fix(desktop): preserve signals in backend exit logs

apps/desktop/src/backend/DesktopBackendManager.test.ts

@@ -431,6 +431,30 @@ describe("DesktopBackendManager", () => {
     }),
   );
 
+  it.effect("reports a SIGKILL exit without an exit code", () =>
+    Effect.gen(function* () {
+      const exitCause = PlatformError.systemError({
+        _tag: "Unknown",
+        module: "ChildProcess",
+        method: "exitCode",
+        cause: new Error("Process interrupted due to receipt of signal: 'SIGKILL'"),
+      });
+      const layerSpawner = Layer.succeed(
+        ChildProcessSpawner.ChildProcessSpawner,
+        ChildProcessSpawner.make(() =>
+          Effect.succeed(makeProcess({ exitCode: Effect.fail(exitCause) })),
+        ),
+      );
+
+      const exit = yield* DesktopBackendManager.runBackendProcess({
+        ...baseConfig,
+        desktopTelemetryStream: Stream.empty,
+      }).pipe(Effect.scoped, Effect.provide(Layer.merge(layerSpawner, layerHealthyHttpClient)));
+
+      assert.deepEqual(exit, { code: Option.none(), reason: "killed by SIGKILL" });
+    }),
+  );
+
   it.effect("reports output stream failures with process and stream context", () =>
     Effect.gen(function* () {
       const outputCause = PlatformError.systemError({

apps/desktop/src/backend/DesktopBackendManager.ts

@@ -568,8 +568,22 @@ export const runBackendProcess = Effect.fn("runBackendProcess")(function* (
   yield* probeReadiness().pipe(Effect.repeat({ while: (ready) => !ready }), Effect.forkScoped);
 
   const exit = yield* handle.exitCode.pipe(
-    Effect.mapError(
-      (cause) =>
+    Effect.map((exitCode) => ({
+      code: Option.some(exitCode),
+      reason: `code=${exitCode}`,
+    })),
+    Effect.catch((cause) => {
+      // Effect's Node spawner exposes signal exits only through this cause message.
+      const signal =
+        cause.cause instanceof Error
+          ? /^Process interrupted due to receipt of signal: '(SIG[A-Z0-9]+)'$/.exec(
+              cause.cause.message,
+            )?.[1]
+          : undefined;
+      if (signal !== undefined) {
+        return Effect.succeed({ code: Option.none(), reason: `killed by ${signal}` });
+      }
+      return Effect.fail(
         new BackendProcessExitStatusError({
           executablePath: options.executablePath,
           entryPath: options.entryPath,
@@ -578,7 +592,8 @@ export const runBackendProcess = Effect.fn("runBackendProcess")(function* (
           pid: Number(handle.pid),
           cause,
         }),
-    ),
+      );
+    }),
     Effect.exit,
   );
   yield* options.onExitObserved?.() ?? Effect.void;
@@ -592,11 +607,7 @@ export const runBackendProcess = Effect.fn("runBackendProcess")(function* (
   if (Exit.isFailure(exit)) {
     return yield* Effect.failCause(exit.cause);
   }
-  const exitCode = exit.value;
-  return {
-    code: Option.some(exitCode),
-    reason: `code=${exitCode}`,
-  } satisfies BackendProcessExit;
+  return exit.value;
 });
 
 export const makeBackendInstance = Effect.fn("makeBackendInstance")(function* (