cpustress+orchestrator: serial CPU/RAM passes + silent-skip guard

Orion's run (log 20:49 → 20:54) shipped GREEN while silently skipping
CPUStress. Two compounding bugs:

1. CPUStress ran --cpu N AND --vm N --vm-bytes 90% concurrently.
   On a 4-core 8 GiB N95, that's 360% RAM overcommit; the OOM-killer
   fired, usually on the agent itself. Replaced with two sequential
   passes — CPU (all methods, --verify) for 3 min, then RAM (--vm 1,
   --vm-bytes capped to MemAvailable − 1.5 GiB, floor 256 MiB, --verify)
   for 3 min. Each pass now also asserts elapsed ≥ target − 2s so a
   premature clean exit counts as failure instead of a silent pass.

2. On systemd-restart after the OOM, the agent hardcoded nextStage :=
   "Inventory" and re-ran it. The orchestrator's /result handler
   advances run state via TriggerStageCompleted against the *current*
   RunState, not against body.Stage — so an Inventory result posted
   while the run was in StateCPUStress silently advanced CPUStress →
   Storage and marked CPUStress passed without it ever running.

Two-layer defense for #2:
- agent-side: /claim response now carries current_state; agent resumes
  at the matching stage on a re-claim (happy path).
- server-side: new TriggerStageMismatch + StageNameForState helper
  backstop. If body.Stage doesn't match the run's current stage, /result
  parks the run in FailedHolding with failed_stage labeled
  "<got> (expected <expected>)" and returns 409.

Other stages audited for similar unbounded concurrency — none found;
only CPUStress was unsafe.

Tests:
- cpustress_test.go — parseMemAvailable parses real meminfo, errors on
  missing/malformed; cap calc hits floor on tiny boxes, uses 1.5 GiB
  headroom on normal/huge boxes.
- statemachine_test.go — TriggerStageMismatch lands at FailedHolding
  from every stage state and is rejected from pre-stage/terminal
  states; StageNameForState round-trips the stageStates map.
- agent_handlers_test.go — TestResult_RejectsMismatchedStage proves
  the Orion scenario now 409s + FailedHolding; TestResult_AcceptsMatchingStage
  proves the guard doesn't break the happy path.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/api/agent_handlers_test.go

@@ -14,6 +14,7 @@ import (
 
 	"vetting/internal/api"
 	"vetting/internal/db"
+	"vetting/internal/events"
 	"vetting/internal/model"
 	"vetting/internal/orchestrator"
 	"vetting/internal/store"
@@ -107,7 +108,7 @@ func TestSensorRejectsBadToken(t *testing.T) {
 func TestHeartbeatShutdownWhenCompleted(t *testing.T) {
 	a, runID, token := setupAgent(t)
 	// Wire a runner so Heartbeat's TouchHeartbeat call doesn't nil-panic.
-	a.Runner = &orchestrator.Runner{Runs: a.Runs, Hosts: a.Hosts, Stages: &store.Stages{DB: a.Runs.DB}}
+	a.Runner = &orchestrator.Runner{Runs: a.Runs, Hosts: a.Hosts, Stages: &store.Stages{DB: a.Runs.DB}, EventHub: events.NewHub()}
 	if err := a.Runs.SetState(context.Background(), runID, model.StateCompleted); err != nil {
 		t.Fatalf("set state: %v", err)
 	}
@@ -126,3 +127,91 @@ func TestHeartbeatShutdownWhenCompleted(t *testing.T) {
 		t.Fatalf("cmd = %v, want shutdown", resp["cmd"])
 	}
 }
+
+// TestResult_RejectsMismatchedStage is the silent-skip guard's unit
+// test. The Orion failure mode: agent crashes mid-CPUStress, systemd
+// restarts it, restarted agent replays Inventory and /results it.
+// Before the guard, the orchestrator advanced StateCPUStress → Storage
+// on TriggerStageCompleted; CPUStress got marked passed without ever
+// running. Guard's contract: if body.Stage doesn't match the stage the
+// run is in, reject with 409 and park the run in FailedHolding with a
+// failed_stage that names *what* was reported vs. what was expected.
+func TestResult_RejectsMismatchedStage(t *testing.T) {
+	a, runID, token := setupAgent(t)
+	a.Runner = &orchestrator.Runner{Runs: a.Runs, Hosts: a.Hosts, Stages: &store.Stages{DB: a.Runs.DB}, EventHub: events.NewHub()}
+	// Park the run in CPUStress — the state Orion was in when its
+	// agent crashed.
+	if err := a.Runs.SetState(context.Background(), runID, model.StateCPUStress); err != nil {
+		t.Fatalf("set state: %v", err)
+	}
+
+	// Restarted agent's hardcoded-Inventory-first behavior: it replays
+	// Inventory and posts a passed result for it.
+	body, _ := json.Marshal(map[string]any{
+		"stage":  "Inventory",
+		"passed": true,
+	})
+	req := routedRequest(runID, http.MethodPost, "/api/v1/runs/"+strconv.FormatInt(runID, 10)+"/result", body)
+	req.Header.Set("Authorization", "Bearer "+token)
+	req.Header.Set("Content-Type", "application/json")
+	rr := httptest.NewRecorder()
+	a.Result(rr, req)
+
+	if rr.Code != http.StatusConflict {
+		t.Fatalf("status = %d, want 409; body = %s", rr.Code, rr.Body.String())
+	}
+	after, err := a.Runs.Get(context.Background(), runID)
+	if err != nil {
+		t.Fatalf("get run: %v", err)
+	}
+	if after.State != model.StateFailedHolding {
+		t.Fatalf("run state = %q, want FailedHolding", after.State)
+	}
+	if after.FailedStage == "" {
+		t.Fatalf("failed_stage is empty; expected mismatch label")
+	}
+	// The label must name both sides so the operator can see the
+	// skew without digging through logs.
+	for _, want := range []string{"Inventory", "CPUStress"} {
+		if !bytes.Contains([]byte(after.FailedStage), []byte(want)) {
+			t.Errorf("failed_stage %q missing %q", after.FailedStage, want)
+		}
+	}
+}
+
+// TestResult_AcceptsMatchingStage confirms the guard's complement: when
+// the agent reports the stage the run is actually in, /result advances
+// the pipeline normally. Without this, a too-strict guard could reject
+// every result and freeze all runs.
+func TestResult_AcceptsMatchingStage(t *testing.T) {
+	a, runID, token := setupAgent(t)
+	a.Runner = &orchestrator.Runner{Runs: a.Runs, Hosts: a.Hosts, Stages: &store.Stages{DB: a.Runs.DB}, EventHub: events.NewHub()}
+	stages := &store.Stages{DB: a.Runs.DB}
+	if err := stages.Seed(context.Background(), runID); err != nil {
+		t.Fatalf("seed stages: %v", err)
+	}
+	if err := a.Runs.SetState(context.Background(), runID, model.StateSMART); err != nil {
+		t.Fatalf("set state: %v", err)
+	}
+
+	body, _ := json.Marshal(map[string]any{
+		"stage":  "SMART",
+		"passed": true,
+	})
+	req := routedRequest(runID, http.MethodPost, "/api/v1/runs/"+strconv.FormatInt(runID, 10)+"/result", body)
+	req.Header.Set("Authorization", "Bearer "+token)
+	req.Header.Set("Content-Type", "application/json")
+	rr := httptest.NewRecorder()
+	a.Result(rr, req)
+
+	if rr.Code != http.StatusOK {
+		t.Fatalf("status = %d, want 200; body = %s", rr.Code, rr.Body.String())
+	}
+	after, err := a.Runs.Get(context.Background(), runID)
+	if err != nil {
+		t.Fatalf("get run: %v", err)
+	}
+	if after.State != model.StateCPUStress {
+		t.Fatalf("run state = %q, want CPUStress after SMART pass", after.State)
+	}
+}