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)

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

@@ -114,8 +114,12 @@ export function apply(ctx: Context, config: Config): void {
   // nonpositive value would let a server that ignores shutdown hang disposal forever. Fail at load.
   assertPositiveInteger('shutdownTimeoutMs', resolved.shutdownTimeoutMs)
   assertPositiveInteger('killGraceMs', resolved.killGraceMs)
-  // A nonpositive stderr cap defeats the retained-tail bound (`slice(-0)` keeps everything).
+  // Byte caps must be positive: a nonpositive stderr cap defeats the retained-tail bound
+  // (`slice(-0)` keeps everything), `maxMessageBytes: 0` makes every response fatal, and a bad
+  // document cap fails later in the read path instead of at load.
   assertPositiveInteger('maxStderrBytes', resolved.maxStderrBytes)
+  assertPositiveInteger('maxMessageBytes', resolved.maxMessageBytes)
+  assertPositiveInteger('maxDocumentBytes', resolved.maxDocumentBytes)
   const childEnv = buildChildEnv(resolved.env)
   // Resolve the executable eagerly so a misconfigured command fails at load, not on first query.
   const executable = resolveExecutable(resolved.command, childEnv)

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

@@ -108,16 +108,17 @@ export class LspInstance {
     if (this.disposed) throw new Error('LSP instance was disposed')
     /* v8 ignore next -- the abortable queue wait rejects a pre-aborted signal before runQuery; this is a belt-and-suspenders guard. */
     if (signal?.aborted) throw abortError(signal)
-    // Observe abort during the handshake wait: a server that never answers `initialize` must not
-    // block the tool-timeout signal here (the timeout policy awaits our quiescence, not the promise).
-    // If abort wins, the handshake is still pending on a live process, so tear the instance down —
-    // otherwise its poisoned `ready` would make every later query for this workspace re-wait.
+    // Observe abort during the handshake wait, and never pool a poisoned instance: if the wait ends
+    // in failure — an abort on a still-pending handshake, OR `initialize` rejecting (utf-8
+    // negotiation, malformed result) without the process exiting — tear the instance down so a
+    // permanently-rejecting/pending `ready` can't make every later query for this workspace fail.
     try {
       await this.abortable(this.ready, signal)
     } catch (error) {
-      if (signal?.aborted && !this.dead) {
+      if (!this.dead) {
         this.disposed = true
-        await this.tearDown(abortError(signal))
+        /* v8 ignore next -- ready rejects with an Error (abort reason or initialize failure); the String() fallback is defensive. */
+        await this.tearDown(error instanceof Error ? error : new Error(String(error)))
       }
       throw error
     }