Refactor ETag generation for oneliners API

Remove the per-user oneliner watermark, which was previously used to
generate ETags for the `/api/oneliners` endpoint. The watermark was
intended to track the last successful oneliner write for each user.

The ETag generation has been refactored to use a deterministic FNV-1a
hash. This hash is computed over a sorted list of tuples containing
`(case_id, last_recording_at_ns, oneliner_mtime_ns)` for all visible
cases. This approach ensures that the ETag changes whenever any
listen-relevant file system modification occurs, such as a new
recording, oneliner regeneration, soft-delete, undo, or
upload-auto-reopen. This new method is more robust and avoids the
complexity of managing per-user state.

The `OnelinerWatermark` type alias and its associated logic have been
removed from `AppState` and the relevant modules (`transcribe::worker`,
`transcribe::recovery`, `routes::oneliners`, `main`). New integration
tests have been added to verify that various delete operations (single
delete, undo delete, bulk delete) correctly trigger an ETag update,
ensuring cache invalidation.

server/src/lib.rs

@@ -9,27 +9,17 @@ pub mod routes;
 pub mod transcribe;
 pub mod web_session;
 
-use std::collections::HashMap;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::Arc;
 
 use axum::extract::FromRef;
 use axum::Router;
-use time::OffsetDateTime;
-use tokio::sync::RwLock;
 
 use analyze::AnalyzeSender;
 use config::Config;
 use transcribe::TranscribeSender;
 use web_session::SessionStore;
 
-/// Per-user UTC timestamp of the last successful oneliner write.
-/// Read on every `/api/oneliners` request to build the ETag; written
-/// from the transcribe worker and the boot recovery scan. Missing entry
-/// → the user has no known oneliner activity yet; the endpoint returns
-/// a full response and sets an ETag based on a `0` seed.
-pub type OnelinerWatermark = Arc<RwLock<HashMap<String, OffsetDateTime>>>;
-
 /// Live "is this worker currently processing a job?" flag.
 /// Set true before each job, false after. UI uses it to distinguish a real
 /// in-flight job from a stale on-disk marker (orphan input, missing
@@ -70,7 +60,6 @@ pub struct AppState {
     pub session_store: SessionStore,
     pub analyze_busy: AnalyzeBusy,
     pub transcribe_busy: TranscribeBusy,
-    pub oneliner_watermark: OnelinerWatermark,
 }
 
 impl FromRef<AppState> for Arc<Config> {
@@ -109,12 +98,6 @@ impl FromRef<AppState> for TranscribeBusy {
     }
 }
 
-impl FromRef<AppState> for OnelinerWatermark {
-    fn from_ref(state: &AppState) -> Self {
-        state.oneliner_watermark.clone()
-    }
-}
-
 /// Test/simple entrypoint: jobs pushed into either channel are dropped
 /// because the receivers are not retained. Use [`create_router_with_state`]
 /// from `main.rs` where real workers own the receivers.
@@ -128,7 +111,6 @@ pub fn create_router(config: Arc<Config>) -> Router {
         session_store: web_session::new_store(),
         analyze_busy: AnalyzeBusy(Arc::new(AtomicBool::new(false))),
         transcribe_busy: TranscribeBusy(Arc::new(AtomicBool::new(false))),
-        oneliner_watermark: Arc::new(RwLock::new(HashMap::new())),
     })
 }