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>

internal/reconcile/classify_test.go

@@ -0,0 +1,70 @@
+package reconcile
+
+import (
+	"testing"
+
+	"gitea.dooplex.hu/admin/felhom-agent/internal/authz"
+)
+
+func TestClassify_BenignClasses(t *testing.T) {
+	for _, c := range []OpClass{ClassStart, ClassStop, ClassSetConfig, ClassCreate, ClassRestart} {
+		if got := Classify(c, Provenance{}); got != Benign {
+			t.Errorf("Classify(%s) = %s, want benign", c, got)
+		}
+	}
+}
+
+func TestClassify_DestructiveClassesNeedSignature(t *testing.T) {
+	for _, c := range []OpClass{ClassGuestDestroy, ClassStorageWipe, ClassRestoreOverwrite, ClassDecommission, ClassKeyRotation} {
+		if got := Classify(c, Provenance{}); got != Destructive {
+			t.Errorf("Classify(%s) = %s, want destructive", c, got)
+		}
+	}
+}
+
+func TestClassify_InternalProvenanceMakesDestroyBenign(t *testing.T) {
+	// Same-transaction create → compensating rollback is benign (§10).
+	if got := Classify(ClassGuestDestroy, Provenance{SameTxnCreated: true}); got != Benign {
+		t.Errorf("same-txn destroy = %s, want benign", got)
+	}
+	// Agent-tagged scratch teardown is benign (§8).
+	if got := Classify(ClassGuestDestroy, Provenance{AgentTaggedScratch: true}); got != Benign {
+		t.Errorf("scratch destroy = %s, want benign", got)
+	}
+}
+
+func TestClassify_KeyRotationAlwaysDestructive(t *testing.T) {
+	// Even with internal provenance, key-rotation stays signed (role-scoping decides
+	// which key) — provenance flags don't apply to it.
+	if got := Classify(ClassKeyRotation, Provenance{SameTxnCreated: true, AgentTaggedScratch: true}); got != Destructive {
+		t.Errorf("key_rotation = %s, want destructive", got)
+	}
+}
+
+func TestClassify_UnknownClassFailsSafe(t *testing.T) {
+	if got := Classify(OpClass("totally_unknown_op"), Provenance{}); got != Destructive {
+		t.Errorf("unknown class = %s, want destructive (fail-safe)", got)
+	}
+}
+
+func TestRoleAuthorizes(t *testing.T) {
+	op := authz.RoleOperational
+	rec := authz.RoleRecovery
+	cases := []struct {
+		role  authz.KeyRole
+		class OpClass
+		want  bool
+	}{
+		{op, ClassGuestDestroy, true},   // operational does ordinary destructive
+		{op, ClassDecommission, true},   //
+		{op, ClassKeyRotation, true},    // operational does planned rotation
+		{rec, ClassGuestDestroy, false}, // recovery may NOT do ordinary destructive
+		{rec, ClassStorageWipe, false},  //
+		{rec, ClassKeyRotation, true},   // recovery authorizes ONLY rotation
+	}
+	for _, c := range cases {
+		if got := roleAuthorizes(c.role, c.class); got != c.want {
+			t.Errorf("roleAuthorizes(%s, %s) = %v, want %v", c.role, c.class, got, c.want)
+		}
+	}
+}