fix(transpiler): preserve null bytes in tagged template literals

The UnsignedCodepointIterator used `minInt(u32) = 0` as the error
sentinel for detecting invalid multibyte UTF-8 sequences. This collided
with the valid null byte codepoint (U+0000), causing null bytes to be
misidentified as decode errors and replaced with U+FFFD. The printer
then emitted the literal 6-character string `\uFFFD` in raw template
literals instead of preserving the null byte.

Fix: use `maxInt` instead of `minInt` as the error sentinel. For u32,
maxInt is 0xFFFFFFFF which is well beyond the valid Unicode range
(max 0x10FFFF) and can never collide with a valid codepoint.

Closes #27553

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/string/immutable/unicode.zig

@@ -101,7 +101,7 @@ pub fn NewCodePointIterator(comptime CodePointType_: type, comptime zeroValue: c
             }
 
             const cp_len = wtf8ByteSequenceLength(it.bytes[pos]);
-            const error_char = comptime std.math.minInt(CodePointType);
+            const error_char = comptime std.math.maxInt(CodePointType);
 
             const codepoint = @as(
                 CodePointType,

test/regression/issue/27553.test.ts

@@ -0,0 +1,79 @@
+import { expect, test } from "bun:test";
+import { bunEnv, bunExe, tempDir } from "harness";
+
+test("String.raw preserves null bytes in tagged template literals", async () => {
+  // Create a source file with a literal null byte (0x00) inside a tagged template literal.
+  // The null byte must be an actual byte in the source, not an escape sequence.
+  const source = Buffer.concat([
+    Buffer.from("const s = String.raw`"),
+    Buffer.from([0x00]),
+    Buffer.from("`;\nconsole.log(s.length);\nconsole.log(s.charCodeAt(0));\n"),
+  ]);
+
+  using dir = tempDir("issue-27553", {
+    "test.js": source,
+  });
+
+  await using proc = Bun.spawn({
+    cmd: [bunExe(), "test.js"],
+    env: bunEnv,
+    cwd: String(dir),
+    stdout: "pipe",
+    stderr: "pipe",
+  });
+
+  const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+
+  expect(stdout).toBe("1\n0\n");
+  expect(exitCode).toBe(0);
+});
+
+test("null bytes in untagged template literals are preserved", async () => {
+  const source = Buffer.concat([
+    Buffer.from("const s = `"),
+    Buffer.from([0x00]),
+    Buffer.from("`;\nconsole.log(s.length);\nconsole.log(s.charCodeAt(0));\n"),
+  ]);
+
+  using dir = tempDir("issue-27553-untagged", {
+    "test.js": source,
+  });
+
+  await using proc = Bun.spawn({
+    cmd: [bunExe(), "test.js"],
+    env: bunEnv,
+    cwd: String(dir),
+    stdout: "pipe",
+    stderr: "pipe",
+  });
+
+  const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+
+  expect(stdout).toBe("1\n0\n");
+  expect(exitCode).toBe(0);
+});
+
+test("null bytes in String.raw with surrounding content", async () => {
+  const source = Buffer.concat([
+    Buffer.from("const s = String.raw`hello"),
+    Buffer.from([0x00]),
+    Buffer.from("world`;\nconsole.log(s.length);\nconsole.log(s.charCodeAt(5));\n"),
+  ]);
+
+  using dir = tempDir("issue-27553-embedded", {
+    "test.js": source,
+  });
+
+  await using proc = Bun.spawn({
+    cmd: [bunExe(), "test.js"],
+    env: bunEnv,
+    cwd: String(dir),
+    stdout: "pipe",
+    stderr: "pipe",
+  });
+
+  const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+
+  expect(stdout).toBe("11\n0\n");
+  expect(exitCode).toBe(0);
+});