🐛 Stop the LSP shutdown context-canceled log

The TS 7 Go server races Session.updateWatches against the exit
notification; handleExit returns io.EOF, the background context is
cancelled, and the bare error is flushed to stderr once the outgoing
queue closes (server.go / logger.go). Send shutdown and close stdin
instead: EOF makes the server exit cleanly (code 0, no output), with the
kill kept as a fallback. testing.md records the cause.

src/util/__tests__/lsp-completion.ts

@@ -11,7 +11,6 @@ import {
     ConfigurationRequest,
     createMessageConnection,
     DidOpenTextDocumentNotification,
-    ExitNotification,
     InitializedNotification,
     InitializeRequest,
     type MessageConnection,
@@ -140,18 +139,24 @@ export class LspSession {
             );
     }
 
-    /** `shutdown` + `exit`, then kill the server; safe after a failed probe. */
+    /** `shutdown` + close stdin, then kill the server; safe after a failed probe. */
     public close(): Promise<void> {
-        return this.#connection
-            .sendRequest(ShutdownRequest.type)
-            .then(() =>
-                this.#connection.sendNotification(ExitNotification.type),
-            )
-            .then(() => delay(EXIT_DELAY_MS))
-            .finally(() => {
-                this.#connection.dispose();
-                this.#child.kill();
-            });
+        return (
+            this.#connection
+                .sendRequest(ShutdownRequest.type)
+                // The TS 7 Go server races a background task against the `exit`
+                // notification and logs a bare `context canceled` to stderr as it
+                // tears down (see development/testing.md § Autocomplete). EOF on
+                // stdin shuts it down cleanly instead: exit 0, no output.
+                .then(() => {
+                    this.#child.stdin.end();
+                })
+                .then(() => delay(EXIT_DELAY_MS))
+                .finally(() => {
+                    this.#connection.dispose();
+                    this.#child.kill();
+                })
+        );
     }
 
     #ensureInitialized(): Promise<void> {