Fix reader read-aloud races and add rows.Err checks

- reader.js: guard read-aloud against the loading placeholder (bodyReady)
  and invalidate stale speechSynthesis callbacks with a generation token
- storage: check rows.Err() after iterating story-view/content-length reads
- metrics: reuse placeholders() instead of duplicating the IN-clause builder

internal/web/static/js/reader.js

@@ -44,6 +44,7 @@
   var open = false;
   var contentCache = {}; // id -> {content, lede}
   var inflight = null;
+  var bodyReady = false; // true once the real article body is rendered (not the loading placeholder)
 
   // ---- read-state store -----------------------------------------------------
   function loadRead() {
@@ -264,6 +265,7 @@
   }
 
   function loadingBody(it) {
+    bodyReady = false; // read-aloud waits for the real body, not this placeholder
     renderBody(it, '<p style="opacity:.55">Loading the full story…</p>');
   }
 
@@ -274,6 +276,7 @@
       html = '<p style="opacity:.7">No article text was captured for this story. Open the original to read it.</p>';
     }
     renderBody(it, html);
+    bodyReady = true;
   }
 
   function fetchContent(it) {
@@ -483,6 +486,8 @@
 
   // ---- read aloud (signed-in only) ------------------------------------------
   var speaking = false;
+  var speakGen = 0;      // bumped on every stop/start; stale utterance callbacks that
+                         // fire after speechSynthesis.cancel() check it and no-op
   var speakParas = [];   // <p> elements being read, for highlight
   var speakQueue = [];   // remaining {el, text} to utter
   function speakingText() {
@@ -502,6 +507,7 @@
   }
   function stopSpeak() {
     if (!TTS_OK) return;
+    speakGen++;
     try { window.speechSynthesis.cancel(); } catch (e) {}
     speaking = false;
     speakQueue = [];
@@ -518,15 +524,18 @@
       speakParas.push(item.el);
       try { item.el.scrollIntoView({ block: "center", behavior: "smooth" }); } catch (e) {}
     }
+    var gen = speakGen;
     var u = new SpeechSynthesisUtterance(item.text);
-    u.onend = function () { if (speaking) speakNext(); };
-    u.onerror = function () { if (speaking) speakNext(); };
+    u.onend = function () { if (speaking && gen === speakGen) speakNext(); };
+    u.onerror = function () { if (speaking && gen === speakGen) speakNext(); };
     try { window.speechSynthesis.speak(u); } catch (e) { stopSpeak(); }
   }
   function startSpeak() {
     if (!TTS_OK) return;
+    if (!bodyReady) { toast("Still loading…"); return; }
     var parts = speakingText();
     if (!parts.length) { toast("Nothing to read yet"); return; }
+    speakGen++;
     try { window.speechSynthesis.cancel(); } catch (e) {}
     speaking = true;
     speakQueue = parts.slice();