Add remote session loading

internal/config/session_template_test.go

@@ -241,3 +241,38 @@ inputs:
 		t.Fatalf("SessionID = %q, want 2026-05-03", cfg.SessionID)
 	}
 }
+
+func TestLoadSessionBytesWithOptionsUsesSameTemplateAndStrictDecode(t *testing.T) {
+	sessionYAML := []byte(`session_id: "{{ session_id }}"
+campaign: sample-campaign
+inputs:
+  audio_s3:
+    prefix: audio/
+`)
+
+	cfg, err := LoadSessionBytesWithOptions("s3://bucket/session.yml", sessionYAML, SessionLoadOptions{SessionID: "2026-05-03"})
+	if err != nil {
+		t.Fatalf("LoadSessionBytesWithOptions() error = %v", err)
+	}
+	if cfg.SessionID != "2026-05-03" {
+		t.Fatalf("SessionID = %q, want 2026-05-03", cfg.SessionID)
+	}
+
+	_, err = LoadSessionBytesWithOptions("s3://bucket/session.yml", []byte("session_id: 2026-05-03\nunknown: true\n"), SessionLoadOptions{})
+	if err == nil {
+		t.Fatal("expected strict decode error, got nil")
+	}
+	if !strings.Contains(err.Error(), "strict decode failed") {
+		t.Fatalf("error = %q, want strict decode context", err.Error())
+	}
+}
+
+func TestLoadSessionBytesWithOptionsMismatchFails(t *testing.T) {
+	_, err := LoadSessionBytesWithOptions("s3://bucket/session.yml", []byte("session_id: 2026-05-03\n"), SessionLoadOptions{SessionID: "2026-04-04"})
+	if err == nil {
+		t.Fatal("expected mismatch error, got nil")
+	}
+	if !strings.Contains(err.Error(), "session_id mismatch") {
+		t.Fatalf("error = %q, want mismatch context", err.Error())
+	}
+}