feat(polecat): self-cleaning model and new review formulas

Polecats now self-clean when done:
- gt done always exits session (no more --exit flag needed)
- gt done requests self-nuke (sandbox cleanup)
- No idle polecats - done means gone
- Refinery re-implements on conflict (never sends work back)

New formulas:
- mol-polecat-review-pr: review external PRs, approve/reject
- mol-polecat-code-review: review code, file beads for findings

Docs updated:
- polecat-lifecycle.md: self-cleaning model, identity vs session
- polecat-CLAUDE.md: updated contract and completion protocol
- mol-polecat-work: updated for self-cleaning

Implementation beads filed:
- gt-yrz4k: gt done always exits
- gt-fqcst: polecat self-nuke mechanism
- gt-zdmde: abstract work unit completion

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/formula/formulas/mol-polecat-work.formula.toml

@@ -1,26 +1,29 @@
 description = """
-Full polecat work lifecycle from assignment through MR submission.
+Full polecat work lifecycle from assignment through completion.
 
 This molecule guides a polecat through a complete work assignment. Each step
 has clear entry/exit criteria and specific commands to run. A polecat can
 crash after any step and resume from the last completed step.
 
-## Polecat Contract (Ephemeral Model)
+## Polecat Contract (Self-Cleaning Model)
 
-You are an ephemeral worker. You:
+You are a self-cleaning worker. You:
 1. Receive work via your hook (pinned molecule + issue)
 2. Work through molecule steps using `bd ready` / `bd close <step>`
-3. Submit to merge queue via `gt done`
-4. Become recyclable - Refinery handles the rest
+3. Complete and self-clean via `gt done` (submit + nuke yourself)
+4. You are GONE - Refinery merges from MQ
+
+**Self-cleaning:** When you run `gt done`, you push your work, submit to MQ,
+nuke your sandbox, and exit. There is no idle state. Done means gone.
 
 **Important:** This formula defines the template. Your molecule already has step
 beads created from it. Use `bd ready` to find them - do NOT read this file directly.
 
 **You do NOT:**
-- Push directly to main (Refinery merges)
+- Push directly to main (Refinery merges from MQ)
 - Close your own issue (Refinery closes after merge)
-- Wait for merge (you're done at MR submission)
-- Handle rebase conflicts (Refinery dispatches fresh polecats for that)
+- Wait for merge (you're gone after `gt done`)
+- Handle rebase conflicts (Refinery spawns fresh polecats for that)
 
 ## Variables
 
@@ -407,30 +410,23 @@ bd sync
 
 [[steps]]
 id = "submit-and-exit"
-title = "Submit to merge queue and exit"
+title = "Submit work and self-clean"
 needs = ["prepare-for-review"]
 description = """
-Submit your work to the merge queue. You become recyclable after this.
+Submit your work and clean up. You cease to exist after this step.
 
-**Ephemeral Polecat Model:**
-Once you submit, you're done. The Refinery will:
-1. Process your merge request
-2. Handle rebasing (mechanical rebases done automatically)
-3. Close your issue after successful merge
-4. Create conflict-resolution tasks if needed (fresh polecat handles those)
+**Self-Cleaning Model:**
+Once you run `gt done`, you're gone. The command:
+1. Pushes your branch to origin
+2. Creates an MR bead in the merge queue
+3. Nukes your sandbox (worktree removal)
+4. Exits your session immediately
 
-**1. Submit with gt done:**
+**Run gt done:**
 ```bash
 gt done
 ```
 
-This single command:
-- Creates an MR bead in the merge queue
-- Notifies the Witness (POLECAT_DONE)
-- Updates your agent state to 'done'
-- Reports cleanup status (ZFC compliance)
-
-**2. Verify submission:**
 You should see output like:
 ```
 ✓ Work submitted to merge queue
@@ -438,20 +434,19 @@ You should see output like:
   Source: polecat/<name>
   Target: main
   Issue: {{issue}}
+✓ Sandbox nuked
+✓ Session exiting
 ```
 
-**3. You're recyclable:**
-Your work is in the queue. The Witness knows you're done.
-Your sandbox can be cleaned up - all work is pushed to origin.
+**What happens next (not your concern):**
+- Refinery processes your MR from the queue
+- Refinery rebases and merges to main
+- Refinery closes the issue
+- If conflicts: Refinery spawns a FRESH polecat to re-implement
 
-If you have context remaining, you may:
-- Pick up new work from `bd ready`
-- Or use `gt handoff` to cycle to a fresh session
+You are NOT involved in any of that. You're gone. Done means gone.
 
-If the Refinery needs conflict resolution, it will dispatch a fresh polecat.
-You do NOT need to wait around.
-
-**Exit criteria:** MR submitted, Witness notified, polecat recyclable."""
+**Exit criteria:** Work submitted, sandbox nuked, session exited."""
 
 [vars]
 [vars.issue]