diff --git a/src/features/background-agent/process-cleanup.test.ts b/src/features/background-agent/process-cleanup.test.ts
index 6b79d594e..19b46fcda 100644
--- a/src/features/background-agent/process-cleanup.test.ts
+++ b/src/features/background-agent/process-cleanup.test.ts
@@ -275,5 +275,42 @@ describe("#given process cleanup registration", () => {
         uncaughtExceptionListenersBefore.length,
       )
     })
+
+    test("#given cleanup itself throws re-entrant uncaughtException #when event fires repeatedly #then listener body runs only once AND no further log calls occur", async () => {
+      // Regression guard for log explosion (157 GB in minutes) observed when
+      // shutdown() code path itself emits uncaughtException (e.g. EPIPE while
+      // closing a broken pipe). Before the fix, every re-entry logged another
+      // line and re-ran cleanup, producing an unbounded loop that filled disk.
+      const reentrantShutdown = mock(() => {
+        process.emit("uncaughtException", new Error("EPIPE re-entry"))
+      })
+      const manager = { shutdown: reentrantShutdown }
+      registeredManagers.push(manager)
+
+      registerManagerForCleanup(manager)
+
+      process.emit("uncaughtException", new Error("boom"))
+      await flushMicrotasks()
+
+      // Primary listener body must run exactly once. Re-entry MUST be short-
+      // circuited — otherwise the shutdown → EPIPE → uncaughtException loop
+      // writes millions of log lines before the forced-exit timer fires.
+      expect(reentrantShutdown.mock.calls.length).toBeLessThanOrEqual(1)
+    })
+
+    test("#given cleanup emits unhandledRejection re-entrantly #when event fires #then listener body runs only once", async () => {
+      const reentrantShutdown = mock(() => {
+        process.emit("unhandledRejection", new Error("re-entry"), Promise.resolve())
+      })
+      const manager = { shutdown: reentrantShutdown }
+      registeredManagers.push(manager)
+
+      registerManagerForCleanup(manager)
+
+      process.emit("unhandledRejection", new Error("boom"), Promise.resolve())
+      await flushMicrotasks()
+
+      expect(reentrantShutdown.mock.calls.length).toBeLessThanOrEqual(1)
+    })
   })
 })
diff --git a/src/features/background-agent/process-cleanup.ts b/src/features/background-agent/process-cleanup.ts
index be4338073..f9d84dd6a 100644
--- a/src/features/background-agent/process-cleanup.ts
+++ b/src/features/background-agent/process-cleanup.ts
@@ -38,6 +38,12 @@ function registerErrorEvent(
   handler: (error: unknown) => void | Promise<void>
 ): (error: unknown) => void {
   const listener = (error: unknown) => {
+    // Detach before running the body so a re-emit from inside log()/handler()
+    // (e.g. EPIPE while closing a broken pipe during shutdown) cannot recurse.
+    // Prior behavior: the listener re-entered itself, re-logged, re-ran cleanup,
+    // and threw EPIPE again — an unbounded loop that filled disks with 100+ GB
+    // of log lines in minutes before the 6 s forced-exit timer could fire.
+    process.off(signal, listener)
     log(`[background-agent] ${signal} received during shutdown cleanup:`, error)
     scheduleForcedExit(handler(error), 1, true)
   }