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/Cargo.lock

@@ -1470,7 +1470,7 @@ checksum = "c41e0c4fef86961ac6d6f8a82609f55f31b05e4fce149ac5710e439df7619ba4"
 
 [[package]]
 name = "mangalord"
-version = "0.49.1"
+version = "0.50.0"
 dependencies = [
  "anyhow",
  "argon2",

backend/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mangalord"
-version = "0.49.1"
+version = "0.50.0"
 edition = "2021"
 default-run = "mangalord"
 

backend/src/api/admin/mod.rs

@@ -5,6 +5,7 @@
 //! `crate::auth::extractor::RequireAdmin`).
 
 pub mod mangas;
+pub mod resync;
 pub mod system;
 pub mod users;
 
@@ -16,5 +17,6 @@ pub fn routes() -> Router<AppState> {
     Router::new()
         .merge(users::routes())
         .merge(mangas::routes())
+        .merge(resync::routes())
         .merge(system::routes())
 }

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)
+    }
+}

backend/src/app.rs

@@ -24,6 +24,7 @@ use crate::crawler::daemon::{self, ChapterDispatcher, DaemonConfig, MetadataPass
 use crate::crawler::jobs::JobPayload;
 use crate::crawler::pipeline::{self, MetadataStats};
 use crate::crawler::rate_limit::HostRateLimiters;
+use crate::crawler::resync::{RealResyncService, ResyncService};
 use crate::crawler::safety::DownloadAllowlist;
 use crate::crawler::session;
 use crate::repo;
@@ -39,6 +40,12 @@ pub struct AppState {
     /// One instance per AppState so tests stay isolated across the
     /// same process.
     pub auth_limiter: Arc<AuthRateLimiter>,
+    /// Admin-triggered force resync. `None` when the crawler daemon
+    /// is disabled (`CRAWLER_DAEMON=false`); admin handlers gate on
+    /// `.is_some()` and return 503 otherwise. Set by [`build`] from the
+    /// same wiring that builds the daemon's chapter dispatcher, so a
+    /// force resync uses the daemon's BrowserManager + rate limiters.
+    pub resync: Option<Arc<dyn ResyncService>>,
 }
 
 /// Bundle returned by [`build`]. The router is what `axum::serve` consumes;
@@ -73,11 +80,12 @@ pub async fn build(config: Config) -> anyhow::Result<AppHandle> {
 
     let storage: Arc<dyn Storage> = Arc::new(LocalStorage::new(config.storage_dir.clone()));
 
-    let daemon = if config.crawler.daemon_enabled {
+    let (daemon, resync) = if config.crawler.daemon_enabled {
-        Some(spawn_crawler_daemon(db.clone(), Arc::clone(&storage), &config.crawler).await?)
+        let spawned = spawn_crawler_daemon(db.clone(), Arc::clone(&storage), &config.crawler).await?;
+        (Some(spawned.handle), Some(spawned.resync))
     } else {
         tracing::info!("crawler daemon disabled (CRAWLER_DAEMON=false)");
-        None
+        (None, None)
     };
 
     let auth_limiter = Arc::new(AuthRateLimiter::new(config.auth.rate_limit));
@@ -87,16 +95,26 @@ pub async fn build(config: Config) -> anyhow::Result<AppHandle> {
         auth: config.auth.clone(),
         upload: config.upload.clone(),
         auth_limiter,
+        resync,
     };
     let router = router(state).layer(cors_layer(&config.cors_allowed_origins));
     Ok(AppHandle { router, daemon })
 }
 
+/// Bundle returned by [`spawn_crawler_daemon`]. The handle owns the
+/// daemon's tasks; `resync` is the operator-trigger service shared with
+/// `AppState` so admin endpoints can call into the same browser /
+/// rate-limit machinery.
+struct SpawnedDaemon {
+    handle: daemon::DaemonHandle,
+    resync: Arc<dyn ResyncService>,
+}
+
 async fn spawn_crawler_daemon(
     db: PgPool,
     storage: Arc<dyn Storage>,
     cfg: &CrawlerConfig,
-) -> anyhow::Result<daemon::DaemonHandle> {
+) -> anyhow::Result<SpawnedDaemon> {
     // Reqwest client with cookie jar pre-seeded so CDN image fetches
     // include PHPSESSID. Same shape as bin/crawler.rs main().
     let cookie_jar = Arc::new(reqwest::cookie::Jar::default());
@@ -198,6 +216,17 @@ async fn spawn_crawler_daemon(
     });
 
     let dispatcher: Arc<dyn ChapterDispatcher> = Arc::new(RealChapterDispatcher {
+        browser_manager: Arc::clone(&browser_manager),
+        db: db.clone(),
+        storage: Arc::clone(&storage),
+        http: http.clone(),
+        rate: Arc::clone(&rate),
+        download_allowlist: cfg.download_allowlist.clone(),
+        max_image_bytes: cfg.max_image_bytes,
+        tor: tor.as_ref().map(Arc::clone),
+    });
+
+    let resync: Arc<dyn ResyncService> = Arc::new(RealResyncService {
         browser_manager: Arc::clone(&browser_manager),
         db: db.clone(),
         storage: Arc::clone(&storage),
@@ -242,7 +271,10 @@ async fn spawn_crawler_daemon(
         },
     );
 
-    Ok(daemon_handle)
+    Ok(SpawnedDaemon {
+        handle: daemon_handle,
+        resync,
+    })
 }
 
 // Real impls of the daemon traits, owning the browser manager + I/O. Kept
@@ -285,6 +317,36 @@ impl MetadataPass for RealMetadataPass {
                 self.browser_manager.invalidate().await;
             }
         }
+        // Cover backfill follows the metadata pass even when the pass
+        // errored — the early-stop walk can complete its work and bail
+        // late, and a transient browser failure shouldn't cancel the
+        // residual cover backlog. The backfill has its own per-call cap
+        // so a runaway error stream can't monopolise the tick.
+        match pipeline::backfill_missing_covers(
+            &self.browser_manager,
+            &self.db,
+            self.storage.as_ref(),
+            &self.http,
+            &self.rate,
+            pipeline::COVER_BACKFILL_DEFAULT_MAX,
+            &self.download_allowlist,
+            self.max_image_bytes,
+            self.tor.as_deref(),
+        )
+        .await
+        {
+            Ok(stats) => {
+                if stats.considered > 0 {
+                    tracing::info!(?stats, "cover backfill complete");
+                }
+            }
+            Err(e) => {
+                tracing::warn!(error = ?e, "cover backfill failed");
+                if crate::crawler::nav::anyhow_looks_browser_dead(&e) {
+                    self.browser_manager.invalidate().await;
+                }
+            }
+        }
         result
     }
 }

backend/src/crawler/mod.rs

@@ -23,6 +23,7 @@ pub mod jobs;
 pub mod nav;
 pub mod pipeline;
 pub mod rate_limit;
+pub mod resync;
 pub mod safety;
 pub mod session;
 pub mod source;

backend/src/crawler/pipeline.rs

@@ -13,7 +13,7 @@ use crate::crawler::jobs::{self, EnqueueResult, JobPayload};
 use crate::crawler::rate_limit::HostRateLimiters;
 use crate::crawler::safety::{fetch_bytes_capped, looks_like_image, DownloadAllowlist};
 use crate::crawler::source::target::TargetSource;
-use crate::crawler::source::{FetchContext, Source};
+use crate::crawler::source::{FetchContext, Source, SourceMangaRef};
 use crate::repo;
 use crate::repo::crawler::UpsertStatus;
 use crate::storage::Storage;
@@ -523,12 +523,133 @@ pub struct EnqueueSummary {
     pub failed: usize,
 }
 
+#[derive(Debug, Default, Clone, Copy)]
+pub struct CoverBackfillStats {
+    pub considered: usize,
+    pub fetched: usize,
+    pub failed: usize,
+}
+
+/// Default per-tick cap for [`backfill_missing_covers`]. The metadata pass
+/// already retries covers when its walk reaches the affected manga; this
+/// backfill exists to catch the residual case where the early-stop
+/// optimisation prevents the walk from reaching mangas whose cover failed
+/// on first attempt. A small cap is enough because the backlog only grows
+/// from sporadic download failures, not from systematic misses.
+pub const COVER_BACKFILL_DEFAULT_MAX: usize = 10;
+
+/// Re-attempt cover downloads for mangas where `cover_image_path IS NULL`
+/// but a live `manga_sources` row exists. Refetches the source detail
+/// page (which is where the cover URL lives) and downloads the cover.
+///
+/// Bounded by `max_mangas` per call so a steady stream of failing covers
+/// — e.g. a CDN host that's persistently 502 — can't monopolise a cron
+/// tick. Orders by `manga_sources.last_seen_at DESC` so the freshest
+/// missing-cover mangas are addressed first.
+///
+/// Failures are logged and counted, not raised: a single bad cover URL
+/// must not stall every other backfill behind it.
+#[allow(clippy::too_many_arguments)]
+pub async fn backfill_missing_covers(
+    browser_manager: &BrowserManager,
+    db: &PgPool,
+    storage: &dyn Storage,
+    http: &reqwest::Client,
+    rate: &HostRateLimiters,
+    max_mangas: usize,
+    allowlist: &DownloadAllowlist,
+    max_image_bytes: usize,
+    tor: Option<&crate::crawler::tor::TorController>,
+) -> anyhow::Result<CoverBackfillStats> {
+    let mut stats = CoverBackfillStats::default();
+    if max_mangas == 0 {
+        return Ok(stats);
+    }
+
+    let entries = repo::crawler::list_missing_covers(db, max_mangas as i64)
+        .await
+        .context("list_missing_covers")?;
+
+    if entries.is_empty() {
+        return Ok(stats);
+    }
+
+    let lease = browser_manager
+        .acquire()
+        .await
+        .context("acquire browser lease for cover backfill")?;
+    let browser_ref: &chromiumoxide::Browser = &lease;
+    let ctx = FetchContext { browser: browser_ref, rate, tor };
+
+    for entry in entries {
+        stats.considered += 1;
+        // Metadata-only TargetSource: skip chapter-list parsing so a
+        // missing-cover refetch doesn't soft-drop chapters on a partial
+        // render. Cover URL alone is what we need.
+        let source = TargetSource::new(entry.source_url.clone()).without_chapter_parsing();
+        let r = SourceMangaRef {
+            source_manga_key: entry.source_manga_key.clone(),
+            title: String::new(),
+            url: entry.source_url.clone(),
+        };
+        let cover_url = match source.fetch_manga(&ctx, &r).await {
+            Ok(manga) => manga.cover_url,
+            Err(e) => {
+                tracing::warn!(
+                    manga_id = %entry.manga_id,
+                    url = %entry.source_url,
+                    error = ?e,
+                    "cover backfill: fetch_manga failed"
+                );
+                stats.failed += 1;
+                continue;
+            }
+        };
+        let Some(cover_url) = cover_url else {
+            tracing::warn!(
+                manga_id = %entry.manga_id,
+                url = %entry.source_url,
+                "cover backfill: source returned no cover_url"
+            );
+            stats.failed += 1;
+            continue;
+        };
+        match download_and_store_cover(
+            db,
+            storage,
+            http,
+            rate,
+            &entry.source_url,
+            entry.manga_id,
+            &cover_url,
+            allowlist,
+            max_image_bytes,
+        )
+        .await
+        {
+            Ok(()) => stats.fetched += 1,
+            Err(e) => {
+                tracing::warn!(
+                    manga_id = %entry.manga_id,
+                    url = %entry.source_url,
+                    error = ?e,
+                    "cover backfill: download failed"
+                );
+                stats.failed += 1;
+            }
+        }
+    }
+
+    drop(lease);
+    Ok(stats)
+}
+
 /// Download a cover image and persist its storage path. Local to the
 /// pipeline because the CLI still calls it from its inline chapter-content
 /// loop; once the worker pool fully replaces that path we can fold this
 /// into `pipeline` proper.
 #[allow(clippy::too_many_arguments)]
-async fn download_and_store_cover(
+pub(crate) async fn download_and_store_cover(
     db: &PgPool,
     storage: &dyn Storage,
     http: &reqwest::Client,

backend/src/crawler/resync.rs

@@ -0,0 +1,277 @@
+//! Admin-triggered resync of a single manga's metadata + cover, or a
+//! single chapter's content.
+//!
+//! The cron tick already retries covers and chapter content on its own
+//! schedule. This module exists for the operator-controlled path:
+//! "this manga's metadata is stale / its cover never landed / this
+//! chapter is broken — pull from source now, not at the next daily
+//! tick." Wired into the admin API, never into the queue, so the work
+//! happens synchronously with the HTTP request and the admin sees the
+//! refreshed row in the response.
+//!
+//! Shares the daemon's [`BrowserManager`], rate limiter, HTTP client,
+//! and TOR controller so a force resync respects the same per-host
+//! pacing and recircuit budget the daily crawl uses — admin actions
+//! must not let an operator accidentally hammer the source.
+
+use std::sync::Arc;
+
+use anyhow::Context;
+use async_trait::async_trait;
+use sqlx::PgPool;
+use uuid::Uuid;
+
+use crate::crawler::browser_manager::BrowserManager;
+use crate::crawler::content::{self, SyncOutcome};
+use crate::crawler::pipeline;
+use crate::crawler::rate_limit::HostRateLimiters;
+use crate::crawler::safety::DownloadAllowlist;
+use crate::crawler::source::target::TargetSource;
+use crate::crawler::source::{FetchContext, Source, SourceMangaRef};
+use crate::crawler::tor::TorController;
+use crate::repo;
+use crate::repo::crawler::UpsertStatus;
+use crate::storage::Storage;
+
+/// Outcome of [`ResyncService::resync_manga`]. Mirrors the bits the
+/// admin UI cares about — was the row actually re-upserted, did the
+/// cover land — so the response can show "metadata refreshed, cover
+/// re-downloaded" or "metadata unchanged" without a second round-trip.
+#[derive(Debug, Clone, Copy)]
+pub struct MangaResyncOutcome {
+    pub manga_id: Uuid,
+    pub metadata_status: UpsertStatus,
+    pub cover_fetched: bool,
+}
+
+/// Outcome of [`ResyncService::resync_chapter`]. `Fetched(pages)` is the
+/// success case; `Skipped` means the source row was already gone or the
+/// chapter had no live source.
+#[derive(Debug, Clone)]
+pub enum ChapterResyncOutcome {
+    Fetched { chapter_id: Uuid, pages: usize },
+    Skipped { chapter_id: Uuid, reason: String },
+}
+
+/// Service exposed by the daemon to the admin API. Optional on
+/// [`AppState`] — `None` when the crawler daemon is disabled
+/// (`CRAWLER_DAEMON=false`), in which case admin handlers return 503.
+#[async_trait]
+pub trait ResyncService: Send + Sync {
+    async fn resync_manga(&self, manga_id: Uuid) -> anyhow::Result<MangaResyncOutcome>;
+    async fn resync_chapter(&self, chapter_id: Uuid) -> anyhow::Result<ChapterResyncOutcome>;
+}
+
+/// Errors with a stable shape so the API layer can map them to the
+/// right HTTP status (404 vs 422 vs 5xx). Anything else surfaces as a
+/// generic 500.
+#[derive(Debug, thiserror::Error)]
+pub enum ResyncError {
+    #[error("manga has no source to resync from")]
+    NoMangaSource,
+    #[error("chapter has no source to resync from")]
+    NoChapterSource,
+}
+
+pub struct RealResyncService {
+    pub browser_manager: Arc<BrowserManager>,
+    pub db: PgPool,
+    pub storage: Arc<dyn Storage>,
+    pub http: reqwest::Client,
+    pub rate: Arc<HostRateLimiters>,
+    pub download_allowlist: DownloadAllowlist,
+    pub max_image_bytes: usize,
+    pub tor: Option<Arc<TorController>>,
+}
+
+#[async_trait]
+impl ResyncService for RealResyncService {
+    async fn resync_manga(&self, manga_id: Uuid) -> anyhow::Result<MangaResyncOutcome> {
+        // Pick the freshest live source row. Multi-source mangas
+        // (theoretical — only one Source impl today) get the row whose
+        // `last_seen_at` is newest; soft-dropped rows are skipped.
+        let row: Option<(String, String, String)> = sqlx::query_as(
+            "SELECT source_id, source_manga_key, source_url \
+               FROM manga_sources \
+              WHERE manga_id = $1 AND dropped_at IS NULL \
+              ORDER BY last_seen_at DESC \
+              LIMIT 1",
+        )
+        .bind(manga_id)
+        .fetch_optional(&self.db)
+        .await
+        .context("look up manga_sources for resync")?;
+        let Some((_source_id, source_manga_key, source_url)) = row else {
+            return Err(ResyncError::NoMangaSource.into());
+        };
+
+        let lease = self
+            .browser_manager
+            .acquire()
+            .await
+            .context("acquire browser lease for manga resync")?;
+        let browser_ref: &chromiumoxide::Browser = &lease;
+        let ctx = FetchContext {
+            browser: browser_ref,
+            rate: &self.rate,
+            tor: self.tor.as_deref(),
+        };
+
+        // Parse chapters too — a force resync is "make this manga fully
+        // current," not just metadata. The full pipeline handles the
+        // partial-render guard for us; we replicate the same caution
+        // here by skipping the chapter sync when the parser returned
+        // empty but the manga previously had chapters.
+        let source = TargetSource::new(source_url.clone());
+        let r = SourceMangaRef {
+            source_manga_key: source_manga_key.clone(),
+            title: String::new(),
+            url: source_url.clone(),
+        };
+        let manga = source
+            .fetch_manga(&ctx, &r)
+            .await
+            .with_context(|| format!("fetch_manga during resync of {manga_id}"))?;
+
+        // Partial-render guard: same logic as run_metadata_pass.
+        let source_id = source.id();
+        if !manga.chapters.is_empty() || {
+            let prior = repo::crawler::live_chapter_count_for_source_manga(
+                &self.db,
+                source_id,
+                &source_manga_key,
+            )
+            .await
+            .unwrap_or(0);
+            prior == 0
+        } {
+            // Either the new fetch surfaced chapters, or there were
+            // none before either — chapter sync is safe to run.
+        } else {
+            tracing::warn!(
+                %manga_id,
+                source_url = %source_url,
+                "resync_manga: fetch returned empty chapters but prior count > 0; skipping chapter sync to avoid soft-drop"
+            );
+        }
+
+        let upsert = repo::crawler::upsert_manga_from_source(
+            &self.db,
+            source_id,
+            &source_url,
+            &manga,
+        )
+        .await
+        .with_context(|| format!("upsert_manga_from_source during resync of {manga_id}"))?;
+
+        // Cover refetch: force-download regardless of UpsertStatus.
+        // Admin clicked "resync" because they want the cover too.
+        let mut cover_fetched = false;
+        if let Some(cover_url) = manga.cover_url.as_deref() {
+            match pipeline::download_and_store_cover(
+                &self.db,
+                self.storage.as_ref(),
+                &self.http,
+                &self.rate,
+                &source_url,
+                upsert.manga_id,
+                cover_url,
+                &self.download_allowlist,
+                self.max_image_bytes,
+            )
+            .await
+            {
+                Ok(()) => cover_fetched = true,
+                Err(e) => tracing::warn!(
+                    %manga_id,
+                    error = ?e,
+                    "resync_manga: cover download failed"
+                ),
+            }
+        }
+
+        // Chapter sync — only when the partial-render guard above
+        // didn't bail.
+        let prior_chapter_count = repo::crawler::live_chapter_count_for_source_manga(
+            &self.db,
+            source_id,
+            &source_manga_key,
+        )
+        .await
+        .unwrap_or(0);
+        if !manga.chapters.is_empty() || prior_chapter_count == 0 {
+            match repo::crawler::sync_manga_chapters(
+                &self.db,
+                source_id,
+                upsert.manga_id,
+                &manga.chapters,
+            )
+            .await
+            {
+                Ok(diff) => tracing::info!(
+                    %manga_id,
+                    new = diff.new,
+                    refreshed = diff.refreshed,
+                    dropped = diff.dropped,
+                    "resync_manga: chapters synced"
+                ),
+                Err(e) => tracing::warn!(
+                    %manga_id,
+                    error = ?e,
+                    "resync_manga: chapter sync failed"
+                ),
+            }
+        }
+
+        drop(lease);
+        Ok(MangaResyncOutcome {
+            manga_id: upsert.manga_id,
+            metadata_status: upsert.status,
+            cover_fetched,
+        })
+    }
+
+    async fn resync_chapter(&self, chapter_id: Uuid) -> anyhow::Result<ChapterResyncOutcome> {
+        let row = repo::chapter::dispatch_target(&self.db, chapter_id)
+            .await
+            .context("look up chapter_sources for resync")?;
+        let Some((manga_id, source_url)) = row else {
+            return Err(ResyncError::NoChapterSource.into());
+        };
+
+        let lease = self
+            .browser_manager
+            .acquire()
+            .await
+            .context("acquire browser lease for chapter resync")?;
+        let result = content::sync_chapter_content(
+            &lease,
+            &self.db,
+            self.storage.as_ref(),
+            &self.http,
+            &self.rate,
+            chapter_id,
+            manga_id,
+            &source_url,
+            true,
+            &self.download_allowlist,
+            self.max_image_bytes,
+            self.tor.as_deref(),
+        )
+        .await;
+        drop(lease);
+
+        match result? {
+            SyncOutcome::Fetched { pages } => {
+                Ok(ChapterResyncOutcome::Fetched { chapter_id, pages })
+            }
+            SyncOutcome::Skipped => Ok(ChapterResyncOutcome::Skipped {
+                chapter_id,
+                reason: "chapter already had pages on disk".to_string(),
+            }),
+            SyncOutcome::SessionExpired => {
+                anyhow::bail!("source session expired — operator must refresh PHPSESSID")
+            }
+        }
+    }
+}

backend/src/error.rs

@@ -21,6 +21,11 @@ pub enum AppError {
     PayloadTooLarge(String),
     #[error("unsupported media type: {0}")]
     UnsupportedMediaType(String),
+    /// 503 — a feature is currently unavailable, distinct from a 5xx
+    /// internal error. Used when admin actions require the crawler
+    /// daemon but it's been disabled (`CRAWLER_DAEMON=false`).
+    #[error("service unavailable: {0}")]
+    ServiceUnavailable(String),
     /// 429 with an optional `Retry-After` header value (in seconds).
     #[error("too many requests")]
     TooManyRequests {
@@ -56,6 +61,7 @@ impl AppError {
             AppError::Conflict(_) => "conflict",
             AppError::PayloadTooLarge(_) => "payload_too_large",
             AppError::UnsupportedMediaType(_) => "unsupported_media_type",
+            AppError::ServiceUnavailable(_) => "service_unavailable",
             AppError::TooManyRequests { .. } => "too_many_requests",
             AppError::ValidationFailed { .. } => "validation_failed",
             AppError::Database(sqlx::Error::RowNotFound) => "not_found",
@@ -85,6 +91,9 @@ impl IntoResponse for AppError {
             AppError::UnsupportedMediaType(msg) => {
                 (StatusCode::UNSUPPORTED_MEDIA_TYPE, msg.clone(), None)
             }
+            AppError::ServiceUnavailable(msg) => {
+                (StatusCode::SERVICE_UNAVAILABLE, msg.clone(), None)
+            }
             AppError::TooManyRequests { retry_after_secs } => {
                 // Emit `Retry-After: N` (RFC 6585 §4) so a well-behaved
                 // client can back off correctly. Done by building the

backend/src/repo/crawler.rs

@@ -542,6 +542,51 @@ pub async fn mark_run_completed(pool: &PgPool, source_id: &str) -> sqlx::Result<
     Ok(())
 }
 
+/// List mangas whose `cover_image_path IS NULL` but a live
+/// `manga_sources` row still attaches them to a source. The bounded
+/// result feeds the cover-backfill pass in [`crate::crawler::pipeline`]:
+/// each entry is one (manga, freshest source row) pair where a cover
+/// re-download is in order.
+///
+/// Per-manga deduplication uses `DISTINCT ON (m.id)` keyed on the row
+/// with the newest `last_seen_at`, so a manga that's surfaced by
+/// multiple sources only produces one row (the freshest). Sort is
+/// stable for tests.
+pub async fn list_missing_covers(
+    pool: &PgPool,
+    max: i64,
+) -> sqlx::Result<Vec<MissingCoverEntry>> {
+    let rows: Vec<(Uuid, String, String)> = sqlx::query_as(
+        r#"
+        SELECT DISTINCT ON (m.id) m.id, ms.source_manga_key, ms.source_url
+          FROM mangas m
+          JOIN manga_sources ms ON ms.manga_id = m.id
+         WHERE m.cover_image_path IS NULL
+           AND ms.dropped_at IS NULL
+         ORDER BY m.id, ms.last_seen_at DESC
+         LIMIT $1
+        "#,
+    )
+    .bind(max)
+    .fetch_all(pool)
+    .await?;
+    Ok(rows
+        .into_iter()
+        .map(|(manga_id, source_manga_key, source_url)| MissingCoverEntry {
+            manga_id,
+            source_manga_key,
+            source_url,
+        })
+        .collect())
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct MissingCoverEntry {
+    pub manga_id: Uuid,
+    pub source_manga_key: String,
+    pub source_url: String,
+}
+
 /// Read the recovery flag for `source_id`. A missing row OR an
 /// unparseable value reads as `true` ("clean") — the former covers the
 /// first-ever run on a virgin DB (no recovery needed), the latter

backend/tests/api_admin_resync.rs

@@ -0,0 +1,350 @@
+//! Integration tests for the admin force-resync endpoints.
+//!
+//! Real resync work requires Chromium, so these tests swap in a stub
+//! [`ResyncService`] to assert the handler-level contract: routing,
+//! admin gate, 503 when the daemon is disabled, 404 / 422 mapping for
+//! missing-resource / no-source cases, and the audit-log side effect.
+
+mod common;
+
+use std::sync::Arc;
+use std::sync::atomic::{AtomicUsize, Ordering};
+
+use async_trait::async_trait;
+use axum::http::StatusCode;
+use serde_json::json;
+use sqlx::PgPool;
+use tower::ServiceExt;
+use uuid::Uuid;
+
+use mangalord::crawler::resync::{
+    ChapterResyncOutcome, MangaResyncOutcome, ResyncError, ResyncService,
+};
+use mangalord::repo;
+use mangalord::repo::crawler::UpsertStatus;
+
+/// Stub that records call counts and returns a canned outcome.
+struct StubResync {
+    manga_calls: AtomicUsize,
+    chapter_calls: AtomicUsize,
+    /// When true, returns NoMangaSource / NoChapterSource.
+    no_source: bool,
+}
+
+impl StubResync {
+    fn new() -> Arc<Self> {
+        Arc::new(Self {
+            manga_calls: AtomicUsize::new(0),
+            chapter_calls: AtomicUsize::new(0),
+            no_source: false,
+        })
+    }
+    fn no_source() -> Arc<Self> {
+        Arc::new(Self {
+            manga_calls: AtomicUsize::new(0),
+            chapter_calls: AtomicUsize::new(0),
+            no_source: true,
+        })
+    }
+}
+
+#[async_trait]
+impl ResyncService for StubResync {
+    async fn resync_manga(&self, manga_id: Uuid) -> anyhow::Result<MangaResyncOutcome> {
+        self.manga_calls.fetch_add(1, Ordering::SeqCst);
+        if self.no_source {
+            return Err(ResyncError::NoMangaSource.into());
+        }
+        Ok(MangaResyncOutcome {
+            manga_id,
+            metadata_status: UpsertStatus::Updated,
+            cover_fetched: true,
+        })
+    }
+    async fn resync_chapter(&self, chapter_id: Uuid) -> anyhow::Result<ChapterResyncOutcome> {
+        self.chapter_calls.fetch_add(1, Ordering::SeqCst);
+        if self.no_source {
+            return Err(ResyncError::NoChapterSource.into());
+        }
+        Ok(ChapterResyncOutcome::Fetched {
+            chapter_id,
+            pages: 7,
+        })
+    }
+}
+
+async fn promote_admin(pool: &PgPool, username: &str) {
+    let u = repo::user::find_by_username(pool, username)
+        .await
+        .unwrap()
+        .unwrap();
+    repo::user::set_is_admin_unchecked(pool, u.id, true)
+        .await
+        .unwrap();
+}
+
+async fn insert_manga(pool: &PgPool, title: &str) -> Uuid {
+    let (id,): (Uuid,) = sqlx::query_as(
+        "INSERT INTO mangas (title, status, alt_titles) VALUES ($1, 'ongoing', ARRAY[]::text[]) RETURNING id",
+    )
+    .bind(title)
+    .fetch_one(pool)
+    .await
+    .unwrap();
+    id
+}
+
+async fn insert_chapter(pool: &PgPool, manga_id: Uuid, number: i32, pages: i32) -> Uuid {
+    let (id,): (Uuid,) = sqlx::query_as(
+        "INSERT INTO chapters (manga_id, number, title, page_count) VALUES ($1, $2, NULL, $3) RETURNING id",
+    )
+    .bind(manga_id)
+    .bind(number)
+    .bind(pages)
+    .fetch_one(pool)
+    .await
+    .unwrap();
+    id
+}
+
+// ----- manga resync ---------------------------------------------------------
+
+#[sqlx::test(migrations = "./migrations")]
+async fn manga_resync_calls_service_and_returns_refreshed_detail(pool: PgPool) {
+    let stub = StubResync::new();
+    let h = common::harness_with_resync(pool.clone(), stub.clone());
+    let (username, cookie) = common::register_user(&h.app).await;
+    promote_admin(&pool, &username).await;
+    let manga_id = insert_manga(&pool, "Hello").await;
+
+    let resp = h
+        .app
+        .oneshot(common::post_json_with_cookie(
+            &format!("/api/v1/admin/mangas/{manga_id}/resync"),
+            json!({}),
+            &cookie,
+        ))
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), StatusCode::OK);
+    let body = common::body_json(resp).await;
+    // Stub returned Updated + cover_fetched=true.
+    assert_eq!(body["metadata_status"], "updated");
+    assert_eq!(body["cover_fetched"], true);
+    // Response includes the refreshed manga detail.
+    assert_eq!(body["manga"]["id"], manga_id.to_string());
+    assert_eq!(body["manga"]["title"], "Hello");
+
+    assert_eq!(stub.manga_calls.load(Ordering::SeqCst), 1);
+
+    // Audit row written.
+    let (audit_count,): (i64,) =
+        sqlx::query_as("SELECT count(*) FROM admin_audit WHERE action = 'manga_resync' AND target_id = $1")
+            .bind(manga_id)
+            .fetch_one(&pool)
+            .await
+            .unwrap();
+    assert_eq!(audit_count, 1);
+}
+
+#[sqlx::test(migrations = "./migrations")]
+async fn manga_resync_returns_404_for_unknown_id(pool: PgPool) {
+    let stub = StubResync::new();
+    let h = common::harness_with_resync(pool.clone(), stub.clone());
+    let (username, cookie) = common::register_user(&h.app).await;
+    promote_admin(&pool, &username).await;
+
+    let resp = h
+        .app
+        .oneshot(common::post_json_with_cookie(
+            &format!("/api/v1/admin/mangas/{}/resync", Uuid::new_v4()),
+            json!({}),
+            &cookie,
+        ))
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), StatusCode::NOT_FOUND);
+    // Service must not have been called when the manga doesn't exist.
+    assert_eq!(stub.manga_calls.load(Ordering::SeqCst), 0);
+}
+
+#[sqlx::test(migrations = "./migrations")]
+async fn manga_resync_maps_no_source_to_422(pool: PgPool) {
+    let stub = StubResync::no_source();
+    let h = common::harness_with_resync(pool.clone(), stub);
+    let (username, cookie) = common::register_user(&h.app).await;
+    promote_admin(&pool, &username).await;
+    let manga_id = insert_manga(&pool, "Manual upload, no crawler source").await;
+
+    let resp = h
+        .app
+        .oneshot(common::post_json_with_cookie(
+            &format!("/api/v1/admin/mangas/{manga_id}/resync"),
+            json!({}),
+            &cookie,
+        ))
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), StatusCode::UNPROCESSABLE_ENTITY);
+    let body = common::body_json(resp).await;
+    assert_eq!(body["error"]["details"]["manga"], "no_source");
+}
+
+#[sqlx::test(migrations = "./migrations")]
+async fn manga_resync_returns_503_when_daemon_disabled(pool: PgPool) {
+    let h = common::harness(pool.clone());
+    let (username, cookie) = common::register_user(&h.app).await;
+    promote_admin(&pool, &username).await;
+    let manga_id = insert_manga(&pool, "Z").await;
+
+    let resp = h
+        .app
+        .oneshot(common::post_json_with_cookie(
+            &format!("/api/v1/admin/mangas/{manga_id}/resync"),
+            json!({}),
+            &cookie,
+        ))
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), StatusCode::SERVICE_UNAVAILABLE);
+    let body = common::body_json(resp).await;
+    assert_eq!(body["error"]["code"], "service_unavailable");
+}
+
+#[sqlx::test(migrations = "./migrations")]
+async fn manga_resync_requires_admin(pool: PgPool) {
+    let stub = StubResync::new();
+    let h = common::harness_with_resync(pool.clone(), stub);
+    // Non-admin user.
+    let (_u, cookie) = common::register_user(&h.app).await;
+    let manga_id = insert_manga(&pool, "M").await;
+    let resp = h
+        .app
+        .oneshot(common::post_json_with_cookie(
+            &format!("/api/v1/admin/mangas/{manga_id}/resync"),
+            json!({}),
+            &cookie,
+        ))
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), StatusCode::FORBIDDEN);
+}
+
+// ----- chapter resync -------------------------------------------------------
+
+#[sqlx::test(migrations = "./migrations")]
+async fn chapter_resync_calls_service_and_returns_refreshed_chapter(pool: PgPool) {
+    let stub = StubResync::new();
+    let h = common::harness_with_resync(pool.clone(), stub.clone());
+    let (username, cookie) = common::register_user(&h.app).await;
+    promote_admin(&pool, &username).await;
+    let manga_id = insert_manga(&pool, "M").await;
+    let chapter_id = insert_chapter(&pool, manga_id, 1, 0).await;
+
+    let resp = h
+        .app
+        .oneshot(common::post_json_with_cookie(
+            &format!("/api/v1/admin/chapters/{chapter_id}/resync"),
+            json!({}),
+            &cookie,
+        ))
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), StatusCode::OK);
+    let body = common::body_json(resp).await;
+    assert_eq!(body["outcome"], "fetched");
+    assert_eq!(body["pages"], 7);
+    assert_eq!(body["chapter"]["id"], chapter_id.to_string());
+    assert_eq!(stub.chapter_calls.load(Ordering::SeqCst), 1);
+
+    let (audit_count,): (i64,) = sqlx::query_as(
+        "SELECT count(*) FROM admin_audit WHERE action = 'chapter_resync' AND target_id = $1",
+    )
+    .bind(chapter_id)
+    .fetch_one(&pool)
+    .await
+    .unwrap();
+    assert_eq!(audit_count, 1);
+}
+
+#[sqlx::test(migrations = "./migrations")]
+async fn chapter_resync_returns_404_for_unknown_id(pool: PgPool) {
+    let stub = StubResync::new();
+    let h = common::harness_with_resync(pool.clone(), stub.clone());
+    let (username, cookie) = common::register_user(&h.app).await;
+    promote_admin(&pool, &username).await;
+
+    let resp = h
+        .app
+        .oneshot(common::post_json_with_cookie(
+            &format!("/api/v1/admin/chapters/{}/resync", Uuid::new_v4()),
+            json!({}),
+            &cookie,
+        ))
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), StatusCode::NOT_FOUND);
+    assert_eq!(stub.chapter_calls.load(Ordering::SeqCst), 0);
+}
+
+#[sqlx::test(migrations = "./migrations")]
+async fn chapter_resync_maps_no_source_to_422(pool: PgPool) {
+    let stub = StubResync::no_source();
+    let h = common::harness_with_resync(pool.clone(), stub);
+    let (username, cookie) = common::register_user(&h.app).await;
+    promote_admin(&pool, &username).await;
+    let manga_id = insert_manga(&pool, "M").await;
+    let chapter_id = insert_chapter(&pool, manga_id, 1, 0).await;
+
+    let resp = h
+        .app
+        .oneshot(common::post_json_with_cookie(
+            &format!("/api/v1/admin/chapters/{chapter_id}/resync"),
+            json!({}),
+            &cookie,
+        ))
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), StatusCode::UNPROCESSABLE_ENTITY);
+    let body = common::body_json(resp).await;
+    assert_eq!(body["error"]["details"]["chapter"], "no_source");
+}
+
+#[sqlx::test(migrations = "./migrations")]
+async fn chapter_resync_returns_503_when_daemon_disabled(pool: PgPool) {
+    let h = common::harness(pool.clone());
+    let (username, cookie) = common::register_user(&h.app).await;
+    promote_admin(&pool, &username).await;
+    let manga_id = insert_manga(&pool, "M").await;
+    let chapter_id = insert_chapter(&pool, manga_id, 1, 0).await;
+
+    let resp = h
+        .app
+        .oneshot(common::post_json_with_cookie(
+            &format!("/api/v1/admin/chapters/{chapter_id}/resync"),
+            json!({}),
+            &cookie,
+        ))
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), StatusCode::SERVICE_UNAVAILABLE);
+}
+
+#[sqlx::test(migrations = "./migrations")]
+async fn chapter_resync_requires_admin(pool: PgPool) {
+    let stub = StubResync::new();
+    let h = common::harness_with_resync(pool.clone(), stub);
+    let (_u, cookie) = common::register_user(&h.app).await;
+    let manga_id = insert_manga(&pool, "M").await;
+    let chapter_id = insert_chapter(&pool, manga_id, 1, 0).await;
+    let resp = h
+        .app
+        .oneshot(common::post_json_with_cookie(
+            &format!("/api/v1/admin/chapters/{chapter_id}/resync"),
+            json!({}),
+            &cookie,
+        ))
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), StatusCode::FORBIDDEN);
+}

backend/tests/api_admin_role.rs

@@ -49,6 +49,7 @@ fn admin_test_router(pool: PgPool) -> (Router, TempDir) {
         auth,
         upload: UploadConfig::default(),
         auth_limiter,
+        resync: None,
     };
     let app = Router::new()
         .nest("/api/v1", api::routes())

backend/tests/common/mod.rs

@@ -74,6 +74,10 @@ fn harness_with_auth_config(
             max_file_bytes: 256 * 1024,
         },
         auth_limiter,
+        // Default harness has no crawler daemon wired up; admin resync
+        // handlers return 503 in this config. Tests that need a stub
+        // resync service swap it in via `harness_with_resync`.
+        resync: None,
     };
     Harness { app: router(state), _storage_dir: storage_dir }
 }
@@ -124,6 +128,37 @@ pub fn harness_with_auth_rate_limit(
     harness_with_auth_config(pool, storage, storage_dir, auth)
 }
 
+/// Like [`harness`] but slots a caller-supplied [`ResyncService`] stub
+/// into `AppState.resync`. Used by the admin resync tests so the
+/// endpoint path is exercised without standing up a real Chromium.
+pub fn harness_with_resync(
+    pool: PgPool,
+    resync: Arc<dyn mangalord::crawler::resync::ResyncService>,
+) -> Harness {
+    let storage_dir = tempfile::tempdir().expect("tempdir");
+    let storage = Arc::new(LocalStorage::new(storage_dir.path()));
+    let auth = AuthConfig {
+        cookie_secure: false,
+        ..AuthConfig::default()
+    };
+    let auth_limiter = Arc::new(AuthRateLimiter::new(auth.rate_limit));
+    let state = AppState {
+        db: pool,
+        storage,
+        auth,
+        upload: UploadConfig {
+            max_request_bytes: 4 * 1024 * 1024,
+            max_file_bytes: 256 * 1024,
+        },
+        auth_limiter,
+        resync: Some(resync),
+    };
+    Harness {
+        app: router(state),
+        _storage_dir: storage_dir,
+    }
+}
+
 /// Wraps a real `Storage` and fails on the N-th `put` call so tests can
 /// assert that handlers roll their DB writes back when storage errors
 /// mid-upload. Reads and other operations delegate to `inner`.

backend/tests/crawler_sync.rs

@@ -829,6 +829,107 @@ async fn sync_tags_garbage_collects_orphan_user_attachments(pool: PgPool) {
     assert_eq!(orphan_rows, 0, "orphan user-attached tag should be reaped");
 }
 
+// ---- list_missing_covers ---------------------------------------------------
+
+#[sqlx::test(migrations = "./migrations")]
+async fn list_missing_covers_only_returns_rows_without_cover(pool: PgPool) {
+    crawler::ensure_source(&pool, "target", "T", "https://x.example")
+        .await
+        .unwrap();
+    let with_cover = sample_manga("with", "With Cover", "h1");
+    let without_cover = sample_manga("without", "No Cover", "h2");
+    let _w = crawler::upsert_manga_from_source(&pool, "target", "https://x.example/with", &with_cover)
+        .await
+        .unwrap();
+    let nc = crawler::upsert_manga_from_source(&pool, "target", "https://x.example/without", &without_cover)
+        .await
+        .unwrap();
+
+    // Manually set a cover for `with` only.
+    sqlx::query("UPDATE mangas SET cover_image_path = 'mangas/x/cover.jpg' WHERE id = $1")
+        .bind(_w.manga_id)
+        .execute(&pool)
+        .await
+        .unwrap();
+
+    let entries = crawler::list_missing_covers(&pool, 50).await.unwrap();
+    assert_eq!(entries.len(), 1, "exactly the manga without a cover");
+    assert_eq!(entries[0].manga_id, nc.manga_id);
+    assert_eq!(entries[0].source_manga_key, "without");
+    assert_eq!(entries[0].source_url, "https://x.example/without");
+}
+
+#[sqlx::test(migrations = "./migrations")]
+async fn list_missing_covers_skips_dropped_source_rows(pool: PgPool) {
+    crawler::ensure_source(&pool, "target", "T", "https://x.example")
+        .await
+        .unwrap();
+    let m = sample_manga("foo", "Foo", "h1");
+    let up = crawler::upsert_manga_from_source(&pool, "target", "https://x.example/foo", &m)
+        .await
+        .unwrap();
+    sqlx::query("UPDATE manga_sources SET dropped_at = NOW() WHERE manga_id = $1")
+        .bind(up.manga_id)
+        .execute(&pool)
+        .await
+        .unwrap();
+
+    let entries = crawler::list_missing_covers(&pool, 50).await.unwrap();
+    assert!(
+        entries.is_empty(),
+        "dropped-source mangas must not be backfilled — no live source to fetch from"
+    );
+}
+
+#[sqlx::test(migrations = "./migrations")]
+async fn list_missing_covers_respects_limit(pool: PgPool) {
+    crawler::ensure_source(&pool, "target", "T", "https://x.example")
+        .await
+        .unwrap();
+    for i in 0..5 {
+        let key = format!("m{i}");
+        let url = format!("https://x.example/{key}");
+        let m = sample_manga(&key, &format!("M{i}"), &format!("h{i}"));
+        let _ = crawler::upsert_manga_from_source(&pool, "target", &url, &m)
+            .await
+            .unwrap();
+    }
+    let entries = crawler::list_missing_covers(&pool, 3).await.unwrap();
+    assert_eq!(entries.len(), 3, "limit caps the result set");
+}
+
+#[sqlx::test(migrations = "./migrations")]
+async fn list_missing_covers_deduplicates_per_manga(pool: PgPool) {
+    // A manga surfaced by two sources should produce ONE backfill
+    // entry, not two — otherwise the per-tick cap could be eaten by
+    // duplicates and starve other mangas.
+    crawler::ensure_source(&pool, "src-a", "A", "https://a.example")
+        .await
+        .unwrap();
+    crawler::ensure_source(&pool, "src-b", "B", "https://b.example")
+        .await
+        .unwrap();
+    let m = sample_manga("foo", "Foo", "h1");
+    let up = crawler::upsert_manga_from_source(&pool, "src-a", "https://a.example/foo", &m)
+        .await
+        .unwrap();
+    // Second source attaches to the SAME manga row.
+    sqlx::query(
+        "INSERT INTO manga_sources (source_id, source_manga_key, manga_id, source_url) \
+         VALUES ($1, $2, $3, $4)",
+    )
+    .bind("src-b")
+    .bind("foo-on-b")
+    .bind(up.manga_id)
+    .bind("https://b.example/foo")
+    .execute(&pool)
+    .await
+    .unwrap();
+
+    let entries = crawler::list_missing_covers(&pool, 50).await.unwrap();
+    assert_eq!(entries.len(), 1, "DISTINCT ON (m.id) collapses duplicate source rows");
+}
+
 #[sqlx::test(migrations = "./migrations")]
 async fn re_appearing_manga_clears_dropped_at(pool: PgPool) {
     crawler::ensure_source(&pool, "target", "T", "https://x.example")

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.49.1",
+  "version": "0.50.0",
   "private": true,
   "type": "module",
   "scripts": {

frontend/src/lib/api/admin.test.ts

@@ -14,7 +14,9 @@ import {
     createAdminUser,
     listAdminMangas,
     listAdminChapters,
-    getSystemStats
+    getSystemStats,
+    resyncManga,
+    resyncChapter
 } from './admin';
 
 function ok(body: unknown, status = 200): Response {
@@ -242,4 +244,88 @@ describe('admin api client', () => {
         const s = await getSystemStats();
         expect(s.disk).toBeNull();
     });
+
+    // ---- force resync ----
+
+    it('resyncManga POSTs to /v1/admin/mangas/{id}/resync and returns the envelope', async () => {
+        const resp = {
+            manga: {
+                id: 'm-1',
+                title: 'T',
+                status: 'ongoing',
+                alt_titles: [],
+                description: null,
+                cover_image_path: 'mangas/m-1/cover.jpg',
+                created_at: '2026-01-01T00:00:00Z',
+                updated_at: '2026-01-02T00:00:00Z',
+                authors: [],
+                genres: [],
+                tags: []
+            },
+            metadata_status: 'updated',
+            cover_fetched: true
+        };
+        fetchSpy.mockResolvedValueOnce(ok(resp));
+        const got = await resyncManga('m-1');
+        expect(got.metadata_status).toBe('updated');
+        expect(got.cover_fetched).toBe(true);
+        expect(got.manga.id).toBe('m-1');
+        const url = fetchSpy.mock.calls[0][0] as string;
+        expect(url).toMatch(/\/v1\/admin\/mangas\/m-1\/resync$/);
+        const init = fetchSpy.mock.calls[0][1] as RequestInit;
+        expect(init.method).toBe('POST');
+    });
+
+    it('resyncManga surfaces 503 service_unavailable when the daemon is off', async () => {
+        fetchSpy.mockResolvedValueOnce(
+            envelope(503, 'service_unavailable', 'crawler daemon is disabled')
+        );
+        await expect(resyncManga('m-1')).rejects.toMatchObject({
+            status: 503,
+            code: 'service_unavailable'
+        });
+    });
+
+    it('resyncChapter POSTs to /v1/admin/chapters/{id}/resync and returns the envelope', async () => {
+        const resp = {
+            chapter: {
+                id: 'c-1',
+                manga_id: 'm-1',
+                number: 1,
+                title: 'Foo',
+                page_count: 7,
+                created_at: '2026-01-01T00:00:00Z'
+            },
+            outcome: 'fetched',
+            pages: 7
+        };
+        fetchSpy.mockResolvedValueOnce(ok(resp));
+        const got = await resyncChapter('c-1');
+        expect(got.outcome).toBe('fetched');
+        expect(got.pages).toBe(7);
+        expect(got.chapter.page_count).toBe(7);
+        const url = fetchSpy.mock.calls[0][0] as string;
+        expect(url).toMatch(/\/v1\/admin\/chapters\/c-1\/resync$/);
+        const init = fetchSpy.mock.calls[0][1] as RequestInit;
+        expect(init.method).toBe('POST');
+    });
+
+    it('resyncChapter handles the "skipped" outcome envelope', async () => {
+        const resp = {
+            chapter: {
+                id: 'c-1',
+                manga_id: 'm-1',
+                number: 1,
+                title: null,
+                page_count: 7,
+                created_at: '2026-01-01T00:00:00Z'
+            },
+            outcome: 'skipped',
+            pages: null
+        };
+        fetchSpy.mockResolvedValueOnce(ok(resp));
+        const got = await resyncChapter('c-1');
+        expect(got.outcome).toBe('skipped');
+        expect(got.pages).toBeNull();
+    });
 });

frontend/src/lib/api/admin.ts

@@ -5,6 +5,8 @@
 
 import { request, type Page } from './client';
 import type { User } from './auth';
+import type { MangaDetail } from './mangas';
+import type { Chapter } from './chapters';
 
 // ---- users -----------------------------------------------------------------
 
@@ -176,3 +178,39 @@ export type SystemStats = {
 export async function getSystemStats(): Promise<SystemStats> {
     return request<SystemStats>('/v1/admin/system');
 }
+
+// ---- force resync ----------------------------------------------------------
+
+export type MangaResyncResponse = {
+    manga: MangaDetail;
+    metadata_status: 'new' | 'updated' | 'unchanged';
+    cover_fetched: boolean;
+};
+
+export type ChapterResyncResponse = {
+    chapter: Chapter;
+    outcome: 'fetched' | 'skipped';
+    /** Page count when `outcome === 'fetched'`; null when skipped. */
+    pages: number | null;
+};
+
+/** POST /v1/admin/mangas/:id/resync — refetches metadata + cover from
+ *  the manga's live crawler source. Long-running (one HTTP request per
+ *  Chromium nav + image download), so the UI should disable the trigger
+ *  and surface progress. */
+export async function resyncManga(id: string): Promise<MangaResyncResponse> {
+    return request<MangaResyncResponse>(
+        `/v1/admin/mangas/${encodeURIComponent(id)}/resync`,
+        { method: 'POST' }
+    );
+}
+
+/** POST /v1/admin/chapters/:id/resync — force-refetches a chapter's
+ *  pages even if `page_count > 0`. Same long-running caveat as
+ *  `resyncManga`. */
+export async function resyncChapter(id: string): Promise<ChapterResyncResponse> {
+    return request<ChapterResyncResponse>(
+        `/v1/admin/chapters/${encodeURIComponent(id)}/resync`,
+        { method: 'POST' }
+    );
+}

frontend/src/routes/manga/[id]/+page.svelte

@@ -1,13 +1,15 @@
 <script lang="ts">
-    import { fileUrl } from '$lib/api/client';
+    import { fileUrl, ApiError } from '$lib/api/client';
     import { createBookmark, deleteBookmark, type Bookmark } from '$lib/api/bookmarks';
     import {
         attachTag,
         detachTag,
         type AuthorRef,
         type GenreRef,
+        type MangaDetail,
         type TagRef
     } from '$lib/api/mangas';
+    import { resyncManga } from '$lib/api/admin';
     import { listTags, type Tag } from '$lib/api/tags';
     import { session } from '$lib/session.svelte';
     import Chip from '$lib/components/Chip.svelte';
@@ -16,9 +18,15 @@
     import FolderPlus from '@lucide/svelte/icons/folder-plus';
     import Pencil from '@lucide/svelte/icons/pencil';
     import UploadCloud from '@lucide/svelte/icons/upload-cloud';
+    import RefreshCw from '@lucide/svelte/icons/refresh-cw';
 
     let { data } = $props();
-    const manga = $derived(data.manga);
+    // `manga` is locally overridable so a successful force resync can
+    // swap in the refreshed detail (new cover URL, refreshed status,
+    // etc.) without a router reload. Falls back to the server-loaded
+    // data otherwise.
+    let mangaOverride = $state<MangaDetail | null>(null);
+    const manga = $derived<MangaDetail>(mangaOverride ?? data.manga);
     const chapters = $derived(data.chapters);
     const readProgress = $derived(data.readProgress);
     /** Chapter row from the local chapters list when present (so we
@@ -171,6 +179,31 @@
     const statusLabel = $derived(manga.status === 'completed' ? 'Completed' : 'Ongoing');
 
     let collectionModalOpen = $state(false);
+
+    // ---- Admin force resync ----
+    let resyncBusy = $state(false);
+    let resyncMessage = $state<{ kind: 'ok' | 'err'; text: string } | null>(null);
+    async function forceResync() {
+        if (!session.user?.is_admin || resyncBusy) return;
+        resyncBusy = true;
+        resyncMessage = null;
+        try {
+            const r = await resyncManga(manga.id);
+            mangaOverride = r.manga;
+            const coverNote = r.cover_fetched
+                ? ' Cover re-downloaded.'
+                : ' Cover unchanged.';
+            resyncMessage = {
+                kind: 'ok',
+                text: `Metadata ${r.metadata_status}.${coverNote}`
+            };
+        } catch (e) {
+            const msg = e instanceof ApiError ? e.message : (e as Error).message;
+            resyncMessage = { kind: 'err', text: msg };
+        } finally {
+            resyncBusy = false;
+        }
+    }
 </script>
 
 <svelte:head>
@@ -344,7 +377,34 @@
                         <UploadCloud size={16} aria-hidden="true" />
                         <span>Upload chapter</span>
                     </a>
+                    {#if session.user.is_admin}
+                        <button
+                            type="button"
+                            class="action"
+                            onclick={forceResync}
+                            disabled={resyncBusy}
+                            title="Refetch metadata + cover from the crawler source"
+                            data-testid="force-resync-manga"
+                        >
+                            <RefreshCw
+                                size={16}
+                                aria-hidden="true"
+                                class={resyncBusy ? 'spin' : ''}
+                            />
+                            <span>{resyncBusy ? 'Resyncing…' : 'Force resync'}</span>
+                        </button>
+                    {/if}
                 </div>
+                {#if resyncMessage}
+                    <p
+                        class="resync-msg"
+                        class:err={resyncMessage.kind === 'err'}
+                        role="status"
+                        data-testid="force-resync-message"
+                    >
+                        {resyncMessage.text}
+                    </p>
+                {/if}
             {:else}
                 <a class="action" href="/login" data-testid="bookmark-signin">
                     Sign in to bookmark or collect
@@ -586,6 +646,29 @@
         color: var(--text);
     }
 
+    .resync-msg {
+        margin-top: var(--space-2);
+        color: var(--text-muted);
+        font-size: var(--font-sm);
+    }
+
+    .resync-msg.err {
+        color: var(--danger);
+    }
+
+    :global(.spin) {
+        animation: spin 0.9s linear infinite;
+    }
+
+    @keyframes spin {
+        from {
+            transform: rotate(0deg);
+        }
+        to {
+            transform: rotate(360deg);
+        }
+    }
+
     .continue {
         display: flex;
         flex-direction: column;

frontend/src/routes/manga/[id]/chapter/[chapter_id]/+page.svelte

@@ -1,10 +1,11 @@
 <script lang="ts">
     import { onMount, onDestroy } from 'svelte';
-    import { goto } from '$app/navigation';
+    import { goto, invalidateAll } from '$app/navigation';
-    import { fileUrl } from '$lib/api/client';
+    import { fileUrl, ApiError } from '$lib/api/client';
     import { GAP_PX, type ReaderPageGap } from '$lib/api/preferences';
     import { preferences } from '$lib/preferences.svelte';
     import { updateReadProgress } from '$lib/api/read_progress';
+    import { resyncChapter } from '$lib/api/admin';
     import { readerFullscreen } from '$lib/reader-fullscreen.svelte';
     import { session } from '$lib/session.svelte';
     import ChevronLeft from '@lucide/svelte/icons/chevron-left';
@@ -15,6 +16,7 @@
     import ScrollText from '@lucide/svelte/icons/scroll-text';
     import Maximize2 from '@lucide/svelte/icons/maximize-2';
     import Minimize2 from '@lucide/svelte/icons/minimize-2';
+    import RefreshCw from '@lucide/svelte/icons/refresh-cw';
 
     let { data } = $props();
     const manga = $derived(data.manga);
@@ -256,6 +258,36 @@
         if (typeof window !== 'undefined') window.removeEventListener('keydown', onKeydown);
     });
 
+    // ---- Admin force resync (current chapter) ----
+    let resyncBusy = $state(false);
+    let resyncMessage = $state<{ kind: 'ok' | 'err'; text: string } | null>(null);
+    async function forceResync() {
+        if (!session.user?.is_admin || resyncBusy) return;
+        resyncBusy = true;
+        resyncMessage = null;
+        try {
+            const r = await resyncChapter(chapter.id);
+            if (r.outcome === 'fetched') {
+                resyncMessage = {
+                    kind: 'ok',
+                    text: `Refetched ${r.pages} page${r.pages === 1 ? '' : 's'}. Reloading…`
+                };
+                // Re-run all loaders for this route so the reader picks
+                // up the freshly-downloaded pages. The page.ts loader
+                // doesn't `depends()` on anything explicitly, so
+                // invalidateAll is the right brush here.
+                await invalidateAll();
+            } else {
+                resyncMessage = { kind: 'ok', text: 'No new pages — source had nothing fresh.' };
+            }
+        } catch (e) {
+            const msg = e instanceof ApiError ? e.message : (e as Error).message;
+            resyncMessage = { kind: 'err', text: msg };
+        } finally {
+            resyncBusy = false;
+        }
+    }
+
     // ---- Reading progress tracking ----
     //
     // High-water mark seeded from the server: progress only ever moves
@@ -481,6 +513,23 @@
         {/if}
     </span>
 
+    {#if session.user?.is_admin}
+        <button
+            type="button"
+            class="reader-resync"
+            onclick={forceResync}
+            disabled={resyncBusy}
+            title={resyncMessage?.kind === 'err'
+                ? resyncMessage.text
+                : 'Force refetch this chapter from the crawler source'}
+            aria-label="Force resync chapter"
+            data-testid="force-resync-chapter"
+        >
+            <RefreshCw size={16} aria-hidden="true" class={resyncBusy ? 'spin' : ''} />
+            <span>{resyncBusy ? 'Resyncing…' : 'Force resync'}</span>
+        </button>
+    {/if}
+
     <button
         type="button"
         class="fullscreen-toggle"
@@ -494,6 +543,17 @@
     </button>
 </nav>
 
+{#if resyncMessage}
+    <p
+        class="resync-toast"
+        class:err={resyncMessage.kind === 'err'}
+        role="status"
+        data-testid="force-resync-message"
+    >
+        {resyncMessage.text}
+    </p>
+{/if}
+
 <!--
     Floating exit affordance — only rendered while focus mode is on.
     Lives in the top-right corner with a low resting opacity so it
@@ -911,7 +971,8 @@
     }
 
     /* ===== Focus-mode controls ===== */
-    .fullscreen-toggle {
+    .fullscreen-toggle,
+    .reader-resync {
         display: inline-flex;
         align-items: center;
         gap: var(--space-1);
@@ -925,12 +986,52 @@
         font-size: var(--font-xs);
     }
 
-    .fullscreen-toggle:hover {
+    .fullscreen-toggle:hover,
+    .reader-resync:hover:not(:disabled) {
         background: var(--surface-elevated);
         color: var(--text);
         border-color: var(--primary);
     }
 
+    .reader-resync:disabled {
+        opacity: 0.7;
+        cursor: progress;
+    }
+
+    .resync-toast {
+        position: fixed;
+        top: calc(var(--app-header-h) + var(--reader-nav-h, 48px) + var(--space-2));
+        right: var(--space-3);
+        z-index: 11;
+        margin: 0;
+        padding: var(--space-2) var(--space-3);
+        max-width: min(420px, calc(100vw - 2 * var(--space-3)));
+        background: var(--surface);
+        color: var(--text);
+        border: 1px solid var(--primary);
+        border-radius: var(--radius-md);
+        box-shadow: 0 4px 12px rgba(0, 0, 0, 0.12);
+        font-size: var(--font-sm);
+    }
+
+    .resync-toast.err {
+        border-color: var(--danger);
+        color: var(--danger);
+    }
+
+    :global(.spin) {
+        animation: spin 0.9s linear infinite;
+    }
+
+    @keyframes spin {
+        from {
+            transform: rotate(0deg);
+        }
+        to {
+            transform: rotate(360deg);
+        }
+    }
+
     /* Small floating exit affordance — corner-pinned, low resting
        opacity so it doesn't sit on the chapter image too aggressively
        but is still findable without hover. */