diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..96a947e
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,7 @@
+.PHONY: sim sim-local
+
+sim:
+	docker compose -f simulator/docker-compose.yml up --build
+
+sim-local:
+	python -m uvicorn simulator.app:app --reload --port 8000
diff --git a/docs/USER_GUIDE.md b/docs/USER_GUIDE.md
index d89da61..232e515 100644
--- a/docs/USER_GUIDE.md
+++ b/docs/USER_GUIDE.md
@@ -286,3 +286,29 @@ Records point at files via `file_path`. Those files live on the player's drive,
 **not** in this git repo (the repo holds only the catalog metadata). Keep your
 `file_path` values consistent with wherever you mount that drive on the machine
 that will eventually run the room.
+
+## Playing with the simulator (curator's X-ray)
+
+The simulator is a web stand-in for the installation's control panel. It runs the
+real `hef.selection` code against a synthetic catalog so you can feel whether the
+dials surface fitting pieces before any hardware exists.
+
+**Run it (Docker):**
+
+    make sim
+
+then open http://localhost:8000.
+
+**Run it (no Docker):**
+
+    pip install -e ".[sim]"
+    make sim-local
+
+**What you see:** the five real dials (mode + Left/Right/Dark/Light), the model
+knobs (brain/mood weights, pool size, approved-only), and the X-ray — the picked
+piece, the ranked candidate pool with distances, and brain/mood coordinate maps
+showing where your knob point and the candidates sit.
+
+By default it loads a generated fixture catalog. To point it at a real catalog,
+set `HEF_SIM_CATALOG=catalog/library.jsonl` (used automatically when that file is
+non-empty).
diff --git a/hef/selection.py b/hef/selection.py
index afef502..5be1f3f 100644
--- a/hef/selection.py
+++ b/hef/selection.py
@@ -58,6 +58,38 @@ def candidates_for_mode(records, mode: str, pool_size: int) -> list[Record]:
 from typing import Optional
 
 
+def ranked_candidates(
+    records,
+    coord: Coordinate,
+    mode: str,
+    *,
+    pool_size: int = 4,
+    weights: Weights = Weights(),
+    approved_only: bool = False,
+) -> list[tuple[Record, float]]:
+    """Mode-eligible records sorted nearest-first, each paired with its distance.
+
+    Applies the same approved_only filter and 'av' pool fallback as select(),
+    then returns up to pool_size nearest (record, distance) pairs. This is the
+    single source of truth for "the pool"; select() picks from it.
+    """
+    if mode not in CONTENT_MODES:
+        raise ValueError(
+            f"ranked_candidates expects a content mode {sorted(CONTENT_MODES)}, "
+            f"got {mode!r}"
+        )
+    pool = records
+    if approved_only:
+        pool = [r for r in pool if r.review_status == "approved"]
+    candidates = candidates_for_mode(pool, mode, pool_size)
+    ranked = sorted(
+        candidates,
+        key=lambda r: (distance(coord, record_coordinate(r), weights), r.id),
+    )
+    nearest = ranked[:pool_size]
+    return [(r, distance(coord, record_coordinate(r), weights)) for r in nearest]
+
+
 def select(
     records,
     coord: Coordinate,
@@ -82,17 +114,17 @@ def select(
         )
     if mode == "none":
         return None
-    pool = records
-    if approved_only:
-        pool = [r for r in pool if r.review_status == "approved"]
-    candidates = candidates_for_mode(pool, mode, pool_size)
-    if not candidates:
-        return None
-    ranked = sorted(
-        candidates,
-        key=lambda r: (distance(coord, record_coordinate(r), weights), r.id),
+    ranked = ranked_candidates(
+        records,
+        coord,
+        mode,
+        pool_size=pool_size,
+        weights=weights,
+        approved_only=approved_only,
     )
-    nearest = ranked[:pool_size]
+    if not ranked:
+        return None
+    nearest = [r for r, _ in ranked]
     if rng is None:
         return nearest[0]
     return rng.choice(nearest)
diff --git a/pyproject.toml b/pyproject.toml
index 96b5411..e948241 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -12,8 +12,15 @@ requires = ["setuptools>=68"]
 build-backend = "setuptools.build_meta"
 
 [tool.setuptools]
-packages = ["hef", "tools"]
+packages = ["hef", "tools", "simulator"]
 
 [project.scripts]
 hef-ingest = "tools.ingest_cli:main"
 hef-review = "tools.review_cli:main"
+
+[project.optional-dependencies]
+sim = [
+    "fastapi>=0.110",
+    "uvicorn[standard]>=0.29",
+    "httpx>=0.27",
+]
diff --git a/simulator/Dockerfile b/simulator/Dockerfile
new file mode 100644
index 0000000..14b9b50
--- /dev/null
+++ b/simulator/Dockerfile
@@ -0,0 +1,10 @@
+FROM python:3.11-slim
+WORKDIR /app
+COPY pyproject.toml ./
+COPY hef ./hef
+COPY tools ./tools
+COPY simulator ./simulator
+COPY catalog ./catalog
+RUN pip install --no-cache-dir -e ".[sim]"
+EXPOSE 8000
+CMD ["uvicorn", "simulator.app:app", "--host", "0.0.0.0", "--port", "8000"]
diff --git a/simulator/__init__.py b/simulator/__init__.py
new file mode 100644
index 0000000..3c28577
--- /dev/null
+++ b/simulator/__init__.py
@@ -0,0 +1 @@
+"""Web-based curator's X-ray simulator for the experience filter."""
diff --git a/simulator/app.py b/simulator/app.py
new file mode 100644
index 0000000..10b6593
--- /dev/null
+++ b/simulator/app.py
@@ -0,0 +1,96 @@
+"""FastAPI service: dials -> real hef.selection -> X-ray (pick + ranked pool)."""
+
+from __future__ import annotations
+
+import os
+from collections import Counter
+from pathlib import Path
+from typing import Literal, Optional
+
+from fastapi import FastAPI
+from fastapi.staticfiles import StaticFiles
+from pydantic import BaseModel, Field
+
+from hef.catalog import load_catalog, record_to_dict
+from hef.selection import (
+    Coordinate,
+    Weights,
+    candidates_for_mode,
+    ranked_candidates,
+    select,
+)
+from simulator.fixtures import generate_fixture_catalog
+
+STATIC_DIR = Path(__file__).parent / "static"
+
+
+class SelectRequest(BaseModel):
+    left: int = Field(ge=0, le=4)
+    right: int = Field(ge=0, le=4)
+    dark: int = Field(ge=0, le=4)
+    light: int = Field(ge=0, le=4)
+    mode: Literal["none", "audio", "video", "av"]
+    pool_size: int = Field(default=4, ge=1, le=25)
+    brain_weight: float = Field(default=1.0, ge=0.0)
+    mood_weight: float = Field(default=1.0, ge=0.0)
+    approved_only: bool = False
+
+
+def load_catalog_or_fixtures() -> list:
+    """Use the real catalog if a non-empty one is configured/exists, else fixtures."""
+    configured = os.environ.get("HEF_SIM_CATALOG")
+    path = Path(configured) if configured else Path("catalog/library.jsonl")
+    if path.exists() and path.stat().st_size > 0:
+        return load_catalog(path)
+    return generate_fixture_catalog()
+
+
+def create_app(records: Optional[list] = None) -> FastAPI:
+    app = FastAPI(title="HEF Experience Simulator")
+    app.state.catalog = records if records is not None else load_catalog_or_fixtures()
+
+    @app.post("/api/select")
+    def api_select(req: SelectRequest):
+        catalog = app.state.catalog
+        coord = Coordinate(req.left, req.right, req.dark, req.light)
+        weights = Weights(brain=req.brain_weight, mood=req.mood_weight)
+        if req.mode == "none":
+            return {"pick": None, "pool": [], "coverage": {"candidates_in_mode": 0}}
+        pool = catalog
+        if req.approved_only:
+            pool = [r for r in pool if r.review_status == "approved"]
+        eligible = candidates_for_mode(pool, req.mode, req.pool_size)
+        ranked = ranked_candidates(
+            catalog, coord, req.mode,
+            pool_size=req.pool_size, weights=weights, approved_only=req.approved_only,
+        )
+        pick = select(
+            catalog, coord, req.mode,
+            pool_size=req.pool_size, weights=weights, approved_only=req.approved_only,
+            rng=None,
+        )
+        return {
+            "pick": record_to_dict(pick) if pick else None,
+            "pool": [
+                {"record": record_to_dict(r), "distance": d, "rank": i + 1}
+                for i, (r, d) in enumerate(ranked)
+            ],
+            "coverage": {"candidates_in_mode": len(eligible)},
+        }
+
+    @app.get("/api/catalog/meta")
+    def api_meta():
+        catalog = app.state.catalog
+        return {
+            "total": len(catalog),
+            "by_mode": dict(Counter(r.mode for r in catalog)),
+            "by_status": dict(Counter(r.review_status for r in catalog)),
+        }
+
+    if STATIC_DIR.exists():
+        app.mount("/", StaticFiles(directory=STATIC_DIR, html=True), name="static")
+
+    return app
+
+
+app = create_app()
diff --git a/simulator/docker-compose.yml b/simulator/docker-compose.yml
new file mode 100644
index 0000000..390bbeb
--- /dev/null
+++ b/simulator/docker-compose.yml
@@ -0,0 +1,7 @@
+services:
+  simulator:
+    build:
+      context: ..
+      dockerfile: simulator/Dockerfile
+    ports:
+      - "8000:8000"
diff --git a/simulator/fixtures.py b/simulator/fixtures.py
new file mode 100644
index 0000000..1d83344
--- /dev/null
+++ b/simulator/fixtures.py
@@ -0,0 +1,59 @@
+"""Deterministic synthetic catalog so the selection model can be felt everywhere.
+
+The real catalog (catalog/library.jsonl) is empty; this generates one record per
+cell of the 5x5 brain x 5x5 mood coordinate space (625 records), with a seeded
+mix of content modes and review statuses and no real media attached.
+"""
+
+from __future__ import annotations
+
+import random
+
+from hef.catalog import Record
+
+MODES = ("audio", "video", "av")
+ARCHIVES = ("internet_archive", "musopen", "librivox", "nasa", "freesound")
+
+_LEFT_WORDS = ("Treatise", "Lecture", "Field Notes", "Reading", "Documentary")
+_RIGHT_WORDS = ("Reverie", "Nocturne", "Bloom", "Drift", "Aurora")
+
+
+def _title(left: int, right: int, dark: int, light: int, mode: str) -> str:
+    a = _LEFT_WORDS[left] if left >= right else _RIGHT_WORDS[right]
+    return f"{a} ({mode}) L{left}R{right}D{dark}Li{light}"
+
+
+def generate_fixture_catalog(seed: int = 1729) -> list[Record]:
+    """One valid Record per coordinate cell (625 total), deterministic for a seed."""
+    rng = random.Random(seed)
+    records: list[Record] = []
+    n = 0
+    for left in range(5):
+        for right in range(5):
+            for dark in range(5):
+                for light in range(5):
+                    mode = rng.choice(MODES)
+                    status = rng.choice(("proposed", "approved"))
+                    is_video = mode in ("video", "av")
+                    records.append(
+                        Record(
+                            id=f"fx-{n:04d}",
+                            title=_title(left, right, dark, light, mode),
+                            source_url=f"https://example.test/fx/{n:04d}",
+                            source_archive=rng.choice(ARCHIVES),
+                            license="public_domain",
+                            mode=mode,
+                            left=left,
+                            right=right,
+                            dark=dark,
+                            light=light,
+                            duration_s=rng.choice((300, 480, 600, 720, 900)),
+                            file_path="",
+                            review_status=status,
+                            resolution="1920x1080" if is_video else "",
+                            rationale=f"fixture at ({left},{right},{dark},{light})",
+                            reviewed_at="2026-06-04T00:00:00Z" if status == "approved" else None,
+                        )
+                    )
+                    n += 1
+    return records
diff --git a/simulator/static/app.js b/simulator/static/app.js
new file mode 100644
index 0000000..12a77f2
--- /dev/null
+++ b/simulator/static/app.js
@@ -0,0 +1,111 @@
+const DIALS = ["left", "right", "dark", "light"];
+const MODEL = ["brain_weight", "mood_weight", "pool_size"];
+
+function buildGrid(el) {
+  el.innerHTML = "";
+  // rows = first axis 0..4 top->bottom, cols = second axis 0..4 left->right
+  for (let a = 0; a < 5; a++) {
+    for (let b = 0; b < 5; b++) {
+      const cell = document.createElement("div");
+      cell.className = "cell";
+      cell.dataset.a = a;
+      cell.dataset.b = b;
+      el.appendChild(cell);
+    }
+  }
+}
+
+function paintGrid(el, axisA, axisB, point, pool) {
+  // clear
+  el.querySelectorAll(".cell").forEach((c) => {
+    c.className = "cell";
+    c.innerHTML = "";
+  });
+  const counts = {};
+  pool.forEach((c) => {
+    const r = c.record;
+    const key = `${r[axisA]},${r[axisB]}`;
+    counts[key] = (counts[key] || 0) + 1;
+  });
+  el.querySelectorAll(".cell").forEach((c) => {
+    const a = +c.dataset.a, b = +c.dataset.b;
+    const key = `${a},${b}`;
+    if (counts[key]) {
+      c.classList.add("cand");
+      const n = document.createElement("span");
+      n.className = "n";
+      n.textContent = counts[key];
+      c.appendChild(n);
+    }
+    if (a === point[axisA] && b === point[axisB]) c.classList.add("point");
+  });
+}
+
+function readState() {
+  const s = { mode: document.getElementById("mode").value, approved_only: document.getElementById("approved_only").checked };
+  DIALS.forEach((d) => (s[d] = +document.getElementById(d).value));
+  s.brain_weight = +document.getElementById("brain_weight").value;
+  s.mood_weight = +document.getElementById("mood_weight").value;
+  s.pool_size = +document.getElementById("pool_size").value;
+  return s;
+}
+
+function syncOutputs() {
+  [...DIALS, ...MODEL].forEach((id) => {
+    const out = document.getElementById(`${id}-out`);
+    if (out) out.textContent = document.getElementById(id).value;
+  });
+}
+
+async function refresh() {
+  syncOutputs();
+  const state = readState();
+  const resp = await fetch("/api/select", {
+    method: "POST",
+    headers: { "Content-Type": "application/json" },
+    body: JSON.stringify(state),
+  });
+  const data = await resp.json();
+
+  const pickEl = document.getElementById("pick");
+  if (!data.pick) {
+    pickEl.innerHTML = '<div class="void">∅ Void / rest — walls dark, audio silent.</div>';
+  } else {
+    const p = data.pick;
+    pickEl.innerHTML =
+      `<div class="title">${p.title}</div>` +
+      `<div>mode ${p.mode} · coord (${p.left},${p.right},${p.dark},${p.light})</div>` +
+      `<div>${p.rationale || ""}</div>`;
+  }
+
+  const poolEl = document.getElementById("pool");
+  poolEl.innerHTML = "";
+  data.pool.forEach((c, i) => {
+    const li = document.createElement("li");
+    if (i === 0) li.className = "winner";
+    li.innerHTML = `${c.record.title} <span class="dist">d=${c.distance.toFixed(2)}</span>`;
+    poolEl.appendChild(li);
+  });
+
+  const point = { left: state.left, right: state.right, dark: state.dark, light: state.light };
+  paintGrid(document.getElementById("brain-grid"), "left", "right", point, data.pool);
+  paintGrid(document.getElementById("mood-grid"), "dark", "light", point, data.pool);
+}
+
+async function loadMeta() {
+  const data = await (await fetch("/api/catalog/meta")).json();
+  const byMode = Object.entries(data.by_mode).map(([k, v]) => `${k}:${v}`).join("  ");
+  document.getElementById("meta").textContent = `${data.total} records · ${byMode}`;
+}
+
+function init() {
+  buildGrid(document.getElementById("brain-grid"));
+  buildGrid(document.getElementById("mood-grid"));
+  document.querySelectorAll("input, select").forEach((el) =>
+    el.addEventListener("input", refresh)
+  );
+  loadMeta();
+  refresh();
+}
+
+document.addEventListener("DOMContentLoaded", init);
diff --git a/simulator/static/index.html b/simulator/static/index.html
new file mode 100644
index 0000000..0a89203
--- /dev/null
+++ b/simulator/static/index.html
@@ -0,0 +1,64 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="utf-8">
+  <meta name="viewport" content="width=device-width, initial-scale=1">
+  <title>HEF — Curator's X-ray</title>
+  <link rel="stylesheet" href="/style.css">
+</head>
+<body>
+  <header>
+    <h1>Experience Filter — Curator's X-ray</h1>
+    <div id="meta" class="meta"></div>
+  </header>
+
+  <main>
+    <section class="controls">
+      <h2>Dials</h2>
+      <label>Mode
+        <select id="mode">
+          <option value="none">None</option>
+          <option value="audio">Audio</option>
+          <option value="video">Video</option>
+          <option value="av" selected>A+V</option>
+        </select>
+      </label>
+      <label>Left (analytical) <output id="left-out">0</output>
+        <input type="range" id="left" min="0" max="4" step="1" value="0"></label>
+      <label>Right (artistic) <output id="right-out">0</output>
+        <input type="range" id="right" min="0" max="4" step="1" value="0"></label>
+      <label>Dark (somber) <output id="dark-out">0</output>
+        <input type="range" id="dark" min="0" max="4" step="1" value="0"></label>
+      <label>Light (uplifting) <output id="light-out">0</output>
+        <input type="range" id="light" min="0" max="4" step="1" value="0"></label>
+
+      <h2>Model knobs</h2>
+      <label>Brain weight <output id="brain_weight-out">1</output>
+        <input type="range" id="brain_weight" min="0" max="4" step="0.5" value="1"></label>
+      <label>Mood weight <output id="mood_weight-out">1</output>
+        <input type="range" id="mood_weight" min="0" max="4" step="0.5" value="1"></label>
+      <label>Pool size <output id="pool_size-out">4</output>
+        <input type="range" id="pool_size" min="1" max="10" step="1" value="4"></label>
+      <label class="check"><input type="checkbox" id="approved_only"> Approved only</label>
+    </section>
+
+    <section class="xray">
+      <div class="pick">
+        <h2>Picked</h2>
+        <div id="pick"></div>
+      </div>
+      <div class="pool">
+        <h2>Pool (nearest first)</h2>
+        <ol id="pool"></ol>
+      </div>
+      <div class="maps">
+        <h2>Coordinate maps</h2>
+        <div class="map"><div class="label">Brain — Left × Right</div><div id="brain-grid" class="grid5"></div></div>
+        <div class="map"><div class="label">Mood — Dark × Light</div><div id="mood-grid" class="grid5"></div></div>
+      </div>
+    </section>
+  </main>
+
+  <script src="/app.js"></script>
+</body>
+</html>
diff --git a/simulator/static/style.css b/simulator/static/style.css
new file mode 100644
index 0000000..79371ce
--- /dev/null
+++ b/simulator/static/style.css
@@ -0,0 +1,26 @@
+:root { color-scheme: dark; }
+* { box-sizing: border-box; }
+body { margin: 0; font-family: -apple-system, system-ui, sans-serif; background: #0e0e16; color: #e6e6ee; }
+header { padding: 12px 20px; border-bottom: 1px solid #2a2a3a; display: flex; justify-content: space-between; align-items: baseline; }
+header h1 { font-size: 18px; margin: 0; }
+.meta { font-size: 12px; color: #9a9ab0; }
+main { display: grid; grid-template-columns: 280px 1fr; gap: 20px; padding: 20px; }
+.controls label { display: block; margin: 8px 0; font-size: 13px; }
+.controls input[type=range] { width: 100%; }
+.controls .check { display: flex; gap: 6px; align-items: center; }
+h2 { font-size: 13px; text-transform: uppercase; letter-spacing: .5px; color: #9a9ab0; }
+.xray { display: grid; grid-template-columns: 1fr 1fr; gap: 20px; align-items: start; }
+.pick #pick { background: #1a1a2e; border: 1px solid #33334a; border-radius: 8px; padding: 14px; min-height: 80px; }
+.pick .title { font-size: 16px; font-weight: 600; }
+.pick .void { color: #7777aa; font-style: italic; }
+.pool ol { margin: 0; padding-left: 18px; font-size: 13px; }
+.pool li { margin: 4px 0; }
+.pool li.winner { color: #7fffd4; font-weight: 600; }
+.pool .dist { color: #9a9ab0; }
+.maps { grid-column: 1 / -1; display: flex; gap: 40px; }
+.grid5 { display: grid; grid-template-columns: repeat(5, 28px); grid-template-rows: repeat(5, 28px); gap: 3px; }
+.grid5 .cell { background: #1c1c2c; border: 1px solid #2a2a3a; border-radius: 3px; position: relative; }
+.grid5 .cell.cand { background: #3a3a66; }
+.grid5 .cell.point { outline: 2px solid #7fffd4; }
+.grid5 .cell .n { position: absolute; right: 2px; bottom: 1px; font-size: 9px; color: #aab; }
+.label { font-size: 11px; color: #9a9ab0; margin-bottom: 4px; }
diff --git a/tests/test_fixtures.py b/tests/test_fixtures.py
new file mode 100644
index 0000000..8e0d8cd
--- /dev/null
+++ b/tests/test_fixtures.py
@@ -0,0 +1,40 @@
+from hef.catalog import validate_catalog
+from hef.selection import CONTENT_MODES
+from simulator.fixtures import generate_fixture_catalog
+
+
+def test_fixture_catalog_is_valid():
+    records = generate_fixture_catalog()
+    validate_catalog(records)  # raises on any invalid record or duplicate id
+
+
+def test_fixture_catalog_spans_the_coordinate_space():
+    records = generate_fixture_catalog()
+    coords = {(r.left, r.right, r.dark, r.light) for r in records}
+    # all 625 cells of the 5x5 brain x 5x5 mood space are present
+    assert len(coords) == 625
+
+
+def test_fixture_catalog_has_every_content_mode():
+    records = generate_fixture_catalog()
+    present = {r.mode for r in records}
+    assert CONTENT_MODES <= present
+
+
+def test_fixture_catalog_mixes_review_statuses():
+    records = generate_fixture_catalog()
+    statuses = {r.review_status for r in records}
+    assert statuses == {"proposed", "approved"}
+
+
+def test_fixture_catalog_references_no_real_media():
+    records = generate_fixture_catalog()
+    assert all(r.file_path == "" for r in records)
+
+
+def test_fixture_catalog_is_deterministic():
+    a = generate_fixture_catalog(seed=42)
+    b = generate_fixture_catalog(seed=42)
+    assert [r.id for r in a] == [r.id for r in b]
+    assert [r.mode for r in a] == [r.mode for r in b]
+    assert [r.review_status for r in a] == [r.review_status for r in b]
diff --git a/tests/test_selection_ranked.py b/tests/test_selection_ranked.py
new file mode 100644
index 0000000..80da4b9
--- /dev/null
+++ b/tests/test_selection_ranked.py
@@ -0,0 +1,87 @@
+import random
+
+import pytest
+
+from hef.catalog import Record
+from hef.selection import Coordinate, Weights, ranked_candidates, select
+
+
+def make_record(**overrides):
+    base = dict(
+        id="r",
+        title="t",
+        source_url="u",
+        source_archive="internet_archive",
+        license="public_domain",
+        mode="video",
+        left=0,
+        right=0,
+        dark=0,
+        light=0,
+        duration_s=600,
+        file_path="",
+    )
+    base.update(overrides)
+    return Record(**base)
+
+
+def test_ranked_candidates_sorts_nearest_first_with_distances():
+    near = make_record(id="near", mode="video", left=1, right=1, dark=0, light=0)
+    far = make_record(id="far", mode="video", left=4, right=4, dark=4, light=4)
+    ranked = ranked_candidates([far, near], Coordinate(0, 0, 0, 0), "video")
+    assert [r.id for r, _ in ranked] == ["near", "far"]
+    assert ranked[0][1] < ranked[1][1]
+
+
+def test_ranked_candidates_caps_at_pool_size():
+    recs = [make_record(id=f"r{i}", mode="video", left=i % 5) for i in range(10)]
+    ranked = ranked_candidates(recs, Coordinate(0, 0, 0, 0), "video", pool_size=3)
+    assert len(ranked) == 3
+
+
+def test_ranked_candidates_filters_by_mode():
+    a = make_record(id="aud", mode="audio")
+    v = make_record(id="vid", mode="video")
+    ranked = ranked_candidates([a, v], Coordinate(0, 0, 0, 0), "audio")
+    assert [r.id for r, _ in ranked] == ["aud"]
+
+
+def test_ranked_candidates_av_falls_back_to_audio_and_video():
+    a = make_record(id="aud", mode="audio")
+    v = make_record(id="vid", mode="video")
+    ranked = ranked_candidates([a, v], Coordinate(0, 0, 0, 0), "av", pool_size=4)
+    assert {r.id for r, _ in ranked} == {"aud", "vid"}
+
+
+def test_ranked_candidates_approved_only():
+    p = make_record(id="prop", mode="video", review_status="proposed")
+    ok = make_record(id="appr", mode="video", review_status="approved")
+    ranked = ranked_candidates([p, ok], Coordinate(0, 0, 0, 0), "video", approved_only=True)
+    assert [r.id for r, _ in ranked] == ["appr"]
+
+
+def test_ranked_candidates_rejects_none_mode():
+    with pytest.raises(ValueError):
+        ranked_candidates([], Coordinate(0, 0, 0, 0), "none")
+
+
+def test_select_returns_rank_one_of_ranked_candidates():
+    recs = [
+        make_record(id="near", mode="video", left=1),
+        make_record(id="far", mode="video", left=4),
+    ]
+    coord = Coordinate(0, 0, 0, 0)
+    ranked = ranked_candidates(recs, coord, "video")
+    assert select(recs, coord, "video", rng=None).id == ranked[0][0].id
+
+
+def test_select_none_mode_still_returns_none():
+    recs = [make_record(id="v", mode="video")]
+    assert select(recs, Coordinate(0, 0, 0, 0), "none") is None
+
+
+def test_select_shuffles_within_pool_when_rng_given():
+    recs = [make_record(id=f"r{i}", mode="video", left=i) for i in range(5)]
+    coord = Coordinate(0, 0, 0, 0)
+    picks = {select(recs, coord, "video", pool_size=5, rng=random.Random(s)).id for s in range(20)}
+    assert len(picks) > 1
diff --git a/tests/test_simulator_api.py b/tests/test_simulator_api.py
new file mode 100644
index 0000000..57e6b24
--- /dev/null
+++ b/tests/test_simulator_api.py
@@ -0,0 +1,102 @@
+import pytest
+from fastapi.testclient import TestClient
+
+from hef.catalog import Record
+from simulator.app import create_app
+
+
+def make_record(**overrides):
+    base = dict(
+        id="r",
+        title="t",
+        source_url="u",
+        source_archive="internet_archive",
+        license="public_domain",
+        mode="video",
+        left=0,
+        right=0,
+        dark=0,
+        light=0,
+        duration_s=600,
+        file_path="",
+    )
+    base.update(overrides)
+    return Record(**base)
+
+
+@pytest.fixture
+def client():
+    records = [
+        make_record(id="v-near", mode="video", left=0, right=0, dark=0, light=0),
+        make_record(id="v-far", mode="video", left=4, right=4, dark=4, light=4),
+        make_record(id="a-one", mode="audio", left=1, right=1, dark=1, light=1),
+        make_record(id="prop", mode="video", left=0, right=0, dark=0, light=1,
+                    review_status="proposed"),
+        make_record(id="appr", mode="video", left=0, right=0, dark=0, light=1,
+                    review_status="approved"),
+    ]
+    return TestClient(create_app(records=records))
+
+
+def _body(**overrides):
+    base = dict(left=0, right=0, dark=0, light=0, mode="video")
+    base.update(overrides)
+    return base
+
+
+def test_select_returns_pick_and_ranked_pool(client):
+    resp = client.post("/api/select", json=_body(mode="video", pool_size=4))
+    assert resp.status_code == 200
+    data = resp.json()
+    assert data["pick"]["id"] == "v-near"
+    ids = [c["record"]["id"] for c in data["pool"]]
+    assert ids[0] == "v-near"
+    assert all("distance" in c and "rank" in c for c in data["pool"])
+    assert [c["rank"] for c in data["pool"]] == list(range(1, len(data["pool"]) + 1))
+
+
+def test_none_mode_is_the_void(client):
+    resp = client.post("/api/select", json=_body(mode="none"))
+    assert resp.status_code == 200
+    data = resp.json()
+    assert data["pick"] is None
+    assert data["pool"] == []
+
+
+def test_dial_out_of_range_is_rejected(client):
+    resp = client.post("/api/select", json=_body(left=7))
+    assert resp.status_code == 422
+
+
+def test_bad_mode_is_rejected(client):
+    resp = client.post("/api/select", json=_body(mode="banana"))
+    assert resp.status_code == 422
+
+
+def test_approved_only_narrows_pool(client):
+    resp = client.post("/api/select", json=_body(left=0, right=0, dark=0, light=1,
+                                                 mode="video", approved_only=True))
+    data = resp.json()
+    assert all(c["record"]["review_status"] == "approved" for c in data["pool"])
+
+
+def test_catalog_meta_reports_counts(client):
+    resp = client.get("/api/catalog/meta")
+    assert resp.status_code == 200
+    data = resp.json()
+    assert data["total"] == 5
+    assert data["by_mode"]["video"] == 4
+    assert data["by_mode"]["audio"] == 1
+    assert set(data["by_status"]) == {"proposed", "approved"}
+
+
+from simulator.app import create_app as _create_app_for_static
+
+
+def test_index_is_served():
+    # The default app mounts the real static dir.
+    client = TestClient(_create_app_for_static())
+    resp = client.get("/")
+    assert resp.status_code == 200
+    assert "text/html" in resp.headers["content-type"]
+    assert "X-ray" in resp.text