Add stopped-workspace disk export and inspection

Finish the 3.1.0 secondary disk-tools milestone so stable workspaces can be
stopped, inspected offline, exported as raw ext4 images, and started again
without changing the primary workspace-first interaction model.

Add workspace stop/start plus workspace disk export/list/read across the CLI,
SDK, and MCP, backed by a new offline debugfs inspection helper and guest-only
validation. Scrub runtime-only guest state before disk inspection/export, and
fix the real guest reliability gaps by flushing the filesystem on stop and
removing stale Firecracker socket files before restart.

Update the docs, examples, changelog, and roadmap to mark 3.1.0 done, and
cover the new lifecycle/disk paths with API, CLI, manager, contract, and
package-surface tests.

Validation: uv lock; UV_CACHE_DIR=.uv-cache make check; UV_CACHE_DIR=.uv-cache
make dist-check; real guest-backed smoke for create, shell/service activity,
stop, workspace disk list/read/export, start, exec, and delete.

docs/roadmap/task-workspace-ga/3.1.0-secondary-disk-tools.md

@@ -1,38 +1,59 @@
 # `3.1.0` Secondary Disk Tools
 
+Status: Done
+
 ## Goal
 
-Add the disk-level tools the vision explicitly places last, while keeping them
-secondary to the workspace identity.
+Add stopped-workspace disk tools the vision explicitly places last, while keeping them secondary
+to the stable workspace identity.
 
 ## Public API Changes
 
-Representative additions:
+Shipped additions:
 
-- stopped-workspace disk export/import helpers
-- offline inspection helpers
-- disk-oriented snapshot inspection
-
-Exact command names should reinforce that these are supporting tools rather than
-the primary product contract.
+- `pyro workspace stop WORKSPACE_ID`
+- `pyro workspace start WORKSPACE_ID`
+- `pyro workspace disk export WORKSPACE_ID --output HOST_PATH`
+- `pyro workspace disk list WORKSPACE_ID [PATH] [--recursive]`
+- `pyro workspace disk read WORKSPACE_ID PATH [--max-bytes N]`
+- matching Python SDK methods:
+  - `stop_workspace`
+  - `start_workspace`
+  - `export_workspace_disk`
+  - `list_workspace_disk`
+  - `read_workspace_disk`
+- matching MCP tools:
+  - `workspace_stop`
+  - `workspace_start`
+  - `workspace_disk_export`
+  - `workspace_disk_list`
+  - `workspace_disk_read`
 
 ## Implementation Boundaries
 
-- keep these tools scoped to seeding, inspection, and offline workflows
+- keep these tools scoped to stopped-workspace inspection, export, and offline workflows
 - do not replace shell, exec, services, diff, export, or reset as the main
   interaction model
 - prefer explicit stopped-workspace or offline semantics
+- require guest-backed workspaces for `workspace disk *`
+- keep disk export raw ext4 only in this milestone
+- scrub runtime-only guest paths such as `/run/pyro-secrets`, `/run/pyro-shells`, and
+  `/run/pyro-services` before offline inspection or export
 
 ## Non-Goals
 
 - no drift into generic image tooling identity
 - no replacement of workspace-level host crossing
+- no disk import
+- no disk mutation
+- no create-from-disk workflow
 
 ## Acceptance Scenarios
 
 - inspect or export a stopped workspace disk for offline analysis
-- import or snapshot content through disk-level tools without changing the main
-  workspace workflow
+- stop a workspace, inspect `/workspace` offline, export raw ext4, then start the same workspace
+  again without resetting `/workspace`
+- verify secret-backed workspaces scrub runtime-only guest paths before stopped-disk inspection
 
 ## Required Repo Updates