fix(lsp): address codex review round 3

Final review pass on the local provider:
- Tear the instance down when `initialize` REJECTS (utf-8 negotiation, malformed
  result), not only on abort, so a permanently-rejecting `ready` is never pooled.
- Use the group-aware SIGKILL on a framing failure so helpers are reached.
- Validate maxMessageBytes and maxDocumentBytes positive at load alongside the
  other byte caps.
- Fix the location renderer's outside-workspace check to match a `..` segment
  exactly, so an in-workspace path like `..generated/a.ts` stays relative.
- Document the accepted ancestor-directory symlink-swap TOCTOU under the
  trusted-host model (O_NOFOLLOW guards only the final component).

packages/lsp/lsp-local/src/connection.ts

@@ -187,9 +187,10 @@ export class LspConnection {
     try {
       messages = this.decoder.push(chunk)
     } catch (error) {
-      // A framing/JSON failure corrupts the stream position irrecoverably: fail the instance.
+      // A framing/JSON failure corrupts the stream position irrecoverably: fail the instance and
+      // SIGKILL the whole group so helper processes don't outlive the leader.
       this.fail(asError(error))
-      this.child.kill('SIGKILL')
+      this.signalGroup('SIGKILL')
       return
     }
     for (const message of messages) this.dispatch(message)