diff --git a/docs/superpowers/specs/2026-06-25-simulator-dev-mode-design.md b/docs/superpowers/specs/2026-06-25-simulator-dev-mode-design.md
new file mode 100644
index 0000000..3bafe46
--- /dev/null
+++ b/docs/superpowers/specs/2026-06-25-simulator-dev-mode-design.md
@@ -0,0 +1,64 @@
+# Simulator Dev Mode — design
+
+> 2026-06-25 · session 0017 · planning-and-executing
+> Anchor: leaf task (simulator dev-tooling — R2b, no upstream design needed)
+
+## Problem
+
+While previewing the experience, the operator can't choose *which* clip in an
+altitude's rotating pool is shown — the server picks a random pool member on each
+landing (content-pipeline §11.1). For by-eye review they want to step through every
+clip in a pool on demand, and to see the engine/clip data behind what's on screen.
+The RenderPlan JSON readout is also always visible, cluttering what should read as
+an audience-facing preview.
+
+## Goal
+
+A single **Dev Mode** toggle at the bottom of the control panel. Off by default
+(persisted in `localStorage`). When on, a panel appears directly below it with all
+dev controls and data; when off, the normal view is just the experience + the three
+control fieldsets.
+
+## Scope
+
+Frontend only — `simulator/static/{index.html,app.js,style.css}`. No API changes:
+every datum Dev Mode shows is already available client-side (`/api/clips`,
+`/api/ring`, the `/api/alteration` response, and the in-memory preload cache). The
+separate `/author.html` remains the place to *edit* labels; Dev Mode is
+inspect-and-select only.
+
+## Dev panel contents (top → bottom)
+
+1. **Pool picker** — a `<select>` of the current altitude's pool members
+   (`clip_id · title`), its value reflecting the clip currently playing. Choosing a
+   member sets `activeClipId` to it and reloads the base media, overriding the random
+   landing pick. A `🎲 Re-roll random` button re-runs the server-canonical random
+   pick for the current scale. The dropdown is rebuilt on every scale landing, so it
+   always lists the current pool; single-clip scales (cosmos/orbit) show one entry.
+2. **Active clip** — `id`, `title`, `source`, `license`, `base_file`.
+3. **Annotations & affect** — each annotation key with salience (or legacy
+   `min_level`), time window (`appear`–`disappear`), and tier count; each affect key
+   with `min_level` and tier count. Read-only.
+4. **RenderPlan** — the relocated `#readout` (the `/api/alteration` JSON).
+5. **Cache & playback** — preload status (`N/total cached`), whether the active
+   clip is served **from memory** (a preloaded blob) vs the network, and live video
+   resolution / duration / loop position.
+
+## Behavior
+
+- **Pool override is per-landing.** Changing altitude re-rolls randomly as today;
+  the operator then picks again from the new scale's pool. The pick is not persisted
+  across landings (YAGNI — "select any video while on an altitude").
+- **Refresh points.** Pool picker + clip metadata + annotations rebuild whenever the
+  scale lands (hooked into `renderScaleReadout()`) and after a manual pick/re-roll.
+  The RenderPlan readout updates on each `update()` (knob change) as today. The
+  cache/playback stats refresh on a light interval (~500 ms) while Dev Mode is on,
+  and the cache count also ticks up as the preloader fills.
+- **`pickRandomMember()`** is factored out of `landScale()` so the initial landing,
+  ring advances, and the Re-roll button all share the one server-canonical pick.
+
+## Testing
+
+No JS unit harness in the repo and no API change, so verification is: `node --check`
+on `app.js`, the Python suite stays green (unaffected), and by-eye review by the
+operator (no headless browser yet — §9 E2E policy noted, machinery pending).
diff --git a/simulator/static/app.js b/simulator/static/app.js
index 51a6082..376d3d5 100644
--- a/simulator/static/app.js
+++ b/simulator/static/app.js
@@ -52,22 +52,28 @@ async function loadData() {
   ringIndex = 0;
 }
 
-// Land on the current scale: pick a random pool member (content-pipeline §11.1).
-// A real server ring picks via a delta=0 advance (Python-canonical pick); the
-// synthesized fallback ring has a pool of one, so it just takes that member.
-async function landScale() {
+// Server-canonical random pick of a pool member for the current scale: a delta=0
+// advance (content-pipeline §11.1, Python owns the randomness). The synthesized
+// fallback ring has a pool of one, so it just returns that member. Returns a
+// clip_id or null. Shared by the initial landing AND the Dev Mode re-roll button.
+async function pickRandomMember() {
   const scale = ring && ring.scales[ringIndex];
-  if (!scale) { activeClipId = null; return; }
+  if (!scale) return null;
   if (serverRing) {
     try {
       const resp = await fetch("/api/ring/advance", {
         method: "POST", headers: { "content-type": "application/json" },
         body: JSON.stringify({ from_index: ringIndex, delta: 0 }),
       });
-      if (resp.ok) { activeClipId = (await resp.json()).target_clip_id; currentClipId = null; return; }
+      if (resp.ok) return (await resp.json()).target_clip_id;
     } catch (_) { /* fall through to the primary member */ }
   }
-  activeClipId = scale.clip_id;
+  return scale.clip_id;
+}
+
+// Land on the current scale: pick a random pool member and force its media to load.
+async function landScale() {
+  activeClipId = await pickRandomMember();
   currentClipId = null;
 }
 
@@ -462,6 +468,7 @@ function renderScaleReadout() {
   const poolTag = poolN > 1 ? ` · pool ${poolN}` : "";
   $("scale-name").textContent = `${s.id} · ${member}  (${ringIndex + 1}/${ring.scales.length}${poolTag})`;
   renderDial();
+  refreshDevClip();      // keep the Dev Mode pool picker + clip data in sync with the landing
 }
 
 function controls() {
@@ -685,6 +692,136 @@ function jumpToScale(idx) {
   if (d) advance(d);
 }
 
+// --- Dev Mode: pool picker + live analysis, all under one toggle ---
+// Off by default, state persisted in localStorage. Everything here is read from
+// data the renderer already has (clips, ring, the alteration response, the preload
+// cache) — no server endpoints. Editing labels stays in /author.html.
+const DEV_KEY = "hef.devMode";
+let devMode = false;
+let devStatsTimer = null;
+
+const escapeHtml = (s) => String(s).replace(/[&<>"]/g,
+  (c) => ({ "&": "&amp;", "<": "&lt;", ">": "&gt;", '"': "&quot;" }[c]));
+
+function applyDevVisibility() {
+  const panel = $("dev-panel");
+  if (panel) panel.classList.toggle("hidden", !devMode);
+  if (devMode) { refreshDevClip(); renderDevStats(); }
+}
+
+function initDev() {
+  const toggle = $("dev-mode");
+  if (!toggle) return;
+  try { devMode = localStorage.getItem(DEV_KEY) === "1"; } catch (_) { devMode = false; }
+  toggle.checked = devMode;
+  toggle.addEventListener("change", () => {
+    devMode = toggle.checked;
+    try { localStorage.setItem(DEV_KEY, devMode ? "1" : "0"); } catch (_) {}
+    applyDevVisibility();
+  });
+  $("pool-select").addEventListener("change", onPoolSelect);
+  $("pool-reroll").addEventListener("click", reroll);
+  // Cache + playback stats are live-ish; cheap to repaint twice a second when shown.
+  devStatsTimer = setInterval(() => { if (devMode) renderDevStats(); }, 500);
+  applyDevVisibility();
+}
+
+// Rebuild the pool picker for the current scale and repaint the clip data. Cheap
+// (pools are <= a handful), so just rebuild on every landing/pick.
+function refreshDevClip() {
+  if (!devMode) return;
+  const sel = $("pool-select");
+  const scale = ring && ring.scales[ringIndex];
+  if (sel && scale) {
+    const pool = (scale.pool && scale.pool.length) ? scale.pool : [{ clip_id: scale.clip_id, title: scale.title }];
+    sel.innerHTML = "";
+    for (const m of pool) {
+      const o = document.createElement("option");
+      o.value = m.clip_id;
+      o.textContent = `${m.clip_id} · ${m.title || (clipsById[m.clip_id] || {}).title || ""}`;
+      sel.appendChild(o);
+    }
+    if (activeClipId) sel.value = activeClipId;
+    sel.disabled = pool.length < 2;
+  }
+  renderDevMeta();
+  renderDevAnno();
+}
+
+function renderDevMeta() {
+  const dl = $("clip-meta");
+  const c = activeClip();
+  if (!dl) return;
+  if (!c) { dl.innerHTML = "<dt>—</dt><dd>no clip</dd>"; return; }
+  const rows = [["id", c.id], ["title", c.title], ["source", c.source],
+               ["license", c.license], ["base_file", c.base_file]];
+  dl.innerHTML = rows.map(([k, v]) =>
+    `<dt>${escapeHtml(k)}</dt><dd>${escapeHtml(v != null ? v : "—")}</dd>`).join("");
+}
+
+function renderDevAnno() {
+  const box = $("clip-anno");
+  const c = activeClip();
+  if (!box) return;
+  const strings = (c && c.strings && c.strings.en) || {};
+  const win = (a) => (typeof a.appear === "number" || typeof a.disappear === "number")
+    ? ` win ${(a.appear ?? 0).toFixed(2)}–${(a.disappear ?? 1).toFixed(2)}` : "";
+  const rows = [];
+  for (const a of (c && c.annotations) || []) {
+    const measure = a.key.startsWith("measure.");
+    const sal = typeof a.salience === "number" ? `sal ${a.salience}`
+              : typeof a.min_level === "number" ? `min L${a.min_level}` : "sal 1";
+    const tiers = tierCount(strings[a.key]);
+    rows.push(`<div class="anno-row"><span class="anno-key ${measure ? "measure" : ""}">${escapeHtml(a.key)}</span>` +
+      `<span class="anno-meta"> · ${sal} · ${tiers} tier${tiers > 1 ? "s" : ""}${win(a)}</span></div>`);
+  }
+  for (const f of (c && c.affect) || []) {
+    const tiers = tierCount(strings[f.key]);
+    rows.push(`<div class="anno-row"><span class="anno-key affect">${escapeHtml(f.key)}</span>` +
+      `<span class="anno-meta"> · min L${f.min_level ?? 1} · ${tiers} tier${tiers > 1 ? "s" : ""}</span></div>`);
+  }
+  box.innerHTML = rows.length ? rows.join("") : `<div class="anno-empty">no annotations or affect</div>`;
+}
+
+function renderDevStats() {
+  const dl = $("dev-stats");
+  if (!dl) return;
+  const c = activeClip();
+  const total = preloadList().length;
+  const cached = Object.keys(mediaBlobs).length;
+  const fromMem = !!(c && mediaBlobs[c.base_file]);
+  const res = vid.videoWidth ? `${vid.videoWidth}×${vid.videoHeight}` : "—";
+  const dur = vid.duration ? `${vid.duration.toFixed(1)}s` : "—";
+  const loop = vid.duration ? `${Math.round(loopT() * 100)}%` : "—";
+  dl.innerHTML =
+    `<dt>cache</dt><dd>${cached}/${total} cached</dd>` +
+    `<dt>active source</dt><dd class="${fromMem ? "mem" : "net"}">${fromMem ? "memory (blob)" : "network"}</dd>` +
+    `<dt>resolution</dt><dd>${res}</dd>` +
+    `<dt>duration</dt><dd>${dur}</dd>` +
+    `<dt>loop pos</dt><dd>${loop}</dd>`;
+}
+
+// Pick a specific pool member (Dev Mode override of the random landing pick).
+function onPoolSelect() {
+  const id = $("pool-select").value;
+  if (!id || id === activeClipId) return;
+  activeClipId = id;
+  currentClipId = null;          // force the base media to reload
+  renderScaleReadout();          // refresh scale name + dev clip data
+  update();                      // reload media + plan
+}
+
+// Re-roll: a fresh server-canonical random pick for the current scale.
+async function reroll() {
+  if (busy) return;
+  const id = await pickRandomMember();
+  if (!id) return;
+  activeClipId = id;
+  currentClipId = null;
+  renderScaleReadout();
+  update();
+}
+
 // Dev live-reload: poll the asset version and reload when it changes, so an open
 // tab never keeps running a stale renderer while we iterate (the readout updates
 // from the live API and masks it otherwise). Reloads on my edits AND on a server
@@ -707,6 +844,7 @@ async function main() {
   await landScale();          // pick the initial scale's pool member before first render
   preloadAllMedia();          // background: cache every clip in memory for instant altitude swaps
   buildDial();                // draw the altitude knob from the ring's scales
+  initDev();                  // wire the Dev Mode toggle + pool picker (reads persisted state)
   renderScaleReadout();
   for (const id of ["content", "left", "right", "mood"]) {
     $(id).addEventListener("input", debounced);
diff --git a/simulator/static/index.html b/simulator/static/index.html
index 68e91ab..1417144 100644
--- a/simulator/static/index.html
+++ b/simulator/static/index.html
@@ -50,11 +50,40 @@
         <label>Mood — dark ◀ 0 ▶ light <input type="range" id="mood" min="-4" max="4" value="0" /></label>
       </fieldset>
 
+      <!-- Dev Mode: a single toggle; everything dev (pool picker + analysis) lives below it. -->
+      <label class="dev-switch" for="dev-mode">
+        <input type="checkbox" id="dev-mode" />
+        <span class="dev-switch-track"><span class="dev-switch-thumb"></span></span>
+        <span class="dev-switch-label">Dev Mode</span>
+      </label>
 
-      <fieldset>
-        <legend>RenderPlan readout</legend>
-        <pre id="readout">—</pre>
-      </fieldset>
+      <div id="dev-panel" class="dev-panel hidden">
+        <fieldset>
+          <legend>Pool — pick a clip</legend>
+          <select id="pool-select" aria-label="Choose a clip from this altitude's pool"></select>
+          <button type="button" id="pool-reroll" class="dev-btn">🎲 Re-roll random</button>
+        </fieldset>
+
+        <fieldset>
+          <legend>Active clip</legend>
+          <dl id="clip-meta" class="dev-dl"></dl>
+        </fieldset>
+
+        <fieldset>
+          <legend>Annotations &amp; affect</legend>
+          <div id="clip-anno" class="dev-anno"></div>
+        </fieldset>
+
+        <fieldset>
+          <legend>RenderPlan</legend>
+          <pre id="readout">—</pre>
+        </fieldset>
+
+        <fieldset>
+          <legend>Cache &amp; playback</legend>
+          <dl id="dev-stats" class="dev-dl"></dl>
+        </fieldset>
+      </div>
     </section>
   </main>
   <script src="/app.js"></script>
diff --git a/simulator/static/style.css b/simulator/static/style.css
index 4e41e39..69cfe18 100644
--- a/simulator/static/style.css
+++ b/simulator/static/style.css
@@ -66,3 +66,34 @@ input[type=range], select { width: 100%; }
 .dial-hub { fill: #2c3c5c; stroke: #9cf; stroke-width: 0.6; }
 .scale-name { display: block; text-align: center; font-size: 12px; color: #cde; }
 .hint { margin: 0.3rem 0 0; font-size: 11px; color: #789; }
+
+/* --- Dev Mode --- a single switch; all dev controls/data live in #dev-panel below it. */
+.dev-switch { display: flex; align-items: center; gap: 0.5rem; cursor: pointer;
+              padding: 0.5rem 0.2rem 0.2rem; border-top: 1px solid #222; user-select: none; }
+.dev-switch input { position: absolute; opacity: 0; width: 0; height: 0; }
+.dev-switch-track { position: relative; width: 34px; height: 18px; border-radius: 9px;
+                    background: #2a2a2a; border: 1px solid #444; transition: background 0.15s; }
+.dev-switch-thumb { position: absolute; top: 1px; left: 1px; width: 14px; height: 14px;
+                    border-radius: 50%; background: #888; transition: transform 0.15s, background 0.15s; }
+.dev-switch input:checked + .dev-switch-track { background: #1d3a2a; border-color: #2e6; }
+.dev-switch input:checked + .dev-switch-track .dev-switch-thumb { transform: translateX(16px); background: #4e9; }
+.dev-switch input:focus-visible + .dev-switch-track { outline: 2px solid #9af; outline-offset: 1px; }
+.dev-switch-label { color: #9af; font-weight: 600; letter-spacing: 0.3px; }
+.dev-panel { display: flex; flex-direction: column; gap: 0.8rem; }
+.dev-panel legend { color: #4e9; }
+.dev-btn { margin-top: 0.5rem; width: 100%; padding: 0.4rem; cursor: pointer;
+           background: #182028; color: #cde; border: 1px solid #2c3c5c; border-radius: 4px; }
+.dev-btn:hover { background: #20303f; }
+.dev-dl { margin: 0; display: grid; grid-template-columns: auto 1fr; gap: 0.15rem 0.6rem; font-size: 12px; }
+.dev-dl dt { color: #789; }
+.dev-dl dd { margin: 0; color: #dde; word-break: break-word; }
+.dev-dl dd.mem { color: #4e9; }
+.dev-dl dd.net { color: #fc6; }
+.dev-anno { font-size: 11px; max-height: 220px; overflow: auto;
+            font-family: ui-monospace, monospace; }
+.dev-anno .anno-row { padding: 0.2rem 0; border-bottom: 1px solid #1d1d1d; }
+.dev-anno .anno-key { color: #aee6ff; }
+.dev-anno .anno-key.affect { color: #e3cfff; }
+.dev-anno .anno-key.measure { color: #ffd79a; }
+.dev-anno .anno-meta { color: #678; }
+.dev-anno .anno-empty { color: #567; font-style: italic; }