fix(ci): pin acp <0.9 and update retry-exhaust test (#3320)

Two remaining CI failures:

1. agent-client-protocol 0.9.0 removed AuthMethod (replaced with
   AuthMethodAgent/EnvVar/Terminal). Pin to <0.9 until the new API
   is evaluated — our usage doesn't map 1:1 to the new types.

2. test_429_exhausts_all_retries_before_raising expected pytest.raises
   but the agent now catches 429s after max retries, tries fallback,
   then returns a result dict. Updated to check final_response.

pyproject.toml

@@ -55,7 +55,7 @@ honcho = ["honcho-ai>=2.0.1,<3"]
 mcp = ["mcp>=1.2.0,<2"]
 homeassistant = ["aiohttp>=3.9.0,<4"]
 sms = ["aiohttp>=3.9.0,<4"]
-acp = ["agent-client-protocol>=0.8.1,<1.0"]
+acp = ["agent-client-protocol>=0.8.1,<0.9"]
 dingtalk = ["dingtalk-stream>=0.1.0,<1"]
 rl = [
   "atroposlib @ git+https://github.com/NousResearch/atropos.git",