feat(pi-acp): opt in persistent sessions

registry/agent/pi/src/adapter.ts

@@ -103,8 +103,21 @@ Object.defineProperty(process, "stdin", {
 
 type SessionManagerLike = {
 	inMemory(cwd?: string): unknown;
+	continueRecent(cwd: string, sessionDir: string): unknown;
 };
 
+/** Select persistent Pi sessions only when the adapter is explicitly configured. */
+export function resolveSessionManager(
+	SessionManager: SessionManagerLike,
+	cwd: string,
+	env: Record<string, string | undefined> = process.env,
+): unknown {
+	const sessionDir = env.PI_SESSION_DIR?.trim();
+	return sessionDir
+		? SessionManager.continueRecent(cwd, sessionDir)
+		: SessionManager.inMemory(cwd);
+}
+
 type ModelLike = {
 	id: string;
 	provider: string;
@@ -873,7 +886,7 @@ export class PiSdkAgent implements Agent {
 		const { session } = await __trace.span("createAgentSession", () =>
 			createAgentSession({
 				cwd: params.cwd,
-				sessionManager: SessionManager.inMemory(params.cwd),
+				sessionManager: resolveSessionManager(SessionManager, params.cwd),
 				resourceLoader,
 				tools: this.wrapTools(
 					createCodingTools(params.cwd, {

registry/agent/pi/tests/adapter.test.mjs

@@ -6,7 +6,9 @@ import { resolve as resolvePath } from "node:path";
 // testing; newSession needs the real Pi SDK, so these drive the translation /
 // lifecycle logic directly with a mock ACP connection + a fake session.
 const packageDir = resolvePath(import.meta.dirname, "..");
-const { PiSdkAgent } = await import(resolvePath(packageDir, "dist", "adapter.js"));
+const { PiSdkAgent, resolveSessionManager } = await import(
+	resolvePath(packageDir, "dist", "adapter.js")
+);
 
 function makeConn(overrides = {}) {
 	return {
@@ -26,6 +28,53 @@ function fakeSession(overrides = {}) {
 	};
 }
 
+test("PI_SESSION_DIR persists and resumes the most recent Pi session", () => {
+	const calls = [];
+	const manager = {
+		inMemory(cwd) {
+			calls.push(["inMemory", cwd]);
+			return "memory";
+		},
+		continueRecent(cwd, sessionDir) {
+			calls.push(["continueRecent", cwd, sessionDir]);
+			return "persistent";
+		},
+	};
+
+	assert.equal(
+		resolveSessionManager(manager, "/workspace", {
+			PI_SESSION_DIR: " /data/pi-sessions ",
+		}),
+		"persistent",
+	);
+	assert.deepEqual(calls, [
+		["continueRecent", "/workspace", "/data/pi-sessions"],
+	]);
+});
+
+test("Pi sessions remain in memory when PI_SESSION_DIR is unset or blank", () => {
+	const calls = [];
+	const manager = {
+		inMemory(cwd) {
+			calls.push(["inMemory", cwd]);
+			return "memory";
+		},
+		continueRecent() {
+			throw new Error("continueRecent should not be called");
+		},
+	};
+
+	assert.equal(resolveSessionManager(manager, "/workspace", {}), "memory");
+	assert.equal(
+		resolveSessionManager(manager, "/workspace", { PI_SESSION_DIR: "  " }),
+		"memory",
+	);
+	assert.deepEqual(calls, [
+		["inMemory", "/workspace"],
+		["inMemory", "/workspace"],
+	]);
+});
+
 // ── Fix #3: editSnapshots is cleared each turn (no unbounded leak) ──
 test("pi #3: prompt() clears leaked edit snapshots from a prior aborted turn", async () => {
 	const agent = new PiSdkAgent(makeConn());

website/public/docs/docs/agents/pi.md

@@ -15,6 +15,13 @@ Set the relevant variable on the session's `env`, sourced from your server's env
 
 See [LLM Credentials](/docs/llm-credentials), and Pi's [providers docs](https://github.com/badlogic/pi-mono/blob/main/packages/coding-agent/docs/providers.md) for the full list.
 
+## Persistent Pi sessions
+
+Pi keeps its own conversation state in memory by default. To preserve and resume
+the most recent Pi session after the adapter restarts, set `PI_SESSION_DIR` in the
+session's `env` to a directory on durable VM storage. Pi writes its session JSONL
+files there; an unset or blank value retains the in-memory default.
+
 ## Skills
 
 Pi discovers `SKILL.md` files from its skills directory. Write the skill into the VM before creating a session and Pi loads it automatically.
@@ -40,4 +47,4 @@ See the [Pi extension documentation](https://github.com/badlogic/pi-mono/tree/ma
 
 ## Customizing the agent
 
-Pi is a built-in agent, but it's just a software package under the hood. To ship your own ACP adapter, swap the underlying agent SDK, or register a tweaked Pi build as a new agent, see [Custom Agents](/docs/agents/custom).
+Pi is a built-in agent, but it's just a software package under the hood. To ship your own ACP adapter, swap the underlying agent SDK, or register a tweaked Pi build as a new agent, see [Custom Agents](/docs/agents/custom).