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.sh

@@ -1298,15 +1298,10 @@ verify_tui_viewport() {
 # ---------------------------------------------------------------------------
 # find_workspace_uuid <workspace> <agent>
 #
-# Workspace-SCOPED resolution of the resume UUID (P0-C). It NEVER returns a
-# global agent_identities id unless that id's project_cwd matches THIS
-# workspace. Resolution order:
+# Workspace-SCOPED resolution of the resume UUID (P0-C). Resolution order:
 #   1) herdr_sessions[] row whose pane.cwd == this workspace -> per-row own id
 #      (claude_session_id_own / agy_conversation_id_own)
-#   2) on-disk scan scoped to this workspace
-#      (claude: ~/.claude/projects/<key>/*.jsonl ; agy: last_conversations.json[cwd])
-#   3) agent_identities cache in d (primary) or $YAML_PATH (fallback), ONLY when its project_cwd == this workspace.
-#      (Note: DB is authority, YAML is mirror; tier-3 never prioritizes mirror over DB)
+#   2) on-disk scan scoped to this workspace, via the agent adapter's discover()
 # Prints the UUID on stdout (empty line if none). Always exits 0.
 # ---------------------------------------------------------------------------
 find_workspace_uuid() {
@@ -1323,8 +1318,8 @@ PYEOF
 #
 # Thin wrapper over find_workspace_uuid: resolves THIS workspace's conversation
 # id (claude jsonl sessionId / agy db uuid) and prints it on stdout (empty line
-# if none). find_workspace_uuid is already a workspace-scoped, 3-tier, race-free
-# resolver (per-row own id -> workspace-scoped disk scan -> cwd-matched cache),
+# if none). find_workspace_uuid is already a workspace-scoped, 2-tier, race-free
+# resolver (per-row own id -> workspace-scoped disk scan),
 # so recording its result into the row before kill guarantees tier-1 on the next
 # resume. Pass session_name to prefer that specific row's recorded id. Always exits 0.
 # ---------------------------------------------------------------------------