Add delete-downloaded-video and real YouTube unsubscribe

Delete local copy:
- MeTubeClient.delete_download() -> POST /delete {ids, where: "done"}
- Only ever acts on a job our own app tracked (metube_job_id we stored from
  its own 'completed' event), never a pre-existing MeTube file
- New "deleted" terminal status; DELETE /api/videos/{id}/download
- Frontend: delete button next to "На сервере" badge, confirm dialog

Unsubscribe (deliberate deviation from the original TZ's MVP exclusion of
subscription management, per explicit user request after being shown the
tradeoff):
- OAuth scope widened from youtube.readonly to full youtube (read/write) --
  existing stored tokens only cover the old scope, so unsubscribing needs a
  fresh reconnect; reads keep working unchanged on the old token meanwhile
- channels.youtube_subscription_id (distinct from the channel id; that's
  what subscriptions.delete actually keys on) captured during subscriptions
  sync
- YouTubeInsufficientScope raised on 401/403 "insufficient authentication
  scopes" and surfaced as a clear 403 asking the user to reconnect, rather
  than a generic API error
- POST /api/channels/{id}/unsubscribe calls subscriptions.delete and marks
  the channel unsubscribed locally on success
- Frontend: "Отписаться" button on ChannelCard with confirm dialog

10 new backend tests (73 total).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/app/services/download_jobs.py

@@ -15,6 +15,10 @@ class MeTubeRejected(Exception):
     pass
 
 
+class DeleteNotAllowed(Exception):
+    pass
+
+
 def get_latest_job(db: Session, video_id: int) -> DownloadJob | None:
     return (
         db.query(DownloadJob)
@@ -55,6 +59,24 @@ def request_download(db: Session, video: Video) -> DownloadJob:
     return job
 
 
+def delete_local_copy(db: Session, video: Video) -> DownloadJob:
+    """Deletes our own previously-downloaded copy from MeTube. Only ever acts
+    on a job this app itself created and tracked (never a file MeTube already
+    had before we existed) -- see AGENTS.md constraint 10."""
+    job = get_latest_job(db, video.id)
+    if job is None or job.status != "completed":
+        raise DeleteNotAllowed("No completed local copy to delete")
+    if not job.metube_job_id:
+        raise DeleteNotAllowed("Missing MeTube job id, cannot request deletion")
+
+    MeTubeClient().delete_download(job.metube_job_id)
+
+    job.status = "deleted"
+    job.media_url = None
+    db.commit()
+    return job
+
+
 def _find_job_by_payload(db: Session, payload: dict) -> DownloadJob | None:
     metube_id = payload.get("id")
     if metube_id:

backend/app/services/google_oauth.py

@@ -14,7 +14,13 @@ from app.models.oauth_credentials import SINGLETON_ID, OAuthCredentials
 logger = logging.getLogger(__name__)
 
 SCOPES = [
-    "https://www.googleapis.com/auth/youtube.readonly",
+    # Full read/write scope, not just youtube.readonly: unsubscribing from a
+    # channel (subscriptions.delete) requires write access. Deliberate
+    # deviation from the original "minimal scope" TZ recommendation, per
+    # explicit user request. Existing stored refresh tokens were granted
+    # under the old readonly-only scope and won't cover this -- users must
+    # reconnect once for this to take effect.
+    "https://www.googleapis.com/auth/youtube",
     "openid",
     "https://www.googleapis.com/auth/userinfo.email",
     "https://www.googleapis.com/auth/userinfo.profile",

backend/app/services/metube_client.py

@@ -77,6 +77,21 @@ class MeTubeClient:
         response.raise_for_status()
         return response.json()
 
+    def delete_download(self, metube_job_id: str) -> dict:
+        """Asks MeTube to remove a finished download from its 'done' list and
+        delete the underlying file (actual file deletion additionally depends
+        on MeTube's own DELETE_FILE_ON_TRASHCAN config, which we don't
+        control). Only ever called with a metube_job_id our own app tracked
+        from a download it started -- never touches files MeTube already had
+        before we existed."""
+        response = httpx.post(
+            f"{self.api_base_url}/delete",
+            json={"ids": [metube_job_id], "where": "done"},
+            timeout=self.timeout,
+        )
+        response.raise_for_status()
+        return response.json()
+
     def build_media_url(self, filename: str) -> str | None:
         """Safely turn a MeTube-reported filename into a public /download/... URL.
 

backend/app/services/sync.py

@@ -78,6 +78,7 @@ def sync_subscriptions(db: Session) -> dict:
             if channel is None:
                 channel = Channel(
                     youtube_channel_id=sub["youtube_channel_id"],
+                    youtube_subscription_id=sub["youtube_subscription_id"],
                     title=sub["title"],
                     description=sub["description"],
                     thumbnail_url=sub["thumbnail_url"],
@@ -88,6 +89,7 @@ def sync_subscriptions(db: Session) -> dict:
                 existing[sub["youtube_channel_id"]] = channel
                 added += 1
             else:
+                channel.youtube_subscription_id = sub["youtube_subscription_id"]
                 channel.title = sub["title"]
                 channel.description = sub["description"]
                 channel.thumbnail_url = sub["thumbnail_url"]
@@ -249,3 +251,21 @@ def sync_videos(db: Session) -> dict:
         raise
     finally:
         _videos_lock.release()
+
+
+class ChannelHasNoSubscriptionId(Exception):
+    pass
+
+
+def unsubscribe_channel(db: Session, channel: Channel) -> None:
+    """Actually unsubscribes on YouTube (subscriptions.delete) -- deliberately
+    out of the original MVP scope, added on explicit user request. Requires
+    the write-capable OAuth scope; see google_oauth.SCOPES."""
+    if not channel.youtube_subscription_id:
+        raise ChannelHasNoSubscriptionId(
+            "This channel was synced before subscription ids were tracked; run a subscriptions sync first"
+        )
+    credentials = google_oauth.get_credentials(db)
+    youtube_client.unsubscribe(credentials, channel.youtube_subscription_id)
+    channel.subscribed = False
+    db.commit()

backend/app/services/youtube_client.py

@@ -19,12 +19,20 @@ class YouTubeAPIError(Exception):
     pass
 
 
+class YouTubeInsufficientScope(Exception):
+    """Raised when Google rejects a call because the stored token was granted
+    under an older, narrower scope (e.g. readonly tokens issued before the
+    unsubscribe feature needed write access) -- the fix is reconnecting."""
+
+    pass
+
+
 def _headers(credentials: Credentials) -> dict:
     return {"Authorization": f"Bearer {credentials.token}"}
 
 
 def _raise_for_status(response: httpx.Response) -> None:
-    if response.status_code == 200:
+    if response.status_code in (200, 204):
         return
     try:
         payload = response.json()
@@ -37,6 +45,11 @@ def _raise_for_status(response: httpx.Response) -> None:
     if response.status_code == 403 and reason in ("quotaExceeded", "dailyLimitExceeded", "rateLimitExceeded"):
         raise YouTubeQuotaExceeded(message)
 
+    if response.status_code in (401, 403) and (
+        reason == "insufficientPermissions" or "insufficient authentication scopes" in message.lower()
+    ):
+        raise YouTubeInsufficientScope(message)
+
     logger.error("YouTube API error %s: %s", response.status_code, message)
     raise YouTubeAPIError(f"{response.status_code}: {message}")
 
@@ -72,6 +85,10 @@ def fetch_subscriptions(credentials: Credentials) -> list[dict]:
                 subscriptions.append(
                     {
                         "youtube_channel_id": channel_id,
+                        # The subscription resource's own id -- distinct from
+                        # the channel id, required to later call
+                        # subscriptions.delete (unsubscribe).
+                        "youtube_subscription_id": item.get("id"),
                         "title": snippet.get("title", ""),
                         "description": snippet.get("description", ""),
                         "thumbnail_url": thumbnail,
@@ -142,6 +159,19 @@ def fetch_videos_details(credentials: Credentials, video_ids: list[str]) -> list
     return results
 
 
+def unsubscribe(credentials: Credentials, youtube_subscription_id: str) -> None:
+    with httpx.Client(timeout=settings.metube_request_timeout_seconds) as client:
+        response = client.delete(
+            f"{API_BASE}/subscriptions",
+            params={"id": youtube_subscription_id},
+            headers=_headers(credentials),
+        )
+    if response.status_code == 404:
+        # Already gone (unsubscribed elsewhere, or stale id) -- treat as success.
+        return
+    _raise_for_status(response)
+
+
 def fetch_uploads_playlists(credentials: Credentials, channel_ids: list[str]) -> dict[str, str]:
     result: dict[str, str] = {}