test: infer the session send return type in refusal coverage

Avoid hardcoding Promise<void> so the test also typechecks with PR154's Promise<boolean> admission result. Type-only correction; no product behavior changes.

tests/byok-refusal.test.ts

@@ -60,7 +60,7 @@ describe("Retry owns no composer recovery draft", () => {
 					return new Response(body, { status: 503 });
 				},
 			});
-			let request!: Promise<void>;
+			let request!: ReturnType<SessionModel["send"]>;
 			retryFailedResponse((input) => request = model.send(input), submittedDraft);
 			await request;
 			assert.equal(model.getState().error?.message, body, "503 stays raw for existing setup/picker routing");