diff --git a/server/asset_pool.py b/server/asset_pool.py
new file mode 100644
index 0000000..f481782
--- /dev/null
+++ b/server/asset_pool.py
@@ -0,0 +1,130 @@
+"""Asset pool — manages generated images and audio on disk with severity tagging."""
+
+import random
+import time
+import uuid
+from dataclasses import dataclass
+from pathlib import Path
+from threading import Lock
+
+from server.config import config
+
+
+@dataclass
+class Asset:
+    """A generated asset with metadata."""
+    filename: str
+    severity: float
+    created_at: float
+    asset_type: str  # "image" or "audio"
+
+    @property
+    def url(self) -> str:
+        subdir = "img" if self.asset_type == "image" else "audio"
+        return f"/assets/{subdir}/{self.filename}"
+
+
+class AssetPool:
+    """Thread-safe pool of generated assets with severity-based selection and rotation."""
+
+    def __init__(
+        self,
+        base_dir: str | None = None,
+        max_images: int | None = None,
+        max_audio: int | None = None,
+    ):
+        self.base_dir = Path(base_dir or config.assets_dir)
+        self.max_images = max_images if max_images is not None else config.escalation.max_images
+        self.max_audio = max_audio if max_audio is not None else config.escalation.max_audio_clips
+        self._images: list[Asset] = []
+        self._audio: list[Asset] = []
+        self._lock = Lock()
+
+        (self.base_dir / "img").mkdir(parents=True, exist_ok=True)
+        (self.base_dir / "audio").mkdir(parents=True, exist_ok=True)
+
+    @property
+    def image_count(self) -> int:
+        with self._lock:
+            return len(self._images)
+
+    @property
+    def audio_count(self) -> int:
+        with self._lock:
+            return len(self._audio)
+
+    def add_image(self, data: bytes, severity: float) -> str:
+        """Save image data to disk and add to pool. Returns URL path."""
+        filename = f"{uuid.uuid4().hex[:12]}.png"
+        path = self.base_dir / "img" / filename
+        path.write_bytes(data)
+
+        asset = Asset(
+            filename=filename,
+            severity=severity,
+            created_at=time.monotonic(),
+            asset_type="image",
+        )
+
+        with self._lock:
+            self._images.append(asset)
+            self._rotate(self._images, self.max_images, "img")
+
+        return asset.url
+
+    def add_audio(self, data: bytes, severity: float) -> str:
+        """Save audio data to disk and add to pool. Returns URL path."""
+        filename = f"{uuid.uuid4().hex[:12]}.wav"
+        path = self.base_dir / "audio" / filename
+        path.write_bytes(data)
+
+        asset = Asset(
+            filename=filename,
+            severity=severity,
+            created_at=time.monotonic(),
+            asset_type="audio",
+        )
+
+        with self._lock:
+            self._audio.append(asset)
+            self._rotate(self._audio, self.max_audio, "audio")
+
+        return asset.url
+
+    def select_image(self, target_severity: float) -> str | None:
+        """Select an image near the target severity. Weighted random, biased toward close matches."""
+        with self._lock:
+            return self._select(self._images, target_severity)
+
+    def select_audio(self, target_severity: float) -> str | None:
+        """Select an audio clip near the target severity."""
+        with self._lock:
+            return self._select(self._audio, target_severity)
+
+    def _select(self, assets: list[Asset], target: float) -> str | None:
+        """Weighted selection: closer severity = higher weight."""
+        if not assets:
+            return None
+        weights = []
+        for a in assets:
+            distance = abs(a.severity - target)
+            weights.append(1.0 / (1.0 + distance))
+        chosen = random.choices(assets, weights=weights, k=1)[0]
+        return chosen.url
+
+    def _rotate(self, assets: list[Asset], max_count: int, subdir: str) -> None:
+        """Remove oldest assets when pool exceeds capacity. Must hold lock."""
+        while len(assets) > max_count:
+            old = assets.pop(0)
+            path = self.base_dir / subdir / old.filename
+            try:
+                path.unlink(missing_ok=True)
+            except OSError:
+                pass
+
+    def get_status(self) -> dict:
+        with self._lock:
+            return {
+                "image_pool_size": len(self._images),
+                "audio_pool_size": len(self._audio),
+            }
diff --git a/tests/test_asset_pool.py b/tests/test_asset_pool.py
new file mode 100644
index 0000000..d4c8fbc
--- /dev/null
+++ b/tests/test_asset_pool.py
@@ -0,0 +1,112 @@
+from pathlib import Path
+
+from server.asset_pool import AssetPool
+
+
+def _make_pool(tmp_path: Path, max_images: int = 10, max_audio: int = 5) -> AssetPool:
+    return AssetPool(
+        base_dir=str(tmp_path),
+        max_images=max_images,
+        max_audio=max_audio,
+    )
+
+
+def _fake_image(tmp_path: Path, pool: AssetPool, severity: float) -> str:
+    content = b"fake png data"
+    return pool.add_image(content, severity=severity)
+
+
+def _fake_audio(tmp_path: Path, pool: AssetPool, severity: float) -> str:
+    content = b"fake wav data"
+    return pool.add_audio(content, severity=severity)
+
+
+class TestAssetPoolInit:
+    def test_creates_directories(self, tmp_path):
+        """Pool creates img/ and audio/ subdirectories."""
+        pool = _make_pool(tmp_path)
+        assert (tmp_path / "img").is_dir()
+        assert (tmp_path / "audio").is_dir()
+
+    def test_empty_pool(self, tmp_path):
+        """New pool has no assets."""
+        pool = _make_pool(tmp_path)
+        assert pool.image_count == 0
+        assert pool.audio_count == 0
+
+
+class TestAddAssets:
+    def test_add_image(self, tmp_path):
+        """Adding an image increments count and returns a URL path."""
+        pool = _make_pool(tmp_path)
+        url = _fake_image(tmp_path, pool, severity=1.0)
+        assert pool.image_count == 1
+        assert url.startswith("/assets/img/")
+        assert url.endswith(".png")
+
+    def test_add_audio(self, tmp_path):
+        """Adding audio increments count and returns a URL path."""
+        pool = _make_pool(tmp_path)
+        url = _fake_audio(tmp_path, pool, severity=1.0)
+        assert pool.audio_count == 1
+        assert url.startswith("/assets/audio/")
+        assert url.endswith(".wav")
+
+    def test_file_exists_on_disk(self, tmp_path):
+        """Added assets exist as real files."""
+        pool = _make_pool(tmp_path)
+        url = _fake_image(tmp_path, pool, severity=1.0)
+        filename = url.split("/")[-1]
+        assert (tmp_path / "img" / filename).exists()
+
+
+class TestSelectAssets:
+    def test_select_image_by_severity(self, tmp_path):
+        """Selects an image closest to target severity."""
+        pool = _make_pool(tmp_path)
+        _fake_image(tmp_path, pool, severity=0.5)
+        _fake_image(tmp_path, pool, severity=2.0)
+        _fake_image(tmp_path, pool, severity=4.0)
+        url = pool.select_image(target_severity=1.8)
+        assert url is not None
+
+    def test_select_audio_by_severity(self, tmp_path):
+        """Selects an audio clip closest to target severity."""
+        pool = _make_pool(tmp_path)
+        _fake_audio(tmp_path, pool, severity=0.5)
+        _fake_audio(tmp_path, pool, severity=3.0)
+        url = pool.select_audio(target_severity=2.5)
+        assert url is not None
+
+    def test_select_from_empty_returns_none(self, tmp_path):
+        """Selecting from empty pool returns None."""
+        pool = _make_pool(tmp_path)
+        assert pool.select_image(target_severity=1.0) is None
+        assert pool.select_audio(target_severity=1.0) is None
+
+
+class TestRotation:
+    def test_image_rotation(self, tmp_path):
+        """Oldest images are removed when pool exceeds max."""
+        pool = _make_pool(tmp_path, max_images=3)
+        for i in range(5):
+            _fake_image(tmp_path, pool, severity=float(i))
+        assert pool.image_count == 3
+
+    def test_audio_rotation(self, tmp_path):
+        """Oldest audio clips are removed when pool exceeds max."""
+        pool = _make_pool(tmp_path, max_audio=2)
+        for i in range(4):
+            _fake_audio(tmp_path, pool, severity=float(i))
+        assert pool.audio_count == 2
+
+
+class TestStatus:
+    def test_status_dict(self, tmp_path):
+        """Status returns pool sizes."""
+        pool = _make_pool(tmp_path)
+        _fake_image(tmp_path, pool, severity=1.0)
+        _fake_audio(tmp_path, pool, severity=1.0)
+        status = pool.get_status()
+        assert status["image_pool_size"] == 1
+        assert status["audio_pool_size"] == 1