test(language-server): cover didClose region-cache clear end-to-end

Replaces the direct-call-only test with an over-stdio test that exercises
server.ts's didClose handler itself, so it fails if the
clearHtmlRegionCache wiring is removed or misparameterized.

packages/language-server/test/language-server.test.ts

@@ -217,3 +217,91 @@ test("coalesces rapid document changes into one pending diagnostic analysis", as
   process.kill();
   await process.exited;
 });
+
+test("didClose drops the region cache so a reopened document at the same version is rescanned", async () => {
+  // Regression coverage for the didClose wiring in server.ts: without the
+  // clearHtmlRegionCache(uri) call there, a document that closes and reopens
+  // at version 1 (a common restart point) matches the stale cache entry from
+  // the prior session. Open first WITHOUT a view block (caching "no HTML
+  // here" for this uri/version), close, then reopen the SAME uri at the SAME
+  // version WITH a view block covering the same offset: correct behaviour
+  // rescans and finds it, a stale cache still says "no HTML here" and
+  // suppresses the completions entirely.
+  const process = Bun.spawn(
+    ["bun", "run", fileURLToPath(new URL("../src/server.ts", import.meta.url))],
+    { stdin: "pipe", stdout: "pipe", stderr: "pipe" },
+  );
+  const uri = "file:///reopen.wrn";
+  const withoutView = `page A {
+  functions {
+    x
+  }
+}
+`;
+  const withView = `page A {
+  view {
+    <
+  }
+}
+`;
+  const position = { line: 2, character: 5 };
+  const reader = process.stdout.getReader();
+  let output = "";
+  async function readUntil(marker: string): Promise<void> {
+    while (!output.includes(marker)) {
+      const chunk = await reader.read();
+      if (chunk.done) break;
+      output += new TextDecoder().decode(chunk.value);
+    }
+  }
+
+  process.stdin.write(packet({ jsonrpc: "2.0", id: 1, method: "initialize", params: {} }));
+  await process.stdin.flush();
+  await readUntil('"id":1');
+
+  process.stdin.write(
+    packet({
+      jsonrpc: "2.0",
+      method: "textDocument/didOpen",
+      params: { textDocument: { uri, version: 1, text: withoutView } },
+    }),
+  );
+  process.stdin.write(
+    packet({
+      jsonrpc: "2.0",
+      id: 2,
+      method: "textDocument/completion",
+      params: { textDocument: { uri }, position },
+    }),
+  );
+  await process.stdin.flush();
+  await readUntil('"id":2');
+  const firstReply = output.slice(output.indexOf('"id":2'));
+  expect(firstReply).not.toContain('"label":"div"');
+
+  process.stdin.write(
+    packet({ jsonrpc: "2.0", method: "textDocument/didClose", params: { textDocument: { uri } } }),
+  );
+  process.stdin.write(
+    packet({
+      jsonrpc: "2.0",
+      method: "textDocument/didOpen",
+      params: { textDocument: { uri, version: 1, text: withView } },
+    }),
+  );
+  process.stdin.write(
+    packet({
+      jsonrpc: "2.0",
+      id: 3,
+      method: "textDocument/completion",
+      params: { textDocument: { uri }, position },
+    }),
+  );
+  await process.stdin.flush();
+  await readUntil('"id":3');
+  const secondReply = output.slice(output.indexOf('"id":3'));
+  expect(secondReply).toContain('"label":"div"');
+
+  process.kill();
+  await process.exited;
+});