agent: report served local-API leaf fingerprint (hub re-key detection, Part A) v0.48.0

HostReport.LeafFingerprint rides the served fp (from EnsureLeaf) on every report; empty when local
API disabled. Collector.SetLeafFingerprint threads it like Capabilities. Hub watches it for a re-key.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Pg8ANF97SEeKYSN5Jxw3qJ

internal/hub/collect.go

@@ -60,6 +60,7 @@ type Collector struct {
 	pbs          PBSReporter
 	temp         TempReader                                    // slice 9: host CPU/chassis temp (nil-safe → nil temp)
 	capProbe     func(ctx context.Context) []capability.Status // v0.44.0: privileged-capability self-check (nil → empty)
+	leafFP       string                                        // v0.48.0: served local-API leaf fp (static per process; "" when local API disabled)
 	hostID       string
 	agentVersion string
 	logger       *slog.Logger
@@ -101,6 +102,14 @@ func (c *Collector) SetCapabilityProber(probe func(ctx context.Context) []capabi
 	return c
 }
 
+// SetLeafFingerprint records the served local-API leaf fp (v0.48.0) to ride every host report (the hub
+// watches it for a re-key). Static per process — set once at startup. "" when the local API is
+// disabled. Returns the collector for chaining.
+func (c *Collector) SetLeafFingerprint(fp string) *Collector {
+	c.leafFP = fp
+	return c
+}
+
 // Collect builds the report. Best-effort liveness: a failed NodeStatus is a hard
 // error (no useful report — the cycle skips the POST); a failed per-guest
 // GuestConfig degrades that guest to status="unknown" without spec but still sends;
@@ -126,9 +135,10 @@ func (c *Collector) Collect(ctx context.Context) (*HostReport, error) {
 		RestoreTests:   c.collectRestoreTests(ctx),
 		PBSSnapshots:   c.collectPBSSnapshots(ctx),
 
-		AuditTail:    []AuditEntry{},
-		Cloudflared:  Cloudflared{Status: c.cloudflaredStatus(ctx)},
-		Capabilities: c.capabilities(ctx),
+		AuditTail:       []AuditEntry{},
+		Cloudflared:     Cloudflared{Status: c.cloudflaredStatus(ctx)},
+		Capabilities:    c.capabilities(ctx),
+		LeafFingerprint: c.leafFP,
 	}
 	// DR recipe host-half — derived from the just-collected guest/storage/PBS facts (no new reads).
 	// Secret-free by construction (identifiers/intents/sizes/coordinates only).

internal/hub/collect_test.go

@@ -146,3 +146,27 @@ func TestCollect_CloudflaredProbeErrorIsUnknown(t *testing.T) {
 		t.Error("empty collections must be non-nil")
 	}
 }
+
+// Part A: the served leaf fp rides the report when set (v0.48.0); empty when the local API is disabled
+// (no SetLeafFingerprint). Companion: the unset case proves the threading is what populates it.
+func TestCollect_LeafFingerprint(t *testing.T) {
+	px := &fakePx{node: "n", ns: newTestNodeStatus()}
+	const fp = "60b5974d586f5f3c8ec41eb998d0f07406178219c36bf6d3ff377570279d8245"
+
+	c := NewCollector(px, fakeProber{status: "active"}, nil, nil, nil, nil, "h", "0.48.0", quietLogger())
+	c.SetLeafFingerprint(fp)
+	r, err := c.Collect(context.Background())
+	if err != nil {
+		t.Fatalf("Collect: %v", err)
+	}
+	if r.LeafFingerprint != fp {
+		t.Fatalf("leaf_fingerprint = %q, want %q", r.LeafFingerprint, fp)
+	}
+
+	// Companion: no SetLeafFingerprint (local API disabled) → empty, never a fabricated value.
+	c2 := NewCollector(px, fakeProber{status: "active"}, nil, nil, nil, nil, "h", "0.48.0", quietLogger())
+	r2, _ := c2.Collect(context.Background())
+	if r2.LeafFingerprint != "" {
+		t.Fatalf("unset leaf_fingerprint = %q, want empty", r2.LeafFingerprint)
+	}
+}

internal/hub/dr_recipe.go

@@ -21,6 +21,7 @@ import "sort"
 //   - restic_repo_coord — RESERVED for a future offsite bulk-volume backup tier. None exists today:
 //     external-drive data has no offsite/second-failure-domain copy (cross-drive backup is rsync to
 //     the SAME internal SSD), so the field named nothing real. Re-add when that tier ships.
+//
 // The pbs coord, by contrast, is resolved LIVE each collect (LiveSnapshotReporter) so the restore
 // SOURCE is present whenever PBS is reachable — not gated on the 6 h verify cadence.
 //

internal/hub/dr_recipe_test.go

@@ -80,7 +80,7 @@ func TestBuildDRRecipeHostHalf_NoPBS(t *testing.T) {
 // TestDRRecipeHostHalf_V1DriveShape pins the v1 host-half drive shape: a drive object carries ONLY
 // {durable_id, mount_path, intent, total_bytes} (fs_type is omitempty) — and specifically NEITHER the
 // dropped "role" NOR "restic_repo_coord" keys. Re-adding either field to DRDrive makes this fail
-// (the companion: `Role string \`json:"role"\`` reintroduces the "role" key → caught here).
+// (the companion: `Role string \`json:"role"\“ reintroduces the "role" key → caught here).
 func TestDRRecipeHostHalf_V1DriveShape(t *testing.T) {
 	h := BuildDRRecipeHostHalf(
 		nil,

internal/hub/loop_test.go

@@ -38,7 +38,9 @@ func (r *fakeReporter) Report(ctx context.Context, _ *HostReport) (*ControlEnvel
 // recordingObserver records the envelopes the loop hands it (slice 10A EnvelopeObserver seam).
 type recordingObserver struct{ envs []*ControlEnvelope }
 
-func (o *recordingObserver) OnEnvelope(_ context.Context, e *ControlEnvelope) { o.envs = append(o.envs, e) }
+func (o *recordingObserver) OnEnvelope(_ context.Context, e *ControlEnvelope) {
+	o.envs = append(o.envs, e)
+}
 
 // The loop notifies the EnvelopeObserver once per successful cycle (with the envelope) AND still
 // adopts PollIntervalSeconds — the two are independent.

internal/hub/report.go

@@ -36,6 +36,13 @@ type HostReport struct {
 	// on a Critical capability flipping to "degraded". Non-nil so it marshals as [].
 	Capabilities []capability.Status `json:"capabilities"`
 
+	// LeafFingerprint is the SHA-256 of the local-API leaf the agent CURRENTLY serves (v0.48.0). The
+	// hub records the first value per host as the baseline and raises `host_leaf_changed` if it ever
+	// changes — a proactive, fleet-wide agent-re-key alert independent of any controller's channel
+	// check. Empty when the local API is disabled (no leaf) → the hub treats "" as unknown, never an
+	// alert. Not a secret (the fp is public; the token is never reported).
+	LeafFingerprint string `json:"leaf_fingerprint"`
+
 	// DR recipe — the agent (storage/guest/PBS) half of the secret-free reconstruction recipe
 	// (SPIKE-dr-recipe-2026-06-16). Derived from the facts above; carries ONLY identifiers/intents/
 	// sizes/coordinates, never a secret. The hub assembles it with the controller's app half.

internal/hub/report_test.go

@@ -24,13 +24,14 @@ func TestHostReport_FieldNamesAndEmptyCollections(t *testing.T) {
 			VMID: 100, Name: "felhom-cust-acme", Status: "running", ControllerVersion: "",
 			Spec: &GuestSpec{Cores: 2, MemoryBytes: 2147483648, DiskBytes: 21474836480},
 		}},
-		StorageTargets: []StorageTarget{},
-		Backups:        []Backup{},
-		RestoreTests:   []RestoreTest{},
-		PBSSnapshots:   []PBSSnapshot{},
-		AuditTail:      []AuditEntry{},
-		Cloudflared:    Cloudflared{Status: "active"},
-		Capabilities:   []capability.Status{},
+		StorageTargets:  []StorageTarget{},
+		Backups:         []Backup{},
+		RestoreTests:    []RestoreTest{},
+		PBSSnapshots:    []PBSSnapshot{},
+		AuditTail:       []AuditEntry{},
+		Cloudflared:     Cloudflared{Status: "active"},
+		Capabilities:    []capability.Status{},
+		LeafFingerprint: "60b5974d586f5f3c8ec41eb998d0f07406178219c36bf6d3ff377570279d8245",
 	}
 	// dr_recipe is always set on the real path (Collect); set it here too so the "no null" invariant
 	// covers it (empty pbs is omitempty → omitted, never null).
@@ -50,6 +51,7 @@ func TestHostReport_FieldNamesAndEmptyCollections(t *testing.T) {
 		// empty collections must be [] not null
 		`"storage_targets":[]`, `"backups":[]`, `"restore_tests":[]`, `"pbs_snapshots":[]`, `"audit_tail":[]`,
 		`"capabilities":[]`,
+		`"leaf_fingerprint":"60b5974d586f5f3c8ec41eb998d0f07406178219c36bf6d3ff377570279d8245"`,
 	} {
 		if !strings.Contains(got, field) {
 			t.Errorf("report JSON missing %s\n got: %s", field, got)

internal/hub/testdata/host-report.golden.json

@@ -133,6 +133,7 @@
   "cloudflared": { "status": "active" },
   "audit_tail": [],
   "capabilities": [],
+  "leaf_fingerprint": "60b5974d586f5f3c8ec41eb998d0f07406178219c36bf6d3ff377570279d8245",
   "dr_recipe": {
     "recipe_version": 1,
     "guests": [