Add `hung-dump.xsh` hang-triage tool to `scripts`

Snapshot diagnostic state for a hung `pytest`/`tractor`
process tree: for each pid (+ `pgrep -P` descendants) dump
the `ps` forest, `/proc/<pid>/wchan` + `stack` (kernel-side
blocked syscall), and `py-spy dump` (python-side stack).

Salvaged from the retired `wkt/warnings_cleanup` branch
(untracked, not upstream); homed here as standalone tooling.

(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code

scripts/hung-dump.xsh

@@ -0,0 +1,89 @@
+"""
+`hung-dump`: snapshot diagnostic state for a hung
+`pytest`/`tractor` process tree.
+
+For each pid (and all `pgrep -P` descendants), prints
+- `ps` forest header,
+- `/proc/<pid>/wchan` + `/proc/<pid>/stack` (kernel-side
+  blocked-on syscall),
+- `sudo py-spy dump` (python-side stack).
+
+Usage (xonsh):
+    source-foreign xonsh ./scripts/hung-dump.xsh
+    hung-dump <pid> [<pid> ...]
+
+Or just:
+    source ./scripts/hung-dump.xsh
+
+Tip — pipe to a paste buffer:
+    hung-dump 1336765 |t /tmp/hung.log
+"""
+
+def _hung_dump(args):
+    import subprocess as sp
+    from pathlib import Path
+
+    if not args:
+        print('usage: hung-dump <pid> [<pid> ...]')
+        return 1
+
+    def kids(pid):
+        try:
+            out = sp.check_output(
+                ['pgrep', '-P', str(pid)],
+                text=True,
+            )
+        except sp.CalledProcessError:
+            return []
+        return [int(p) for p in out.split() if p]
+
+    def tree(pid):
+        out = [pid]
+        for k in kids(pid):
+            out.extend(tree(k))
+        return out
+
+    pids = [
+        p
+        for r in (int(a) for a in args)
+        for p in tree(r)
+    ]
+
+    print(f'# tree: {pids}')
+    print('\n## ps forest')
+    $[ps -o pid,ppid,pgid,stat,cmd -p @(','.join(map(str, pids)))]
+
+    for p in pids:
+        print(f'\n## pid {p}')
+        for f in ('wchan', 'stack'):
+            path = Path(f'/proc/{p}/{f}')
+            try:
+                txt = path.read_text().rstrip()
+                print(f'-- /proc/{p}/{f} --\n{txt}')
+            except PermissionError:
+                # `stack` requires CAP_SYS_PTRACE; retry
+                # via sudo -n so creds-cached users don't
+                # block on prompt.
+                try:
+                    txt = sp.check_output(
+                        ['sudo', '-n', 'cat', str(path)],
+                        text=True,
+                        stderr=sp.DEVNULL,
+                    ).rstrip()
+                    print(f'-- /proc/{p}/{f} (via sudo) --\n{txt}')
+                except sp.CalledProcessError:
+                    print(
+                        f'-- /proc/{p}/{f}: '
+                        'PermissionError (try `sudo true` first) --'
+                    )
+            except FileNotFoundError:
+                print(f'-- /proc/{p}/{f}: proc gone --')
+
+        print(f'-- py-spy {p} --')
+        try:
+            $[sudo -n py-spy dump --pid @(p)]
+        except Exception as e:
+            print(f'  (py-spy failed: {e})')
+
+
+aliases['hung-dump'] = _hung_dump