feat: cover retry backfill + admin force-resync for manga & chapter (0.50.0)

Adds a per-tick cover-backfill pass to the crawler daemon so mangas whose
cover download failed on first attempt get retried — the metadata pass's
early-stop optimisation otherwise prevents the walk from revisiting them.

Adds admin-only POST /admin/mangas/:id/resync and POST /admin/chapters/:id/resync
that refetch metadata + cover (or chapter content with force_refetch) from the
crawler source synchronously and return the refreshed row. Surfaced in the
UI as "Force resync" buttons on the manga detail and reader pages,
admin-only via session.user.is_admin.

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

backend/src/api/admin/resync.rs

@@ -0,0 +1,176 @@
+//! Admin-triggered force resync of a single manga's metadata + cover,
+//! or a single chapter's content.
+//!
+//! Both endpoints are admin-only (`RequireAdmin`, cookie-only) and run
+//! synchronously with the request — the response carries the refreshed
+//! resource so the UI can swap it in without a follow-up GET. The work
+//! itself is delegated to [`ResyncService`] (set on AppState by
+//! `app::build` when the crawler daemon is enabled); when the daemon
+//! is disabled, both handlers return 503.
+
+use axum::extract::{Path, State};
+use axum::routing::post;
+use axum::{Json, Router};
+use serde::Serialize;
+use serde_json::json;
+use uuid::Uuid;
+
+use crate::app::AppState;
+use crate::auth::extractor::RequireAdmin;
+use crate::crawler::resync::{ChapterResyncOutcome, ResyncError};
+use crate::domain::manga::MangaDetail;
+use crate::domain::Chapter;
+use crate::error::{AppError, AppResult};
+use crate::repo;
+use crate::repo::crawler::UpsertStatus;
+
+pub fn routes() -> Router<AppState> {
+    Router::new()
+        .route("/admin/mangas/:id/resync", post(resync_manga))
+        .route("/admin/chapters/:id/resync", post(resync_chapter))
+}
+
+#[derive(Debug, Serialize)]
+pub struct MangaResyncResponse {
+    pub manga: MangaDetail,
+    /// `"new" | "updated" | "unchanged"` — mirrors [`UpsertStatus`].
+    pub metadata_status: &'static str,
+    pub cover_fetched: bool,
+}
+
+#[derive(Debug, Serialize)]
+pub struct ChapterResyncResponse {
+    pub chapter: Chapter,
+    /// `"fetched" | "skipped"` — whether new pages landed or the
+    /// service short-circuited (e.g. chapter already had pages and the
+    /// session was lost so force was downgraded).
+    pub outcome: &'static str,
+    /// Page count when `outcome == "fetched"`. `None` for `skipped`.
+    pub pages: Option<usize>,
+}
+
+async fn resync_manga(
+    State(state): State<AppState>,
+    admin: RequireAdmin,
+    Path(manga_id): Path<Uuid>,
+) -> AppResult<Json<MangaResyncResponse>> {
+    if !repo::manga::exists(&state.db, manga_id).await? {
+        return Err(AppError::NotFound);
+    }
+    let resync = state
+        .resync
+        .as_ref()
+        .ok_or_else(|| AppError::ServiceUnavailable(
+            "crawler daemon is disabled; force resync unavailable".into(),
+        ))?;
+
+    let outcome = resync.resync_manga(manga_id).await.map_err(map_resync_err)?;
+
+    // Audit the action with the actor + the resync outcome so an
+    // operator-of-operators can answer "who refetched this manga, and
+    // did the cover land?" from the log alone.
+    repo::admin_audit::insert(
+        &state.db,
+        admin.0.id,
+        "manga_resync",
+        "manga",
+        Some(manga_id),
+        json!({
+            "metadata_status": status_str(outcome.metadata_status),
+            "cover_fetched": outcome.cover_fetched,
+        }),
+    )
+    .await?;
+
+    let manga = repo::manga::get_detail(&state.db, manga_id).await?;
+    Ok(Json(MangaResyncResponse {
+        manga,
+        metadata_status: status_str(outcome.metadata_status),
+        cover_fetched: outcome.cover_fetched,
+    }))
+}
+
+async fn resync_chapter(
+    State(state): State<AppState>,
+    admin: RequireAdmin,
+    Path(chapter_id): Path<Uuid>,
+) -> AppResult<Json<ChapterResyncResponse>> {
+    let resync = state
+        .resync
+        .as_ref()
+        .ok_or_else(|| AppError::ServiceUnavailable(
+            "crawler daemon is disabled; force resync unavailable".into(),
+        ))?;
+
+    // Look up the manga the chapter belongs to so we can return the
+    // refreshed chapter row in the response and 404 for unknown ids.
+    let manga_id: Option<Uuid> =
+        sqlx::query_scalar("SELECT manga_id FROM chapters WHERE id = $1")
+            .bind(chapter_id)
+            .fetch_optional(&state.db)
+            .await?;
+    let Some(manga_id) = manga_id else {
+        return Err(AppError::NotFound);
+    };
+
+    let outcome = resync
+        .resync_chapter(chapter_id)
+        .await
+        .map_err(map_resync_err)?;
+
+    let (outcome_str, pages) = match &outcome {
+        ChapterResyncOutcome::Fetched { pages, .. } => ("fetched", Some(*pages)),
+        ChapterResyncOutcome::Skipped { .. } => ("skipped", None),
+    };
+
+    repo::admin_audit::insert(
+        &state.db,
+        admin.0.id,
+        "chapter_resync",
+        "chapter",
+        Some(chapter_id),
+        json!({
+            "outcome": outcome_str,
+            "pages": pages,
+        }),
+    )
+    .await?;
+
+    let chapter = repo::chapter::find_by_id_in_manga(&state.db, manga_id, chapter_id)
+        .await?
+        .ok_or(AppError::NotFound)?;
+    Ok(Json(ChapterResyncResponse {
+        chapter,
+        outcome: outcome_str,
+        pages,
+    }))
+}
+
+fn status_str(s: UpsertStatus) -> &'static str {
+    match s {
+        UpsertStatus::New => "new",
+        UpsertStatus::Updated => "updated",
+        UpsertStatus::Unchanged => "unchanged",
+    }
+}
+
+/// Map [`ResyncError`] (and the anyhow envelopes wrapping it) onto the
+/// right [`AppError`]. Anything else surfaces as a generic 500 via the
+/// `Other` arm — the operator sees the underlying anyhow chain in
+/// server logs, the client sees a clean envelope.
+fn map_resync_err(err: anyhow::Error) -> AppError {
+    if let Some(rerr) = err.downcast_ref::<ResyncError>() {
+        match rerr {
+            ResyncError::NoMangaSource => AppError::ValidationFailed {
+                message: "manga has no live crawler source — cannot resync".into(),
+                details: json!({ "manga": "no_source" }),
+            },
+            ResyncError::NoChapterSource => AppError::ValidationFailed {
+                message: "chapter has no live crawler source — cannot resync".into(),
+                details: json!({ "chapter": "no_source" }),
+            },
+        }
+    } else {
+        AppError::Other(err)
+    }
+}