diff --git a/bun.lock b/bun.lock
index 9339758..ba2a9f4 100644
--- a/bun.lock
+++ b/bun.lock
@@ -13,6 +13,7 @@
         "@biomejs/biome": "^2.4.8",
         "@types/bun": "^1.3.10",
         "@types/node": "^25.5.0",
+        "typescript": "^5.9.3",
       },
     },
   },
@@ -49,6 +50,8 @@
 
     "commander": ["commander@12.1.0", "", {}, "sha512-Vw8qHK3bZM9y/P10u3Vib8o/DdkvA2OtPtZvD871QKjy74Wj1WSKFILMPRPSdUSx5RFK1arlJzEtA4PkFgnbuA=="],
 
+    "typescript": ["typescript@5.9.3", "", { "bin": { "tsc": "bin/tsc", "tsserver": "bin/tsserver" } }, "sha512-jl1vZzPDinLr9eUt3J/t7V6FgNEw9QjvBPdysz9KfQDD41fQrC2Y4vKQdiaUpFT4bXlb1RHhLpp8wtm6M5TgSw=="],
+
     "undici-types": ["undici-types@7.18.2", "", {}, "sha512-AsuCzffGHJybSaRrmr5eHr81mwJU3kjw6M+uprWvCXiNeN9SOGwQ3Jn8jb8m3Z6izVgknn1R0FTCEAP2QrLY/w=="],
 
     "zod": ["zod@4.1.8", "", {}, "sha512-5R1P+WwQqmmMIEACyzSvo4JXHY5WiAFHRMg+zBZKgKS+Q1viRa0C1hmUKtHltoIFKtIdki3pRxkmpP74jnNYHQ=="],
diff --git a/package.json b/package.json
index ed100af..4e8ea17 100644
--- a/package.json
+++ b/package.json
@@ -25,7 +25,8 @@
     "setup": "bash ./scripts/setup.sh",
     "lint": "biome check .",
     "lint:fix": "biome check . --fix",
-    "format": "biome format . --write"
+    "format": "biome format . --write",
+    "typecheck": "tsc --noEmit"
   },
   "dependencies": {
     "chalk": "^5.3.0",
@@ -35,7 +36,8 @@
   "devDependencies": {
     "@biomejs/biome": "^2.4.8",
     "@types/bun": "^1.3.10",
-    "@types/node": "^25.5.0"
+    "@types/node": "^25.5.0",
+    "typescript": "^5.9.3"
   },
   "keywords": [
     "opencode",
diff --git a/tests/close.test.ts b/tests/close.test.ts
index 0e5899f..0e1c251 100644
--- a/tests/close.test.ts
+++ b/tests/close.test.ts
@@ -149,14 +149,13 @@ describe("closeMultiModel", () => {
     // Freeze timestamp for deterministic tag name
     const fixedDate = new Date("2023-01-01T00:00:00.000Z");
     const OriginalDate = Date;
-    // @ts-expect-error
     global.Date = class extends OriginalDate {
       constructor() {
         super();
         // biome-ignore lint/correctness/noConstructorReturn: time-mocking required
         return fixedDate;
       }
-      toISOString() {
+      override toISOString() {
         return "2023-01-01T00:00:00.000Z";
       }
     } as any;
@@ -167,7 +166,6 @@ describe("closeMultiModel", () => {
       force: true,
     });
     // Restore Date
-    // @ts-expect-error
     global.Date = OriginalDate;
 
     expect(result.success).toBe(true);
@@ -241,14 +239,13 @@ describe("closeMultiModel", () => {
     // Freeze timestamp for deterministic tag name
     const fixedDate = new Date("2023-01-01T00:00:00.000Z");
     const OriginalDate = Date;
-    // @ts-expect-error
     global.Date = class extends OriginalDate {
       constructor() {
         super();
         // biome-ignore lint/correctness/noConstructorReturn: time-mocking required
         return fixedDate;
       }
-      toISOString() {
+      override toISOString() {
         return "2023-01-01T00:00:00.000Z";
       }
     } as any;
@@ -260,7 +257,6 @@ describe("closeMultiModel", () => {
     });
 
     // Restore Date after invocation
-    // @ts-expect-error
     global.Date = OriginalDate;
 
     // Verify result indicates successful cleanup
@@ -308,14 +304,13 @@ describe("closeMultiModel", () => {
     // Tag command will fail
     const fixedDate = new Date("2023-01-01T00:00:00.000Z");
     const OriginalDate = Date;
-    // @ts-expect-error
     global.Date = class extends OriginalDate {
       constructor() {
         super();
         // biome-ignore lint/correctness/noConstructorReturn: time-mocking required
         return fixedDate;
       }
-      toISOString() {
+      override toISOString() {
         return "2023-01-01T00:00:00.000Z";
       }
     } as any;
@@ -332,7 +327,6 @@ describe("closeMultiModel", () => {
       force: true,
     });
     // Restore Date
-    // @ts-expect-error
     global.Date = OriginalDate;
 
     expect(result.success).toBe(true);
@@ -374,14 +368,13 @@ describe("closeMultiModel", () => {
     // Freeze timestamp for deterministic tag name
     const fixedDate = new Date("2023-01-01T00:00:00.000Z");
     const OriginalDate = Date;
-    // @ts-expect-error
     global.Date = class extends OriginalDate {
       constructor() {
         super();
         // biome-ignore lint/correctness/noConstructorReturn: time-mocking required
         return fixedDate;
       }
-      toISOString() {
+      override toISOString() {
         return "2023-01-01T00:00:00.000Z";
       }
     } as any;
@@ -392,7 +385,6 @@ describe("closeMultiModel", () => {
       force: true,
     });
     // Restore Date
-    // @ts-expect-error
     global.Date = OriginalDate;
 
     expect(result.success).toBe(true);