Add workspace snapshots and full reset

Implement the 2.8.0 workspace milestone with named snapshots and full-sandbox reset across the CLI, Python SDK, and MCP server.

Persist the immutable baseline plus named snapshot archives under each workspace, add workspace reset metadata, and make reset recreate the sandbox while clearing command history, shells, and services without changing the workspace identity or diff baseline.

Refresh the 2.8.0 docs, roadmap, and Python example around reset-over-repair, then validate with uv lock, UV_CACHE_DIR=.uv-cache make check, UV_CACHE_DIR=.uv-cache make dist-check, and a real guest-backed create/snapshot/reset/diff smoke test outside the sandbox.

README.md

@@ -20,7 +20,7 @@ It exposes the same runtime in three public forms:
 - First run transcript: [docs/first-run.md](docs/first-run.md)
 - Terminal walkthrough GIF: [docs/assets/first-run.gif](docs/assets/first-run.gif)
 - PyPI package: [pypi.org/project/pyro-mcp](https://pypi.org/project/pyro-mcp/)
-- What's new in 2.7.0: [CHANGELOG.md#270](CHANGELOG.md#270)
+- What's new in 2.8.0: [CHANGELOG.md#280](CHANGELOG.md#280)
 - Host requirements: [docs/host-requirements.md](docs/host-requirements.md)
 - Integration targets: [docs/integrations.md](docs/integrations.md)
 - Public contract: [docs/public-contract.md](docs/public-contract.md)
@@ -57,7 +57,7 @@ What success looks like:
 ```bash
 Platform: linux-x86_64
 Runtime: PASS
-Catalog version: 2.7.0
+Catalog version: 2.8.0
 ...
 [pull] phase=install environment=debian:12
 [pull] phase=ready environment=debian:12
@@ -79,6 +79,8 @@ After the quickstart works:
 - create a persistent workspace with `uvx --from pyro-mcp pyro workspace create debian:12 --seed-path ./repo`
 - update a live workspace from the host with `uvx --from pyro-mcp pyro workspace sync push WORKSPACE_ID ./changes`
 - diff the live workspace against its create-time baseline with `uvx --from pyro-mcp pyro workspace diff WORKSPACE_ID`
+- capture a checkpoint with `uvx --from pyro-mcp pyro workspace snapshot create WORKSPACE_ID checkpoint`
+- reset a broken workspace with `uvx --from pyro-mcp pyro workspace reset WORKSPACE_ID --snapshot checkpoint`
 - export a changed file or directory with `uvx --from pyro-mcp pyro workspace export WORKSPACE_ID note.txt --output ./note.txt`
 - open a persistent interactive shell with `uvx --from pyro-mcp pyro workspace shell open WORKSPACE_ID`
 - start long-running workspace services with `uvx --from pyro-mcp pyro workspace service start WORKSPACE_ID app --ready-file .ready -- sh -lc 'touch .ready && while true; do sleep 60; done'`
@@ -135,7 +137,7 @@ uvx --from pyro-mcp pyro env list
 Expected output:
 
 ```bash
-Catalog version: 2.7.0
+Catalog version: 2.8.0
 debian:12 [installed|not installed] Debian 12 environment with Git preinstalled for common agent workflows.
 debian:12-base [installed|not installed] Minimal Debian 12 environment for shell and core Unix tooling.
 debian:12-build [installed|not installed] Debian 12 environment with Git and common build tools preinstalled.
@@ -214,6 +216,9 @@ pyro workspace create debian:12 --seed-path ./repo
 pyro workspace sync push WORKSPACE_ID ./changes --dest src
 pyro workspace exec WORKSPACE_ID -- cat src/note.txt
 pyro workspace diff WORKSPACE_ID
+pyro workspace snapshot create WORKSPACE_ID checkpoint
+pyro workspace reset WORKSPACE_ID --snapshot checkpoint
+pyro workspace reset WORKSPACE_ID
 pyro workspace export WORKSPACE_ID src/note.txt --output ./note.txt
 pyro workspace shell open WORKSPACE_ID
 pyro workspace shell write WORKSPACE_ID SHELL_ID --input 'pwd'
@@ -234,10 +239,12 @@ Persistent workspaces start in `/workspace` and keep command history until you d
 machine consumption, add `--json` and read the returned `workspace_id`. Use `--seed-path` when
 you want the workspace to start from a host directory or a local `.tar` / `.tar.gz` / `.tgz`
 archive instead of an empty workspace. Use `pyro workspace sync push` when you want to import
-later host-side changes into a started workspace. Sync is non-atomic in `2.7.0`; if it fails
-partway through, delete and recreate the workspace from its seed. Use `pyro workspace diff` to
-compare the live `/workspace` tree to its immutable create-time baseline, and `pyro workspace export`
-to copy one changed file or directory back to the host. Use `pyro workspace exec` for one-shot
+later host-side changes into a started workspace. Sync is non-atomic in `2.8.0`; if it fails
+partway through, prefer `pyro workspace reset` to recover from `baseline` or one named snapshot.
+Use `pyro workspace diff` to compare the live `/workspace` tree to its immutable create-time
+baseline, and `pyro workspace export` to copy one changed file or directory back to the host. Use
+`pyro workspace snapshot *` and `pyro workspace reset` when you want explicit checkpoints and
+full-sandbox recovery. Use `pyro workspace exec` for one-shot
 non-interactive commands inside a live workspace, and `pyro workspace shell *` when you need a
 persistent PTY session that keeps interactive shell state between calls. Use
 `pyro workspace service *` when the workspace needs one or more long-running background processes.