fix(retry): fence the queue lease, clean up after a kill, name dead-lettered posts

P2 (hardening) of the retry audit, closing the report's remaining findings.

- Lease fencing. `lease_next` now stamps a random `lease_token`, and every
  write-back a worker makes (the 30s heartbeat, `delete_row`, `reschedule`,
  `mark_done`) is guarded by it. A lease that expired while its holder was
  stalled and was then re-leased used to let *both* holders write the same row:
  one duplicated the send, the other silently discarded the new holder's retry
  (a 0-row update was not even logged). Now a worker that no longer holds the
  lease drops its attempt at the next heartbeat and writes nothing. Reaching
  existing databases needed a migration chain, which `db.rs` had been
  pre-committed to: `MIGRATIONS` + `migrate` track `PRAGMA user_version`, with
  `schema_init` as the version-0 baseline. Verified on a database created
  before this change: user_version 0 -> 1, column added, rows intact.
- Dead-letter notifications no longer mislabel an unparsable payload. A row
  whose payload no longer deserializes as a `Task` (an older version's shape,
  corruption) used to skip the cache invalidation *and* report "Forward failed
  permanently" for a send task, because both were derived from the parsed
  value. The identity now comes off the raw JSON, so the stale link-cache entry
  is dropped and the message names the post.
- Temp files are marked and swept. Every temp file/dir the project creates now
  carries `x_media::TEMP_FILE_PREFIX`, and startup removes entries with that
  prefix older than an hour — a killed process leaves its downloads (up to
  hundreds of MB) behind because no destructor runs, and the age gate keeps the
  sweep away from a second instance's in-flight files. Verified live: the log
  reports the sweep, an aged leftover goes, a fresh prefixed file and an
  unrelated file stay.

AGENTS.md

@@ -38,13 +38,13 @@ The `x-media` library: `site::fetch(url)` dispatches through the `SITES` registr
 |---|---|
 | `crates/x-media/src/` | Fetch library. `site/mod.rs` = dispatcher + `Fetched`/`FetchError`/`download_media`/`media_size`; `media.rs` = `Media` enum; `examples/fetch.rs` = end-to-end usage sample |
 | `crates/x-media/src/site/<twitter\|pixiv\|bsky\|misskey\|bilibili>/` | One directory per site: `mod.rs` (re-exports), `interface.rs` (PATTERN, `enabled()`, `fetch_from_url()`, `cache_key`/`is_retryable`/`media_headers`, unit struct `<Name>Site` implementing `site::Site`, `From<SiteStruct> for Fetched`), `model.rs` (serde DTOs). Pixiv adds `api.rs` (auth + transport); twitter adds `auth.rs` (logged-in GraphQL `TweetDetail` fallback for NSFW tweets, gated on `TWITTER_AUTH_TOKEN`; without the token a withheld tweet stays `FetchError::Sensitive` and the bot reports it as age-restricted instead of "no media"). Misskey targets misskey.io only (`POST /api/notes/show`, 400+`NO_SUCH_NOTE` → NotFound). Bilibili fetches dynamics (images/animated images only — an attached video degrades to its cover, and its title stands in for the post text, which AV dynamics do not have) from `/x/polymer/web-dynamic/v1/detail` sent with `features=itemOpusStyle` (without that flag the legacy serialization drops an image/text post's body and headline entirely — `desc` comes back `null`; the adapter still parses the legacy `major.draw`/`desc`/`archive` shapes as a fallback). No WBI signature is involved; device cookies `buvid3`/`buvid4` are fetched automatically from `/x/frontend/finger/spi` because bilibili's `-352` risk control starts rejecting plain requests, `BILIBILI_COOKIE` is the escalation when an IP stays blocked; `b23.tv` short links are deliberately unmatched. Twitter's `from_syndication_json` HTML-decodes the API text — syndication and GraphQL `full_text` both arrive pre-escaped (`&gt;` `&lt;` `&amp;` `&#39;`) — so the stored text is raw and the caption escap…
-| `crates/xmedia-bot/src/main.rs` | Entry point: env/log init, command registration (`register_commands` — `setMyCommands` plus the profile description texts), shared `send::BOT` force-init, queue worker start, site login validation (`site::validate_all`), 300 s edit-expiry sweep (expired prompts are rewritten in place to `EDIT_PROMPT_EXPIRED_TEXT` with an empty keyboard — an edit, never a new message, so a background timer cannot wake a chat), dptree handler tree, webhook vs polling dispatch |
+| `crates/xmedia-bot/src/main.rs` | Entry point: env/log init, command registration (`register_commands` — `setMyCommands` plus the profile description texts), shared `send::BOT` force-init, startup sweep of this project's leftover temp files (`x_media::TEMP_FILE_PREFIX` + an age gate, since a killed process runs no destructors), queue worker start, site login validation (`site::validate_all`), 300 s edit-expiry sweep (expired prompts are rewritten in place to `EDIT_PROMPT_EXPIRED_TEXT` with an empty keyboard — an edit, never a new message, so a background timer cannot wake a chat), dptree handler tree, webhook vs polling dispatch |
 | `crates/xmedia-bot/src/config.rs` | Manual env parsing into `Config` |
-| `crates/xmedia-bot/src/db.rs` | `DbPool`: one shared SQLite connection pool (`POOL_SIZE = 4`, WAL, busy_timeout) for all three tables over `$DATA_DIR/task_queue.db` (default `data/`) — the three stores share it; `open_store` creates file + schema, `with_conn` runs all rusqlite I/O in `spawn_blocking` |
+| `crates/xmedia-bot/src/db.rs` | `DbPool`: one shared SQLite connection pool (`POOL_SIZE = 4`, WAL, busy_timeout) for all three tables over `$DATA_DIR/task_queue.db` (default `data/`) — the three stores share it; `open_store` creates file + schema and then applies the `PRAGMA user_version` migration chain (`MIGRATIONS` + `migrate` — append-only; `schema_init` is the version-0 baseline and must not gain columns an existing database would never receive), `with_conn` runs all rusqlite I/O in `spawn_blocking` |
 | `crates/xmedia-bot/src/handlers/` | Handler modules: `mod.rs` (message entry point, `reply`, `log_key`, the group-only `GROUP_LINK_HINT` for a supported link posted outside a private chat), `commands.rs` (teloxide `BotCommands` enum + command executor, incl. `/test <url>` (send-only) / `/debug <url>` (parse-only) and the admin-only `/bot_dict` state dump; `/set_format` rejects unknown `{…}` placeholders and resets with `-`), `urls.rs` (URL extraction + bounded job channel (256) drained by `URL_WORKERS = 8` workers (`start_url_workers`) — backpressure instead of unbounded spawns; teloxide's per-chat workers are sequential — batch-forwards need concurrency), `inline.rs`/`callback.rs` (inline queries / edit-before-forward buttons, incl. `skip`; a forward that fails retryably is both queued *and* settles the prompt — the queued row carries the message ids itself, and a prompt left live let a second Confirm copy the same messages twice and let Skip answer "nothing was forwarded" while the row still delivered), `statics.rs` (global statics) |
 | `crates/xmedia-bot/src/state.rs` | `ChatStore`: parking_lot `Mutex<HashMap>` cache + SQLite write-through (`chat_state` table) |
 | `crates/xmedia-bot/src/link_cache.rs` | `LinkCache`: SQLite-backed cache (`link_cache` table) of successfully sent posts — raw caption fields + Telegram `file_id`s; repeat links re-send locally (no fetch/upload), TTL + prune, invalidated on permanent send failure |
-| `crates/xmedia-bot/src/queue.rs` | `PersistentTaskQueue`: SQLite-backed queue (`tasks` table), `QUEUE_WORKERS = 4` concurrent workers (lease via `BEGIN IMMEDIATE` + `locked_until` TTL), retry→dead-letter, a finished row's `DELETE`/reschedule retried and a failed delete falling back to a `done` tombstone (the lease query and the sweep only look at `pending`/`in_progress`, so a task that already ran cannot be resurrected and re-run), `notify_one` worker wakeup plus a separate `Notify` for the 30 s lease-expiry sweep (a shared one let the sweep steal the workers' wakeup permit), `busy_timeout` on all connections |
+| `crates/xmedia-bot/src/queue.rs` | `PersistentTaskQueue`: SQLite-backed queue (`tasks` table), `QUEUE_WORKERS = 4` concurrent workers (lease via `BEGIN IMMEDIATE` + `locked_until` TTL), retry→dead-letter, a `lease_token` fence: `lease_next` stamps a random token and every write-back (heartbeat, `delete`, `reschedule`, `mark_done`) is guarded by it, so a lease that expired and was re-leased cannot be written by its former holder — a lost lease stops the attempt instead; a finished row's `DELETE`/reschedule retried and a failed delete falling back to a `done` tombstone (the lease query and the sweep only look at `pending`/`in_progress`, so a task that already ran cannot be resurrected and re-run), `notify_one` worker wakeup plus a separate `Notify` for the 30 s lease-expiry sweep (a shared one let the sweep steal the workers' wakeup permit), `busy_timeout` on all connections |
 | `crates/xmedia-bot/src/ctx.rs` | `AppContext`: the injected collaborators (`sender` + `ChatStore`/`PersistentTaskQueue`/`LinkCache`/`Config`), `from_statics` for production and the `CONTEXT` static the worker closures hold. `test_support::TestStores` backs handler tests with a tempdir store set |
 | `crates/xmedia-bot/src/send/` | `send/mod.rs`: `Task`/`MediaItemPayload` payloads, `SendError`/`Classification`, `send_media_sequence`/`send_animation`/`forward_messages`; `send/input_media.rs`: payload → `InputFile`/`InputMedia` + `build_media_group` (caption on the first item only); `send/upload.rs`: the download-and-reupload fallback (`prepare_upload_item`/`send_batch_via_upload`, photo downscale handoff); `send/post_send.rs`: link-cache write, `KEEP_ALIVE` registry, `settle_task`, `post_send_actions`, `handle_task`/`dead_letter_notify` |
 | `crates/xmedia-bot/src/media_sender.rs` | `MediaSender` trait: the user-flow surface (`send_media_group`/`send_animation`/`copy_messages`/`send_message`/`answer_callback_query`/`edit_message_caption`/`delete_message`/`send_chat_action`) implemented by teloxide `Bot` (per-chat rate-limited) and by a recording `MockSender` in tests. Admin/setup APIs (`get_chat`, `set_my_commands`, …) stay on the concrete `Bot` |