From ccbe190d64ae01a0c0fe0cad9e27552e7affbe37 Mon Sep 17 00:00:00 2001
From: can1357 <me@can.ac>
Date: Wed, 22 Jul 2026 20:27:43 +0200
Subject: [PATCH] fix(sdk): inherit role thinking level on startup retry
 fallback

A retry-chain entry without its own :level suffix now inherits the
unavailable primary's configured thinking level, matching runtime
fallback-chain semantics. Regression test asserts a level that differs
from the fallback model's default.
---
 packages/coding-agent/src/sdk.ts                       | 7 +++++++
 packages/coding-agent/test/sdk-model-selection.test.ts | 8 +++++---
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/packages/coding-agent/src/sdk.ts b/packages/coding-agent/src/sdk.ts
index c31b31bb1..d1dd84548 100644
--- a/packages/coding-agent/src/sdk.ts
+++ b/packages/coding-agent/src/sdk.ts
@@ -2143,6 +2143,13 @@ export async function createAgentSession(options: CreateAgentSessionOptions = {}
 				let selectedModel = primary.model;
 				let selectedThinkingLevel = primary.thinkingLevel;
 				let selectedExplicitThinkingLevel = primary.explicitThinkingLevel;
+				// A chain entry without its own `:level` suffix inherits the
+				// unavailable primary's configured thinking level, matching
+				// runtime fallback-chain semantics.
+				if (retryFallback && !selectedExplicitThinkingLevel && retryFallback.originalThinkingLevel !== undefined) {
+					selectedThinkingLevel = retryFallback.originalThinkingLevel;
+					selectedExplicitThinkingLevel = true;
+				}
 				let authFallbackUsed = false;
 				if (options.modelPatternAuthFallback) {
 					const primaryKey = await modelRegistry.getApiKey(primary.model);
diff --git a/packages/coding-agent/test/sdk-model-selection.test.ts b/packages/coding-agent/test/sdk-model-selection.test.ts
index efa2558f6..56af7b8e9 100644
--- a/packages/coding-agent/test/sdk-model-selection.test.ts
+++ b/packages/coding-agent/test/sdk-model-selection.test.ts
@@ -363,7 +363,7 @@ describe("createAgentSession deferred model pattern resolution", () => {
 		authStorage.setRuntimeApiKey("runtime-provider", "test-key");
 		authStoragesToClose.push(authStorage);
 		const modelRegistry = new ModelRegistry(authStorage, path.join(tempDir, "missing-role-models.yml"));
-		const parsed = parseArgs(["--model", "slow:high"]);
+		const parsed = parseArgs(["--model", "slow:low"]);
 		const exitSpy = vi.spyOn(process, "exit").mockImplementation((code?: number | string | null) => {
 			throw new Error(`buildSessionOptions unexpectedly exited with ${code}`);
 		});
@@ -375,7 +375,7 @@ describe("createAgentSession deferred model pattern resolution", () => {
 				modelRegistry,
 				settings,
 			);
-			expect(cliOptions.modelPattern).toBe("slow:high");
+			expect(cliOptions.modelPattern).toBe("slow:low");
 
 			const { session, modelFallbackMessage } = await createAgentSession({
 				...cliOptions,
@@ -398,7 +398,9 @@ describe("createAgentSession deferred model pattern resolution", () => {
 			try {
 				expect(session.model?.provider).toBe("runtime-provider");
 				expect(session.model?.id).toBe("runtime-reasoning-model");
-				expect(session.thinkingLevel).toBe(Effort.High);
+				// `low` differs from the fallback model's default (`high`), so this
+				// proves the suffix is inherited rather than the model default applied.
+				expect(session.thinkingLevel).toBe(Effort.Low);
 				expect(modelFallbackMessage).toBeUndefined();
 			} finally {
 				await session.dispose();