fix(history): prevent duplicate prepend with seen-set and fetch guard; reset seen on channel switch

internal/httpapi/static/app.js

@@ -1,5 +1,5 @@
 // Shared state
-const st = { tailLoading: false, atBottom: true, current: '#', earliest: null, sse: null, channels: [], twLoaded: false };
+const st = { tailLoading: false, atBottom: true, current: '#', earliest: null, sse: null, channels: [], twLoaded: false, seen: new Set(), loadingHistory: false };
 
 function measureBars(){
   const hdr = document.querySelector('header.nav');
@@ -13,6 +13,8 @@ function escapeHtml(s){ return s.replace(/[&<>"]/g, c=>({'&':'&amp;','<':'&lt;',
 function linkify(t){ return t.replace(/https?:\/\/\S+/g, function(u){ return '<a href="' + u + '" target="_blank" rel="noopener">' + u + '</a>'; }); }
 function lineHTML(m){ const ts = '<span class=ts>[' + m.time + ']</span>'; const nick = '<b style="color:' + colorFor(m.author) + '">' + m.author + '</b>'; const body = escapeHtml(m.body); return ts + ' ' + nick + ': ' + linkify(body); }
 
+function msgKey(m){ return m.time + '|' + m.author + '|' + m.body; }
+
 function snapBottom(){ window.scrollTo(0, document.documentElement.scrollHeight); }
 function pinBottomMulti(){ if(!st.atBottom) return; [0,16,64,200].forEach(d=> setTimeout(()=>requestAnimationFrame(snapBottom), d)); }
 
@@ -28,8 +30,8 @@ async function api(path, params){
 
 function ensureTwitterWidgets(){ if(st.twLoaded) return; st.twLoaded = true; const s=document.createElement('script'); s.async=true; s.src='https://platform.twitter.com/widgets.js'; document.head.appendChild(s); }
 
-function appendBatch(arr){ const el=document.getElementById('tail'); const frag=document.createDocumentFragment(); arr.forEach(m=>{ const div=document.createElement('div'); div.className='msg'; div.innerHTML=lineHTML(m); frag.appendChild(div); processLinks(div); }); el.appendChild(frag); pinBottomMulti(); }
-function prependBatch(arr){ const el=document.getElementById('tail'); const oldTop=el.firstChild; const beforeTop = oldTop ? oldTop.getBoundingClientRect().top : 0; const frag=document.createDocumentFragment(); arr.forEach(m=>{ const div=document.createElement('div'); div.className='msg'; div.innerHTML=lineHTML(m); frag.appendChild(div); processLinks(div); }); el.insertBefore(frag, el.firstChild); if(oldTop){ const afterTop = oldTop.getBoundingClientRect().top; const delta = afterTop - beforeTop; window.scrollBy(0, delta); } }
+function appendBatch(arr){ const el=document.getElementById('tail'); const frag=document.createDocumentFragment(); arr.forEach(m=>{ const key=msgKey(m); if(st.seen.has(key)) return; st.seen.add(key); const div=document.createElement('div'); div.className='msg'; div.dataset.key=key; div.innerHTML=lineHTML(m); frag.appendChild(div); processLinks(div); }); el.appendChild(frag); pinBottomMulti(); }
+function prependBatch(arr){ const el=document.getElementById('tail'); const oldTop=el.firstChild; const beforeTop = oldTop ? oldTop.getBoundingClientRect().top : 0; const frag=document.createDocumentFragment(); arr.forEach(m=>{ const key=msgKey(m); if(st.seen.has(key)) return; st.seen.add(key); const div=document.createElement('div'); div.className='msg'; div.dataset.key=key; div.innerHTML=lineHTML(m); frag.appendChild(div); processLinks(div); }); el.insertBefore(frag, el.firstChild); if(oldTop){ const afterTop = oldTop.getBoundingClientRect().top; const delta = afterTop - beforeTop; window.scrollBy(0, delta); } }
 
 function processLinks(scope){ const links = scope.querySelectorAll('a[href]:not([data-card])'); links.forEach(a=>{ a.setAttribute('data-card','1');
   // Fetch and render card
@@ -77,8 +79,8 @@ function processLinks(scope){ const links = scope.querySelectorAll('a[href]:not(
 async function loadChannels(){ try{ const data = await api('/api/channels'); st.channels = data; renderChannels(); if(data.length>0){ selectChannel(data[0]); } } catch(e){} }
 function renderChannels(){ const list=document.getElementById('nav-chans') || document.getElementById('brand-chans')?.querySelector('ul'); if(!list) return; list.innerHTML=''; st.channels.forEach(c=>{ const li=document.createElement('li'); const a=document.createElement('a'); a.href='#'; a.textContent=c + (c===st.current? ' ✓':''); a.onclick=(ev)=>{ev.preventDefault(); selectChannel(c);}; li.appendChild(a); list.appendChild(li); }); }
 
-async function selectChannel(ch){ if(st.sse){ st.sse.close(); st.sse=null; } st.current=ch; renderChannels(); const el=document.getElementById('tail'); if(!el) return; el.textContent=''; const data = await api('/api/tail',{query:{channel:ch,limit:50}}); appendBatch(data); requestAnimationFrame(()=>{ snapBottom(); st.atBottom=true; }); st.earliest = data.length? data[0].time : null; startStream(); initScrollHandlers(); }
-function initScrollHandlers(){ const el=document.getElementById('tail'); if(!el) return; const onScroll = async ()=>{ const nearBottom = (window.innerHeight + window.pageYOffset + 16) >= document.documentElement.scrollHeight; st.atBottom = nearBottom; const nearTop = window.pageYOffset <= 4; if(nearTop && st.earliest){ try{ const older = await api('/api/history',{query:{channel:st.current,before:st.earliest,limit:50}}); if(older.length){ prependBatch(older); st.earliest = older[0].time; } } catch(e){} } }; window.removeEventListener('scroll', st._scrollHandler || (()=>{})); st._scrollHandler = onScroll; window.addEventListener('scroll', onScroll, {passive:true}); }
+async function selectChannel(ch){ if(st.sse){ st.sse.close(); st.sse=null; } st.current=ch; st.seen = new Set(); st.loadingHistory = false; renderChannels(); const el=document.getElementById('tail'); if(!el) return; el.textContent=''; const data = await api('/api/tail',{query:{channel:ch,limit:50}}); appendBatch(data); requestAnimationFrame(()=>{ snapBottom(); st.atBottom=true; }); st.earliest = data.length? data[0].time : null; startStream(); initScrollHandlers(); }
+function initScrollHandlers(){ const el=document.getElementById('tail'); if(!el) return; const onScroll = async ()=>{ const nearBottom = (window.innerHeight + window.pageYOffset + 16) >= document.documentElement.scrollHeight; st.atBottom = nearBottom; const nearTop = window.pageYOffset <= 4; if(nearTop && st.earliest && !st.loadingHistory){ try{ st.loadingHistory = true; const before = st.earliest; const older = await api('/api/history',{query:{channel:st.current,before:before,limit:50}}); if(older.length){ prependBatch(older); st.earliest = older[0].time; } } catch(e){} finally { st.loadingHistory = false; } } }; window.removeEventListener('scroll', st._scrollHandler || (()=>{})); st._scrollHandler = onScroll; window.addEventListener('scroll', onScroll, {passive:true}); }
 
 function startStream(){ const el=document.getElementById('tail'); if(!el) return; const url=new URL('/api/stream', window.location.origin); url.searchParams.set('channel', st.current); const es=new EventSource(url); st.sse=es; es.onmessage=(ev)=>{ try{ const m=JSON.parse(ev.data); appendBatch([m]); }catch(e){} }; es.onerror=()=>{ es.close(); st.sse=null; setTimeout(startStream, 3000); } }