Record effective sessions in debug provenance

internal/core/debugbundle/bundle_test.go

@@ -179,6 +179,30 @@ func TestWriteInvocationPreservesReasoningEffortOverrideStates(t *testing.T) {
 		})
 	}
 }
+
+func TestWriteInvocationOmitsEmptySessionID(t *testing.T) {
+	for _, sessionID := range []string{"", "session-123"} {
+		bundle, err := Allocate(t.TempDir(), testBundleRunID, time.Unix(0, 42))
+		if err != nil {
+			t.Fatal(err)
+		}
+		if err := bundle.Summary().WriteInvocation(Invocation{Operation: "run", SessionID: sessionID}); err != nil {
+			t.Fatal(err)
+		}
+		data, err := os.ReadFile(filepath.Join(bundle.SummaryRoot(), ArtifactInvocationMetadata))
+		if err != nil {
+			t.Fatal(err)
+		}
+		var payload map[string]any
+		if err := json.Unmarshal(data, &payload); err != nil {
+			t.Fatal(err)
+		}
+		value, found := payload["session_id"]
+		if found != (sessionID != "") || (found && value != sessionID) {
+			t.Fatalf("session found=%t value=%#v, want found=%t value=%q; JSON=%s", found, value, sessionID != "", sessionID, data)
+		}
+	}
+}
 func TestSummaryWriterInternalWritesConfineArtifacts(t *testing.T) {
 	bundle, err := Allocate(t.TempDir(), testBundleRunID, time.Unix(0, 42))
 	if err != nil {

internal/core/debugbundle/summary.go

@@ -40,6 +40,7 @@ type Invocation struct {
 	OnlyLanes               []string  `json:"only_lanes,omitempty"`
 	ChunkCacheOverride      string    `json:"chunk_cache_override,omitempty"`
 	ReasoningEffortOverride *string   `json:"reasoning_effort_override,omitempty"`
+	SessionID               string    `json:"session_id,omitempty"`
 	RunID                   string    `json:"run_id"`
 	StartedAt               time.Time `json:"started_at"`
 }