Derive stable prompt sessions for CLI runs

internal/framework/pipeline/runner.go

@@ -191,7 +191,7 @@ func (r *Runner) Run(ctx context.Context, input RunInput) (output RunOutput, err
 		return failOutput(output), fmt.Errorf("write source debug artifact: %w", err)
 	}
 	sourceInput := sourceInputMaterial(input.Path, input.RawInput)
-	sessionID := resolvedSessionID(input.SessionID, doc.ID)
+	sessionID := strings.TrimSpace(input.SessionID)
 	output.Manifest.Metadata, err = manifestMetadataWithSessionID(output.Manifest.Metadata, sessionID)
 	if err != nil {
 		return failOutput(output), err
@@ -896,13 +896,6 @@ func sourceInputOriginURI(inputPath string) string {
 	return fileURI(inputPath)
 }
 
-func resolvedSessionID(explicit string, sourceDocumentID string) string {
-	if trimmed := strings.TrimSpace(explicit); trimmed != "" {
-		return trimmed
-	}
-	return strings.TrimSpace(sourceDocumentID)
-}
-
 func manifestMetadataWithSessionID(metadata map[string]any, sessionID string) (map[string]any, error) {
 	out, err := cloneMetadata(metadata)
 	if err != nil {

internal/framework/pipeline/runner_session_test.go

@@ -0,0 +1,37 @@
+package pipeline
+
+import (
+	"context"
+	"testing"
+)
+
+func TestRunnerUsesProvidedSessionWithoutSourceFallback(t *testing.T) {
+	for _, test := range []struct {
+		name    string
+		session string
+		wantSet bool
+		want    string
+	}{
+		{name: "provided", session: " supplied-session ", wantSet: true, want: "supplied-session"},
+		{name: "empty", wantSet: false},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			prepared, _ := preparedTerminalDebugPipeline(t)
+			output, err := New().Run(context.Background(), RunInput{
+				Prepared:  prepared,
+				RawInput:  []byte("input"),
+				SessionID: test.session,
+			})
+			if err != nil {
+				t.Fatal(err)
+			}
+			value, found := output.Manifest.Metadata["session_id"]
+			if found != test.wantSet {
+				t.Fatalf("manifest session presence = %t, want %t; metadata = %#v", found, test.wantSet, output.Manifest.Metadata)
+			}
+			if found && value != test.want {
+				t.Fatalf("manifest session = %#v, want %q", value, test.want)
+			}
+		})
+	}
+}