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>

plugins/codeman/skills/codeman/reference/verbs.md

@@ -95,6 +95,9 @@ Differences from `quick-start` worth knowing before you debug one:
 - the id is at `.data.session.id`, not `.data.sessionId`;
 - `workingDir` must already exist (400 `INVALID_INPUT`, "workingDir does not exist"),
   and in multi-user mode must be inside the caller's own workspace (403 `FORBIDDEN`);
+  one that does not answer or cannot be read (an unreachable network mount, a
+  permission error) is 422 `OPERATION_FAILED`, never "does not exist", so do not
+  create a replacement for it;
 - hitting the session cap here is `OPERATION_FAILED`, where `quick-start` returns
   `SESSION_BUSY` for the identical condition.