fix(agent-targets): reject inherited keys in resolveTarget

- Update resolveTarget to use hasOwnProperty to exclude inherited prototype keys
- Add test to verify resolveTarget returns null for inherited keys like constructor, __proto__, toString, hasOwnProperty
- Ensure inherited prototype-chain keys are recognized as unknown targets and rejected explicitly

Author: powxenv

src/lib/agent-targets.test.ts

@@ -157,6 +157,13 @@ describe('TARGET_ALIASES + resolveTarget', () => {
     expect(resolveTarget('definitely-not-an-agent')).toBeNull();
   });
 
+  it('resolveTarget rejects inherited prototype-chain keys as unknown', () => {
+    // Inherited keys (constructor, __proto__, ...) are truthy on a plain object.
+    for (const token of ['constructor', '__proto__', 'toString', 'hasOwnProperty']) {
+      expect(resolveTarget(token), token).toBeNull();
+    }
+  });
+
   it('acceptedTargetTokens is exactly the ids plus the aliases', () => {
     expect(new Set(acceptedTargetTokens())).toEqual(
       new Set([...Object.keys(TARGETS), ...Object.keys(TARGET_ALIASES)]),

src/lib/agent-targets.ts

@@ -168,7 +168,10 @@ export const TARGET_ALIASES: Record<string, AgentTarget> = {
 /** Resolve a `--target` token (id or alias) to a canonical id, or null if unknown. */
 export function resolveTarget(raw: string): AgentTarget | null {
   if (Object.prototype.hasOwnProperty.call(TARGETS, raw)) return raw as AgentTarget;
-  return TARGET_ALIASES[raw] ?? null;
+  // hasOwnProperty avoids inherited keys (constructor, __proto__).
+  return Object.prototype.hasOwnProperty.call(TARGET_ALIASES, raw)
+    ? TARGET_ALIASES[raw]!
+    : null;
 }
 
 /** Every accepted `--target` token (ids + aliases), for help/error text. */