diff --git a/hub/internal/server/digest_seal_on_terminal_test.go b/hub/internal/server/digest_seal_on_terminal_test.go
new file mode 100644
index 00000000..edefb739
--- /dev/null
+++ b/hub/internal/server/digest_seal_on_terminal_test.go
@@ -0,0 +1,56 @@
+package server
+
+import (
+	"context"
+	"net/http"
+	"testing"
+)
+
+// TestDigestSealedOnCrash verifies the #118 §4 fold-on-close: when an agent
+// flips to a crash/failure terminal state (not the operator stop path), the run
+// digest is folded current + outcome-stamped right then, so the first Insight
+// open is an O(1) read rather than a full O(n) backfill.
+func TestDigestSealedOnCrash(t *testing.T) {
+	s, token := newA2ATestServer(t)
+	ctx := context.Background()
+	const sesID = "ses-crash"
+	const agentID = "agent-crash"
+
+	seedSessionWithAgent(t, s, defaultTeamID, sesID, agentID)
+	insertEventRow(t, s, agentID, sesID, 1, "text", `{"text":"a"}`)
+	insertEventRow(t, s, agentID, sesID, 2, "tool_call", `{"name":"read","id":"c1"}`)
+	insertEventRow(t, s, agentID, sesID, 3, "text", `{"text":"b"}`)
+
+	// Pre-condition: no digest row yet.
+	dr, err := s.digestReader(defaultTeamID)
+	if err != nil {
+		t.Fatalf("digestReader: %v", err)
+	}
+	if _, ok, _ := loadAgentDigest(ctx, dr, agentID); ok {
+		t.Fatal("digest unexpectedly present before terminal transition")
+	}
+
+	// Crash the agent via the same PATCH the host-runner reconcile uses.
+	status, body := doReq(t, s, token, http.MethodPatch,
+		"/v1/teams/"+defaultTeamID+"/agents/"+agentID+"/",
+		map[string]any{"status": "crashed"})
+	if status != http.StatusNoContent {
+		t.Fatalf("PATCH crashed: status=%d body=%s", status, body)
+	}
+
+	// Post-condition: digest exists, watermark caught up to the last event, and
+	// the terminal outcome is stamped — i.e. no read-time backfill is owed.
+	d, ok, err := loadAgentDigest(ctx, dr, agentID)
+	if err != nil {
+		t.Fatalf("loadAgentDigest: %v", err)
+	}
+	if !ok {
+		t.Fatal("digest not sealed after crash (no row) — fold-on-close missing")
+	}
+	if d.WatermarkSeq != 3 {
+		t.Fatalf("watermark = %d, want 3 (digest left stale after crash)", d.WatermarkSeq)
+	}
+	if d.Outcome == "" {
+		t.Fatal("digest outcome not stamped on crash")
+	}
+}
diff --git a/hub/internal/server/handlers_agents.go b/hub/internal/server/handlers_agents.go
index ee254f96..f69bd51a 100644
--- a/hub/internal/server/handlers_agents.go
+++ b/hub/internal/server/handlers_agents.go
@@ -404,6 +404,12 @@ func (s *Server) handlePatchAgent(w http.ResponseWriter, r *http.Request) {
 			   AND status = 'active'`,
 			NowUTC(), team, id)
 		_, _ = auth.RevokeAgentTokens(r.Context(), s.writeDB, id, NowUTC())
+		// Fold + stamp the run digest now (#118 §4). The operator stop path
+		// finalizes via stopSessionInternal; a crash/failure flows through
+		// here instead, so without this the first Insight open after the crash
+		// pays the full O(n) backfill. finalizeDigestOutcome brings the digest
+		// current off the read path.
+		s.finalizeDigestOutcome(r.Context(), team, id)
 	}
 	// ADR-029 D-3: auto-derive the linked task's status from the
 	// agent's terminal transition. Most-recent-spawn drives; older
@@ -454,6 +460,9 @@ func (s *Server) applyAgentTerminationEffects(ctx context.Context, team, id, rea
 	}
 	s.recordAudit(ctx, team, "agent.terminate", "agent", id,
 		"terminate "+handle, map[string]any{"handle": handle})
+	// Seal the run digest for the session-less terminate too (#118 §4) — the
+	// live-session branch above already finalizes via stopSessionInternal.
+	s.finalizeDigestOutcome(ctx, team, id)
 }
 
 // handleStopAgent is POST /v1/teams/{team}/agents/{agent}/stop — the