diff --git a/src/tests/backends.integration.test.ts b/src/tests/backends.integration.test.ts
new file mode 100644
index 0000000..9cf8ad1
--- /dev/null
+++ b/src/tests/backends.integration.test.ts
@@ -0,0 +1,217 @@
+/**
+ * Cross-backend session integration — opt-in, against REAL backends.
+ *
+ * Proves the two things a meta-harness must never get wrong, with the actual
+ * agent binaries/SDKs (not fakes), through the real SessionManager verbs:
+ *
+ *   FRESH   — a brand-new session on each backend takes a turn and replies.
+ *   RESUME  — a conversation STARTED on backend S, then forked onto a
+ *             DIFFERENT backend T, carries its history: T answers a question
+ *             about a fact only established during S's turn. This is codeoid's
+ *             headline promise ("branch claude, continue on codex") and it
+ *             exercises the exact seedFromHistory path fork/switch use.
+ *
+ * Gated: skipped unless CODEOID_INTEGRATION=1. The backends exercised come
+ * from CODEOID_INTEGRATION_BACKENDS (comma list, default "claude,codex") and
+ * MUST be installed + authenticated on the runner. Example:
+ *
+ *   CODEOID_INTEGRATION=1 CODEOID_INTEGRATION_BACKENDS=claude,codex,pi \
+ *     bun test src/tests/backends.integration.test.ts
+ *
+ * Verified locally against claude (Agent SDK) + codex (@openai/codex@0.144.1):
+ * fresh turns reply, and claude↔codex resume carries the fact both ways.
+ */
+
+import { afterAll, beforeAll, describe, expect, it } from "bun:test";
+import { mkdtempSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { randomUUID } from "node:crypto";
+import { Store } from "../daemon/store.js";
+import { TranscriptStore } from "../daemon/transcript.js";
+import { SessionManager } from "../daemon/session-manager.js";
+import { createDefaultProviderRegistry } from "../daemon/providers/registry.js";
+import { ALL_SCOPES } from "../protocol/scopes.js";
+import type { AuthContext, DaemonMessage } from "../protocol/types.js";
+
+const RUN = process.env.CODEOID_INTEGRATION === "1";
+const BACKENDS = (process.env.CODEOID_INTEGRATION_BACKENDS ?? "claude,codex")
+  .split(",")
+  .map((s) => s.trim())
+  .filter(Boolean);
+
+const AUTH: AuthContext = {
+  sub: "user:it",
+  scopes: [...ALL_SCOPES] as AuthContext["scopes"],
+  delegationDepth: 0,
+  accountId: "acc-it",
+  projectId: "proj-it",
+};
+
+let tmp: string;
+let store: Store;
+let transcript: TranscriptStore;
+let manager: SessionManager;
+let available: string[] = [];
+
+beforeAll(() => {
+  if (!RUN) {
+    // eslint-disable-next-line no-console
+    console.log("[backends integration] SKIPPED — set CODEOID_INTEGRATION=1 (+ authed backends) to run.");
+    return;
+  }
+  tmp = mkdtempSync(join(tmpdir(), "codeoid-backends-it-"));
+  store = new Store(join(tmp, "codeoid.db"));
+  transcript = new TranscriptStore(join(tmp, "transcripts"));
+  // Enable the binary backends; claude is always registered, gemini/openai
+  // gate on their keys inside createDefaultProviderRegistry.
+  const registry = createDefaultProviderRegistry({
+    providers: { codex: { enabled: true }, pi: { enabled: true } },
+  } as never);
+  manager = new SessionManager(store, transcript, undefined, undefined, undefined, {
+    providers: registry,
+  } as never);
+  available = BACKENDS.filter((id) => registry.has(id));
+  const missing = BACKENDS.filter((id) => !registry.has(id));
+  if (missing.length > 0) {
+    // eslint-disable-next-line no-console
+    console.log(`[backends integration] requested but NOT available (skipping those): ${missing.join(", ")}`);
+  }
+});
+
+afterAll(async () => {
+  if (!RUN) return;
+  // No arbitrary settle delay: every turn was awaited to idle via
+  // sendAndSettle, and flush() drains queued transcript writes.
+  try {
+    await transcript.flush();
+  } catch {}
+  try {
+    store.close();
+  } catch {}
+  try {
+    rmSync(tmp, { recursive: true, force: true });
+  } catch {}
+});
+
+// ── Harness ────────────────────────────────────────────────────────────────
+
+function makeClient(): { id: string; auth: AuthContext; received: DaemonMessage[]; send: (m: DaemonMessage) => void } {
+  const received: DaemonMessage[] = [];
+  return { id: randomUUID(), auth: AUTH, received, send: (m) => received.push(m) };
+}
+
+type Client = ReturnType<typeof makeClient>;
+
+async function createOn(c: Client, providerId: string): Promise<string> {
+  const resp = await manager.handle(
+    { type: "session.create", id: randomUUID(), name: providerId, workdir: tmp, providerId } as never,
+    AUTH,
+    c as never,
+  );
+  expect((resp as { type: string }).type).toBe("response.ok");
+  return (resp as { data: { id: string } }).data.id;
+}
+
+/** Send a turn and wait for the session to return to idle (or error). */
+async function sendAndSettle(c: Client, sessionId: string, text: string): Promise<void> {
+  await manager.handle({ type: "session.attach", id: randomUUID(), sessionId } as never, AUTH, c as never);
+  const start = c.received.length;
+  await manager.handle({ type: "session.send", id: randomUUID(), sessionId, text } as never, AUTH, c as never);
+  const deadline = Date.now() + 120_000;
+  while (Date.now() < deadline) {
+    const settled = c.received
+      .slice(start)
+      .some((m) => m.type === "session.status_change" && ((m as { status: string }).status === "idle" || (m as { status: string }).status === "error"));
+    if (settled) return;
+    await new Promise((r) => setTimeout(r, 50));
+  }
+  throw new Error(`[${sessionId}] never settled after send`);
+}
+
+function partText(content: unknown): string {
+  if (typeof content === "string") return content;
+  if (Array.isArray(content)) return content.map((p) => (typeof p === "string" ? p : ((p as { text?: string }).text ?? ""))).join("");
+  return "";
+}
+
+/** All assistant text broadcast for `sessionId` after index `since`. */
+function assistantText(c: Client, sessionId: string, since: number): string {
+  return c.received
+    .slice(since)
+    .filter((m) => m.type === "session.message" && (m as { sessionId: string }).sessionId === sessionId && (m as { role?: string }).role === "assistant")
+    .map((m) => partText((m as { content: unknown }).content))
+    .join("\n");
+}
+
+function assertNoError(c: Client, sessionId: string, since: number): void {
+  const errs = c.received
+    .slice(since)
+    .filter(
+      (m) =>
+        m.type === "session.status_change" &&
+        (m as { sessionId: string }).sessionId === sessionId &&
+        (m as { status: string }).status === "error",
+    );
+  expect(errs.length, `backend errored during turn: ${JSON.stringify(errs)}`).toBe(0);
+}
+
+// ── Tests ────────────────────────────────────────────────────────────────
+
+describe("backends integration (real)", () => {
+  (RUN ? it : it.skip)(
+    "at least one requested backend is available",
+    () => {
+      expect(available.length).toBeGreaterThan(0);
+    },
+  );
+
+  // FRESH: every enabled backend takes a brand-new turn and replies.
+  for (const backend of BACKENDS) {
+    (RUN ? it : it.skip)(
+      `FRESH: ${backend} — a new session takes a turn and replies`,
+      async () => {
+        if (!available.includes(backend)) return; // requested but unavailable
+        const c = makeClient();
+        const sid = await createOn(c, backend);
+        const since = c.received.length;
+        await sendAndSettle(c, sid, "Reply with exactly the word: ok");
+        assertNoError(c, sid, since);
+        expect(assistantText(c, sid, since).toLowerCase()).toContain("ok");
+      },
+      150_000,
+    );
+  }
+
+  // RESUME: fork a conversation from S onto a DIFFERENT backend T; T must
+  // answer using the fact only established during S's turn.
+  for (const source of BACKENDS) {
+    for (const target of BACKENDS) {
+      if (source === target) continue;
+      (RUN ? it : it.skip)(
+        `RESUME: ${source} → ${target} — forked backend recalls the fact`,
+        async () => {
+          if (!available.includes(source) || !available.includes(target)) return;
+          const c = makeClient();
+          const sid = await createOn(c, source);
+          await sendAndSettle(c, sid, "My favorite number is 42. Reply with just: noted");
+
+          const fork = await manager.handle(
+            { type: "session.fork", id: randomUUID(), sessionId: sid, providerId: target } as never,
+            AUTH,
+            c as never,
+          );
+          expect((fork as { type: string }).type).toBe("response.ok");
+          const forkData = (fork as { data: { id: string; providerId?: string } }).data;
+          expect(forkData.providerId).toBe(target);
+
+          const since = c.received.length;
+          await sendAndSettle(c, forkData.id, "What is my favorite number? Reply with ONLY the number.");
+          assertNoError(c, forkData.id, since);
+          expect(assistantText(c, forkData.id, since)).toContain("42");
+        },
+        200_000,
+      );
+    }
+  }
+});
diff --git a/src/tests/provider-pi.integration.test.ts b/src/tests/provider-pi.integration.test.ts
new file mode 100644
index 0000000..907fab5
--- /dev/null
+++ b/src/tests/provider-pi.integration.test.ts
@@ -0,0 +1,139 @@
+/**
+ * REAL pi integration tests — opt-in. The counterpart to
+ * provider-codex.integration.test.ts, for the pi harness.
+ *
+ * The offline suite (provider-pi.test.ts) runs against fake-pi. These drive
+ * codeoid's real PiProvider against the actual pi binary (bundled
+ * @earendil-works/pi-coding-agent, a system pi, or providers.pi.command) so
+ * the full spawn → JSONL framing → bridge approvals → turn-accounting pipeline
+ * is exercised against the real thing.
+ *
+ * Gated: skipped unless CODEOID_PI_INTEGRATION=1 AND pi resolves on this host.
+ * pi ALSO needs a provider configured/authenticated (an API key in the env, or
+ * `pi` logged in) — without it a turn fails on "No API key found". Example:
+ *
+ *   CODEOID_PI_INTEGRATION=1 GOOGLE_API_KEY=... \
+ *     bun test src/tests/provider-pi.integration.test.ts
+ *
+ *   P1  a fresh text turn runs to turn_done with a reply, no error
+ *   P2  pi runs a shell tool end-to-end and its output reaches codeoid
+ *
+ * See also backends.integration.test.ts, which exercises pi (when enabled) in
+ * the cross-backend FRESH + RESUME matrix through the real SessionManager.
+ */
+
+import { afterAll, describe, expect, it } from "bun:test";
+import { mkdtempSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { PiProvider } from "../daemon/providers/pi/index.js";
+import { resolvePiCommand } from "../daemon/providers/pi/resolve.js";
+import { Store } from "../daemon/store.js";
+import type { ProviderEvent, TurnOpts, TurnRun } from "../daemon/providers/interface.js";
+
+const resolved = resolvePiCommand(undefined);
+const RUN = process.env.CODEOID_PI_INTEGRATION === "1" && resolved !== null;
+const maybe = RUN ? it : it.skip;
+
+if (!RUN) {
+  // eslint-disable-next-line no-console
+  console.log(
+    `[pi integration] SKIPPED — set CODEOID_PI_INTEGRATION=1 and install+auth pi to run (resolved=${resolved ? resolved.command : "none"}).`,
+  );
+}
+
+const WORK = RUN ? mkdtempSync(join(tmpdir(), "codeoid-pi-it-")) : "/tmp";
+let store: Store | null = null;
+afterAll(() => {
+  if (!RUN) return;
+  store?.close();
+  rmSync(WORK, { recursive: true, force: true });
+});
+
+function makeProvider(): PiProvider {
+  store ??= new Store(join(WORK, "pi.db"));
+  return new PiProvider({
+    sessionId: "pi-it",
+    initialBackingId: "pi-it",
+    command: resolved!.command,
+    argsPrefix: resolved!.argsPrefix,
+    store,
+  });
+}
+
+function turnOpts(userMessage: string, overrides: Partial<TurnOpts> = {}): TurnOpts {
+  return {
+    history: [],
+    userMessage,
+    workdir: WORK,
+    // Autonomous-equivalent: auto-approve everything the bridge asks about.
+    canUseTool: async () => ({ behavior: "allow" as const }),
+    ...overrides,
+  };
+}
+
+async function collect(run: TurnRun, ms: number): Promise<ProviderEvent[]> {
+  const events: ProviderEvent[] = [];
+  const timer = setTimeout(() => void run.interrupt(), ms);
+  try {
+    for await (const event of run.events) {
+      events.push(event);
+      if (event.type === "turn_done" || event.type === "error") break;
+    }
+  } finally {
+    clearTimeout(timer);
+  }
+  return events;
+}
+
+function errorText(events: ProviderEvent[]): string {
+  return events
+    .filter((e) => e.type === "error")
+    .map((e) => (e as { message: string }).message)
+    .join(" | ");
+}
+
+describe("PiProvider — REAL pi integration", () => {
+  maybe(
+    "P1: a fresh text turn runs to completion with a reply and no error",
+    async () => {
+      const p = makeProvider();
+      try {
+        const events = await collect(p.runTurn(turnOpts("Reply with exactly the word: ok")), 90_000);
+        expect(errorText(events)).toBe("");
+        expect(events.some((e) => e.type === "turn_done")).toBe(true);
+        const text = events
+          .filter((e) => e.type === "text_done" || e.type === "text_delta")
+          .map((e) => (e as { content: string }).content)
+          .join("");
+        expect(text.trim().length).toBeGreaterThan(0);
+      } finally {
+        await p.teardown();
+      }
+    },
+    120_000,
+  );
+
+  maybe(
+    "P2: pi runs a shell tool end-to-end and its output reaches codeoid",
+    async () => {
+      const p = makeProvider();
+      try {
+        const events = await collect(
+          p.runTurn(
+            turnOpts(
+              "Run this shell command and reply with ONLY the number it prints: printf 'a\\nb\\n' | wc -l",
+            ),
+          ),
+          120_000,
+        );
+        expect(errorText(events)).toBe("");
+        expect(events.some((e) => e.type === "tool_complete")).toBe(true);
+        expect(events.some((e) => e.type === "turn_done")).toBe(true);
+      } finally {
+        await p.teardown();
+      }
+    },
+    150_000,
+  );
+});