diff --git a/backend/src/pi/pi-process-manager.ts b/backend/src/pi/pi-process-manager.ts
index 139a350d..226f967f 100644
--- a/backend/src/pi/pi-process-manager.ts
+++ b/backend/src/pi/pi-process-manager.ts
@@ -37,6 +37,7 @@ type SpawnFn = (
 
 export class PiProcessManager {
   private runtimes = new Map<string, SessionRuntime>();
+  private agentSnapshotCleanups = new WeakMap<ChildProcessWithoutNullStreams, () => void>();
   private spawnFn: (
     sessionId: string, author: string, provider: string | undefined, principal?: PrincipalContext,
     runtimeConfigPath?: string,
@@ -58,6 +59,13 @@ export class PiProcessManager {
     }
   }
 
+  private cleanupAgentSnapshot(child: ChildProcessWithoutNullStreams): void {
+    const cleanup = this.agentSnapshotCleanups.get(child);
+    if (!cleanup) return;
+    this.agentSnapshotCleanups.delete(child);
+    cleanup();
+  }
+
   private spawnPi(
     spawnFn: SpawnFn, sessionId: string, author: string, provider: string | undefined,
     principal?: PrincipalContext, runtimeConfigPath?: string,
@@ -104,16 +112,19 @@ export class PiProcessManager {
         cwd: this.cfg.harnessDir,
         env,
       });
-      child.once("exit", agent.cleanup);
-      child.once("close", agent.cleanup);
+      this.agentSnapshotCleanups.set(child, agent.cleanup);
+      child.once("exit", () => this.cleanupAgentSnapshot(child!));
+      child.once("close", () => this.cleanupAgentSnapshot(child!));
       // Log stderr for debugging (was silently drained)
       child.stderr.on("data", (d: Buffer) => console.error(`[pi:${sessionId}] stderr:`, d.toString().trim()));
       return child;
     } catch (error) {
       if (child) {
         try { child.kill(); } catch { /* preserve the initialization error */ }
+        this.cleanupAgentSnapshot(child);
+      } else {
+        agent.cleanup();
       }
-      agent.cleanup();
       throw error;
     }
   }
@@ -208,6 +219,7 @@ export class PiProcessManager {
       if (rt && this.runtimes.get(sessionId) === rt) this.runtimes.delete(sessionId);
       releaseRuntimeConfig();
       try { child.kill(); } catch { /* preserve the initialization error */ }
+      this.cleanupAgentSnapshot(child);
       throw error;
     }
   }
@@ -276,6 +288,7 @@ export class PiProcessManager {
     this.runtimes.delete(id);
     expected.releaseRuntimeConfig?.();
     expected.child.kill();
+    this.cleanupAgentSnapshot(expected.child);
     return true;
   }
 }
diff --git a/backend/test/pi-process-manager.test.ts b/backend/test/pi-process-manager.test.ts
index 3238ecb1..4227d231 100644
--- a/backend/test/pi-process-manager.test.ts
+++ b/backend/test/pi-process-manager.test.ts
@@ -306,10 +306,18 @@ test("createFor kills a spawned child when post-spawn initialization throws", ()
   child.stdout = {
     on: () => { throw new Error("READER_INIT_SENTINEL"); },
   };
-  const mgr = new PiProcessManager(loadConfig({}), { spawnFn: () => child as any });
+  let snapshotDir: string | undefined;
+  const mgr = new PiProcessManager(loadConfig({}), {
+    spawnFn: (_command, _args, options) => {
+      snapshotDir = options.env.PI_CODING_AGENT_DIR;
+      return child as any;
+    },
+  });
 
   expect(() => mgr.createFor("broken-init", {})).toThrow("READER_INIT_SENTINEL");
 
+  expect(snapshotDir).toBeTruthy();
+  expect(existsSync(snapshotDir!)).toBe(false);
   expect(child.kill).toHaveBeenCalledOnce();
   expect(mgr.get("broken-init")).toBeUndefined();
   expect(mgr.count()).toBe(0);