🤖 fix: preserve reasoning intent when switching to binary models

When switching from a full-reasoning model to Grok (binary on/off),
map any non-"off" level (low/medium/high) to "high" to preserve the
user's intent to have reasoning enabled.

This prevents silently switching reasoning off when changing models.

Author: kylecarbs

src/browser/utils/thinking/policy.test.ts

@@ -90,10 +90,15 @@ describe("enforceThinkingPolicy", () => {
       expect(enforceThinkingPolicy("anthropic:claude-opus-4", "high")).toBe("high");
     });
 
-    test("falls back to medium when requested level not allowed", () => {
-      // Simulating behavior with gpt-5-pro (only allows "high")
-      // When requesting "low", falls back to first allowed level which is "high"
+    test("maps non-off levels to highest available when requested level not allowed", () => {
+      // gpt-5-pro only allows "high"
       expect(enforceThinkingPolicy("openai:gpt-5-pro", "low")).toBe("high");
+      expect(enforceThinkingPolicy("openai:gpt-5-pro", "medium")).toBe("high");
+
+      // Grok only allows "off" and "high" - preserve reasoning intent
+      expect(enforceThinkingPolicy("xai:grok-4-1-fast", "low")).toBe("high");
+      expect(enforceThinkingPolicy("xai:grok-4-1-fast", "medium")).toBe("high");
+      expect(enforceThinkingPolicy("xai:grok-4-1-fast", "off")).toBe("off");
     });
   });
 });

src/browser/utils/thinking/policy.ts

@@ -78,7 +78,7 @@ export function getThinkingPolicyForModel(modelString: string): ThinkingPolicy {
 
   // Check models.json for supports_reasoning
   const metadata = getModelMetadata(modelString);
-  if (metadata && metadata.supports_reasoning === false) {
+  if (metadata?.supports_reasoning === false) {
     return ["off"];
   }
 
@@ -91,8 +91,10 @@ export function getThinkingPolicyForModel(modelString: string): ThinkingPolicy {
  *
  * Fallback strategy:
  * 1. If requested level is allowed, use it
- * 2. If "medium" is allowed, use it (reasonable default)
- * 3. Otherwise use first allowed level
+ * 2. If requested level is non-"off" but not allowed, map to highest allowed non-"off" level
+ *    (preserves user intent to have reasoning enabled for binary models like Grok)
+ * 3. If "medium" is allowed, use it (reasonable default)
+ * 4. Otherwise use first allowed level
  */
 export function enforceThinkingPolicy(
   modelString: string,
@@ -104,6 +106,18 @@ export function enforceThinkingPolicy(
     return requested;
   }
 
+  // If user requested a non-"off" level but it's not allowed, preserve reasoning intent
+  // by mapping to the highest non-"off" level available (e.g., "medium" → "high" for Grok)
+  if (requested !== "off") {
+    const nonOffLevels = allowed.filter((level) => level !== "off");
+    if (nonOffLevels.length > 0) {
+      // Return highest available: prefer high > medium > low
+      if (nonOffLevels.includes("high")) return "high";
+      if (nonOffLevels.includes("medium")) return "medium";
+      if (nonOffLevels.includes("low")) return "low";
+    }
+  }
+
   // Fallback: prefer "medium" if allowed, else use first allowed level
   return allowed.includes("medium") ? "medium" : allowed[0];
 }