refactor(send): split the 2100-line module by concern

send.rs had grown back into the shape handlers.rs was split out of: payload
types, error classification, the download-and-reupload fallback, the senders
and the whole post-send/queue shell in one file. Split by concern, leaving
call sites (`crate::send::x`) unchanged:

- `send/input_media.rs`: payload → `InputFile`/`InputMedia` selection and
  `build_media_group` (with its caption-on-first-item rule).
- `send/upload.rs`: the fallback pipeline (download with the upload cap,
  photo downscale handoff, smaller-URL fallback, multipart upload).
- `send/post_send.rs`: link-cache write, the `KEEP_ALIVE` registry for locally
  produced media, `settle_task`, the post-send actions and the queue entry
  points; the parts other modules call are re-exported.
- `send/mod.rs`: payloads, error classification, classification helpers and
  the senders themselves, plus the test module.

No behaviour change: 128 + 1326 + 366 + 345 lines, 70 tests still pass.
AGENTS.md updated for the new layout and for `ctx.rs`.

AGENTS.md

@@ -37,8 +37,9 @@ The `x-media` library: `site::fetch(url)` dispatches through the `SITES` registr
 | `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, `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/send.rs` | Media senders, upload fallback, error classification, queue task handlers |
-| `crates/xmedia-bot/src/media_sender.rs` | `MediaSender` trait: the send surface (`send_media_group`/`send_animation`/`copy_messages`/`send_message`/`send_chat_action`) implemented by teloxide `Bot` (per-chat rate-limited) and by a scripted `MockSender` in tests |
+| `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` |
 | `crates/xmedia-bot/src/rate_limit.rs` | Per-chat token bucket (`CAPACITY = 20`, ~20 msg/min refill) paced before sends reach the API so batch forwards don't trip flood control |
 
 ## Development Commands
@@ -72,8 +73,8 @@ Docker: `docker build -t tgxmb .` then `docker run --rm -d --name tgxmb --env-fi
 | File | Why it matters |
 |---|---|
 | `crates/xmedia-bot/src/main.rs` | Startup sequence, webhook vs polling, graceful shutdown (SIGINT via teloxide ctrlc / SIGTERM via `stop_token` for docker, → sweep stop → admin msg → queue stop) |
-| `crates/xmedia-bot/src/handlers/` | `statics.rs` = `CHAT_STORE`/`TASK_QUEUE`/`CONFIG` singletons (open `$DATA_DIR/task_queue.db`, default `data/` **relative to CWD**, dir auto-created); `commands.rs` = command dispatch (incl. the `/test <url>` parse-only debug command and the admin-only `/bot_dict` state dump); `urls.rs` = URL extraction + the per-URL pipeline (`enqueue_retry` lives in `send.rs`); `inline.rs`/`callback.rs` = inline queries / edit-before-forward buttons |
-| `crates/xmedia-bot/src/send.rs` | Constants `MAX_MEDIA_GROUP = 9`; fallback chain; `classify_request_error`; download-and-reupload fallback triggered only by Telegram API errors (`is_media_fetch_failure` / `is_size_error`) |
+| `crates/xmedia-bot/src/handlers/` | `statics.rs` = `CHAT_STORE`/`TASK_QUEUE`/`CONFIG` singletons (open `$DATA_DIR/task_queue.db`, default `data/` **relative to CWD**, dir auto-created); `commands.rs` = command dispatch (incl. the `/test <url>` parse-only debug command and the admin-only `/bot_dict` state dump); `urls.rs` = URL extraction + the per-URL pipeline (`enqueue_retry` lives in `send/post_send.rs`); `inline.rs` = debounced inline queries; `callback.rs` = edit-before-forward buttons (dptree entry + testable `handle_callback` core) |
+| `crates/xmedia-bot/src/send/` | `mod.rs`: constants `MAX_MEDIA_GROUP = 9`; `classify_request_error`; the senders. `upload.rs`: download-and-reupload fallback triggered only by Telegram API errors (`is_media_fetch_failure` / `is_size_error`). `post_send.rs`: settlement (`settle_task`), cache write, post-send actions, queue handlers. `input_media.rs`: payload → `InputMedia` |
 | `crates/xmedia-bot/src/photo.rs` | Pure-Rust photo processing (no ffmpeg): `png` (image-png) decode/encode + `zune-jpeg` decode + `fast_image_resize` Lanczos3 downscale + `jpeg-encoder`. Photos over Telegram's limits (width + height > 10000 px → `PHOTO_INVALID_DIMENSIONS`; bytes > 10 MiB) are decoded, downscaled keeping the format, PNG bit depth > 24 (RGBA 32-bit / 16-bit per channel) reduced to 24-bit RGB with alpha flattened white (≤24-bit untouched, never upconverted), and transcoded to JPEG only if still over the cap; memory budget guarded, otherwise the item's smaller fallback URL |
 | `crates/x-media/src/site/mod.rs` | Dispatcher, `Fetched`/`FetchError`, shared `CLIENT`, `download_media` (adds `Referer: https://www.pixiv.net/` for `pximg.net` hotlink protection) |
 | `crates/x-media/src/site/pixiv/api.rs` | OAuth token exchange (hardcoded app client id/secret), access-token cache, ugoira zip→MP4 via ffmpeg in `spawn_blocking` |
@@ -101,5 +102,5 @@ Docker: `docker build -t tgxmb .` then `docker run --rm -d --name tgxmb --env-fi
 - Live-network tests exist in `site/twitter/interface.rs` (5), `site/bsky/interface.rs` (2), `site/misskey/interface.rs` (1), `site/pixiv/api.rs` (1); `photo.rs` adds one `#[ignore = "heavy: …"]` test. `site/mod.rs` also has a **token-gated but not `#[ignore]`d** pixiv download test (`download_media_pixiv_original_with_referer`): it hits `i.pximg.net` whenever `PIXIV_REFRESH_TOKEN` is set, so a local `cargo test --workspace` is not fully offline and can flake on a pixiv CDN body timeout. Test gating convention (enforced by `.github/workflows/ci.yml`): pure unit tests always run; live-network tests carry `#[ignore = "live network: ..."]` (run via `cargo test --workspace -- --ignored live`); token-gated pixiv tests early-return when `PIXIV_REFRESH_TOKEN` is absent **or empty** (an unset GitHub secret arrives as `""` — `is_err()` alone would run them tokenless and fail). Run the full offline suite with `cargo test --workspace`.
 - Fixtures are inline `serde_json::json!` builder fns (`fixture()`, `thread_json()`, `illust_json()`), not files. The shared `CLIENT` sets `pool_max_idle_per_host(0)` under `#[cfg(test)]` to avoid cross-runtime `DispatchGone`.
 - **CI** — `.github/workflows/ci.yml` runs `cargo fmt --check` + `cargo clippy --workspace --all-targets -- -D warnings` + `cargo test --workspace` + a `actions-rust-lang/audit` dependency-vulnerability gate (offline, no secrets, on every push/PR) and a `live` job (schedule/manual/tag only, `PIXIV_REFRESH_TOKEN`/`TWITTER_AUTH_TOKEN` from secrets, `continue-on-error`) for the `#[ignore]`d live + token tests. `.github/workflows/docker.yml` builds/pushes the image only.
-- Untested and hard to test without a mock seam: `main.rs`, `config.rs`, `db.rs`, `media_sender.rs` (holds `MockSender` itself); `handlers/mod.rs`, `handlers/callback.rs`, `handlers/statics.rs` (need a real teloxide `Bot`); `media.rs`, `lib.rs`, all `model.rs`. `handlers/urls.rs`/`handlers/commands.rs`/`send.rs`/`state.rs`/`queue.rs`/`link_cache.rs`/`rate_limit.rs` are covered through their injected stores and the scripted `MockSender`.
+- Untested and hard to test without a mock seam: `main.rs`, `config.rs`, `db.rs`, `handlers/statics.rs`, `media_sender.rs` (holds the `MockSender` itself); in `x-media`: `media.rs`, `lib.rs`, all `model.rs`. The `commands.rs` *executor* needs a real `Bot` (only its pure report builder is tested). Everything else — `handlers/{mod,callback,inline,urls}.rs`, `send/*`, `ctx.rs`, `state.rs`, `queue.rs`, `link_cache.rs`, `rate_limit.rs` — is driven through `TestStores`/`ctx::test_support` and the scripted `MockSender`.
 - No coverage tracking.