fix: reuse cached config profile git mounts

- Reuse valid deterministic git mount clones on repeated starts
- Remove incomplete clone destinations before retrying
- Add regression coverage for cached and partial clones
- Document OpenSpec change fix-config-profile-git-mount-clone-reuse

Quality gates: pytest (13 passed), ruff, mypy

openspec/changes/fix-config-profile-git-mount-clone-reuse/.pi-map.index.md

@@ -0,0 +1,20 @@
+# openspec/changes/fix-config-profile-git-mount-clone-reuse (index)
+dir: openspec/changes/fix-config-profile-git-mount-clone-reuse
+
+## role
+Documents and tracks a bug fix for reusing cached Config Profile git mount clones during tool instance startup.
+## parent
+index: openspec/changes/.pi-map.index.md
+map: openspec/changes/.pi-map.md
+## children
+-
+## files
+- change.md
+- tasks.md
+## links
+index: openspec/changes/fix-config-profile-git-mount-clone-reuse/.pi-map.index.md
+map: openspec/changes/fix-config-profile-git-mount-clone-reuse/.pi-map.md
+## workflows
+-
+## dirty
+-