feat(transcode): the local cache disables itself, and drains at boot

Completes the pattern the thumbnail migration established, for
`.transcoded/`.

`initialize` no longer creates the tree. Creating it at boot is exactly
what kept `.thumbnails/` alive across restarts — the import removed it,
the next boot put it back, and the absence the read path gates on was
unreachable by construction. The write path already calls
`create_dir_all` on the parent before writing, so eager creation
achieved nothing except defeating the drain.

It now probes instead: one `stat`, cached for the process lifetime, and
the local-cache reads short-circuit on a relaxed atomic load when the
tree is gone. Fails open, so a service built without `initialize`
behaves as before.

One difference from the thumbnail tiers, and it is not a stalled
migration: callers with no content hash — external mounts — cannot use
the content-keyed tier at all, so they still read and write here. On an
install without such mounts the directory drains once and stays gone;
on one with them it persists, correctly.

`transcode_import?repair=true` joins the startup defaults on the same
terms as the thumbnail imports, and with the weakest safety argument
needed of the three: a transcode is a pure function of its source, so
anything deleted in error is recomputed on the next request. The
`default_startup_jobs` test failed on the change rather than being
updated silently, which is what it is for.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/config/env.md

@@ -18,7 +18,7 @@ Most runtime variables use the `OXICLOUD_` prefix. A few build-time or allocator
 | `OXICLOUD_CHUNK_DIR` | `{STORAGE_PATH}/.uploads` | Root directory for chunked-upload sessions (REST + NextCloud). Direct (non-chunked) uploads stream straight into the blob store and need no spool directory. Placement guidance: see [Storage Fine Tuning](./storage-fine-tuning.md). |
 | `OXICLOUD_REUSE_PORT` | `false` | Enable `SO_REUSEPORT` so multiple processes can share the same port. **Disabled by default** — a second accidental instance will fail with "address already in use". Enable only for deliberate multi-worker setups (process supervisor, rolling restart). Not supported on Windows. |
 | `OXICLOUD_METRICS_LISTEN` | (unset) | Prometheus `/metrics` listener address (e.g. `127.0.0.1:9090`, IPv6 allowed as `[::1]:9090`). **Unset = disabled**: no `/metrics` endpoint is bound and no metrics recorder is installed (zero runtime cost). When set, a separate HTTP listener on this address serves the text-format scrape. **Deliberately NOT merged into the main API** — no auth, CSRF, or DPoP layer in front. Bind to loopback or a private interface unless you intend to expose metrics publicly. Starter counters: `oxicloud_dpop_verify_failed_total{reason}`, `oxicloud_dpop_proof_missing_total`, `oxicloud_dpop_header_missing_on_bound_session_total`, `oxicloud_dpop_replay_detected_total`, `oxicloud_dpop_nonce_challenges_issued_total`. |
-| `OXICLOUD_STARTUP_JOBS` | `thumb_derived_import?repair=true,thumb_attached_import?repair=true` | Background jobs dispatched once at boot, comma-separated, each `name` or `name?flag=true` using the same syntax as `POST /api/admin/jobs/{name}/trigger`. Flags: `force`, `deep`, `repair`, `storage`. **The default migrates thumbnails out of the legacy `.thumbnails/` directory and deletes the originals**, so the migration completes without anyone triggering it from the admin panel; each sidecar is read back through the normal stack before it is unlinked, and every deletion is audited. An explicit value **replaces** the default; set it empty (`OXICLOUD_STARTUP_JOBS=`) to disable startup jobs, or to `thumb_derived_import,thumb_attached_import` to import without deleting. **Non-blocking** — readiness never waits on a job; entries run sequentially in the background. **Fail-fast** — an unknown job name or flag panics at boot, because a silently-dropped entry means a migration that never runs. A run interrupted by a restart resumes from its cursor on the next boot, so a long migration finishes across restarts. Safe to leave at the default: the jobs are idempotent, and once drained a run does nothing. See [Thumbnail Migration](./thumbnail-migration.md) for the upgrade runbook. |
+| `OXICLOUD_STARTUP_JOBS` | `thumb_derived_import?repair=true,thumb_attached_import?repair=true,transcode_import?repair=true` | Background jobs dispatched once at boot, comma-separated, each `name` or `name?flag=true` using the same syntax as `POST /api/admin/jobs/{name}/trigger`. Flags: `force`, `deep`, `repair`, `storage`. **The default migrates thumbnails out of the legacy `.thumbnails/` directory and deletes the originals**, so the migration completes without anyone triggering it from the admin panel; each sidecar is read back through the normal stack before it is unlinked, and every deletion is audited. An explicit value **replaces** the default; set it empty (`OXICLOUD_STARTUP_JOBS=`) to disable startup jobs, or to `thumb_derived_import,thumb_attached_import` to import without deleting. **Non-blocking** — readiness never waits on a job; entries run sequentially in the background. **Fail-fast** — an unknown job name or flag panics at boot, because a silently-dropped entry means a migration that never runs. A run interrupted by a restart resumes from its cursor on the next boot, so a long migration finishes across restarts. Safe to leave at the default: the jobs are idempotent, and once drained a run does nothing. See [Thumbnail Migration](./thumbnail-migration.md) for the upgrade runbook. |
 
 ## Database
 

docs/plan/job-registry.md

@@ -746,7 +746,7 @@ optionally with the same query syntax the admin trigger URL uses.
 **The default is both migration jobs, in repair mode:**
 
 ```
-OXICLOUD_STARTUP_JOBS=thumb_derived_import?repair=true,thumb_attached_import?repair=true
+OXICLOUD_STARTUP_JOBS=thumb_derived_import?repair=true,thumb_attached_import?repair=true,transcode_import?repair=true
 ```
 
 An explicit value replaces that list; an empty value disables startup

example.env

@@ -62,7 +62,7 @@ OXICLOUD_SERVER_HOST=0.0.0.0
 # storage).
 #
 # DEFAULT (applied when this variable is unset):
-#   thumb_derived_import?repair=true,thumb_attached_import?repair=true
+#   thumb_derived_import?repair=true,thumb_attached_import?repair=true,transcode_import?repair=true
 #
 # Those two migrate thumbnails out of the legacy .thumbnails/ directory
 # into blob storage and then delete the originals, so the migration

src/common/config.rs

@@ -2401,8 +2401,15 @@ fn parse_startup_job(raw: &str) -> Result<StartupJob, String> {
 /// Set `OXICLOUD_STARTUP_JOBS=` (empty) to disable startup jobs
 /// entirely; any explicit value replaces this list rather than adding
 /// to it.
-const DEFAULT_STARTUP_JOBS: &str =
-    "thumb_derived_import?repair=true,thumb_attached_import?repair=true";
+/// `transcode_import` joins them for the same reason and on the same
+/// terms. Its artifacts are the most disposable of the three — a
+/// transcode is a pure function of its source, so anything deleted in
+/// error is recomputed on the next request — and its `.skip` markers
+/// collapse to one row per distinct content, which is the saving that
+/// only happens once the import runs.
+const DEFAULT_STARTUP_JOBS: &str = "thumb_derived_import?repair=true,\
+     thumb_attached_import?repair=true,\
+     transcode_import?repair=true";
 
 /// Parse the whole `OXICLOUD_STARTUP_JOBS` value. Empty → no startup
 /// jobs (an explicit opt-out); unset → [`DEFAULT_STARTUP_JOBS`].
@@ -3999,7 +4006,14 @@ mod tests {
     fn default_startup_jobs_drain_both_thumbnail_tiers() {
         let jobs = AppConfig::default().startup_jobs;
         let names: Vec<&str> = jobs.iter().map(|j| j.name.as_str()).collect();
-        assert_eq!(names, ["thumb_derived_import", "thumb_attached_import"]);
+        assert_eq!(
+            names,
+            [
+                "thumb_derived_import",
+                "thumb_attached_import",
+                "transcode_import"
+            ]
+        );
         assert!(jobs.iter().all(|j| j.args.repair));
         assert!(jobs.iter().all(|j| !j.args.deep && !j.args.force));
     }

src/infrastructure/services/image_transcode_service.rs

@@ -16,7 +16,7 @@
 use bytes::Bytes;
 use image::ImageFormat;
 use std::path::{Path, PathBuf};
-use std::sync::atomic::{AtomicU64, Ordering};
+use std::sync::atomic::{AtomicBool, AtomicU64, Ordering};
 use std::sync::{Arc, OnceLock};
 use tokio::fs;
 
@@ -173,6 +173,15 @@ pub struct ImageTranscodeService {
     /// `OnceLock` rather than a `Mutex`: set exactly once at boot, read on
     /// every request, never replaced.
     dedup: OnceLock<Arc<crate::infrastructure::services::dedup_service::DedupService>>,
+    /// Whether `.transcoded/` still exists, probed once by
+    /// [`Self::initialize`]. `false` short-circuits the local-cache reads
+    /// without a syscall.
+    ///
+    /// Starts `true` so a service constructed without `initialize` (tests)
+    /// behaves as before. Failing open is the safe direction: the wrong
+    /// value costs syscalls, the opposite would hide cached entries that
+    /// are still there.
+    legacy_cache: AtomicBool,
 }
 
 impl ImageTranscodeService {
@@ -203,6 +212,7 @@ impl ImageTranscodeService {
             memory_cache,
             stats: Arc::new(AtomicTranscodeStats::default()),
             dedup: OnceLock::new(),
+            legacy_cache: AtomicBool::new(true),
         }
     }
 
@@ -234,16 +244,52 @@ impl ImageTranscodeService {
     /// absence that `transcode_import` works toward unreachable, which is
     /// exactly the bug that kept `.thumbnails/` alive across restarts.
     pub async fn initialize(&self) -> std::io::Result<()> {
-        fs::create_dir_all(&self.cache_dir).await?;
-        fs::create_dir_all(self.cache_dir.join("webp")).await?;
+        // Probes, does NOT create.
+        //
+        // Creating the tree at boot is what kept `.thumbnails/` alive across
+        // restarts: the import removed it, the next boot put it back, and
+        // the absence the read path gates on was unreachable by
+        // construction. The write path below already calls `create_dir_all`
+        // on the parent before writing, so nothing needs it created eagerly
+        // — the only thing eager creation achieved was defeating the drain.
+        //
+        // One `stat` on the root, cached for the process lifetime. It can
+        // only be stale in the harmless direction: a drain completing
+        // mid-life leaves the flag true until restart, costing the same
+        // failed opens as before. It never goes false while entries remain,
+        // because only `transcode_import` removes the tree and it removes
+        // the whole thing at once.
+        let present = fs::metadata(&self.cache_dir).await.is_ok();
+        self.legacy_cache.store(present, Ordering::Relaxed);
+
         tracing::info!(
-            "🖼️ Image transcode service initialized (rayon pool: {} threads, cache dir: {:?})",
+            "🖼️ Image transcode service initialized (rayon pool: {} threads)",
             transcode_thread_count(),
-            self.cache_dir
         );
+        if present {
+            tracing::info!(
+                target: "oxicloud::transcode",
+                event = "transcode.legacy_cache_present",
+                path = ?self.cache_dir,
+                "legacy transcode cache present — reads fall back to it. Run \
+                 transcode_import with ?repair=true to drain it."
+            );
+        }
         Ok(())
     }
 
+    /// Whether the legacy local cache is worth touching.
+    ///
+    /// Unlike the thumbnail tiers this may legitimately never reach `false`:
+    /// callers with no content hash (external mounts) cannot use the
+    /// content-keyed tier at all, so they still read and write here. On an
+    /// install without such mounts the directory drains once and stays
+    /// gone; on one with them it persists, and that is correct rather than
+    /// a stalled migration.
+    fn legacy_cache_active(&self) -> bool {
+        self.legacy_cache.load(Ordering::Relaxed)
+    }
+
     /// Check if a mime type can be transcoded.
     ///
     /// JPEG is deliberately excluded: the `image` crate's WebP encoder is
@@ -402,7 +448,7 @@ impl ImageTranscodeService {
         //
         // Drained by `transcode_import`; kept as a fallback until it is gone.
         let cache_path = self.get_cache_path(file_id, target_format);
-        if tokio::fs::try_exists(&cache_path).await.unwrap_or(false) {
+        if self.legacy_cache_active() && tokio::fs::try_exists(&cache_path).await.unwrap_or(false) {
             match fs::read(&cache_path).await {
                 Ok(data) => {
                     self.stats.disk_hits.fetch_add(1, Ordering::Relaxed);
@@ -417,7 +463,8 @@ impl ImageTranscodeService {
 
         // ── Negative verdict persisted on disk (survives restarts) ──
         let skip_marker = self.get_skip_marker_path(file_id, target_format);
-        if tokio::fs::try_exists(&skip_marker).await.unwrap_or(false) {
+        if self.legacy_cache_active() && tokio::fs::try_exists(&skip_marker).await.unwrap_or(false)
+        {
             self.stats.disk_hits.fetch_add(1, Ordering::Relaxed);
             tracing::debug!("💾 Transcode negative disk marker HIT: {}", file_id);
             return Ok(Bytes::new());