The active-agents view already showed sessions and repo changes, but it hid file-lock ownership and offered no conflict signal when repo-root edits were claimed by another branch. This change caches the lock registry per repo, appends lock counts to session rows, warns on foreign-branch locks in repo-root changes, refreshes that cache from lock-file watcher events, and keeps the lock registry file itself out of the CHANGES tree.

Constraint: Repo-root change warnings compare against the repo worktree's current branch, because CHANGES rows belong to that checkout rather than an arbitrary active session
Rejected: Re-read the lock file inside every getChildren() call | repeated IO on tree expansion with no freshness benefit over watcher events
Confidence: high
Scope-risk: narrow
Directive: Keep runtime and template VS Code extension copies in sync whenever the tree-provider data model changes
Tested: node --test test/vscode-active-agents-session-state.test.js; openspec validate agent-codex-vscode-tree-lock-decorations-clean-2026-04-22-11-09 --type change --strict
Not-tested: Interactive rendering in a real VS Code window