feat: support smolmachines bottle commit

docs/prds/prd-new-commit-bottle-state.md

@@ -7,10 +7,11 @@
 
 ## Summary
 
-Add a `commit` CLI command that freezes a running Docker bottle's
-container state to a named Docker image. Operators can then resume the
-bottle from that exact filesystem snapshot, or export the image with
-`docker save` to migrate work to a different host.
+Add a `commit` CLI command that freezes a running bottle's state to a
+resumable local artifact. Docker bottles are stored as Docker images;
+smolmachines bottles are stored as `.smolmachine` artifacts. Operators
+can then resume the bottle from that exact filesystem snapshot, or
+export the artifact to migrate work to a different host.
 
 ## Problem
 
@@ -29,30 +30,29 @@ snapshot before a planned host reboot or hardware migration.
 
 ## Goals / Success Criteria
 
-- `./cli.py commit [<slug>]` takes a snapshot of the running Docker
-  agent container and stores it as a local Docker image.
+- `./cli.py commit [<slug>]` takes a snapshot of the running agent and
+  stores it as a local artifact.
 - Without a slug argument the command shows the same interactive picker
   as `start` (the list of active slugs).
-- The committed image tag is stored in per-bottle state so that the next
-  `./cli.py resume <slug>` automatically uses the committed image instead
-  of rebuilding from the Dockerfile.
+- The committed artifact reference is stored in per-bottle state so
+  that the next `./cli.py resume <slug>` automatically uses the
+  snapshot instead of rebuilding from the Dockerfile.
 - `mark_preserved` is called so the state dir survives the normal
   session-end cleanup.
-- A `docker save` hint is printed so operators know how to export the
-  image for migration.
-- The command errors clearly on non-Docker backends (smolmachines does
-  not expose a container-level commit API in its current CLI surface).
+- A backend-specific export hint is printed so operators know how to
+  migrate the snapshot.
+- The command errors clearly on unsupported backends.
 
 ## Non-goals
 
-- Smolmachines or macOS-container backend support.
+- macOS-container backend support.
 - Automatic commit on agent exit.
 - Image push to a remote registry.
 - Storing the image tag in the manifest or sharing it between operators.
 
 ## Design
 
-### Image tag
+### Docker image tag
 
 `bot-bottle-committed-<slug>:latest` — namespaced under `bot-bottle-`
 to match existing image naming conventions; `committed` distinguishes it
@@ -68,13 +68,15 @@ directory:
 ~/.bot-bottle/state/<identity>/
     metadata.json
     Dockerfile            (capability-block override; optional)
-    committed-image       (committed image tag; optional)
+    committed-image       (committed artifact reference; optional)
     transcript/
 ```
 
 `bottle_state.committed_image_path(identity)` returns the path.
 `write_committed_image` / `read_committed_image` are the read/write
-helpers, matching the existing `per_bottle_dockerfile` pattern.
+helpers, matching the existing `per_bottle_dockerfile` pattern. Docker
+stores a Docker tag in this file; smolmachines stores the absolute path
+to the committed `.smolmachine` artifact.
 
 ### `commit` command
 
@@ -83,14 +85,15 @@ helpers, matching the existing `per_bottle_dockerfile` pattern.
 ```
 
 1. Resolve slug (arg or interactive picker from `enumerate_active_agents`).
-2. Check metadata: if `backend` is set and is not `docker`, die with a
-   clear "not supported" error.
-3. Derive container name: `bot-bottle-<slug>` (matches the agent
-   provision plan's `instance_name` convention).
-4. Run `docker commit <container> bot-bottle-committed-<slug>:latest`.
-5. Write the image tag to `~/.bot-bottle/state/<slug>/committed-image`.
+2. Check metadata and branch by backend.
+3. For Docker, derive container name `bot-bottle-<slug>` and run
+   `docker commit <container> bot-bottle-committed-<slug>:latest`.
+4. For smolmachines, derive machine name `bot-bottle-<slug>` and run
+   `smolvm pack create --from-vm <machine> -o ~/.bot-bottle/state/<slug>/committed-smolmachine`.
+5. Write the Docker image tag or smolmachine artifact path to
+   `~/.bot-bottle/state/<slug>/committed-image`.
 6. Call `mark_preserved(<slug>)` so the state dir survives session-end.
-7. Print the resume hint and a `docker save` export example.
+7. Print the resume hint and a backend-specific export example.
 
 ### Resume from committed image
 
@@ -120,6 +123,22 @@ If the committed image has been deleted from the local daemon (e.g.
 after `docker rmi` or a `docker system prune`), the launch falls back
 to a normal Dockerfile build, matching the pre-commit behavior.
 
+### Resume from committed smolmachine
+
+`bot_bottle/backend/smolmachines/launch.py` checks the committed
+reference before the normal Docker build -> pack cache path:
+
+```python
+committed = read_committed_image(plan.slug)
+if committed and Path(committed).is_file():
+    return Path(committed)
+return _ensure_smolmachine(plan.agent_image, dockerfile=plan.agent_dockerfile_path)
+```
+
+The returned path is passed to `smolvm machine create --from`, so the
+resumed VM boots from the committed snapshot. If the artifact has been
+deleted, launch falls back to the normal build and pack flow.
+
 ## Testing strategy
 
 - Unit tests for `write_committed_image` / `read_committed_image` in
@@ -127,10 +146,14 @@ to a normal Dockerfile build, matching the pre-commit behavior.
   pattern.
 - Unit tests for `commit_container` in `tests/unit/test_docker_util_image.py`,
   mocking `subprocess.run` and asserting on the `docker commit` argv.
-- Unit tests for `cmd_commit` argument parsing and the "unsupported
-  backend" error path, mocking `enumerate_active_agents` and
-  `commit_container`.
+- Unit tests for `cmd_commit` argument parsing, Docker commit,
+  smolmachines pack, and the unsupported backend error path, mocking
+  `enumerate_active_agents`, `commit_container`, and
+  `pack_create_from_vm`.
 - Unit tests for the launch-step committed-image branch: patch
   `read_committed_image` to return a tag, patch `image_exists` to return
   True, and assert that `build_image` is not called and `plan.image` is
   overridden.
+- Unit tests for the smolmachines launch-step committed-artifact branch:
+  patch `read_committed_image` to return an existing path and assert the
+  normal `_ensure_smolmachine` path is skipped.