diff --git a/backend/app/api/sources.py b/backend/app/api/sources.py
index d5ef480..fd2b109 100644
--- a/backend/app/api/sources.py
+++ b/backend/app/api/sources.py
@@ -1,8 +1,10 @@
-"""FC-3a: CRUD over Source rows."""
+"""FC-3a: CRUD over Source rows. FC-3c adds POST /<id>/check."""
 
 from quart import Blueprint, jsonify, request
+from sqlalchemy import select
 
 from ..extensions import get_session
+from ..models import DownloadEvent, Source
 from ..services.source_service import (
     KNOWN_PLATFORMS,
     ArtistNotFoundError,
@@ -114,3 +116,41 @@ async def delete_source(source_id: int):
         except LookupError:
             return _bad("not_found", status=404)
     return "", 204
+
+
+@sources_bp.route("/<int:source_id>/check", methods=["POST"])
+async def check_source(source_id: int):
+    """FC-3c: enqueue a download for this source.
+
+    Returns 202 with the new DownloadEvent id. If a pending/running
+    event already exists for this source, returns 409 with that id."""
+    async with get_session() as session:
+        source = (await session.execute(
+            select(Source).where(Source.id == source_id)
+        )).scalar_one_or_none()
+        if source is None:
+            return _bad("not_found", status=404, detail=f"source id={source_id}")
+        if not source.enabled:
+            return _bad("source_disabled", detail="enable the source first")
+
+        in_flight = (await session.execute(
+            select(DownloadEvent.id).where(
+                DownloadEvent.source_id == source_id,
+                DownloadEvent.status.in_(["pending", "running"]),
+            ).order_by(DownloadEvent.id.desc()).limit(1)
+        )).scalar_one_or_none()
+        if in_flight is not None:
+            return jsonify(
+                {"download_event_id": in_flight, "status": "already_running"}
+            ), 409
+
+        event = DownloadEvent(source_id=source_id, status="pending")
+        session.add(event)
+        await session.commit()
+        await session.refresh(event)
+        event_id = event.id
+
+    from ..tasks.download import download_source
+    download_source.delay(source_id)
+
+    return jsonify({"download_event_id": event_id, "status": "pending"}), 202
diff --git a/tests/test_api_sources_check.py b/tests/test_api_sources_check.py
new file mode 100644
index 0000000..c532738
--- /dev/null
+++ b/tests/test_api_sources_check.py
@@ -0,0 +1,77 @@
+import pytest
+
+from backend.app import create_app
+from backend.app.models import Artist, DownloadEvent, Source
+
+pytestmark = pytest.mark.integration
+
+
+@pytest.fixture
+async def app():
+    return create_app()
+
+
+@pytest.fixture
+async def client(app):
+    async with app.test_client() as c:
+        yield c
+
+
+@pytest.fixture
+async def seed(db):
+    artist = Artist(name="Alice", slug="alice")
+    db.add(artist)
+    await db.flush()
+    source = Source(
+        artist_id=artist.id, platform="patreon",
+        url="https://patreon.com/alice", enabled=True,
+        config_overrides={},
+    )
+    db.add(source)
+    await db.commit()
+    return source
+
+
+@pytest.mark.asyncio
+async def test_check_202_creates_pending_event(client, seed, monkeypatch):
+    monkeypatch.setattr(
+        "backend.app.tasks.download.download_source.delay",
+        lambda *a, **k: None,
+    )
+    resp = await client.post(f"/api/sources/{seed.id}/check")
+    assert resp.status_code == 202
+    body = await resp.get_json()
+    assert body["status"] == "pending"
+    assert isinstance(body["download_event_id"], int)
+
+
+@pytest.mark.asyncio
+async def test_check_404_for_unknown_source(client):
+    resp = await client.post("/api/sources/99999/check")
+    assert resp.status_code == 404
+
+
+@pytest.mark.asyncio
+async def test_check_400_for_disabled_source(client, db, seed):
+    seed.enabled = False
+    await db.commit()
+    resp = await client.post(f"/api/sources/{seed.id}/check")
+    assert resp.status_code == 400
+    body = await resp.get_json()
+    assert body["error"] == "source_disabled"
+
+
+@pytest.mark.asyncio
+async def test_check_409_when_already_running(client, db, seed, monkeypatch):
+    monkeypatch.setattr(
+        "backend.app.tasks.download.download_source.delay",
+        lambda *a, **k: None,
+    )
+    existing = DownloadEvent(source_id=seed.id, status="running")
+    db.add(existing)
+    await db.commit()
+    await db.refresh(existing)
+    resp = await client.post(f"/api/sources/{seed.id}/check")
+    assert resp.status_code == 409
+    body = await resp.get_json()
+    assert body["download_event_id"] == existing.id