pnpm build-storybook

.github/workflows/code-update-e2e.yml

@@ -106,6 +106,7 @@ jobs:
           pnpm --filter @posthog/shared run build
           pnpm --filter @posthog/git run build
           pnpm --filter @posthog/enricher run build
+          pnpm --filter @posthog/harness run build
           pnpm --filter @posthog/agent run build
 
       - name: Build old + new update pair

.github/workflows/pr-build-installer.yml

@@ -93,6 +93,7 @@ jobs:
           pnpm --filter @posthog/shared run build
           pnpm --filter @posthog/git run build
           pnpm --filter @posthog/enricher run build
+          pnpm --filter @posthog/harness run build
           pnpm --filter @posthog/agent run build
 
       # build/Assets.car is gitignored; regenerate it so the packaged app ships

.github/workflows/test.yml

@@ -140,8 +140,9 @@ jobs:
           pnpm --filter @posthog/shared build
           pnpm --filter @posthog/git build
           pnpm --filter @posthog/enricher build
-          pnpm --filter agent build &
           wait
+          pnpm --filter @posthog/harness build
+          pnpm --filter agent build
 
       - name: Package Electron app
         run: pnpm --filter code run package

packages/agent/package.json

@@ -80,6 +80,10 @@
       "types": "./dist/handoff-checkpoint.d.ts",
       "import": "./dist/handoff-checkpoint.js"
     },
+    "./pi": {
+      "types": "./dist/pi/rpc-client.d.ts",
+      "import": "./dist/pi/rpc-client.js"
+    },
     "./server": {
       "types": "./dist/server/agent-server.d.ts",
       "import": "./dist/server/agent-server.js"
@@ -132,13 +136,15 @@
     "@agentclientprotocol/sdk": "1.1.0",
     "@anthropic-ai/claude-agent-sdk": "0.3.197",
     "@anthropic-ai/sdk": "0.109.0",
+    "@earendil-works/pi-coding-agent": "catalog:",
     "@hono/node-server": "^1.19.9",
     "@openai/codex": "0.140.0",
     "@opentelemetry/api-logs": "^0.208.0",
     "@opentelemetry/exporter-logs-otlp-http": "^0.208.0",
     "@opentelemetry/resources": "^2.0.0",
     "@opentelemetry/sdk-logs": "^0.208.0",
     "@opentelemetry/semantic-conventions": "^1.28.0",
+    "@posthog/harness": "workspace:*",
     "@types/jsonwebtoken": "^9.0.10",
     "commander": "^14.0.2",
     "fflate": "^0.8.2",

packages/agent/src/pi/rpc-client.test.ts

@@ -0,0 +1,27 @@
+import { RpcClient } from "@earendil-works/pi-coding-agent";
+import { describe, expect, it } from "vitest";
+import { createPiRpcClient } from "./rpc-client";
+
+describe("createPiRpcClient", () => {
+  it("creates Pi's native RPC client for the harness entry", () => {
+    const client = createPiRpcClient({
+      cwd: "/workspace",
+      model: "claude-opus-4-8",
+      apiKey: "token",
+      env: { POSTHOG_REGION: "us" },
+    });
+
+    expect(client).toBeInstanceOf(RpcClient);
+    expect(client).toMatchObject({
+      options: {
+        cwd: "/workspace",
+        model: "claude-opus-4-8",
+        env: {
+          POSTHOG_API_KEY: "token",
+          POSTHOG_REGION: "us",
+        },
+        provider: "posthog",
+      },
+    });
+  });
+});

packages/agent/src/pi/rpc-client.ts

@@ -0,0 +1,37 @@
+import { fileURLToPath } from "node:url";
+import {
+  RpcClient,
+  type RpcClientOptions,
+} from "@earendil-works/pi-coding-agent";
+
+export type PiRpcClient = RpcClient;
+
+export type PiRpcClientOptions = Pick<
+  RpcClientOptions,
+  "cwd" | "env" | "model"
+> & {
+  /** PostHog token passed only to the isolated RPC host process. */
+  apiKey?: string;
+};
+
+/**
+ * Create a native Pi RPC client backed by the PostHog harness.
+ *
+ * The client owns an isolated child process. Call `start()` before sending
+ * commands and `stop()` when the run is finished.
+ */
+export function createPiRpcClient(
+  options: PiRpcClientOptions = {},
+): PiRpcClient {
+  const { apiKey, env, ...rpcOptions } = options;
+
+  return new RpcClient({
+    ...rpcOptions,
+    cliPath: fileURLToPath(new URL("./rpc-host.js", import.meta.url)),
+    env: {
+      ...env,
+      ...(apiKey ? { POSTHOG_API_KEY: apiKey } : {}),
+    },
+    provider: "posthog",
+  });
+}

packages/agent/src/pi/rpc-host.ts

@@ -0,0 +1,22 @@
+import { createHarnessRuntime, runRpcMode } from "@posthog/harness";
+
+function argumentValue(name: string): string | undefined {
+  const index = process.argv.indexOf(name);
+  return index === -1 ? undefined : process.argv[index + 1];
+}
+
+const runtime = await createHarnessRuntime({
+  cwd: process.cwd(),
+  apiKey: process.env.POSTHOG_API_KEY ?? process.env.POSTHOG_PERSONAL_API_KEY,
+});
+
+const requestedModel = argumentValue("--model")?.replace(/^posthog\//, "");
+if (requestedModel) {
+  const model = runtime.services.modelRegistry.find("posthog", requestedModel);
+  if (!model) {
+    throw new Error(`PostHog model not found: ${requestedModel}`);
+  }
+  await runtime.session.setModel(model);
+}
+
+await runRpcMode(runtime);

packages/agent/tsup.config.ts

@@ -112,6 +112,8 @@ export default defineConfig([
       "src/posthog-api.ts",
       "src/posthog-products.ts",
       "src/pr-url-detector.ts",
+      "src/pi/rpc-client.ts",
+      "src/pi/rpc-host.ts",
       "src/resume.ts",
       "src/types.ts",
       "src/adapters/claude/questions/utils.ts",