fix(cases): bounded path probe landing fixes (#516)

- hooks-config: a probe the bulk cap refused gets ONE bounded re-probe past the
  cap (probeBeforeTouching), and whatever is still unknown is skipped. The
  per-spawn hook and statusLine helpers used to fall back to an unbounded
  lstat/readFile there, which on a dead workspace never settled and could take
  the last threadpool workers (and hang the boot hook sweep). New test: cap
  engaged, stat/lstat/readFile hanging on two more paths; both helpers return.
- describeUnknownPath()/unknownPathReason(): POST /api/sessions, quick-start and
  GET /api/cases/:name now say a folder was not checked (other mounts are still
  not answering) instead of blaming a healthy folder at the stall ceiling.
  errorCodes unchanged.
- #535 x #516: Create in a custom folder probes the parent through the bounded
  probe before realpath/stat/lstat/readdir touch it; an unknown parent is 422
  OPERATION_FAILED (UNREACHABLE) within the probe timeout. New test.
- Docs: MAX_STALLED default is 2 (follows UV_THREADPOOL_SIZE), CaseInfo
  .unreachable covers a refused probe, the boot sweep skips an unanswering
  workspace, a CLAUDE.md gotcha for bounded probes, verbs.md documents the 422
  (plugin mirror synced), api-reference documents the custom-folder 422.
- Tests: the launcher case-lookup describe is no longer nested in the Grok
  block, and the cap-below-ceiling test no longer depends on an inherited
  UV_THREADPOOL_SIZE / CODEMAN_PATH_PROBE_MAX_STALLED.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/api-reference.md

@@ -709,7 +709,7 @@ The target is judged before anything is written:
 - It must be absolute with no `..` and none of the shell metacharacters a session working directory is rejected for (spaces are fine). `400 INVALID_INPUT` otherwise.
 - It must not be a system directory (`/etc`, `/usr`, `/proc`, ...), the home folder itself, Codeman's own data folder, or a credential/config tree (`~/.ssh`, `~/.aws`, `~/.claude`, ...). Judged on the path as typed and on its symlink-resolved form, against both the given and the symlink-resolved roots. `400`.
 - It must not be, or be inside, the cases directory (the caller's own and the shared one): a case there is a plain create without `path`. `400`.
-- Its parent must already exist (one folder is created, never a chain): `404 NOT_FOUND`.
+- Its parent must already exist (one folder is created, never a chain): `404 NOT_FOUND`. A parent that does not answer (an unreachable network mount) or cannot be read is `422 OPERATION_FAILED`, checked through the bounded path probe before anything else touches it.
 - The folder must not exist, or must be an **empty** directory; a folder with contents is Link Existing's job: `409 ALREADY_EXISTS`. A symlink or a plain file at the target is `400`.
 - `409 ALREADY_EXISTS` also for a case name already in use (in the cases dir or the registry) and for a folder that is already a case.