diff --git a/apps/server/src/orchestration-v2/Adapters/AntigravityAdapterV2.test.ts b/apps/server/src/orchestration-v2/Adapters/AntigravityAdapterV2.test.ts
index 0f5670f1d2de0..63cbea5dc7f01 100644
--- a/apps/server/src/orchestration-v2/Adapters/AntigravityAdapterV2.test.ts
+++ b/apps/server/src/orchestration-v2/Adapters/AntigravityAdapterV2.test.ts
@@ -289,6 +289,25 @@ describe("AntigravityAdapterV2 client file system", () => {
         context("fs/read_text_file"),
       );
       assert.equal(pasted.content, "pasted");
+      yield* fileSystem.writeFileString(insidePath, "\uFEFFfirst\né中🙂\nlast");
+      const sliced = yield* readTextFile(
+        { sessionId: "mock-session-1", path: insidePath, line: 2, limit: 1 },
+        context("fs/read_text_file"),
+      );
+      assert.equal(sliced.content, "é中🙂");
+      yield* fileSystem.writeFileString(insidePath, "inside");
+      for (const [name, bytes] of [
+        ["image.png", new Uint8Array([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a])],
+        ["data.bin", new Uint8Array([0x61, 0, 0x62])],
+      ] as const) {
+        const binaryPath = path.join(workspace, name);
+        yield* fileSystem.writeFile(binaryPath, bytes);
+        const binaryRead = yield* readTextFile(
+          { sessionId: "mock-session-1", path: binaryPath },
+          context("fs/read_text_file"),
+        ).pipe(Effect.flip);
+        assert.propertyVal(binaryRead, "code", -32602, `${name} is refused as binary`);
+      }
 
       const outsideRead = yield* readTextFile(
         { sessionId: "mock-session-1", path: outsideFile },
diff --git a/apps/server/src/provider/acp/AntigravityClientFiles.ts b/apps/server/src/provider/acp/AntigravityClientFiles.ts
index c6079234d916c..225c2684d02b9 100644
--- a/apps/server/src/provider/acp/AntigravityClientFiles.ts
+++ b/apps/server/src/provider/acp/AntigravityClientFiles.ts
@@ -78,13 +78,25 @@ export const readAntigravityClientTextFile = Effect.fn("AntigravityClientFiles.r
         `File '${input.request.path}' is not a readable text file under ${CLIENT_FILE_MAX_BYTES} bytes.`,
       );
     }
-    const text = yield* input.fileSystem
-      .readFileString(filePath)
+    const bytes = yield* input.fileSystem
+      .readFile(filePath)
       .pipe(
         Effect.mapError(() =>
           EffectAcpErrors.AcpRequestError.internalError(`Could not read '${input.request.path}'.`),
         ),
       );
+    const text = yield* Effect.try({
+      try: () => new TextDecoder("utf-8", { fatal: true }).decode(bytes),
+      catch: () =>
+        EffectAcpErrors.AcpRequestError.invalidParams(
+          `File '${input.request.path}' is not a UTF-8 text file.`,
+        ),
+    });
+    if (text.includes("\0")) {
+      return yield* EffectAcpErrors.AcpRequestError.invalidParams(
+        `File '${input.request.path}' contains binary data.`,
+      );
+    }
     const line = input.request.line ?? undefined;
     const limit = input.request.limit ?? undefined;
     if (line === undefined && limit === undefined) {