Add per-day session timeline and collapse cache-breaks list

- analyze-sessions.mjs: track per-session start/end/tokens and emit
  by_day[] in JSON output (date, dow, tokens, peak concurrency,
  per-session spans). Hoist shared token-sum in commit loop.
- template.html: new "session timeline by day" section — horizontal
  day pills (% of total + session count) drive a lane-packed gantt of
  concurrent sessions, colored by project, with hover details and
  ←/→ keyboard nav. Extract drillList() helper and use it for both
  top-prompts and cache-breaks (5 visible + "show more" toggle).

plugins/session-report/skills/session-report/analyze-sessions.mjs

@@ -166,6 +166,7 @@ const toolUseIdToPrompt = new Map() // tool_use id -> promptKey (Agent spawned d
 const agentIdToPrompt = new Map() // agentId -> promptKey
 const prompts = new Map() // promptKey -> { text, ts, project, sessionId, ...usage }
 const sessionTurns = new Map() // sessionId -> [promptKey, ...] in transcript order
+const sessionSpans = new Map() // sessionId -> {project, firstTs, lastTs, tokens}
 
 function promptRecord(key, init) {
   let r = prompts.get(key)
@@ -333,11 +334,29 @@ async function processFile(p, info, buckets) {
     }
   }
 
+  // session span (for by_day timeline) — subagent files roll into parent sessionId
+  let span = sessionSpans.get(info.sessionId)
+  if (!span) {
+    span = { project: info.project, firstTs: null, lastTs: null, tokens: 0 }
+    sessionSpans.set(info.sessionId, span)
+  }
+  if (firstTs !== null) {
+    if (span.firstTs === null || firstTs < span.firstTs) span.firstTs = firstTs
+    if (span.lastTs === null || lastTs > span.lastTs) span.lastTs = lastTs
+  }
+
   // commit API calls
   for (const [key, { usage, ts, skill, prompt }] of fileApiCalls) {
     if (key && seenRequestIds.has(key)) continue
     seenRequestIds.add(key)
 
+    const tot =
+      (usage.input_tokens || 0) +
+      (usage.cache_creation_input_tokens || 0) +
+      (usage.cache_read_input_tokens || 0) +
+      (usage.output_tokens || 0)
+    span.tokens += tot
+
     const targets = [overall, project]
     if (subagent) targets.push(subagent)
     if (skill && skillStats) {
@@ -359,11 +378,6 @@ async function processFile(p, info, buckets) {
 
     // subagent token accounting on parent buckets
     if (info.kind === 'subagent') {
-      const tot =
-        (usage.input_tokens || 0) +
-        (usage.cache_creation_input_tokens || 0) +
-        (usage.cache_read_input_tokens || 0) +
-        (usage.output_tokens || 0)
       overall.subagentTokens += tot
       project.subagentTokens += tot
       if (subagent) subagent.subagentTokens += tot
@@ -656,10 +670,55 @@ function printJson({ overall, perProject, perSubagent, perSkill }) {
       [...perSkill].map(([k, v]) => [k, summarize(v)]),
     ),
     top_prompts: topPrompts(100),
+    by_day: buildByDay(),
   }
   process.stdout.write(JSON.stringify(out, null, 2) + '\n')
 }
 
+// Group sessions into local-date buckets for the timeline view. A session is
+// placed on the day its first message landed; tokens for that session (incl.
+// subagents) count toward that day even if it ran past midnight.
+function buildByDay() {
+  const DOW = ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat']
+  const days = new Map() // yyyy-mm-dd -> {date, dow, tokens, sessions:[]}
+  for (const [id, s] of sessionSpans) {
+    if (s.firstTs === null || s.tokens === 0) continue
+    const d0 = new Date(s.firstTs)
+    const key = `${d0.getFullYear()}-${String(d0.getMonth() + 1).padStart(2, '0')}-${String(d0.getDate()).padStart(2, '0')}`
+    let day = days.get(key)
+    if (!day) {
+      day = { date: key, dow: DOW[d0.getDay()], tokens: 0, sessions: [] }
+      days.set(key, day)
+    }
+    const base = new Date(
+      d0.getFullYear(),
+      d0.getMonth(),
+      d0.getDate(),
+    ).getTime()
+    day.tokens += s.tokens
+    day.sessions.push({
+      id,
+      project: s.project,
+      tokens: s.tokens,
+      start_min: Math.max(0, Math.round((s.firstTs - base) / 60000)),
+      end_min: Math.max(1, Math.round((s.lastTs - base) / 60000)),
+    })
+  }
+  for (const d of days.values()) {
+    // peak concurrency via 10-min buckets, capped at 24h for display
+    const b = new Array(144).fill(0)
+    for (const s of d.sessions) {
+      const lo = Math.min(143, Math.floor(s.start_min / 10))
+      const hi = Math.min(144, Math.ceil(Math.min(s.end_min, 1440) / 10))
+      for (let i = lo; i < hi; i++) b[i]++
+    }
+    d.peak = Math.max(0, ...b)
+    d.peak_at_min = d.peak > 0 ? b.indexOf(d.peak) * 10 : 0
+    d.sessions.sort((a, b) => a.start_min - b.start_min)
+  }
+  return [...days.values()].sort((a, b) => a.date.localeCompare(b.date))
+}
+
 function promptTotal(r) {
   return (
     r.inputUncached + r.inputCacheCreate + r.inputCacheRead + r.outputTokens

plugins/session-report/skills/session-report/template.html

@@ -102,6 +102,42 @@
              color: var(--dim); margin: 6px 0; }
   .callout b, .callout code { color: var(--term-fg); }
 
+  /* ——— day pills + session gantt ——— */
+  .days { display: flex; gap: 8px; flex-wrap: wrap; margin-bottom: 14px; }
+  .dpill { flex: 1; min-width: 84px; max-width: 140px; background: none;
+           border: 1px solid var(--subtle); border-radius: 4px;
+           padding: 9px 6px; font: inherit; color: var(--dim);
+           cursor: pointer; text-align: center; }
+  .dpill:hover { border-color: var(--dim); background: var(--hover); }
+  .dpill .dow { font-size: 10px; color: var(--subtle); display: block; }
+  .dpill .date { font-size: 11px; color: var(--term-fg); font-weight: 500;
+                 display: block; margin: 2px 0 4px; }
+  .dpill .pct { font-size: 16px; font-weight: 700; color: var(--term-fg); display: block; }
+  .dpill .ns { font-size: 10px; color: var(--subtle); display: block; margin-top: 2px; }
+  .dpill.heaviest .pct { color: var(--clay); }
+  .dpill.sel { border-color: var(--clay); background: rgba(217,119,87,0.10); }
+  .gantt-hd { display: flex; justify-content: space-between; align-items: baseline;
+              margin-bottom: 6px; }
+  .gantt-hd .day { color: var(--term-fg); font-weight: 500; }
+  .gantt-hd .stats { font-size: 11px; color: var(--dim); }
+  .gantt-hd .stats b { color: var(--clay); }
+  .gantt { position: relative; border-top: 1px solid var(--outline);
+           border-bottom: 1px solid var(--outline); min-height: 32px; }
+  .lane { position: relative; height: 16px;
+          border-bottom: 1px dashed rgba(255,255,255,0.04); }
+  .seg { position: absolute; top: 2px; height: 12px; border-radius: 2px;
+         opacity: .85; cursor: crosshair; }
+  .seg:hover { opacity: 1; outline: 1px solid var(--term-fg); z-index: 2; }
+  .gantt-rule { position: absolute; top: 0; bottom: 0; width: 0;
+                border-left: 1px dashed var(--subtle); opacity: .4;
+                pointer-events: none; }
+  .gantt-axis { display: flex; justify-content: space-between;
+                font-size: 10px; color: var(--subtle); padding: 4px 0; }
+  .gantt-leg { font-size: 10px; color: var(--subtle); margin-top: 8px;
+               display: flex; gap: 14px; flex-wrap: wrap; }
+  .gantt-leg .sw { display: inline-block; width: 14px; height: 10px;
+                   border-radius: 2px; vertical-align: middle; margin-right: 4px; }
+
   /* ——— block-char bars ——— */
   .bar { display: grid; grid-template-columns: 26ch 1fr 8ch; gap: 14px;
          padding: 2px 0; align-items: center; }
@@ -231,6 +267,21 @@
       <div class="section-body" id="project-bars"></div>
     </section>
 
+    <section id="timeline-section">
+      <div class="hr"></div>
+      <h2>session timeline by day<span class="hint">click a day · ←/→ to navigate</span></h2>
+      <div class="section-body">
+        <div class="days" id="day-pills"></div>
+        <div class="gantt-hd">
+          <span class="day" id="g-day">—</span>
+          <span class="stats" id="g-stats"></span>
+        </div>
+        <div class="gantt-axis"><span>00:00</span><span>06:00</span><span>12:00</span><span>18:00</span><span>24:00</span></div>
+        <div class="gantt" id="gantt"></div>
+        <div class="gantt-leg" id="gantt-leg"></div>
+      </div>
+    </section>
+
     <section>
       <div class="hr"></div>
       <h2>most expensive prompts<span class="hint">click to expand context</span></h2>
@@ -335,6 +386,65 @@
     `<div class="val">${typeof v==='number'&&v>=1e4?fmt(v):v}</div>`+
     (d?`<div class="detail">${d}</div>`:'')+`</div>`).join('');
 
+  // session timeline by day
+  (function() {
+    const days = (DATA.by_day||[]).slice(-14);
+    if (!days.length) { $('timeline-section').style.display='none'; return; }
+    const PCOL = ['rgb(177,185,249)','rgb(78,186,101)','#D97757','rgb(255,193,7)',
+                  'rgb(255,107,128)','#9b8cff','#6ec1d6','#c792ea'];
+    const dayTotal = days.reduce((a,d)=>a+d.tokens,0) || 1;
+    const tokMax = Math.max(...days.map(d=>d.tokens));
+    const projects = [...new Set(days.flatMap(d=>d.sessions.map(s=>s.project)))];
+    const colorOf = p => PCOL[projects.indexOf(p)%PCOL.length];
+    const hhmm = m => (m>=1440?`+${Math.floor(m/1440)}d `:'') +
+      `${String(Math.floor(m/60)%24).padStart(2,'0')}:${String(m%60).padStart(2,'0')}`;
+    const md = iso => { const [,mo,da]=iso.split('-'); return `${MON[+mo-1]} ${+da}`; };
+    let sel = days.findIndex(d=>d.tokens===tokMax);
+
+    function pills() {
+      $('day-pills').innerHTML = days.map((d,i)=>
+        `<button class="dpill${d.tokens===tokMax?' heaviest':''}${i===sel?' sel':''}" data-i="${i}">`+
+        `<span class="dow">${esc(d.dow)}</span>`+
+        `<span class="date">${esc(md(d.date))}</span>`+
+        `<span class="pct">${(100*d.tokens/dayTotal).toFixed(1)}%</span>`+
+        `<span class="ns">${d.sessions.length} sess</span></button>`
+      ).join('');
+      $('day-pills').querySelectorAll('.dpill').forEach(el=>
+        el.onclick=()=>{sel=+el.dataset.i;pills();gantt();});
+    }
+    function gantt() {
+      const d = days[sel], DAY = 1440;
+      $('g-day').textContent = `${d.dow} ${md(d.date)}`;
+      $('g-stats').innerHTML = `${d.sessions.length} sessions · ${fmt(d.tokens)} tokens`+
+        ` · peak <b>${d.peak}</b> concurrent at <b>${hhmm(d.peak_at_min)}</b>`;
+      const lanes = [];
+      for (const s of d.sessions) {
+        let placed = false;
+        for (const L of lanes) if (L[L.length-1].end_min <= s.start_min) { L.push(s); placed=true; break; }
+        if (!placed) lanes.push([s]);
+      }
+      let h = '';
+      for (let t=0;t<=24;t+=6) h += `<div class="gantt-rule" style="left:${100*t/24}%"></div>`;
+      h += lanes.map(L=>`<div class="lane">${L.map(s=>{
+        const end = Math.min(s.end_min, DAY);
+        const w = Math.max(0.15, 100*(end-s.start_min)/DAY);
+        const tip = `folder: ${short(s.project)}\n`+
+          `${hhmm(s.start_min)}–${hhmm(s.end_min)} · ${fmt(s.tokens)} tokens\n`+
+          `session ${s.id}`;
+        return `<span class="seg" style="left:${100*s.start_min/DAY}%;width:${w}%;`+
+          `background:${colorOf(s.project)}" title="${esc(tip)}"></span>`;
+      }).join('')}</div>`).join('');
+      $('gantt').innerHTML = h || '<div class="callout">no sessions</div>';
+    }
+    document.addEventListener('keydown',e=>{
+      if (e.key==='ArrowRight'&&sel<days.length-1){sel++;pills();gantt();e.preventDefault();}
+      if (e.key==='ArrowLeft'&&sel>0){sel--;pills();gantt();e.preventDefault();}
+    });
+    $('gantt-leg').innerHTML = projects.slice(0,12).map(p=>
+      `<span><span class="sw" style="background:${colorOf(p)}"></span>${esc(short(p))}</span>`).join('');
+    pills(); gantt();
+  })();
+
   // block-char project bars
   (function() {
     const W = 48;
@@ -366,57 +476,52 @@
     return h + '</div>';
   }
 
-  // top prompts — share of grand total
-  (function() {
-    const ps = (DATA.top_prompts||[]).slice(0,100);
+  // expandable drill-down list with "show N more" toggle
+  function drillList(hostId, items, rowFn, empty) {
     const SHOW = 5;
-    const row = p => {
-      const inTot = p.input.uncached+p.input.cache_create+p.input.cache_read;
-      return `<details><summary>`+
-        `<span class="amt">${share(p.total_tokens)}</span>`+
-        `<span class="desc">${esc(p.text)}</span>`+
-        `<span class="meta">${niceDate(p.ts)} · ${esc(short(p.project))} · ${p.api_calls} calls`+
-          (p.subagent_calls?` · ${p.subagent_calls} subagents`:'')+
-          ` · ${pct(p.input.cache_read,inTot)} cached</span>`+
-        `</summary><div class="body">`+
-        renderContext(p.context)+
-        `<div>session <code>${esc(p.session)}</code></div>`+
-        `<div>in: uncached ${fmt(p.input.uncached)} · cache-create ${fmt(p.input.cache_create)} · `+
-        `cache-read ${fmt(p.input.cache_read)} · out ${fmt(p.output)}</div>`+
-        `</div></details>`;
-    };
-    const head = ps.slice(0,SHOW).map(row).join('');
-    const rest = ps.slice(SHOW).map(row).join('');
-    $('top-prompts').innerHTML = ps.length
-      ? head + (rest
-          ? `<div id="tp-rest" hidden>${rest}</div>`+
-            `<button id="tp-more" class="more-btn">show ${ps.length-SHOW} more</button>`
-          : '')
-      : '<div class="callout">No prompts in range.</div>';
-    const btn = $('tp-more');
+    const host = $(hostId);
+    if (!items.length) { host.innerHTML = `<div class="callout">${empty}</div>`; return; }
+    const head = items.slice(0,SHOW).map(rowFn).join('');
+    const rest = items.slice(SHOW).map(rowFn).join('');
+    host.innerHTML = head + (rest
+      ? `<div hidden>${rest}</div><button class="more-btn">show ${items.length-SHOW} more</button>`
+      : '');
+    const btn = host.querySelector('.more-btn');
     if (btn) btn.onclick = () => {
-      const r = $('tp-rest'); r.hidden = !r.hidden;
-      btn.textContent = r.hidden ? `show ${ps.length-SHOW} more` : 'show less';
+      const r = btn.previousElementSibling; r.hidden = !r.hidden;
+      btn.textContent = r.hidden ? `show ${items.length-SHOW} more` : 'show less';
     };
-  })();
+  }
 
-  // cache breaks
-  (function() {
-    const bs = (DATA.cache_breaks||[]).slice(0,100);
-    $('cache-breaks').innerHTML = bs.map(b =>
-      `<details><summary>`+
-      `<span class="amt">${fmt(b.uncached)}</span>`+
-      `<span class="desc">${esc(short(b.project))} · `+
-        `${b.kind==='subagent'?esc(b.agentType||'subagent'):'main'}</span>`+
-      `<span class="meta">${niceDate(b.ts)} · ${pct(b.uncached,b.total)} of ${fmt(b.total)} uncached</span>`+
+  drillList('top-prompts', (DATA.top_prompts||[]).slice(0,100), p => {
+    const inTot = p.input.uncached+p.input.cache_create+p.input.cache_read;
+    return `<details><summary>`+
+      `<span class="amt">${share(p.total_tokens)}</span>`+
+      `<span class="desc">${esc(p.text)}</span>`+
+      `<span class="meta">${niceDate(p.ts)} · ${esc(short(p.project))} · ${p.api_calls} calls`+
+        (p.subagent_calls?` · ${p.subagent_calls} subagents`:'')+
+        ` · ${pct(p.input.cache_read,inTot)} cached</span>`+
       `</summary><div class="body">`+
-      renderContext(b.context,
-        `<div class="ctx-break"><b>${fmt(b.uncached)}</b> uncached `+
-        `(${pct(b.uncached,b.total)} of ${fmt(b.total)}) — cache break here</div>`)+
-      `<div>session <code>${esc(b.session)}</code></div>`+
-      `</div></details>`
-    ).join('') || '<div class="callout">No cache breaks over threshold.</div>';
-  })();
+      renderContext(p.context)+
+      `<div>session <code>${esc(p.session)}</code></div>`+
+      `<div>in: uncached ${fmt(p.input.uncached)} · cache-create ${fmt(p.input.cache_create)} · `+
+      `cache-read ${fmt(p.input.cache_read)} · out ${fmt(p.output)}</div>`+
+      `</div></details>`;
+  }, 'No prompts in range.');
+
+  drillList('cache-breaks', (DATA.cache_breaks||[]).slice(0,100), b =>
+    `<details><summary>`+
+    `<span class="amt">${fmt(b.uncached)}</span>`+
+    `<span class="desc">${esc(short(b.project))} · `+
+      `${b.kind==='subagent'?esc(b.agentType||'subagent'):'main'}</span>`+
+    `<span class="meta">${niceDate(b.ts)} · ${pct(b.uncached,b.total)} of ${fmt(b.total)} uncached</span>`+
+    `</summary><div class="body">`+
+    renderContext(b.context,
+      `<div class="ctx-break"><b>${fmt(b.uncached)}</b> uncached `+
+      `(${pct(b.uncached,b.total)} of ${fmt(b.total)}) — cache break here</div>`)+
+    `<div>session <code>${esc(b.session)}</code></div>`+
+    `</div></details>`,
+  'No cache breaks over threshold.');
 
   // sortable table
   function table(el, cols, rows) {