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.

docs/public-contract.md

@@ -24,6 +24,10 @@ Top-level commands:
 - `pyro workspace exec`
 - `pyro workspace export`
 - `pyro workspace diff`
+- `pyro workspace snapshot create`
+- `pyro workspace snapshot list`
+- `pyro workspace snapshot delete`
+- `pyro workspace reset`
 - `pyro workspace service start`
 - `pyro workspace service list`
 - `pyro workspace service status`
@@ -63,11 +67,14 @@ Behavioral guarantees:
 - `pyro workspace sync push WORKSPACE_ID SOURCE_PATH [--dest WORKSPACE_PATH]` imports later host-side directory or archive content into a started workspace.
 - `pyro workspace export WORKSPACE_ID PATH --output HOST_PATH` exports one file or directory from `/workspace` back to the host.
 - `pyro workspace diff WORKSPACE_ID` compares the current `/workspace` tree to the immutable create-time baseline.
+- `pyro workspace snapshot *` manages explicit named snapshots in addition to the implicit `baseline`.
+- `pyro workspace reset WORKSPACE_ID [--snapshot SNAPSHOT_NAME|baseline]` recreates the full sandbox and restores `/workspace` from the chosen snapshot.
 - `pyro workspace service *` manages long-running named services inside one started workspace with typed readiness probes.
 - `pyro workspace exec` runs in the persistent `/workspace` for that workspace and does not auto-clean.
 - `pyro workspace shell *` manages persistent PTY sessions inside a started workspace.
 - `pyro workspace logs` returns persisted command history for that workspace until `pyro workspace delete`.
 - Workspace create/status results expose `workspace_seed` metadata describing how `/workspace` was initialized.
+- Workspace create/status/reset results expose `reset_count` and `last_reset_at`.
 - `pyro workspace status` includes aggregate `service_count` and `running_service_count` fields.
 
 ## Python SDK Contract
@@ -89,6 +96,10 @@ Supported public entrypoints:
 - `Pyro.push_workspace_sync(workspace_id, source_path, *, dest="/workspace")`
 - `Pyro.export_workspace(workspace_id, path, *, output_path)`
 - `Pyro.diff_workspace(workspace_id)`
+- `Pyro.create_snapshot(workspace_id, snapshot_name)`
+- `Pyro.list_snapshots(workspace_id)`
+- `Pyro.delete_snapshot(workspace_id, snapshot_name)`
+- `Pyro.reset_workspace(workspace_id, *, snapshot="baseline")`
 - `Pyro.start_service(workspace_id, service_name, *, command, cwd="/workspace", readiness=None, ready_timeout_seconds=30, ready_interval_ms=500)`
 - `Pyro.list_services(workspace_id)`
 - `Pyro.status_service(workspace_id, service_name)`
@@ -124,6 +135,10 @@ Stable public method names:
 - `push_workspace_sync(workspace_id, source_path, *, dest="/workspace")`
 - `export_workspace(workspace_id, path, *, output_path)`
 - `diff_workspace(workspace_id)`
+- `create_snapshot(workspace_id, snapshot_name)`
+- `list_snapshots(workspace_id)`
+- `delete_snapshot(workspace_id, snapshot_name)`
+- `reset_workspace(workspace_id, *, snapshot="baseline")`
 - `start_service(workspace_id, service_name, *, command, cwd="/workspace", readiness=None, ready_timeout_seconds=30, ready_interval_ms=500)`
 - `list_services(workspace_id)`
 - `status_service(workspace_id, service_name)`
@@ -157,6 +172,10 @@ Behavioral defaults:
 - `Pyro.push_workspace_sync(...)` imports later host-side directory or archive content into a started workspace.
 - `Pyro.export_workspace(...)` exports one file or directory from `/workspace` to an explicit host path.
 - `Pyro.diff_workspace(...)` compares the current `/workspace` tree to the immutable create-time baseline.
+- `Pyro.create_snapshot(...)` captures one named `/workspace` checkpoint.
+- `Pyro.list_snapshots(...)` lists the implicit `baseline` plus any named snapshots.
+- `Pyro.delete_snapshot(...)` deletes one named snapshot while leaving `baseline` intact.
+- `Pyro.reset_workspace(...)` recreates the full sandbox from `baseline` or one named snapshot and clears command, shell, and service history.
 - `Pyro.start_service(...)` starts one named long-running process in a started workspace and waits for its typed readiness probe when configured.
 - `Pyro.list_services(...)`, `Pyro.status_service(...)`, `Pyro.logs_service(...)`, and `Pyro.stop_service(...)` manage those persisted workspace services.
 - `Pyro.exec_vm(...)` runs one command and auto-cleans that VM after the exec completes.
@@ -190,6 +209,10 @@ Persistent workspace tools:
 - `workspace_exec`
 - `workspace_export`
 - `workspace_diff`
+- `snapshot_create`
+- `snapshot_list`
+- `snapshot_delete`
+- `workspace_reset`
 - `service_start`
 - `service_list`
 - `service_status`
@@ -214,6 +237,8 @@ Behavioral defaults:
 - `workspace_sync_push` imports later host-side directory or archive content into a started workspace, with an optional `dest` under `/workspace`.
 - `workspace_export` exports one file or directory from `/workspace` to an explicit host path.
 - `workspace_diff` compares the current `/workspace` tree to the immutable create-time baseline.
+- `snapshot_create`, `snapshot_list`, and `snapshot_delete` manage explicit named snapshots in addition to the implicit `baseline`.
+- `workspace_reset` recreates the full sandbox and restores `/workspace` from `baseline` or one named snapshot.
 - `service_start`, `service_list`, `service_status`, `service_logs`, and `service_stop` manage persistent named services inside a started workspace.
 - `vm_exec` runs one command and auto-cleans that VM after the exec completes.
 - `workspace_exec` runs one command in a persistent `/workspace` and leaves the workspace alive.