fix(model-capabilities): honor root thinking flags

src/shared/model-capabilities.test.ts

@@ -115,6 +115,22 @@ describe("getModelCapabilities", () => {
     })
   })
 
+  test("respects root-level thinking flags when providers do not nest them under capabilities", () => {
+    const result = getModelCapabilities({
+      providerID: "custom-proxy",
+      modelID: "gpt-5.4",
+      runtimeModel: {
+        supportsThinking: true,
+      },
+      bundledSnapshot,
+    })
+
+    expect(result).toMatchObject({
+      canonicalModelID: "gpt-5.4",
+      supportsThinking: true,
+    })
+  })
+
   test("accepts runtime variant arrays without corrupting them into numeric keys", () => {
     const result = getModelCapabilities({
       providerID: "openai",

src/shared/model-capabilities.ts

@@ -276,6 +276,11 @@ function readRuntimeModelThinkingSupport(runtimeModel: Record<string, unknown> |
     return capabilityValue
   }
 
+  const rootThinkingSupport = readRuntimeModelBoolean(runtimeModel, ["thinking", "supportsThinking"])
+  if (rootThinkingSupport !== undefined) {
+    return rootThinkingSupport
+  }
+
   const runtimeCapabilities = readRuntimeModelCapabilities(runtimeModel)
   if (!runtimeCapabilities) {
     return undefined