diff --git a/src/utils/websearch/__tests__/hook-utils.test.ts b/src/utils/websearch/__tests__/hook-utils.test.ts
new file mode 100644
index 00000000..0ad12f7f
--- /dev/null
+++ b/src/utils/websearch/__tests__/hook-utils.test.ts
@@ -0,0 +1,280 @@
+import { expect, test, describe } from "bun:test";
+import { isCcsWebSearchHook, deduplicateCcsHooks } from "../hook-utils";
+
+describe("isCcsWebSearchHook", () => {
+  test("Returns true for CCS hook with forward slashes (Unix path)", () => {
+    const hook = {
+      matcher: "WebSearch",
+      hooks: [
+        {
+          command: "node /home/user/.ccs/hooks/websearch-transformer/index.js",
+        },
+      ],
+    };
+    expect(isCcsWebSearchHook(hook)).toBe(true);
+  });
+
+  test("Returns true for CCS hook with backslashes (Windows path)", () => {
+    const hook = {
+      matcher: "WebSearch",
+      hooks: [
+        {
+          command: "node C:\\Users\\user\\.ccs\\hooks\\websearch-transformer\\index.js",
+        },
+      ],
+    };
+    expect(isCcsWebSearchHook(hook)).toBe(true);
+  });
+
+  test("Returns true for mixed path separators", () => {
+    const hook = {
+      matcher: "WebSearch",
+      hooks: [
+        {
+          command: "node /home/user\\.ccs/hooks\\websearch-transformer/index.js",
+        },
+      ],
+    };
+    expect(isCcsWebSearchHook(hook)).toBe(true);
+  });
+
+  test("Returns false for non-WebSearch matcher", () => {
+    const hook = {
+      matcher: "SomethingElse",
+      hooks: [
+        {
+          command: "node /home/user/.ccs/hooks/websearch-transformer/index.js",
+        },
+      ],
+    };
+    expect(isCcsWebSearchHook(hook)).toBe(false);
+  });
+
+  test("Returns false for WebSearch with non-CCS hook command", () => {
+    const hook = {
+      matcher: "WebSearch",
+      hooks: [
+        {
+          command: "node /some/other/path/custom-hook.js",
+        },
+      ],
+    };
+    expect(isCcsWebSearchHook(hook)).toBe(false);
+  });
+
+  test("Returns false when hooks array is missing", () => {
+    const hook = {
+      matcher: "WebSearch",
+    };
+    expect(isCcsWebSearchHook(hook)).toBe(false);
+  });
+
+  test("Returns false when hooks array is empty", () => {
+    const hook = {
+      matcher: "WebSearch",
+      hooks: [],
+    };
+    expect(isCcsWebSearchHook(hook)).toBe(false);
+  });
+
+  test("Returns false when command is missing", () => {
+    const hook = {
+      matcher: "WebSearch",
+      hooks: [{}],
+    };
+    expect(isCcsWebSearchHook(hook)).toBe(false);
+  });
+
+  test("Returns false when command is not a string", () => {
+    const hook = {
+      matcher: "WebSearch",
+      hooks: [
+        {
+          command: 123,
+        },
+      ],
+    };
+    expect(isCcsWebSearchHook(hook)).toBe(false);
+  });
+});
+
+describe("deduplicateCcsHooks", () => {
+  test("No-op when 0 CCS hooks (returns false)", () => {
+    const settings = {
+      hooks: {
+        PreToolUse: [
+          {
+            matcher: "SomeOtherMatcher",
+            hooks: [{ command: "other-command" }],
+          },
+        ],
+      },
+    };
+    const result = deduplicateCcsHooks(settings);
+    expect(result).toBe(false);
+    expect(settings.hooks.PreToolUse).toHaveLength(1);
+  });
+
+  test("No-op when 1 CCS hook (returns false)", () => {
+    const settings = {
+      hooks: {
+        PreToolUse: [
+          {
+            matcher: "WebSearch",
+            hooks: [
+              {
+                command: "node /home/user/.ccs/hooks/websearch-transformer/index.js",
+              },
+            ],
+          },
+        ],
+      },
+    };
+    const result = deduplicateCcsHooks(settings);
+    expect(result).toBe(false);
+    expect(settings.hooks.PreToolUse).toHaveLength(1);
+  });
+
+  test("Removes duplicates when 2+ CCS hooks (returns true, keeps first)", () => {
+    const settings = {
+      hooks: {
+        PreToolUse: [
+          {
+            matcher: "WebSearch",
+            hooks: [
+              {
+                command: "node /home/user/.ccs/hooks/websearch-transformer/index.js",
+              },
+            ],
+          },
+          {
+            matcher: "WebSearch",
+            hooks: [
+              {
+                command: "node C:\\Users\\user\\.ccs\\hooks\\websearch-transformer\\index.js",
+              },
+            ],
+          },
+          {
+            matcher: "WebSearch",
+            hooks: [
+              {
+                command: "node /another/path/.ccs/hooks/websearch-transformer/index.js",
+              },
+            ],
+          },
+        ],
+      },
+    };
+    const result = deduplicateCcsHooks(settings);
+    expect(result).toBe(true);
+    expect(settings.hooks.PreToolUse).toHaveLength(1);
+    expect(settings.hooks.PreToolUse[0]).toEqual({
+      matcher: "WebSearch",
+      hooks: [
+        {
+          command: "node /home/user/.ccs/hooks/websearch-transformer/index.js",
+        },
+      ],
+    });
+  });
+
+  test("Preserves non-CCS hooks in array", () => {
+    const nonCcsHook = {
+      matcher: "SomeOtherMatcher",
+      hooks: [{ command: "other-command" }],
+    };
+    const settings = {
+      hooks: {
+        PreToolUse: [
+          nonCcsHook,
+          {
+            matcher: "WebSearch",
+            hooks: [
+              {
+                command: "node /home/user/.ccs/hooks/websearch-transformer/index.js",
+              },
+            ],
+          },
+          {
+            matcher: "WebSearch",
+            hooks: [
+              {
+                command: "node C:\\Users\\user\\.ccs\\hooks\\websearch-transformer\\index.js",
+              },
+            ],
+          },
+        ],
+      },
+    };
+    const result = deduplicateCcsHooks(settings);
+    expect(result).toBe(true);
+    expect(settings.hooks.PreToolUse).toHaveLength(2);
+    expect(settings.hooks.PreToolUse[0]).toEqual(nonCcsHook);
+  });
+
+  test("Returns false when hooks is undefined", () => {
+    const settings = {};
+    const result = deduplicateCcsHooks(settings);
+    expect(result).toBe(false);
+  });
+
+  test("Returns false when PreToolUse is undefined", () => {
+    const settings = {
+      hooks: {},
+    };
+    const result = deduplicateCcsHooks(settings);
+    expect(result).toBe(false);
+  });
+
+  test("Handles multiple non-CCS hooks with duplicates", () => {
+    const settings = {
+      hooks: {
+        PreToolUse: [
+          {
+            matcher: "OtherMatcher1",
+            hooks: [{ command: "command1" }],
+          },
+          {
+            matcher: "WebSearch",
+            hooks: [
+              {
+                command: "node /path1/.ccs/hooks/websearch-transformer/index.js",
+              },
+            ],
+          },
+          {
+            matcher: "OtherMatcher2",
+            hooks: [{ command: "command2" }],
+          },
+          {
+            matcher: "WebSearch",
+            hooks: [
+              {
+                command: "node /path2/.ccs/hooks/websearch-transformer/index.js",
+              },
+            ],
+          },
+        ],
+      },
+    };
+    const result = deduplicateCcsHooks(settings);
+    expect(result).toBe(true);
+    expect(settings.hooks.PreToolUse).toHaveLength(3);
+    // First and third should be non-CCS hooks, second should be the first CCS hook
+    expect(settings.hooks.PreToolUse[0].matcher).toBe("OtherMatcher1");
+    expect(settings.hooks.PreToolUse[1].matcher).toBe("WebSearch");
+    expect(settings.hooks.PreToolUse[2].matcher).toBe("OtherMatcher2");
+  });
+
+  test("Edge case: Empty PreToolUse array", () => {
+    const settings = {
+      hooks: {
+        PreToolUse: [],
+      },
+    };
+    const result = deduplicateCcsHooks(settings);
+    expect(result).toBe(false);
+    expect(settings.hooks.PreToolUse).toHaveLength(0);
+  });
+});
diff --git a/src/utils/websearch/hook-config.ts b/src/utils/websearch/hook-config.ts
index 4b80e088..99276543 100644
--- a/src/utils/websearch/hook-config.ts
+++ b/src/utils/websearch/hook-config.ts
@@ -134,6 +134,10 @@ export function ensureHookConfig(): boolean {
         return normalized.includes('.ccs/hooks/websearch-transformer');
       });
 
+      // INVARIANT: webSearchHookIndex remains valid after deduplication because:
+      // - findIndex() returns the FIRST matching CCS hook
+      // - deduplicateCcsHooks() keeps the FIRST CCS hook and removes subsequent duplicates
+      // This means the index always points to the preserved hook.
       if (webSearchHookIndex !== -1) {
         // Hook exists - first clean up any duplicates
         const hadDuplicates = deduplicateCcsHooks(settings);