feat(tools): require cancellation signal on every invocation

packages/timeout/timeout-policy/src/index.ts

@@ -54,8 +54,7 @@ export function apply(ctx: Context): void {
     using d = deadline(exec.signal, timeoutMs, TOOL_TIMEOUT)
     // Swap the derived deadline onto exec for dispatch, then restore the
     // caller's own signal so post-execute listeners never see this plugin's
-    // (possibly already-aborted) timeout signal. `undefined` is not assignable to
-    // the optional `signal` under exactOptionalPropertyTypes, so branch on it.
+    // (possibly already-aborted) timeout signal.
     const upstream = exec.signal
     exec.signal = d.signal
     try {
@@ -69,8 +68,7 @@ export function apply(ctx: Context): void {
       }
       return result
     } finally {
-      if (upstream === undefined) delete exec.signal
-      else exec.signal = upstream
+      exec.signal = upstream
     }
   })
 }