🐛 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.

development/testing.md

@@ -165,10 +165,13 @@ transport and protocol plumbing are not hand-rolled (see
   any order; the file is an integration test (~1.6 s) that needs `node_modules`.
   `didOpen` is handled in order before the completion request, so no settle
   delay is needed.
-- The Go server logs `context canceled` on stderr once per server as it shuts
-  down (nine lines per `test:unit` run). It is benign and predates the protocol
-  client — the hand-rolled client produced the same line — so it is left as is
-  rather than filtered out of the server's stderr.
+- The TS 7 Go server has a shutdown race: `handleExit` returns `io.EOF`, which
+  cancels the background context while `Session.updateWatches` is still running
+  (`internal/project/session.go`), so the bare `context canceled` error is
+  flushed straight to stderr once the outgoing queue is closed, and the server
+  exits 1 even though LSP expects 0 after `shutdown`. The helper therefore sends
+  `shutdown` and then closes stdin instead of sending `exit`; EOF makes the
+  server exit cleanly (code 0, no output), and the kill is kept as a fallback.
 
 ## Known issues