Log AI requests, and stop hiding a failed job-file write

There is no nginx access log on this host and the CSRF prepend exits with an
empty body, so a request that never arrived and one that arrived and failed
were indistinguishable — the page just sat at "starting…". The job-file write
was also suppressed with @, which would produce exactly that hang: a token
returned for a job that can never report.

Plugin/unraid/api/ai.php

@@ -85,6 +85,21 @@ const VV_AI_JOB_TTL      = 3600;  // seconds before a job file is reaped
 $isPost = $_SERVER['REQUEST_METHOD'] === 'POST';
 $action = trim($isPost ? ($_POST['action'] ?? '') : ($_GET['action'] ?? 'stats'));
 
+// Request trace. There is no nginx access log on this host and the CSRF prepend exits with an
+// empty body, so without this there is no way to tell "the request never arrived" from "the
+// request arrived and failed" — which is exactly the ambiguity that made the first hang
+// undiagnosable. Excludes poll, which would otherwise write a line per second per open tab.
+function vv_ai_log(string $msg): void {
+    if (!is_dir('/var/log/varaverk')) return;
+    @file_put_contents('/var/log/varaverk/ai.log',
+        date('Y-m-d H:i:s') . ' ' . $msg . "\n", FILE_APPEND | LOCK_EX);
+}
+if ($action !== 'poll') {
+    vv_ai_log(sprintf('%s action=%s from=%s',
+        $_SERVER['REQUEST_METHOD'] ?? '?', $action ?: '(none)',
+        $_SERVER['REMOTE_ADDR'] ?? '?'));
+}
+
 // ── stats ─────────────────────────────────────────────────────────────────────
 if ($action === 'stats') {
     echo json_encode(['ok' => true, 'stats' => vv_ai_stats()]);
@@ -169,7 +184,13 @@ if ($action === 'ask') {
         echo json_encode(['ok' => false, 'error' => 'ai_chat_worker.php not found']); exit;
     }
 
-    @file_put_contents($jobFile, json_encode(['status' => 'pending']));
+    // Not suppressed: if the job file cannot be written the worker has nowhere to report and
+    // the page polls a token that will never resolve — which looks exactly like a hang.
+    if (file_put_contents($jobFile, json_encode(['status' => 'pending'])) === false) {
+        vv_ai_log('ask FAILED — cannot write ' . $jobFile);
+        echo json_encode(['ok' => false, 'error' => 'Cannot write job file to ' . VV_AI_JOB_DIR]);
+        exit;
+    }
 
     $cmd = 'nohup php ' . escapeshellarg($worker) . ' '
          . escapeshellarg($jobFile) . ' '
@@ -178,7 +199,10 @@ if ($action === 'ask') {
          . escapeshellarg($kind) . ' '
          . escapeshellarg(($_POST['think'] ?? '1') === '1' ? '1' : '0')
          . ' >/dev/null 2>&1 </dev/null &';
-    exec($cmd);
+    $out = []; $rc = 0;
+    exec($cmd, $out, $rc);
+    vv_ai_log(sprintf('ask token=%s rc=%d kind=%s q=%s',
+        substr($token, 0, 12), $rc, $kind ?: '-', mb_substr($question, 0, 80)));
 
     echo json_encode(['ok' => true, 'token' => $token]);
     exit;