fix(lsp): address codex review round 1

Lifecycle and safety fixes from the external review:
- Observe abort while awaiting the initialize handshake, so a server that never
  replies can't defeat the tool-timeout signal.
- On an aborted request the server won't cancel, tear the instance down after a
  bounded grace instead of releasing the serialized queue with work still live
  (prevents overlapping document lifecycles).
- Re-check provider disposal after the canonicalize/read awaits so a query can't
  spawn an unowned server after disposeAll().
- Read the source through one open handle (stat + read on the same fd) to close
  the realpath-vs-read TOCTOU; decode with a fatal UTF-8 decoder so a legitimate
  U+FFFD is not misclassified as invalid.
- Validate and read the source BEFORE spawning a server (pre-start rejection).
- Require an explicit openClose for option-form textDocumentSync.
- Reject nonpositive teardown budgets and non-executable absolute commands at
  load; surface unsupported operations as structured LSP_UNSUPPORTED_OPERATION.
- Retain the stderr tail (fatal diagnostics land at exit), not the prefix.
- Catalog the seam vocabulary in docs/core-data-structures/lsp.md.

packages/lsp/lsp-local/tests/host.spec.ts

@@ -102,4 +102,12 @@ describe('readHostSource', () => {
     await writeFile(join(ws, 'bin.ts'), Buffer.from([0xff, 0xfe, 0x00]))
     await expect(readHostSource('bin.ts', ws, BIG)).rejects.toThrow(/not valid UTF-8/)
   })
+
+  it('keeps a valid U+FFFD replacement character in otherwise-valid UTF-8', async () => {
+    // The literal replacement char is valid UTF-8; a fatal decoder must accept it (only malformed
+    // byte sequences are rejected).
+    await writeFile(join(ws, 'repl.ts'), 'const s = "<22>"\n')
+    const source = await readHostSource('repl.ts', ws, BIG)
+    expect(source.text).toBe('const s = "<22>"\n')
+  })
 })