diff --git a/.github/workflows/build-core.yml b/.github/workflows/build-core.yml
index 6464254a2..0e3b108c4 100644
--- a/.github/workflows/build-core.yml
+++ b/.github/workflows/build-core.yml
@@ -7,8 +7,8 @@ on:
 
 jobs:
   build:
-    name: Core - Build and Test
-    runs-on: ubuntu-latest
+    name: Build Core Library
+    runs-on: macos-latest
     steps:
       - name: Checkout code
         uses: actions/checkout@v4
@@ -31,7 +31,62 @@ jobs:
           cd packages/core
           bun run build
 
-      - name: Run tests
+      - name: Run native tests
         run: |
           cd packages/core
-          bun run test
+          bun run test:native
+
+      - name: Upload build artifacts
+        uses: actions/upload-artifact@v4
+        with:
+          name: build-artifacts
+          path: |
+            packages/core/dist
+            packages/core/node_modules/@opentui/core-*
+          retention-days: 1
+
+  test:
+    name: Test - ${{ matrix.os }} (${{ matrix.arch }})
+    needs: build
+    runs-on: ${{ matrix.runner }}
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: macos
+            arch: arm64
+            runner: macos-latest
+          - os: macos
+            arch: x64
+            runner: macos-13
+          - os: linux
+            arch: x64
+            runner: ubuntu-latest
+          - os: linux
+            arch: arm64
+            runner: ubuntu-24.04-arm
+          - os: windows
+            arch: x64
+            runner: windows-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Setup Bun
+        uses: oven-sh/setup-bun@v2
+        with:
+          bun-version: latest
+
+      - name: Download build artifacts
+        uses: actions/download-artifact@v4
+        with:
+          name: build-artifacts
+          path: packages/core
+
+      - name: Install dependencies
+        run: bun install
+
+      - name: Run TypeScript tests
+        run: |
+          cd packages/core
+          bun run test:js
diff --git a/packages/core/src/lib/tree-sitter/cache.test.ts b/packages/core/src/lib/tree-sitter/cache.test.ts
index fefdc0426..e602cb061 100644
--- a/packages/core/src/lib/tree-sitter/cache.test.ts
+++ b/packages/core/src/lib/tree-sitter/cache.test.ts
@@ -212,7 +212,9 @@ describe("TreeSitterClient Caching", () => {
   })
 
   test("should handle directory creation errors gracefully", async () => {
-    const invalidDataPath = "/invalid/path/that/cannot/be/created"
+    // Use a null byte in the path to ensure it is invalid on all platforms.
+    // This helps test error handling for directory creation in a cross-platform way.
+    const invalidDataPath = "/invalid\x00/path/with/null/byte"
     const client = new TreeSitterClient({ dataPath: invalidDataPath })
 
     await expect(client.initialize()).rejects.toThrow()
diff --git a/packages/core/src/lib/tree-sitter/client.ts b/packages/core/src/lib/tree-sitter/client.ts
index 2cb702c43..c3306d51c 100644
--- a/packages/core/src/lib/tree-sitter/client.ts
+++ b/packages/core/src/lib/tree-sitter/client.ts
@@ -12,10 +12,9 @@ import type {
   SimpleHighlight,
 } from "./types"
 import { getParsers } from "./default-parsers"
-import { resolve, isAbsolute } from "path"
+import { resolve, isAbsolute, parse } from "path"
 import { existsSync } from "fs"
 import { registerEnvVar, env } from "../env"
-import { parse } from "path"
 
 registerEnvVar({
   name: "OTUI_TREE_SITTER_WORKER_PATH",
diff --git a/packages/core/src/renderables/Text.test.ts b/packages/core/src/renderables/Text.test.ts
index 7a66adb8b..de216adc3 100644
--- a/packages/core/src/renderables/Text.test.ts
+++ b/packages/core/src/renderables/Text.test.ts
@@ -32,6 +32,8 @@ describe("TextRenderable Selection", () => {
       })
 
       await currentMouse.drag(text.x, text.y, text.x + 5, text.y)
+      // Add delay to ensure all drag events are processed on slow CI machines
+      await new Promise((resolve) => setTimeout(resolve, 50))
       await renderOnce()
 
       const selectedText = text.getSelectedText()
@@ -46,6 +48,8 @@ describe("TextRenderable Selection", () => {
 
       // Select "Hello 🌍" (7 characters: H,e,l,l,o, ,🌍)
       await currentMouse.drag(text.x, text.y, text.x + 7, text.y)
+      // Add delay to ensure all drag events are processed on slow CI machines
+      await new Promise((resolve) => setTimeout(resolve, 50))
       await renderOnce()
 
       const selectedText = text.getSelectedText()
diff --git a/packages/core/src/testing/mock-keys.test.ts b/packages/core/src/testing/mock-keys.test.ts
index 7293bec91..0cecb6373 100644
--- a/packages/core/src/testing/mock-keys.test.ts
+++ b/packages/core/src/testing/mock-keys.test.ts
@@ -184,7 +184,7 @@ describe("mock-keys", () => {
 
     expect(timestamps).toHaveLength(2)
     expect(timestamps[1] - timestamps[0]).toBeGreaterThanOrEqual(8) // Allow some tolerance
-    expect(timestamps[1] - timestamps[0]).toBeLessThan(20)
+    expect(timestamps[1] - timestamps[0]).toBeLessThan(50) // Increased tolerance for CI/slower machines
   })
 
   test("pressKey with shift modifier", () => {
diff --git a/packages/core/src/zig/renderer.zig b/packages/core/src/zig/renderer.zig
index f3f921105..b1daa8fed 100644
--- a/packages/core/src/zig/renderer.zig
+++ b/packages/core/src/zig/renderer.zig
@@ -39,6 +39,32 @@ pub const DebugOverlayCorner = enum {
     bottomRight,
 };
 
+const StdoutWriter = union(enum) {
+    real: std.io.BufferedWriter(4096, std.fs.File.Writer),
+    null: void,
+
+    pub fn writer(self: *StdoutWriter) Writer {
+        return .{ .context = self };
+    }
+
+    pub fn flush(self: *StdoutWriter) !void {
+        switch (self.*) {
+            .real => |*w| try w.flush(),
+            .null => {},
+        }
+    }
+
+    const WriteError = std.fs.File.WriteError;
+    const Writer = std.io.Writer(*StdoutWriter, WriteError, write);
+
+    fn write(self: *StdoutWriter, data: []const u8) WriteError!usize {
+        switch (self.*) {
+            .real => |*w| return w.writer().write(data),
+            .null => return data.len,
+        }
+    }
+};
+
 pub const CliRenderer = struct {
     width: u32,
     height: u32,
@@ -80,7 +106,7 @@ pub const CliRenderer = struct {
     lastRenderTime: i64,
     allocator: Allocator,
     renderThread: ?std.Thread = null,
-    stdoutWriter: std.io.BufferedWriter(4096, std.fs.File.Writer),
+    stdoutWriter: StdoutWriter,
     debugOverlay: struct {
         enabled: bool,
         corner: DebugOverlayCorner,
@@ -141,17 +167,9 @@ pub const CliRenderer = struct {
         const currentBuffer = try OptimizedBuffer.init(allocator, width, height, .{ .pool = pool, .width_method = .unicode, .id = "current buffer" }, graphemes_data, display_width);
         const nextBuffer = try OptimizedBuffer.init(allocator, width, height, .{ .pool = pool, .width_method = .unicode, .id = "next buffer" }, graphemes_data, display_width);
 
-        const stdoutWriter = if (testing) blk: {
-            // In testing mode, use /dev/null to discard output
-            const devnull = std.fs.openFileAbsolute("/dev/null", .{ .mode = .write_only }) catch {
-                // Fallback to stdout if /dev/null can't be opened
-                logger.warn("Failed to open /dev/null, falling back to stdout\n", .{});
-                break :blk std.io.BufferedWriter(4096, std.fs.File.Writer){ .unbuffered_writer = std.io.getStdOut().writer() };
-            };
-            break :blk std.io.BufferedWriter(4096, std.fs.File.Writer){ .unbuffered_writer = devnull.writer() };
-        } else blk: {
+        const stdoutWriter: StdoutWriter = if (testing) .{ .null = {} } else blk: {
             const stdout = std.io.getStdOut();
-            break :blk std.io.BufferedWriter(4096, std.fs.File.Writer){ .unbuffered_writer = stdout.writer() };
+            break :blk .{ .real = std.io.BufferedWriter(4096, std.fs.File.Writer){ .unbuffered_writer = stdout.writer() } };
         };
 
         // stat sample arrays