diff --git a/internal/session/summary.go b/internal/session/summary.go
index ef95ed6..5656573 100644
--- a/internal/session/summary.go
+++ b/internal/session/summary.go
@@ -26,6 +26,25 @@ type SessionSummary struct {
 	FilesModified   []string  `json:"files_modified"`
 	FilesDeleted    []string  `json:"files_deleted"`
 	NotesUpdated    bool      `json:"notes_updated"`
+
+	// EndReason is "child_exited" for direct mode, "tmux_session_ended" for
+	// persistent mode (both owner-create and adopted reattach). Optional;
+	// pre-v0.5.3 summaries omit it.
+	EndReason string `json:"end_reason,omitempty"`
+
+	// DetectedVia distinguishes the mechanism that observed session end:
+	// "child_exit" for direct mode, "polling" for persistent mode.
+	DetectedVia string `json:"detected_via,omitempty"`
+
+	// SessionOwnership is "created" if this ctask process originated the
+	// session (owner-create) or "adopted" if it took over an orphaned
+	// persistent session. Omitted in direct mode.
+	SessionOwnership string `json:"session_ownership,omitempty"`
+
+	// AdoptedFromOrphanAt records the moment adoption took place. Set only
+	// for adopted reattach.
+	AdoptedFromOrphanAt *time.Time `json:"adopted_from_orphan_at,omitempty"`
+
 	// EndManifest captures the workspace file list at end-of-session so the
 	// next session can diff current state against it (Layer 3). This field
 	// is ctask-internal; it is not part of the public summary format shown
diff --git a/internal/session/summary_test.go b/internal/session/summary_test.go
index 82efe7c..4e8f1c6 100644
--- a/internal/session/summary_test.go
+++ b/internal/session/summary_test.go
@@ -169,3 +169,64 @@ func TestFormatLaunchContextRendersChanged(t *testing.T) {
 		}
 	}
 }
+
+func TestSummaryNewFieldsRoundTrip(t *testing.T) {
+	tmp := t.TempDir()
+	path := filepath.Join(tmp, ".ctask", "last-session-summary.json")
+
+	adoptedAt := time.Now().UTC().Truncate(time.Second)
+	s := &SessionSummary{
+		SessionID:           "host-1-20260508140000",
+		Hostname:            "host",
+		Agent:               "claude",
+		Mode:                "local",
+		StartedAt:           adoptedAt,
+		EndedAt:             adoptedAt.Add(10 * time.Minute),
+		DurationSeconds:     600,
+		EndReason:           "tmux_session_ended",
+		DetectedVia:         "polling",
+		SessionOwnership:    "adopted",
+		AdoptedFromOrphanAt: &adoptedAt,
+	}
+	if err := WriteSummary(path, s); err != nil {
+		t.Fatalf("WriteSummary: %v", err)
+	}
+	got, err := ReadSummary(path)
+	if err != nil {
+		t.Fatalf("ReadSummary: %v", err)
+	}
+	if got.EndReason != "tmux_session_ended" {
+		t.Errorf("EndReason: got %q", got.EndReason)
+	}
+	if got.DetectedVia != "polling" {
+		t.Errorf("DetectedVia: got %q", got.DetectedVia)
+	}
+	if got.SessionOwnership != "adopted" {
+		t.Errorf("SessionOwnership: got %q", got.SessionOwnership)
+	}
+	if got.AdoptedFromOrphanAt == nil || !got.AdoptedFromOrphanAt.Equal(adoptedAt) {
+		t.Errorf("AdoptedFromOrphanAt: got %v, want %v", got.AdoptedFromOrphanAt, adoptedAt)
+	}
+}
+
+func TestSummaryNewFieldsOmittedWhenEmpty(t *testing.T) {
+	tmp := t.TempDir()
+	path := filepath.Join(tmp, ".ctask", "last-session-summary.json")
+
+	s := &SessionSummary{
+		SessionID: "x", Hostname: "h", Agent: "claude", Mode: "local",
+		StartedAt: time.Now().UTC(), EndedAt: time.Now().UTC(),
+	}
+	if err := WriteSummary(path, s); err != nil {
+		t.Fatalf("WriteSummary: %v", err)
+	}
+	body, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("read: %v", err)
+	}
+	for _, key := range []string{"end_reason", "detected_via", "session_ownership", "adopted_from_orphan_at"} {
+		if strings.Contains(string(body), key) {
+			t.Errorf("expected %q to be omitted; body:\n%s", key, body)
+		}
+	}
+}