diff --git a/src/main/services/workspace-command.ts b/src/main/services/workspace-command.ts
index c9a3cc56..3f3094fb 100644
--- a/src/main/services/workspace-command.ts
+++ b/src/main/services/workspace-command.ts
@@ -75,12 +75,18 @@ export function runCommand(workspaceRoot: string, command: string, options: { ti
     child.stdout.on("data", collect);
     child.stderr.on("data", collect);
     child.on("error", (error) => finish(`ERROR: ${error.message}`));
-    child.on("close", (code) => {
-      finish(`exit code ${code ?? 0}\n${output.text().trim() || "(no output)"}`);
-    });
+    child.on("close", (code, signal) => finish(formatCommandResult(code, signal, output.text())));
   });
 }
 
+/** The tool result for a finished command; no exit code means it was killed, which is never success. */
+export function formatCommandResult(code: number | null, signal: NodeJS.Signals | null, text: string): string {
+  const body = text.trim() || "(no output)";
+  if (code !== null) return `exit code ${code}\n${body}`;
+  const how = signal ? `was killed by ${signal} before it exited` : "ended without an exit code";
+  return `ERROR: the command ${how}; treat it as failed.\n${body}`;
+}
+
 /** Kills a process and every process it started; returns why that failed, or null. */
 function killProcessTree(pid: number | undefined): string | null {
   if (pid === undefined) return null;
diff --git a/tests/unit/workspace-command.test.ts b/tests/unit/workspace-command.test.ts
index 31e97af9..25e01cc1 100644
--- a/tests/unit/workspace-command.test.ts
+++ b/tests/unit/workspace-command.test.ts
@@ -2,7 +2,7 @@ import { mkdtempSync, readFileSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { describe, expect, test, vi } from "vitest";
-import { BoundedOutput, runCommand } from "../../src/main/services/workspace-command";
+import { BoundedOutput, formatCommandResult, runCommand } from "../../src/main/services/workspace-command";
 import { stopRun, withRunControl } from "../../src/main/services/run-control";
 
 describe("bounded command output", () => {
@@ -66,3 +66,12 @@ describe("run_command and run stops", () => {
     warn.mockRestore();
   });
 });
+
+describe("command results", () => {
+  test("a signal-terminated command is reported as killed, never as exit code 0", () => {
+    expect(formatCommandResult(0, null, "built")).toBe("exit code 0\nbuilt");
+    expect(formatCommandResult(2, null, "")).toBe("exit code 2\n(no output)");
+    expect(formatCommandResult(null, "SIGKILL", "partial")).toBe("ERROR: the command was killed by SIGKILL before it exited; treat it as failed.\npartial");
+    expect(formatCommandResult(null, null, "")).toBe("ERROR: the command ended without an exit code; treat it as failed.\n(no output)");
+  });
+});