gpu-worker: pool + queue health in (health) RPC response

bend co-lives with ecdsa-emit-pool on each foxhop production host.
When pool dies but bend stays up, .lsp cells pile un-emitted; bend
sits idle waiting for .ready bins that never arrive. Today's incident
took 30+ min to surface because feeder couldn't tell from bend health
alone — needed a separate SSH+pgrep per host.

Add pool/queue counts to (health) so one RPC returns the full picture:
  (ok (load-avg L) (vram-free-mb V) (uptime-ms U)
      (pool-procs P) (queue-ready R) (queue-emitting E) (queue-done D))

Helpers:
  health-pool-procs        pgrep -cf ecdsa-emit-pool
  health-queue-count EXT   ls $BEND_QUEUE_DIR/*.EXT | wc -l

BEND_QUEUE_DIR env var — set when bend is launched on a host with an
associated pool. Absent → queue counts return -1 (caller treats as
'unknown / not applicable').

Caller now has single-RPC view of bend + pool + queue health; feeder
can drop its separate SSH pool-watchdog probe in favor of the bend
(health) RPC field.

examples/cuda-fanout/gpu-worker.lsp

@@ -350,11 +350,98 @@
               ((eof-object? line) 0)
               (else (parse-leading-number line))))))))))
 
+;;; -- pool / queue health -------------------------------------------
+;;;
+;;; bend co-lives with an ecdsa-emit-pool on each foxhop production host.
+;;; When the pool dies but bend stays up, .lsp cells pile up un-emitted
+;;; and bend sits idle waiting for .ready bins that never arrive. The
+;;; feeder daemon polls bend's (health) to know whether to push more
+;;; work — adding pool/queue counts here means a single RPC tells the
+;;; feeder everything: bend health, pool health, queue depth.
+;;;
+;;; BEND_QUEUE_DIR env var — set when bend is launched on a host with
+;;; an associated pool. Absent on hosts that only run bend without a
+;;; pool. When absent, queue counts return -1 (caller treats as
+;;; "unknown / not applicable").
+
+(define (run-and-count cmd-args)
+  ;; Spawn cmd-args, read all stdout lines, return integer line count.
+  ;; Returns 0 on spawn failure. Used to count ls / pgrep output.
+  (cond
+    ((not (file-exists? (car cmd-args))) 0)
+    (else
+     (let ((pair (spawn-process-stdio (car cmd-args) (cdr cmd-args))))
+       (cond
+         ((eq? pair #f) 0)
+         (else
+          (let loop ((count 0))
+            (let ((line (read-line (cdr pair))))
+              (cond
+                ((or (eq? line #f) (eof-object? line))
+                 (close-port (car pair))
+                 (close-port (cdr pair))
+                 count)
+                (else (loop (+ count 1))))))))))))
+
+(define (health-pool-procs)
+  ;; Count of ecdsa-emit-pool processes on this host. 0 = pool dead.
+  (let* ((pair (spawn-process-stdio "/usr/bin/pgrep"
+                 '("-cf" "ecdsa-emit-pool"))))
+    (cond
+      ((eq? pair #f) 0)
+      (else
+       (let ((line (read-line (cdr pair))))
+         (close-port (car pair))
+         (close-port (cdr pair))
+         (cond
+           ((or (eq? line #f) (eof-object? line)) 0)
+           (else (or (string->number (parse-trim line)) 0))))))))
+
+(define (parse-trim s)
+  ;; Strip leading/trailing whitespace from a single-line string.
+  (let* ((n (string-length s))
+         (lo (let ll ((i 0))
+               (cond
+                 ((>= i n) i)
+                 ((char-whitespace? (string-ref s i)) (ll (+ i 1)))
+                 (else i))))
+         (hi (let lh ((i (- n 1)))
+               (cond
+                 ((< i lo) lo)
+                 ((char-whitespace? (string-ref s i)) (lh (- i 1)))
+                 (else (+ i 1))))))
+    (substring s lo hi)))
+
+(define (health-queue-count ext)
+  ;; Count of files matching $BEND_QUEUE_DIR/*.<ext>. Returns -1 when
+  ;; BEND_QUEUE_DIR env is unset (caller treats as unknown).
+  (let ((qdir (get-environment-variable "BEND_QUEUE_DIR")))
+    (cond
+      ((or (eq? qdir #f) (string=? qdir "")) -1)
+      (else
+       (let* ((pattern (string-append qdir "/*." ext))
+              (pair (spawn-process-stdio "/bin/sh"
+                      (list "-c"
+                            (string-append "ls " pattern " 2>/dev/null | wc -l")))))
+         (cond
+           ((eq? pair #f) 0)
+           (else
+            (let ((line (read-line (cdr pair))))
+              (close-port (car pair))
+              (close-port (cdr pair))
+              (cond
+                ((or (eq? line #f) (eof-object? line)) 0)
+                (else (or (string->number (parse-trim line)) 0)))))))))))
+
 (define (handle-health)
   (list 'ok
         (list 'load-avg (health-load-avg))
         (list 'vram-free-mb (health-vram-free-mb))
-        (list 'uptime-ms (current-time-ms))))
+        (list 'uptime-ms (current-time-ms))
+        (list 'pool-procs (health-pool-procs))
+        (list 'queue-ready (health-queue-count "ready"))
+        (list 'queue-emitting (health-queue-count "emitting"))
+        (list 'queue-done (health-queue-count "done"))))
 
 ;;; -- dispatch --------------------------------------------------