refactor(uuid): resolve B-10 by deprecating agent_identities and removing PyYAML dependency

- Remove dead agent_identities read path and PyYAML import from workspace_uuid.py
- Defer eager PyYAML import in verify_session.py to lazy YAML fallback branch
- Simplify UUID resolution to 2-tier model (tier-1 own row ID -> tier-2 adapter scan)
- Clean up unused Drift D and ghost cache clearing in reconcile.sh and stop_session.sh
- Add 3 regression guards in tests/test_tier1_unit.py (266/266 PASS)
- Update IMPROVEMENTS.md, VERSIONS.md, and SKILL.md files

.agents/skills/lib_py/workspace_uuid.py

@@ -1,7 +1,7 @@
 # workspace_uuid.py — workspace UUID discovery logic
 # Extracted from lib.sh find_workspace_uuid PYEOF block
 
-import os, sys, json, sqlite3
+import os, sys, json
 from lib_py.verify_session import verify_session_uuid, mam_orchestrator_uuids, mam_row_own_uuid
 
 OWN_KEY = {
@@ -80,38 +80,6 @@ def find_workspace_uuid_main():
         for cand in adapter.discover(ctx):
             emit(cand)
 
-    ai = d.get('agent_identities') if isinstance(d, dict) else None
-    if not isinstance(ai, dict) or not ai:
-        ai = {}
-        try:
-            yaml_path = os.environ['YAML_PATH']
-            db_path = os.path.splitext(yaml_path)[0] + '.db'
-            if os.path.exists(db_path):
-                conn = sqlite3.connect(db_path, timeout=60.0)
-                conn.execute('PRAGMA busy_timeout = 60000')
-                try:
-                    row = conn.execute('SELECT data FROM state WHERE id=1').fetchone()
-                    if row:
-                        ai = json.loads(row[0]).get('agent_identities') or {}
-                except sqlite3.OperationalError:
-                    pass
-                conn.close()
-            elif os.path.exists(yaml_path):
-                import yaml
-                with open(yaml_path) as f:
-                    _ydoc = yaml.safe_load(f) or {}
-                ai = _ydoc.get('agent_identities') or {}
-        except Exception as e:
-            print(f"WARN: tier-3 identity lookup failed: {e}", file=sys.stderr)
-    if not isinstance(ai, dict):
-        ai = {}
-
-    ai_agent = ai.get(agent) or {}
-    if ai_agent.get('project_cwd') == ws:
-        cand = ai_agent.get('session_id') or ai_agent.get('conversation_id')
-        if cand and verify_session_uuid(ws, agent, cand, mode="revalidate"):
-            emit(cand)
-
     print('')
 
 if __name__ == '__main__':