fix(coding-agent): retried role restore after extension providers

Initial startup resume runs before extension providers register, so a role model supplied by an extension fell back to the saved default. Retry the preferred session-model candidates once provider registrations are processed and re-resolve thinking level for the new model.\n\nFixes #1649

packages/coding-agent/src/sdk.ts

@@ -1008,16 +1008,21 @@ export async function createAgentSession(options: CreateAgentSessionOptions = {}
 	);
 	let model = options.model;
 	let modelFallbackMessage: string | undefined;
-	// If session has data, try to restore model from it.
-	// Skip restore when an explicit model was requested.
-	const sessionModelStrings = getRestorableSessionModels(
-		existingSession.models,
-		sessionManager.getLastModelChangeRole(),
-	);
-	if (!hasExplicitModel && !model && hasExistingSession && sessionModelStrings.length > 0) {
+	// Identify session model strings to restore in fallback order. We do an
+	// initial pass here so model-dependent setup (thinking-level resolution,
+	// host preconnect) can use the restored model; extension-registered
+	// providers aren't visible yet, so we retry the preferred candidates once
+	// extensions register below.
+	const sessionModelStrings =
+		!hasExplicitModel && hasExistingSession
+			? getRestorableSessionModels(existingSession.models, sessionManager.getLastModelChangeRole())
+			: [];
+	let restoredSessionModelIndex = -1;
+	if (!hasExplicitModel && !model && sessionModelStrings.length > 0) {
 		await logger.time("restoreSessionModel", async () => {
 			let failedSessionModel: string | undefined;
-			for (const sessionModelStr of sessionModelStrings) {
+			for (let i = 0; i < sessionModelStrings.length; i++) {
+				const sessionModelStr = sessionModelStrings[i];
 				const parsedModel = parseModelString(sessionModelStr);
 				if (!parsedModel) {
 					failedSessionModel ??= sessionModelStr;
@@ -1027,6 +1032,7 @@ export async function createAgentSession(options: CreateAgentSessionOptions = {}
 				const restoredModel = modelRegistry.find(parsedModel.provider, parsedModel.id);
 				if (restoredModel && (await hasModelApiKey(restoredModel))) {
 					model = restoredModel;
+					restoredSessionModelIndex = i;
 					break;
 				}
 				failedSessionModel ??= sessionModelStr;
@@ -1455,6 +1461,31 @@ export async function createAgentSession(options: CreateAgentSessionOptions = {}
 			extensionsResult.runtime.pendingProviderRegistrations = [];
 		}
 
+		// Retry preferred session-model candidates now that extension providers
+		// are registered. The initial restore above runs before extensions load,
+		// so a role model supplied by an extension would have fallen back to the
+		// session's saved default; reclaim it here so resume honors the last
+		// active role.
+		if (!hasExplicitModel && restoredSessionModelIndex > 0 && sessionModelStrings.length > 0) {
+			for (let i = 0; i < restoredSessionModelIndex; i++) {
+				const sessionModelStr = sessionModelStrings[i];
+				const parsedModel = parseModelString(sessionModelStr);
+				if (!parsedModel) continue;
+				const restoredModel = modelRegistry.find(parsedModel.provider, parsedModel.id);
+				if (restoredModel && (await hasModelApiKey(restoredModel))) {
+					model = restoredModel;
+					modelFallbackMessage = undefined;
+					restoredSessionModelIndex = i;
+					effectiveThinkingLevel = logger.time("resolveThinkingLevelForModel", () =>
+						autoThinking
+							? resolveProvisionalAutoLevel(restoredModel)
+							: resolveThinkingLevelForModel(restoredModel, effectiveThinkingLevel),
+					);
+					preconnectModelHost(restoredModel.baseUrl);
+					break;
+				}
+			}
+		}
 		// Resolve deferred --model pattern now that extension models are registered.
 		if (!model && options.modelPattern) {
 			const availableModels = modelRegistry.getAll();

packages/coding-agent/test/sdk-model-selection.test.ts

@@ -149,4 +149,69 @@ describe("createAgentSession deferred model pattern resolution", () => {
 			authStorage.close();
 		}
 	});
+
+	test("restores role model from extension provider after startup resume", async () => {
+		const defaultModel = getBundledModel("anthropic", "claude-sonnet-4-5");
+		if (!defaultModel) {
+			throw new Error("Expected bundled anthropic default model");
+		}
+
+		const authStorage = await AuthStorage.create(path.join(tempDir, "testauth.db"));
+		authStorage.setRuntimeApiKey(defaultModel.provider, "test-key");
+		const modelRegistry = new ModelRegistry(authStorage, path.join(tempDir, "models.yml"));
+
+		const targetSessionFile = path.join(tempDir, "resume-extension.jsonl");
+		const timestamp = "2026-06-01T00:00:00.000Z";
+		await Bun.write(
+			targetSessionFile,
+			`${[
+				{ type: "session", version: 3, id: "resume-ext", timestamp, cwd: tempDir },
+				{
+					type: "model_change",
+					id: "default-model",
+					parentId: null,
+					timestamp,
+					model: `${defaultModel.provider}/${defaultModel.id}`,
+					role: "default",
+				},
+				{
+					type: "model_change",
+					id: "smol-model",
+					parentId: "default-model",
+					timestamp,
+					model: "runtime-provider/runtime-model",
+					role: "smol",
+				},
+			]
+				.map(entry => JSON.stringify(entry))
+				.join("\n")}\n`,
+		);
+		const sessionManager = await SessionManager.open(targetSessionFile, path.join(tempDir, "sessions"));
+
+		const { session } = await createAgentSession({
+			cwd: tempDir,
+			agentDir: tempDir,
+			authStorage,
+			modelRegistry,
+			sessionManager,
+			settings: Settings.isolated(),
+			disableExtensionDiscovery: true,
+			extensions: [providerExtension],
+			skills: [],
+			contextFiles: [],
+			promptTemplates: [],
+			slashCommands: [],
+			enableMCP: false,
+			enableLsp: false,
+			skipPythonPreflight: true,
+		});
+
+		try {
+			expect(session.model?.provider).toBe("runtime-provider");
+			expect(session.model?.id).toBe("runtime-model");
+		} finally {
+			await session.dispose();
+			authStorage.close();
+		}
+	});
 });