feat(api): rich 409 merge hint and POST tags merge endpoint with backfill enqueue

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_api_tag_merge.py

@@ -0,0 +1,112 @@
+import pytest
+
+from backend.app import create_app
+
+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
+
+
+async def _mk(client, name, kind):
+    r = await client.post("/api/tags", json={"name": name, "kind": kind})
+    return (await r.get_json())["id"]
+
+
+@pytest.mark.asyncio
+async def test_rename_collision_returns_rich_409(client):
+    tgt = await _mk(client, "Canonical", "general")
+    src = await _mk(client, "Duplicate", "general")
+    resp = await client.patch(f"/api/tags/{src}", json={"name": "Canonical"})
+    assert resp.status_code == 409
+    body = await resp.get_json()
+    assert body["target"]["id"] == tgt
+    assert body["target"]["name"] == "Canonical"
+    assert body["source_image_count"] == 0
+    assert body["will_alias"] is False
+
+
+@pytest.mark.asyncio
+async def test_merge_endpoint_moves_and_deletes(client, monkeypatch):
+    calls = []
+    from backend.app.tasks import ml as ml_tasks
+
+    monkeypatch.setattr(
+        ml_tasks.apply_allowlist_tags,
+        "delay",
+        lambda **kw: calls.append(kw),
+    )
+    tgt = await _mk(client, "Keep", "general")
+    src = await _mk(client, "Gone", "general")
+    resp = await client.post(
+        f"/api/tags/{src}/merge", json={"target_id": tgt}
+    )
+    assert resp.status_code == 200
+    body = await resp.get_json()
+    assert body["target"]["id"] == tgt
+    assert body["source_deleted"] is True
+    # source is gone: renaming something else onto its old name no longer collides
+    other = await _mk(client, "Other", "general")
+    r2 = await client.patch(f"/api/tags/{other}", json={"name": "Gone"})
+    assert r2.status_code == 200
+
+
+@pytest.mark.asyncio
+async def test_merge_enqueues_backfill_when_target_allowlisted(
+    client, monkeypatch
+):
+    calls = []
+    from backend.app.tasks import ml as ml_tasks
+
+    monkeypatch.setattr(
+        ml_tasks.apply_allowlist_tags,
+        "delay",
+        lambda **kw: calls.append(kw),
+    )
+    tgt = await _mk(client, "AllowTgt", "general")
+    src = await _mk(client, "AllowSrc", "general")
+    # No public route adds a tag to the allowlist (it happens via
+    # accept-suggestion); set the row directly through the app session.
+    from backend.app.extensions import get_session
+    from backend.app.models.tag_allowlist import TagAllowlist
+
+    async with get_session() as s:
+        s.add(TagAllowlist(tag_id=tgt))
+        await s.commit()
+
+    resp = await client.post(
+        f"/api/tags/{src}/merge", json={"target_id": tgt}
+    )
+    assert resp.status_code == 200
+    assert calls == [{"tag_id": tgt}]
+
+
+@pytest.mark.asyncio
+async def test_merge_self_is_400(client):
+    t = await _mk(client, "Selfie", "general")
+    resp = await client.post(f"/api/tags/{t}/merge", json={"target_id": t})
+    assert resp.status_code == 400
+
+
+@pytest.mark.asyncio
+async def test_merge_missing_target_is_404(client):
+    t = await _mk(client, "Lonely", "general")
+    resp = await client.post(
+        f"/api/tags/{t}/merge", json={"target_id": 999999}
+    )
+    assert resp.status_code == 404
+
+
+@pytest.mark.asyncio
+async def test_merge_requires_target_id(client):
+    t = await _mk(client, "NoBody", "general")
+    resp = await client.post(f"/api/tags/{t}/merge", json={})
+    assert resp.status_code == 400