feat: the extension adds Discord channels to an artist you pick, and its tests gate the XPI (milestone 429)

Server (#4420)
- extension_service gains a Discord pattern (server or channel, jump links,
  ptb/canary; not DMs or threads), mirrored in platforms.js and pinned by
  the shared artist-url-samples.json.
- probe on a Discord URL matches the source by ids under any artist, reports
  a whole-server source as covering the channel, suggests the artist who owns
  another source on the same server, and names server/channel via the stored
  token (best-effort, bounded, no rate-limit waits).
- quick-add takes artist_id / artist_name; Discord URLs are stored canonical.

Extension (#4421, #4422)
- Content script on discord.com; SPA navigation by URL polling (the old
  pushState patch ran in the isolated world and never fired); stale probes
  are dropped.
- Discord chip opens an Add panel: this channel or the whole server, and the
  suggested artist / a search / a new name.
- Popup: sources show artist, platform and state; a Discord token export is
  verified by FC and the result shown. Token capture covers ptb/canary.
- Pure logic in lib/chip.js and lib/popup-format.js, with specs.

CI (#4423)
- extension.yml's lane (web-ext lint, vitest, XPI contents) moves into
  build.yml as extension-test and joins the needs of sign-extension,
  build-web and build-agent. As a separate workflow it gated nothing: a red
  extension suite still signed and shipped the XPI (rule 177).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LVjrnpQjRgHdvq95rASoiR

tests/test_api_extension.py

@@ -355,6 +355,177 @@ async def test_quick_add_source_attaches_to_existing_artist(client, ext_key, db,
     assert artist_count == 1  # no duplicate created
 
 
+# --- Discord: channels are added to a CHOSEN artist (milestone 429) ---
+
+
+_GUILD = "111111111111111111"
+_CHAN = "222222222222222222"
+_OTHER_CHAN = "333333333333333333"
+
+
+async def _discord_source(db, name, url):
+    artist = Artist(name=name, slug=name.lower(), is_subscription=True)
+    db.add(artist)
+    await db.flush()
+    src = Source(artist_id=artist.id, platform="discord", url=url,
+                 enabled=True, config_overrides={})
+    db.add(src)
+    await db.commit()
+    return artist, src
+
+
+@pytest.mark.asyncio
+async def test_a_discord_channel_is_added_to_the_artist_the_operator_picked(
+    client, ext_key, db, db_sync,
+):
+    artist = Artist(name="Tamada", slug="tamada", is_subscription=True)
+    db.add(artist)
+    await db.commit()
+    resp = await client.post(
+        "/api/extension/quick-add-source",
+        # A jump link on the ptb host still names the channel.
+        json={"url": f"https://ptb.discord.com/channels/{_GUILD}/{_CHAN}/999",
+              "artist_id": artist.id},
+        headers={"X-Extension-Key": ext_key},
+    )
+    assert resp.status_code == 201, await resp.get_json()
+    body = await resp.get_json()
+    assert body["artist"]["id"] == artist.id
+    assert body["created_artist"] is False
+    # Stored canonical, so the manual form and the ingester read the same URL.
+    assert body["source"]["url"] == f"https://discord.com/channels/{_GUILD}/{_CHAN}"
+    assert body["source"]["platform"] == "discord"
+
+
+@pytest.mark.asyncio
+async def test_a_discord_add_can_name_a_new_artist(client, ext_key):
+    resp = await client.post(
+        "/api/extension/quick-add-source",
+        json={"url": f"https://discord.com/channels/{_GUILD}", "artist_name": "Studio Q"},
+        headers={"X-Extension-Key": ext_key},
+    )
+    assert resp.status_code == 201
+    body = await resp.get_json()
+    assert body["artist"]["name"] == "Studio Q"
+    assert body["created_artist"] is True
+    assert body["source"]["url"] == f"https://discord.com/channels/{_GUILD}"
+
+
+@pytest.mark.asyncio
+async def test_a_discord_add_with_no_artist_and_no_token_names_the_server(client, ext_key):
+    """No stored token means no server name to read; the fallback still names
+    a readable artist rather than slugifying the ids."""
+    resp = await client.post(
+        "/api/extension/quick-add-source",
+        json={"url": f"https://discord.com/channels/{_GUILD}/{_CHAN}"},
+        headers={"X-Extension-Key": ext_key},
+    )
+    assert resp.status_code == 201
+    assert (await resp.get_json())["artist"]["name"] == f"Discord {_GUILD}"
+
+
+@pytest.mark.asyncio
+async def test_re_adding_a_discord_channel_keeps_its_artist(client, ext_key, db):
+    """Identity by source (#130), compared by ids: a row stored with a
+    trailing slash is the same channel, and naming another artist does not
+    move it."""
+    owner, src = await _discord_source(
+        db, "Owner", f"https://discord.com/channels/{_GUILD}/{_CHAN}/",
+    )
+    resp = await client.post(
+        "/api/extension/quick-add-source",
+        json={"url": f"https://discord.com/channels/{_GUILD}/{_CHAN}",
+              "artist_name": "Someone Else"},
+        headers={"X-Extension-Key": ext_key},
+    )
+    assert resp.status_code == 200
+    body = await resp.get_json()
+    assert body["source"]["id"] == src.id
+    assert body["artist"]["id"] == owner.id
+
+
+@pytest.mark.asyncio
+async def test_quick_add_with_a_missing_artist_id_is_404(client, ext_key):
+    resp = await client.post(
+        "/api/extension/quick-add-source",
+        json={"url": f"https://discord.com/channels/{_GUILD}/{_CHAN}", "artist_id": 987654},
+        headers={"X-Extension-Key": ext_key},
+    )
+    assert resp.status_code == 404
+
+
+@pytest.mark.asyncio
+async def test_quick_add_rejects_a_non_integer_artist_id(client, ext_key):
+    resp = await client.post(
+        "/api/extension/quick-add-source",
+        json={"url": f"https://discord.com/channels/{_GUILD}/{_CHAN}", "artist_id": "7"},
+        headers={"X-Extension-Key": ext_key},
+    )
+    assert resp.status_code == 400
+
+
+async def _probe(client, ext_key, url):
+    resp = await client.get(
+        "/api/extension/probe", query_string={"url": url},
+        headers={"X-Extension-Key": ext_key},
+    )
+    assert resp.status_code == 200
+    return await resp.get_json()
+
+
+@pytest.mark.asyncio
+async def test_probe_a_fresh_discord_channel_is_new_with_both_urls(client, ext_key):
+    body = await _probe(client, ext_key, f"https://discord.com/channels/{_GUILD}/{_CHAN}")
+    assert body["state"] == "new"
+    assert body["platform"] == "discord"
+    d = body["discord"]
+    assert d["server_id"] == _GUILD and d["channel_id"] == _CHAN
+    assert d["server_url"] == f"https://discord.com/channels/{_GUILD}"
+    assert d["channel_url"] == f"https://discord.com/channels/{_GUILD}/{_CHAN}"
+    # No token stored → no names, and no error.
+    assert d["server_name"] is None and d["channel_name"] is None
+
+
+@pytest.mark.asyncio
+async def test_probe_suggests_the_artist_who_owns_another_channel_on_the_server(
+    client, ext_key, db,
+):
+    owner, _ = await _discord_source(
+        db, "Owner", f"https://discord.com/channels/{_GUILD}/{_OTHER_CHAN}",
+    )
+    body = await _probe(client, ext_key, f"https://discord.com/channels/{_GUILD}/{_CHAN}")
+    assert body["state"] == "artist_match"
+    assert body["artist"]["id"] == owner.id
+    assert "source" not in body
+
+
+@pytest.mark.asyncio
+async def test_probe_finds_the_channel_under_any_artist(client, ext_key, db):
+    owner, src = await _discord_source(
+        db, "Owner", f"https://discord.com/channels/{_GUILD}/{_CHAN}",
+    )
+    body = await _probe(client, ext_key, f"https://discord.com/channels/{_GUILD}/{_CHAN}/555")
+    assert body["state"] == "source_match"
+    assert body["source"]["id"] == src.id
+    assert body["artist"]["id"] == owner.id
+    assert body["covered_by_server"] is False
+
+
+@pytest.mark.asyncio
+async def test_probe_a_channel_is_covered_by_a_whole_server_source(client, ext_key, db):
+    _, src = await _discord_source(db, "Owner", f"https://discord.com/channels/{_GUILD}")
+    body = await _probe(client, ext_key, f"https://discord.com/channels/{_GUILD}/{_CHAN}")
+    assert body["state"] == "source_match"
+    assert body["source"]["id"] == src.id
+    assert body["covered_by_server"] is True
+
+
+@pytest.mark.asyncio
+async def test_probe_a_discord_dm_is_not_a_source(client, ext_key):
+    body = await _probe(client, ext_key, f"https://discord.com/channels/@me/{_CHAN}")
+    assert body["state"] == "unknown_platform"
+
+
 # --- /api/extension/manifest ---------------------------------------
 
 

tests/test_extension_artist_patterns.py

@@ -104,9 +104,8 @@ def test_the_sample_table_covers_every_platform_that_has_a_pattern():
     samples would make this file pass by testing less — the failure mode that
     makes absence-based tests untrustworthy (snippet #3352).
 
-    Discord is deliberately absent from both: it has no artist pattern on
-    either side, because it is channel-based and has no creator page to put a
-    button on.
+    Discord is in the table since milestone 429: its "slug" is the
+    server/channel pair, and the Add panel picks the artist.
     """
     from backend.app.services.extension_service import _PLATFORM_PATTERNS