fix(herdr): ensure unique agent name via sha1 truncation and align mock errors

- Replace legacy s[:16]-s[-15:] truncation with 8-char SHA-1 hash suffix in sanitize.py and lib.sh to prevent workspace name collisions
- Align mock Herdr error messages in tests/conftest.py to real Herdr 0.8.0 output format
- Add missing required/invalid_agent_name to early abort regex in lib.sh
- Remove legacy heuristics in lib.sh has-session and unify mock agent lookups
- Add unit tests in tests/test_sanitize_and_mock_errors.py (256/256 passed)

tests/test_sanity.py

@@ -54,7 +54,8 @@ def test_create_session_full(mam_sandbox, mock_herdr, mock_agents):
     assert len(agents) == 1, "There should be exactly one registered agent in the mock herdr state."
     
     session_name = list(agents.keys())[0]
-    assert session_name.endswith("-creator-claude")
+    from lib_py.agents.sanitize import sanitize_herdr_agent_name
+    assert len(session_name) <= 32
     assert agents[session_name]["status"] == "running"
     assert agents[session_name]["agent"] == "claude"
     
@@ -67,6 +68,7 @@ def test_create_session_full(mam_sandbox, mock_herdr, mock_agents):
         
     sessions = reg.get("herdr_sessions", [])
     assert len(sessions) == 1
+    assert session_name == sanitize_herdr_agent_name(sessions[0]["name"])
     assert sessions[0]["name"].endswith("-creator-claude")
     assert sessions[0]["status"] == "running"
     assert sessions[0]["role"] == "Creator"