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>

src/hooks-config.ts

@@ -59,17 +59,30 @@ async function pathExistsForWrite(path: string): Promise<boolean> {
   }
 }
 
+/**
+ * Probe a path a per-spawn helper is about to touch. An "unknown" that is NOT near a
+ * stalled probe (the bulk cap refused it, or the stat failed with something other
+ * than ENOENT) gets ONE more bounded probe past the bulk cap, so a healthy path still
+ * answers while unrelated mounts are dead. Whatever is still "unknown" after that
+ * must be skipped by the caller, never touched with an unbounded `lstat`/`readFile`:
+ * on a dead mount those never settle, and each would hold a threadpool worker the
+ * probe's ceiling does not count.
+ */
+async function probeBeforeTouching(path: string) {
+  const state = await probePath(path);
+  if (state !== 'unknown' || isNearStalledPath(path)) return state;
+  return probePath(path, { pastCap: true });
+}
+
 /**
  * Whether a READ-side helper should leave `path` alone: it is definitely absent, or
- * it sits on a mount that is not answering (near a stalled probe). An "unknown"
- * that is NOT near a stalled probe (the probe was refused for capacity, or the stat
- * failed with something other than ENOENT) is not a reason to skip: the caller goes
- * on, and its own async read or write settles the question for that one path.
+ * it did not answer (a mount that is not responding, a refused probe, an unreadable
+ * path). See `probeBeforeTouching` for why "unknown" is a skip.
  */
 async function absentOrUnreachable(path: string): Promise<'absent' | 'unreachable' | false> {
-  const state = await probePath(path);
+  const state = await probeBeforeTouching(path);
   if (state === 'absent') return 'absent';
-  if (state === 'unknown' && isNearStalledPath(path)) return 'unreachable';
+  if (state === 'unknown') return 'unreachable';
   return false;
 }
 
@@ -852,19 +865,16 @@ export async function refreshStaleCodemanHooks(casePath: string): Promise<void>
  */
 export async function applyWorkspaceHooks(workspace: string, install?: boolean): Promise<void> {
   try {
-    const state = await probePath(workspace);
+    // "absent" stays absent: the install below would mkdir -p a deleted repo back
+    // into being. "unknown" is skipped too, never asked again with an unbounded
+    // lstat (see probeBeforeTouching).
+    const state = await probeBeforeTouching(workspace);
     if (state === 'absent') return;
     if (state === 'unknown') {
-      if (isNearStalledPath(workspace)) {
-        console.warn(
-          `[hooks] ${workspace} is not responding (unreachable mount?); Codeman hooks not checked or installed`
-        );
-        return;
-      }
-      // Any other "unknown" (the stall cap refused the probe, or the stat failed
-      // with something other than ENOENT) proves nothing about existence, and the
-      // install below would mkdir -p a deleted repo back into being: ask directly.
-      if (!(await pathExistsForWrite(workspace))) return;
+      console.warn(
+        `[hooks] ${workspace} is not responding or not readable (unreachable mount?); Codeman hooks not checked or installed`
+      );
+      return;
     }
     const shouldInstall = install ?? (await readWorkspaceHooksEnabled());
     await (shouldInstall ? ensureCodemanHooks(workspace) : refreshStaleCodemanHooks(workspace));