docs: initialize concurrent task documentation gates

.project-docs/05-agent-entry/concurrent-task-gate.md

@@ -0,0 +1,34 @@
+# Concurrent Task Gate
+
+Complete this gate before the Planning Gate.
+
+## Invariants
+
+- One active task owns one worktree.
+- Concurrent tasks use different branches and worktrees.
+- Resume the same task in its existing worktree; `start` returns a completed task's registry status to `planning`.
+- When an isolated `start` omits `--destination`, use `<primary-repository-parent>/.codex-worktrees/<repository>/<task_id>`.
+- Never stash, reset, move, delete, or adopt unknown work automatically.
+- Feature tasks write only their own task record and uniquely named supporting records.
+- Peer document defects reported as `PEER_DOC_WARNING` require scope assessment, not peer-document repair before starting the current task. Current-task identity and registry ownership faults remain blocking.
+- Keep the active task record present until ownership is released.
+- Treat `start`, `touch`, `complete`, `release`, and `retire` as serialized registry transactions; lock timeout or malformed registry state blocks the gate.
+- Feature-task write boundaries in this gate supersede legacy instructions to update shared or canonical project documents.
+
+## Required Output
+
+- Task ID:
+- Mode: Feature | Integration
+- Branch:
+- Worktree:
+- Base commit:
+- Ownership result: Claimed | Resumed | Isolated | Blocked
+- Managed worktree: Yes | No
+- Other active local tasks:
+
+## Block Conditions
+
+- The worktree belongs to another active task and isolation did not succeed.
+- An unowned worktree contains staged, unstaged, or untracked changes.
+- No reliable committed base was selected for a new worktree.
+- The runtime cannot keep later Git and file operations rooted in the isolated worktree.