fix: decouple oneliner-heal from request handler tasks

heal_orphans_if_idle called regenerate_missing_oneliners_for_user
inline on the request task, blocking the browser for up to N×60s
when orphans existed (observed with 16 cases after manual cleanup).

Now: CAS on new OnelinerHealBusy flag + tokio::spawn + BusyGuard
reset-on-drop. Handler returns immediately; the existing
OnelinerUpdated SSE event delivers results via the usual reload.
Startup recovery shares the flag so a concurrent page-load during
boot cannot fire a parallel regen loop against Ollama.

Regression test uses wiremock + timeout(150ms) + .expect(5) to
verify both non-blocking return and dedup of parallel invocations.

server/src/routes/user_web.rs

@@ -11,7 +11,6 @@ use tracing::{info, warn};
 
 use time::{Date, OffsetDateTime, format_description::well_known::Rfc3339};
 
-use crate::PipelineState;
 use crate::analyze::{
     ANALYSIS_INPUT_FILE, DOCUMENT_FILE, auto_trigger, recovery as analyze_recovery,
 };
@@ -25,6 +24,7 @@ use crate::paths;
 use crate::routes::case_actions::read_document;
 use crate::routes::web::{RecordingView, scan_recordings};
 use crate::transcribe::recovery as transcribe_recovery;
+use crate::{BusyGuard, PipelineState};
 
 /// UI-layer oneliner status for the case list. Combines the persisted
 /// [`OnelinerState`] with derived transit states that only make sense
@@ -299,8 +299,8 @@ impl PipelineState {
         user_root: &Path,
         slug: &str,
         http_client: &reqwest::Client,
-        config: &Config,
-        vocab: &Gazetteer,
+        config: &Arc<Config>,
+        vocab: &Arc<Gazetteer>,
         events_tx: &EventSender,
     ) {
         if !self.analyze_busy.0.load(Ordering::Acquire) {
@@ -309,18 +309,45 @@ impl PipelineState {
         if !self.transcribe_busy.0.load(Ordering::Acquire) {
             transcribe_recovery::enqueue_pending_for_user(user_root, slug, &self.transcribe_tx)
                 .await;
-            // Oneliner self-heal: if the transcribe worker is busy, it will
-            // write a fresh oneliner at batch-end anyway — skip to avoid a
-            // redundant LLM call.
-            transcribe_recovery::regenerate_missing_oneliners_for_user(
-                user_root,
-                slug,
-                http_client,
-                config,
-                vocab,
-                events_tx,
-            )
-            .await;
+            // Oneliner self-heal: if the transcribe worker is busy, it
+            // will write a fresh oneliner at batch-end anyway — skip to
+            // avoid a redundant LLM call. Otherwise, fire the regen in a
+            // detached task so the request handler returns immediately;
+            // SSE `OnelinerUpdated` events deliver results to the browser.
+            // The CAS on `oneliner_heal_busy` guards against concurrent
+            // page-loads spawning their own parallel regen loops against
+            // the same cases.
+            if self
+                .oneliner_heal_busy
+                .0
+                .compare_exchange(false, true, Ordering::AcqRel, Ordering::Acquire)
+                .is_ok()
+            {
+                let user_root = user_root.to_path_buf();
+                let slug_owned = slug.to_owned();
+                let http_client = http_client.clone();
+                let config = Arc::clone(config);
+                let vocab = Arc::clone(vocab);
+                let events_tx = events_tx.clone();
+                let busy = Arc::clone(&self.oneliner_heal_busy.0);
+                info!(user = %slug, "oneliner heal spawned");
+                tokio::spawn(async move {
+                    // `BusyGuard::Drop` resets the flag to `false` — even
+                    // on panic inside the regen loop. The redundant
+                    // `store(true)` inside `BusyGuard::new` is harmless;
+                    // the CAS above already owns the flag transition.
+                    let _guard = BusyGuard::new(busy);
+                    transcribe_recovery::regenerate_missing_oneliners_for_user(
+                        &user_root,
+                        &slug_owned,
+                        &http_client,
+                        &config,
+                        &vocab,
+                        &events_tx,
+                    )
+                    .await;
+                });
+            }
         }
     }
 }