fix(ollama): remove Ollama from isReasoningTagProvider (#2279)

Ollama's OpenAI-compatible endpoint handles reasoning natively via the
`reasoning` field in streaming chunks. Treating Ollama as a
reasoning-tag provider incorrectly forces <think>/<final> tag
enforcement, which causes stripBlockTags() to discard all output
(since Ollama models don't emit <final> tags), resulting in
'(no output)' for every Ollama model.

This fix removes 'ollama' from the isReasoningTagProvider() check,
allowing Ollama models to work correctly through the standard
content/reasoning field separation.

src/utils/provider-utils.test.ts

@@ -0,0 +1,39 @@
+import { describe, expect, it } from "vitest";
+import { isReasoningTagProvider } from "./provider-utils.js";
+
+describe("isReasoningTagProvider", () => {
+  it("returns false for ollama — native reasoning field, no tags needed (#2279)", () => {
+    expect(isReasoningTagProvider("ollama")).toBe(false);
+    expect(isReasoningTagProvider("Ollama")).toBe(false);
+  });
+
+  it("returns true for google-gemini-cli", () => {
+    expect(isReasoningTagProvider("google-gemini-cli")).toBe(true);
+  });
+
+  it("returns true for google-generative-ai", () => {
+    expect(isReasoningTagProvider("google-generative-ai")).toBe(true);
+  });
+
+  it("returns true for google-antigravity", () => {
+    expect(isReasoningTagProvider("google-antigravity")).toBe(true);
+    expect(isReasoningTagProvider("google-antigravity/gemini-3")).toBe(true);
+  });
+
+  it("returns true for minimax", () => {
+    expect(isReasoningTagProvider("minimax")).toBe(true);
+    expect(isReasoningTagProvider("minimax-cn")).toBe(true);
+  });
+
+  it("returns false for null/undefined/empty", () => {
+    expect(isReasoningTagProvider(null)).toBe(false);
+    expect(isReasoningTagProvider(undefined)).toBe(false);
+    expect(isReasoningTagProvider("")).toBe(false);
+  });
+
+  it("returns false for standard providers", () => {
+    expect(isReasoningTagProvider("anthropic")).toBe(false);
+    expect(isReasoningTagProvider("openai")).toBe(false);
+    expect(isReasoningTagProvider("openrouter")).toBe(false);
+  });
+});