diff --git a/apps/sidecar/test/suspend-key-preservation.poc.test.ts b/apps/sidecar/test/suspend-key-preservation.poc.test.ts
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+++ b/apps/sidecar/test/suspend-key-preservation.poc.test.ts
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+// Spike PoC for CL-6581 / CL-6239: proves a suspend teardown can preserve an
+// agent's Ed25519 signing identity WITHOUT vendoring `@intx/hub-agent`.
+//
+// Background: `@intx/hub-agent`'s `AgentKeyStore` persists each agent's
+// reconnect-challenge keypair under `agentDir(dataDir, address)/keys/`
+// (`agent-key-store.ts`). Its `AgentRepoStore.remove` -- reached from every
+// `sendAgentUndeploy`, hibernate or not, via `session-manager.js`'s
+// `deleteAgentDir` -- unconditionally `fsp.rm`s the whole `agentDir`,
+// destroying the key subdirectory with it. That code lives entirely inside
+// the published npm package (this repo carries no `vendor/intx/hub-agent`
+// tree), so it cannot be edited directly.
+//
+// This test shows the fix does not require editing it: `agentDir(dataDir,
+// address)` is a stable PUBLIC export (`@intx/hub-agent`'s `index.ts`), so a
+// caller that snapshots the directory before the destructive `remove()` and
+// restores it before the next `deploy` sees the *same* keypair come back out
+// of `loadOrGenerateKey` -- `isNew: false` -- with no fork of the package.
+//
+// This file is a standalone PoC, not production wiring: it exercises
+// `@intx/hub-agent`'s real, unmodified `createAgentKeyStore` /
+// `createAgentRepoStore` / `agentDir` directly against a tmp dir. Wiring the
+// same snapshot/restore into `workflow-host-wiring`'s `reclaimDirs`-aware
+// `undeploy`/`deploy` hooks is the actual feature build, owned by a
+// different lane.
+
+import { describe, test, expect } from "bun:test";
+import fs from "node:fs/promises";
+import os from "node:os";
+import path from "node:path";
+
+import {
+  createAgentKeyStore,
+  createAgentRepoStore,
+  agentDir,
+} from "@intx/hub-agent";
+import {
+  generateKeyPair,
+  signEd25519,
+  verifySSHSignature,
+} from "@intx/crypto";
+
+const cryptoOps = {
+  generateKeyPair,
+  signEd25519,
+  verifySSHSig: verifySSHSignature,
+};
+
+async function makeTmpDataDir(): Promise<string> {
+  return fs.mkdtemp(path.join(os.tmpdir(), "hub-agent-suspend-poc-"));
+}
+
+describe("suspend key preservation without vendoring @intx/hub-agent", () => {
+  test("an unprotected undeploy destroys the agent's keypair (establishes the baseline bug)", async () => {
+    const dataDir = await makeTmpDataDir();
+    const keyStore = createAgentKeyStore({ dataDir, ...cryptoOps });
+    const repoStore = createAgentRepoStore({ dataDir });
+    const address = "run_baseline@example.com";
+
+    const { keyPair: minted } = await keyStore.loadOrGenerateKey(address);
+    expect(minted.privateKey.length).toBe(32);
+
+    // The exact call `session-manager.js`'s `deleteAgentDir` makes from
+    // `hub-link.js`'s `handleAgentUndeploy`, unconditionally, on every
+    // `sendAgentUndeploy` -- hibernate reason or not.
+    await repoStore.remove(address);
+
+    expect(await fs.readdir(dataDir)).toEqual([]);
+
+    const freshKeyStore = createAgentKeyStore({ dataDir, ...cryptoOps });
+    const { keyPair: regenerated, isNew } =
+      await freshKeyStore.loadOrGenerateKey(address);
+    expect(isNew).toBe(true);
+    expect(regenerated.privateKey).not.toEqual(minted.privateKey);
+  });
+
+  test("snapshot-before-remove + restore-before-redeploy preserves identity across the same destructive call", async () => {
+    const dataDir = await makeTmpDataDir();
+    const vaultDir = await makeTmpDataDir();
+    const keyStore = createAgentKeyStore({ dataDir, ...cryptoOps });
+    const repoStore = createAgentRepoStore({ dataDir });
+    const address = "run_hibernate@example.com";
+
+    const { keyPair: original } = await keyStore.loadOrGenerateKey(address);
+
+    // -- workbench-owned "undeploy" hook, gated on
+    // `reason === IDLE_HIBERNATE_UNDEPLOY_REASON` in the real wiring --
+    // snapshots the whole agent directory via the public `agentDir` export
+    // before the package's own teardown deletes it.
+    const dir = agentDir(dataDir, address);
+    const vaultEntry = path.join(vaultDir, path.basename(dir));
+    await fs.cp(dir, vaultEntry, { recursive: true });
+
+    // The real, unmodified destructive call.
+    await repoStore.remove(address);
+    keyStore.forgetAgent(address);
+    expect(await fs.readdir(dataDir)).toEqual([]);
+
+    // -- workbench-owned "deploy" hook, run before the redeploy reaches
+    // `loadOrGenerateKey` -- restores the snapshot.
+    await fs.cp(vaultEntry, dir, { recursive: true });
+    await fs.rm(vaultEntry, { recursive: true });
+
+    const { keyPair: restored, isNew } =
+      await keyStore.loadOrGenerateKey(address);
+    expect(isNew).toBe(false);
+    expect(restored.privateKey).toEqual(original.privateKey);
+    expect(restored.publicKey).toEqual(original.publicKey);
+  });
+});