diff --git a/src/agents/bash-tools.exec.background-abort.test.ts b/src/agents/bash-tools.exec.background-abort.test.ts
new file mode 100644
index 00000000000..77477118fff
--- /dev/null
+++ b/src/agents/bash-tools.exec.background-abort.test.ts
@@ -0,0 +1,76 @@
+import { afterEach, expect, test } from "vitest";
+
+import { getFinishedSession, getSession, resetProcessRegistryForTests } from "./bash-process-registry.js";
+import { createExecTool } from "./bash-tools.exec.js";
+import { killProcessTree } from "./shell-utils.js";
+
+const sleep = (ms: number) => new Promise((resolve) => setTimeout(resolve, ms));
+
+afterEach(() => {
+  resetProcessRegistryForTests();
+});
+
+test("background exec is not killed when tool signal aborts", async () => {
+  const tool = createExecTool({ allowBackground: true, backgroundMs: 0 });
+  const abortController = new AbortController();
+
+  const result = await tool.execute(
+    "toolcall",
+    { command: "node -e \"setTimeout(() => {}, 5000)\"", background: true },
+    abortController.signal,
+  );
+
+  expect(result.details.status).toBe("running");
+  const sessionId = (result.details as { sessionId: string }).sessionId;
+
+  abortController.abort();
+
+  await new Promise((resolve) => setTimeout(resolve, 150));
+
+  const running = getSession(sessionId);
+  const finished = getFinishedSession(sessionId);
+
+  try {
+    expect(finished).toBeUndefined();
+    expect(running?.exited).toBe(false);
+  } finally {
+    const pid = running?.pid;
+    if (pid) killProcessTree(pid);
+  }
+});
+
+test("background exec still times out after tool signal abort", async () => {
+  const tool = createExecTool({ allowBackground: true, backgroundMs: 0 });
+  const abortController = new AbortController();
+
+  const result = await tool.execute(
+    "toolcall",
+    {
+      command: "node -e \"setTimeout(() => {}, 5000)\"",
+      background: true,
+      timeout: 0.2,
+    },
+    abortController.signal,
+  );
+
+  expect(result.details.status).toBe("running");
+  const sessionId = (result.details as { sessionId: string }).sessionId;
+
+  abortController.abort();
+
+  let finished = getFinishedSession(sessionId);
+  const deadline = Date.now() + 2000;
+  while (!finished && Date.now() < deadline) {
+    await sleep(20);
+    finished = getFinishedSession(sessionId);
+  }
+
+  const running = getSession(sessionId);
+
+  try {
+    expect(finished?.status).toBe("failed");
+  } finally {
+    const pid = running?.pid;
+    if (pid) killProcessTree(pid);
+  }
+});
diff --git a/src/agents/bash-tools.exec.ts b/src/agents/bash-tools.exec.ts
index efa57a4ab23..d97b0e6533f 100644
--- a/src/agents/bash-tools.exec.ts
+++ b/src/agents/bash-tools.exec.ts
@@ -262,21 +262,28 @@ export function createExecTool(
         fn();
       };
 
-      const onAbort = () => {
+      // Tool-call abort should not kill backgrounded sessions; timeouts still must.
+      const onAbortSignal = () => {
+        if (yielded || session.backgrounded) return;
         killSession(session);
       };
 
-      if (signal?.aborted) onAbort();
+      // Timeouts always terminate, even for backgrounded sessions.
+      const onTimeout = () => {
+        timedOut = true;
+        killSession(session);
+      };
+
+      if (signal?.aborted) onAbortSignal();
       else if (signal) {
-        signal.addEventListener("abort", onAbort, { once: true });
+        signal.addEventListener("abort", onAbortSignal, { once: true });
       }
 
       const effectiveTimeout =
         typeof params.timeout === "number" ? params.timeout : defaultTimeoutSec;
       if (effectiveTimeout > 0) {
         timeoutTimer = setTimeout(() => {
-          timedOut = true;
-          onAbort();
+          onTimeout();
         }, effectiveTimeout * 1000);
       }