v0.4.0: slice 4 Phase B — reversibility gate + signed-op consuming layer

The security core of slice 4: hub-supplied intent is no longer trusted for
destructive change. The gate fronts the per-guest queue's executor, so every
mutation passes it. Reuses internal/authz for all crypto (surface untouched).

- Classifier (doc 03 §4): benign vs destructive by provenance + data-bearing-
  ness, NOT by verb. Destroy/overwrite of customer data is destructive unless
  agent-internal provenance (same-journaled-txn create, or agent-tagged scratch)
  makes it benign — and that provenance is journal-recorded, NEVER hub-sourced.
  Unknown op class fails safe to destructive.
- Reversibility gate: benign -> allowed unsigned; destructive -> requires a
  verified, role-scoped, action-bound operator signature, else pending_signature
  and never executed. Every decision audited (signal, never the guard).
- Signed-op consuming layer over authz.Verifier.Verify (locked pipeline
  untouched): role-scoping (doc 04 §4 — recovery=rotation only, operational=
  ordinary destructive + planned rotation) + op-to-action binding (op+host+
  guest+params must match the gated action).
- Signed-job orchestration: idempotency dedupe by nonce + journal-wrapped
  execution via an injected DestructiveExecutor (nil this slice — inert).
- Crash recovery (Note 1): Engine.Recover consumes the journal InFlight() set at
  startup (resume-or-rollback) — covers an op that crashed after the POST and
  before its terminal record, which idempotency dedupe alone cannot. Added
  TaskStatusOnce to the GuestAPI seam. Wired into daemon startup.
- Note 2: memory comparison canonicalized to MiB (desiredMemoryMiB) so a
  non-MiB-aligned MemoryBytes converges in one pass, not perpetual drift.
- Daemon: builds the verifier from config signers (none = nil verifier, the
  common slice-4 state), the gate (+SlogAudit), runs Recover before mutating.

Adversarial matrix proven against the REAL authz.Verifier with in-test-minted
SSHSIGs (framing replicated in reconcile's test binary; authz untouched, no
signing added to the verify-only package): unsigned job + unsigned desired-state
delta -> pending_signature; unknown signer/expired/replay-across-restart/wrong
host -> typed authz rejections; wrong guest/op/params -> binding_mismatch;
recovery key on ordinary destructive -> role_denied; hub-supplied scratch tag
ignored -> refused; valid+role+target+fresh nonce -> accepted then replay
rejected. Full module race-clean + vet-clean on the Linux build server.

Inert this slice: no destructive deltas served until slice 10; the destructive
path is classified, gated, and tested but not wired to live execution.

CHECKPOINT: Phase B complete (slice 4 done). Awaiting validation.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -15,7 +15,7 @@
 - Module `gitea.dooplex.hu/admin/felhom-agent`; binary `felhom-agent` (`cmd/felhom-agent/`).
 - **Pure Go stdlib + `golang.org/x/crypto` only** — no web frameworks.
 - `go.mod` directive **go 1.25.0**; dep `golang.org/x/crypto v0.52.0` (declares go 1.25, will NOT build on Go 1.24). The **build server (192.168.0.180) runs go1.26.0** (upstream Go on PATH, backward-compatible). Build/run the agent there for live tests (same LAN as the demo host).
-- Version: `version` var in `cmd/felhom-agent/main.go`, overridable via `-ldflags "-X main.version=<v>"`; `--version` flag. **Current: v0.4.0-rc1** (slice-4 Phase A checkpoint; v0.4.0 lands with Phase B). Bump on meaningful changes + add a CHANGELOG entry.
+- Version: `version` var in `cmd/felhom-agent/main.go`, overridable via `-ldflags "-X main.version=<v>"`; `--version` flag. **Current: v0.4.0** (slice 4 complete: reconcile engine + reversibility gate). Bump on meaningful changes + add a CHANGELOG entry.
 
 ## Layout
 
@@ -48,8 +48,9 @@ Built in slices, all on `main`:
 - **v0.3.0** slice 3 — `internal/hub`: the first **daemon loop** (no-`--selftest` mode) posting a read-only `HostReport` to the hub (= the heartbeat). Report's storage/backup/restore/pbs/audit fields are **defined-but-empty** (slices 5/6); the envelope's desired-state/signed-ops fields are **parsed-but-ignored** (slice 4).
 - **v0.3.1** — slice-3 validation follow-ups.
 - **v0.3.2** — slice-4 pre-check: reversible `SetConfig` step added to `--selftest=task`; passed live on guest 9999. Findings: LXC `description` write is **synchronous** (empty UPID — dual-mode modeling confirmed); PVE appends a trailing `\n` to `description` on read (reconcile must normalize). First live `VM.Config.*` exercise.
-- **v0.4.0-rc1** — slice-4 **Phase A** (structural): `internal/reconcile` — engine, per-guest serializer (§10), desired-state model + `DesiredProvider` seam, normalization layer (`NormDescription` promoted out of main.go), plan/diff engine (benign Start/Stop/SetConfig set), durable op journal + idempotency store. Wired into `runDaemon` sharing the queue. Runs **live but unfed** (EmptyProvider → zero mutations until slice 10). Checkpoint: awaiting validation before Phase B.
-- **Next: slice 4 Phase B** — the benign/destructive classifier, the reversibility gate, and the signed-op consuming layer over `internal/authz` (doc 03 §4 / doc 04), in front of the queue's executor → lands **v0.4.0**.
+- **v0.4.0-rc1** — slice-4 **Phase A** (structural): `internal/reconcile` — engine, per-guest serializer (§10), desired-state model + `DesiredProvider` seam, normalization layer (`NormDescription` promoted out of main.go), plan/diff engine (benign Start/Stop/SetConfig set), durable op journal + idempotency store. Wired into `runDaemon` sharing the queue. Runs **live but unfed** (EmptyProvider → zero mutations until slice 10).
+- **v0.4.0** — slice-4 **Phase B** (security core): the benign/destructive **classifier** (provenance + data-bearing, not by verb; scratch/same-txn provenance is agent-internal, never hub-sourced), the **reversibility gate** (destructive → `pending_signature` unless a verified, role-scoped, action-bound operator signature), the **signed-op consuming layer** over `internal/authz` (role-scoping per doc 04 §4, op-to-action binding, idempotency-by-nonce, audit), and the **crash-recovery consumer** (`Recover` over `InFlight()`, resume-or-rollback). The gate fronts the queue's executor (every mutation passes it). **Inert this slice** — no destructive deltas served until slice 10; the destructive path is classified, gated, and adversarially tested but not wired to live execution. `authz` surface untouched.
+- **Next: slice 5/6 (storage manifest, backup/restore)** — the slices that fill the host-report's empty storage/backup collections and add the destructive executors the gate already guards.
 
 ## Demo host (for live tests)