Fix categories not being deep merged in mergeConfigs

When merging user and project configs, categories were simply
spread instead of deep merged. This caused user-level category
model settings to be completely overwritten by project-level
configs, even when the project config only specified partial
overrides like temperature.

Add deepMerge for categories field and comprehensive tests.

src/plugin-config.test.ts

@@ -0,0 +1,119 @@
+import { describe, expect, it } from "bun:test";
+import { mergeConfigs } from "./plugin-config";
+import type { OhMyOpenCodeConfig } from "./config";
+
+describe("mergeConfigs", () => {
+  describe("categories merging", () => {
+    // #given base config has categories, override has different categories
+    // #when merging configs
+    // #then should deep merge categories, not override completely
+
+    it("should deep merge categories from base and override", () => {
+      const base = {
+        categories: {
+          general: {
+            model: "openai/gpt-5.2",
+            temperature: 0.5,
+          },
+          quick: {
+            model: "anthropic/claude-haiku-4-5",
+          },
+        },
+      } as OhMyOpenCodeConfig;
+
+      const override = {
+        categories: {
+          general: {
+            temperature: 0.3,
+          },
+          visual: {
+            model: "google/gemini-3-pro-preview",
+          },
+        },
+      } as unknown as OhMyOpenCodeConfig;
+
+      const result = mergeConfigs(base, override);
+
+      // #then general.model should be preserved from base
+      expect(result.categories?.general?.model).toBe("openai/gpt-5.2");
+      // #then general.temperature should be overridden
+      expect(result.categories?.general?.temperature).toBe(0.3);
+      // #then quick should be preserved from base
+      expect(result.categories?.quick?.model).toBe("anthropic/claude-haiku-4-5");
+      // #then visual should be added from override
+      expect(result.categories?.visual?.model).toBe("google/gemini-3-pro-preview");
+    });
+
+    it("should preserve base categories when override has no categories", () => {
+      const base: OhMyOpenCodeConfig = {
+        categories: {
+          general: {
+            model: "openai/gpt-5.2",
+          },
+        },
+      };
+
+      const override: OhMyOpenCodeConfig = {};
+
+      const result = mergeConfigs(base, override);
+
+      expect(result.categories?.general?.model).toBe("openai/gpt-5.2");
+    });
+
+    it("should use override categories when base has no categories", () => {
+      const base: OhMyOpenCodeConfig = {};
+
+      const override: OhMyOpenCodeConfig = {
+        categories: {
+          general: {
+            model: "openai/gpt-5.2",
+          },
+        },
+      };
+
+      const result = mergeConfigs(base, override);
+
+      expect(result.categories?.general?.model).toBe("openai/gpt-5.2");
+    });
+  });
+
+  describe("existing behavior preservation", () => {
+    it("should deep merge agents", () => {
+      const base: OhMyOpenCodeConfig = {
+        agents: {
+          oracle: { model: "openai/gpt-5.2" },
+        },
+      };
+
+      const override: OhMyOpenCodeConfig = {
+        agents: {
+          oracle: { temperature: 0.5 },
+          explore: { model: "anthropic/claude-haiku-4-5" },
+        },
+      };
+
+      const result = mergeConfigs(base, override);
+
+      expect(result.agents?.oracle?.model).toBe("openai/gpt-5.2");
+      expect(result.agents?.oracle?.temperature).toBe(0.5);
+      expect(result.agents?.explore?.model).toBe("anthropic/claude-haiku-4-5");
+    });
+
+    it("should merge disabled arrays without duplicates", () => {
+      const base: OhMyOpenCodeConfig = {
+        disabled_hooks: ["comment-checker", "think-mode"],
+      };
+
+      const override: OhMyOpenCodeConfig = {
+        disabled_hooks: ["think-mode", "session-recovery"],
+      };
+
+      const result = mergeConfigs(base, override);
+
+      expect(result.disabled_hooks).toContain("comment-checker");
+      expect(result.disabled_hooks).toContain("think-mode");
+      expect(result.disabled_hooks).toContain("session-recovery");
+      expect(result.disabled_hooks?.length).toBe(3);
+    });
+  });
+});

src/plugin-config.ts

@@ -55,6 +55,7 @@ export function mergeConfigs(
     ...base,
     ...override,
     agents: deepMerge(base.agents, override.agents),
+    categories: deepMerge(base.categories, override.categories),
     disabled_agents: [
       ...new Set([
         ...(base.disabled_agents ?? []),