fix(pty,subprocess,lsp): address review round on cancellation, lookup, and contracts

- pty-local: a pre-write inspection rejection no longer releases a canceled
  send while its foreground SIGINT is in flight; the interrupt path retains
  the slot and its post-signal tail resumes polling. Regression pins the
  failure-shaped cancellation and a close-during-write release.
- pty-local: SEND_ACTIVE names which provider operation is draining; README
  states the never-settling-provider outcome (slot retained, close recovers).
- subprocess-local: resolveExecutable rejects relative paths containing
  separators instead of expanding them per PATH entry with a misleading
  not-found error; seam JSDoc pins the rule for every provider.
- subprocess-local: LocalTerminalHandle documents why the seam's
  in-flight-join promise holds without operation tracking.
- lsp-local: the oversized-source diagnostic reports the observed byte lower
  bound; README documents that processId: null trades away server-side
  orphan cleanup after a hard-killed harness.
- pty/subprocess seams: cross-reference the twin five-member signal unions.
- pty-local: TODO markers for send-state consolidation and initialize-race
  relocation.

packages/cordis/tool-cordis/src/api-catalog.ts

@@ -988,7 +988,7 @@ export const SERVICE_API: readonly ServiceApiEntry[] = [
     methods: [
       {
         signature: 'abstract resolveExecutable( command: string, env?: Readonly<Record<string, string>>, signal?: AbortSignal, ): Promise<string>',
-        jsDoc: '/**\n * Resolve one configured executable in this provider\'s execution world.\n * Absolute paths are verified; bare names use the provider\'s scrubbed PATH\n * plus explicit environment overrides.\n * @param command - absolute executable path or bare PATH name.\n * @param env - explicit environment entries used for lookup.\n * @param signal - aborts remote or local lookup.\n * @returns a canonical executable path.\n */',
+        jsDoc: '/**\n * Resolve one configured executable in this provider\'s execution world.\n * Absolute paths are verified; bare names use the provider\'s scrubbed PATH\n * plus explicit environment overrides. Relative paths containing separators\n * are rejected: no current consumer defines which directory they would\n * resolve against, so providers fail loud instead of guessing.\n * @param command - absolute executable path or bare PATH name.\n * @param env - explicit environment entries used for lookup.\n * @param signal - aborts remote or local lookup.\n * @returns a canonical executable path.\n */',
       },
       {
         signature: 'abstract spawn(spec: SubprocessSpawnSpec): SubprocessHandle',