fix(node:http): implement headersDistinct and trailersDistinct getters

Adds the missing `headersDistinct` and `trailersDistinct` getters to
IncomingMessage. These getters return headers/trailers with each value
wrapped in an array, matching Node.js behavior.

Closes #24268

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/js/node/_http_incoming.ts

@@ -396,6 +396,24 @@ const IncomingMessagePrototype = {
   set trailers(value) {
     // noop
   },
+  get headersDistinct() {
+    const headers = this.headers;
+    const distinct = {};
+    for (const key in headers) {
+      const value = headers[key];
+      distinct[key] = Array.isArray(value) ? value : [value];
+    }
+    return distinct;
+  },
+  get trailersDistinct() {
+    const trailers = this.trailers;
+    const distinct = {};
+    for (const key in trailers) {
+      const value = trailers[key];
+      distinct[key] = Array.isArray(value) ? value : [value];
+    }
+    return distinct;
+  },
   setTimeout(msecs, callback) {
     void this.take;
     const req = this[kHandle] || this[webRequestOrResponse];

test/regression/issue/24268.test.ts

@@ -0,0 +1,103 @@
+import { expect, test } from "bun:test";
+import { once } from "node:events";
+import http from "node:http";
+import type { AddressInfo } from "node:net";
+
+test("IncomingMessage.headersDistinct returns headers with array values", async () => {
+  let headersDistinct: any;
+  let trailersDistinct: any;
+  let headers: any;
+
+  await using server = http.createServer((req, res) => {
+    headers = req.headers;
+    headersDistinct = req.headersDistinct;
+    trailersDistinct = req.trailersDistinct;
+    res.end("ok");
+  });
+
+  await once(server.listen(0), "listening");
+  const PORT = (server.address() as AddressInfo).port;
+
+  // Make a request
+  const response = await fetch(`http://localhost:${PORT}/`, {
+    headers: {
+      "Content-Type": "application/json",
+      "X-Custom-Header": "test-value",
+      "User-Agent": "bun-test",
+    },
+  });
+
+  await response.text();
+
+  // headersDistinct should be an object (not null or undefined)
+  expect(typeof headersDistinct).toBe("object");
+  expect(headersDistinct).not.toBeNull();
+
+  // All header values should be arrays
+  for (const key in headersDistinct) {
+    expect(Array.isArray(headersDistinct[key])).toBe(true);
+    expect(headersDistinct[key].length).toBeGreaterThan(0);
+    for (const val of headersDistinct[key]) {
+      expect(typeof val).toBe("string");
+    }
+  }
+
+  // Check specific headers we sent
+  expect(headersDistinct["content-type"]).toEqual(["application/json"]);
+  expect(headersDistinct["x-custom-header"]).toEqual(["test-value"]);
+  expect(headersDistinct["user-agent"]).toEqual(["bun-test"]);
+
+  // Compare with headers - headersDistinct should have the same keys but all values as arrays
+  for (const key in headers) {
+    const headerValue = headers[key];
+    const distinctValue = headersDistinct[key];
+    expect(Array.isArray(distinctValue)).toBe(true);
+    if (Array.isArray(headerValue)) {
+      expect(distinctValue).toEqual(headerValue);
+    } else {
+      expect(distinctValue).toEqual([headerValue]);
+    }
+  }
+
+  // trailersDistinct should also be an object
+  expect(typeof trailersDistinct).toBe("object");
+  expect(trailersDistinct).not.toBeNull();
+});
+
+test("IncomingMessage.headersDistinct handles set-cookie arrays correctly", async () => {
+  let responseHeadersDistinct: any;
+  let responseHeaders: any;
+
+  await using server = http.createServer((req, res) => {
+    res.setHeader("Set-Cookie", ["session=abc123", "token=xyz789"]);
+    res.end("ok");
+  });
+
+  await once(server.listen(0), "listening");
+  const PORT = (server.address() as AddressInfo).port;
+
+  // Use http.request to get access to the response's IncomingMessage
+  await new Promise<void>((resolve, reject) => {
+    const req = http.request(`http://localhost:${PORT}/`, res => {
+      responseHeaders = res.headers;
+      responseHeadersDistinct = res.headersDistinct;
+
+      res.on("data", () => {});
+      res.on("end", () => {
+        resolve();
+      });
+      res.on("error", reject);
+    });
+
+    req.on("error", reject);
+    req.end();
+  });
+
+  // headers should have set-cookie as an array
+  expect(Array.isArray(responseHeaders["set-cookie"])).toBe(true);
+  expect(responseHeaders["set-cookie"]).toEqual(["session=abc123", "token=xyz789"]);
+
+  // headersDistinct should also have set-cookie as an array (same format)
+  expect(Array.isArray(responseHeadersDistinct["set-cookie"])).toBe(true);
+  expect(responseHeadersDistinct["set-cookie"]).toEqual(["session=abc123", "token=xyz789"]);
+});