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justinandClaude Opus 5 bad5a5706f feat(guard): read the Zerto task, and ask before guarding unknown tools

Two changes that both come from the same mistake: assuming an answer
instead of reading one.

1. Read the task after inserting a checkpoint.

   POST /v1/vpgs/{id}/checkpoints returns a TASK ID, not a result. A 200
   only means queued. The outcome lives in GET /v1/tasks/{id} under
   Status.State: 1 InProgress, 4 Failed, 5 Stopped, 6 Completed, with
   4/5/6 terminal.

   tag_vpgs now waits for that task and refuses unless it Completed, and
   reports task_id and task_state. Measured: two inserts fired back to
   back at one VPG give Completed for the first and Failed for the
   second. That is exactly the case an earlier comment in this file
   called "silently dropped" -- it was never silent, we just never read
   the task. Comment corrected.

   Previously a failed insert surfaced only as wait_for_tag timing out
   45s later with a misleading hint about Azure/AWS. Now it says the
   task failed and the operation did not happen.

2. Unknown tools ask the human instead of passing through.

   The catalog is opt-in, so an unlisted tool ran unguarded. But the set
   of mutating tools is unbounded and grows with every MCP installed,
   while the set of read-only ones is small, so a mutating-only list is
   permanently behind and being behind fails open.

   Adds read_only_tools and zerto_check_tool(server, tool, vm) returning
   read_only / mutating / unknown. unknown does not mean safe: it means
   nobody classified it, so the tool hands the agent a question to put
   to the human, and the human decides whether to checkpoint. On yes the
   agent guards; on no it runs and says plainly that Zerto cannot rewind
   it; if they want it remembered, zerto_add_mutating_tool.

   This stays advisory. An MCP server cannot see or block another
   server's tool calls, so real enforcement belongs in a host PreToolUse
   hook. The skill carries the flow.

Known issue, not addressed here: two concurrent tool calls race on
Keycloak token acquisition in the shared client and one gets HTTP 401.

pytest 41 passed (12 new).

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_016yVfC5nvZowoLFnEGWhLGn

2026-09-21 14:47:19 -04:00

4.1 KiB

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name, description

name	description
zerto-rewind	Before changing a VM, find its Zerto VPGs and insert a tagged checkpoint. Recover files from that tag with FLR after a human confirms. Use whenever an agent will mutate a guest that might be protected by Zerto.

Zerto rewind

Zerto already journals the VM. This skill makes the agent use that journal. Git does not have the guest file. Official ZVM MCP does not insert tagged checkpoints.

You talk to one MCP: zerto_rewind_mcp. Do not also require official ZVM MCP.

Loop (mandatory)

Before every tool call that might touch a guest:

Take the hostname / VM name / Zerto vmIdentifier from the tool args.
Call zerto_check_tool(server, tool, vm). Act on the verdict:

verdict	what you do
`read_only`	Run the tool. No checkpoint.
`mutating`	Guard first. Do not ask — it is already known to change the guest.
`unknown`	Ask the human. Do not assume it is safe, and do not silently guard.

For mutating, or for unknown where the human said yes: call zerto_guard_before_mutate with change_id and action.
If ok is not true: stop. Do not mutate.
Then run the call.

unknown is the normal case, not an edge case. The catalogs are short and the world of tools is not, so most tools are unclassified. Unknown means nobody has said this is read-only — it does not mean safe. Put the decision to the human:

winrm/run_ps is not a known read-only command. It may change web01. Insert a Zerto tagged checkpoint first so this is reversible?

If they say yes, guard, then run. If they say no, run it and tell them plainly that it is not reversible through Zerto. If they want it remembered, call zerto_add_mutating_tool (server, tool, vm_arg) so it is guarded automatically next time instead of asking again.

find_protection outcomes

outcome	what you do
none	Unprotected or unknown. Refuse the change. Say Zerto cannot rewind this.
ambiguous	Two or more VMs matched. Ask for a `vmIdentifier`. Do not guess.
ok, no taggable VPG	Syncing or not Protecting. Refuse. A resync deletes checkpoints.
ok, taggable VPGs	Tag every protecting VPG with the same tag. Wait until listed (the tool blocks).

A VM can be in up to three VPGs (local backup + remote DR is common). Tag all of them.

Recover

Human must confirm. Pass confirmed=true only after they say yes.

Bad config / dropped file: zerto_recover_file from that tag. Pass the guest path (/home/j/app.yaml or C:\Users\j\app.conf); the server maps it into the FLR namespace. Locally replicated VPGs only -- FLR happens at the recovery site, so a cloud-replicated VPG must be recovered from that ZCA. The tool refuses and names the site.
Inspect a whole VM: zerto_offsite_clone or zerto_start_failover_test.
Never Failover Live. Never Move. Those are DR, not rewind.

zerto_recover_file unmounts its own FLR session and reports the result in unmount. If unmount.ok is false, or a previous recovery died mid-flight, the mount is still up: FLR cannot run during clone, test, live failover or EJC, so a stuck session blocks the next recovery. Find it with zerto_list_flr_sessions and clear it with zerto_end_flr_session.

Facts that bite

A tagged checkpoint is crash-consistent, not app-quiesced.
Tagged checkpoints are not supported when the protected site is Azure or AWS. Talk to the vSphere protected ZVM.
10.9 FLR Operator RBAC fails; Administrator is the documented workaround.
FLR cannot run during clone, test, live failover, or EJC.
Linux FLR: files >1.5GB are a bad idea; some characters in names are refused.

Tag

The checkpoint name is the only field the Zerto API takes, so it carries the whole story:

ai:<agent> | <action> | vm=<vm> | change=<change-id> | <utc>
ai:claude | edit /etc/nginx/nginx.conf | vm=web01 | change=chg-412 | 20260921T150405Z

Always pass action: a plain description of the change you are about to make. An operator scrolling the journal in the Zerto UI should be able to tell which agent inserted the checkpoint and why, without reading your transcript.

Same string on every VPG for that call.

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