diff --git a/server/src/services/native-runtime/native-session-executor.test.ts b/server/src/services/native-runtime/native-session-executor.test.ts
index 2e48766402..c7dfb730c4 100644
--- a/server/src/services/native-runtime/native-session-executor.test.ts
+++ b/server/src/services/native-runtime/native-session-executor.test.ts
@@ -291,7 +291,8 @@ beforeEach(() => {
 });
 
 describe("remote runner process supervision", () => {
-  it("detaches runnerd from the provider RPC and monitors its durable identity", async () => {
+  it.each(["delivered", "sandbox_missing", "logging_failed"] as const)(
+    "detaches runnerd and contains asynchronous signal failures (%s)", async (signalOutcome) => {
     let launchNonce = "";
     const execute = vi.fn(
       async (input: {
@@ -354,6 +355,7 @@ describe("remote runner process supervision", () => {
           };
         }
         if (label === "paperclip-runner-signal") {
+          if (signalOutcome !== "delivered") throw new Error("Sandbox with ID test-deleted-sandbox not found");
           return {
             exitCode: 0,
             signal: null,
@@ -366,6 +368,9 @@ describe("remote runner process supervision", () => {
       },
     );
     const onSpawn = vi.fn(async () => undefined);
+    const onLog = vi.fn(async () => {
+      if (signalOutcome === "logging_failed") throw new Error("Run log already closed");
+    });
     const launcher = createRemoteRunnerProcessLauncher({
       target: {
         kind: "remote",
@@ -381,6 +386,7 @@ describe("remote runner process supervision", () => {
       diagnosticsDirectory: "/runtime/diagnostics",
       runnerInstanceId: "runner-remote",
       onSpawn,
+      onLog,
     });
 
     const handle = launcher({
@@ -424,6 +430,17 @@ describe("remote runner process supervision", () => {
         ),
       ).toBe(true),
     );
+    if (signalOutcome !== "delivered") {
+      await vi.waitFor(() => expect(onLog).toHaveBeenCalledWith(
+        "stderr", "Remote runner signal failed; process termination is not confirmed.\n",
+      ));
+      // Let rejected logging callbacks settle too. Neither failure may escape
+      // this fire-and-forget Node child-process-compatible kill boundary.
+      await new Promise<void>((resolve) => setImmediate(resolve));
+    } else {
+      expect(onLog).not.toHaveBeenCalled();
+    }
+    expect(handle.child.exitCode).toBeNull();
   });
 
   it("terminates a detached runner when its process identity cannot be adopted", async () => {
diff --git a/server/src/services/native-runtime/native-session-executor.ts b/server/src/services/native-runtime/native-session-executor.ts
index deb42387db..c1de7cf35e 100644
--- a/server/src/services/native-runtime/native-session-executor.ts
+++ b/server/src/services/native-runtime/native-session-executor.ts
@@ -9593,7 +9593,16 @@ export function createRemoteRunnerProcessLauncher(input: {
           ],
           bypassSession: true,
           timeoutMs: 10_000,
-        });
+        }).catch(async () => {
+          // kill() follows Node's synchronous child-process contract. A deleted
+          // sandbox or failed signal RPC must not reject outside that boundary
+          // and crash the controller. This is not a termination receipt: the
+          // monitor and cleanup verification still decide whether work stopped.
+          await input.onLog?.(
+            "stderr",
+            "Remote runner signal failed; process termination is not confirmed.\n",
+          );
+        }).catch(() => undefined);
         return true;
       },
     };