test: fix clink agent tests to mock shutil.which() for executable resolution

The previous commit (f98046c) added shutil.which() to resolve executables,
which broke two tests that only mocked subprocess execution. This commit
adds shutil.which() mocking to both test files to restore test compatibility.

Co-authored-by: Claude <noreply@anthropic.com>

tests/test_clink_codex_agent.py

@@ -1,4 +1,5 @@
 import asyncio
+import shutil
 from pathlib import Path
 
 import pytest
@@ -41,7 +42,11 @@ async def _run_agent_with_process(monkeypatch, agent, role, process):
     async def fake_create_subprocess_exec(*_args, **_kwargs):
         return process
 
+    def fake_which(executable_name):
+        return f"/usr/bin/{executable_name}"
+
     monkeypatch.setattr(asyncio, "create_subprocess_exec", fake_create_subprocess_exec)
+    monkeypatch.setattr(shutil, "which", fake_which)
     return await agent.run(role=role, prompt="do something", files=[], images=[])
 
 

tests/test_clink_gemini_agent.py

@@ -1,4 +1,5 @@
 import asyncio
+import shutil
 from pathlib import Path
 
 import pytest
@@ -41,7 +42,11 @@ async def _run_agent_with_process(monkeypatch, agent, role, process):
     async def fake_create_subprocess_exec(*_args, **_kwargs):
         return process
 
+    def fake_which(executable_name):
+        return f"/usr/bin/{executable_name}"
+
     monkeypatch.setattr(asyncio, "create_subprocess_exec", fake_create_subprocess_exec)
+    monkeypatch.setattr(shutil, "which", fake_which)
     return await agent.run(role=role, prompt="do something", files=[], images=[])