Defer oneliner regeneration until batch end

Avoid redundant LLM calls by waiting until all recordings in a batch
have been processed before regenerating the oneliner. This change
introduces a helper function `has_pending_recordings` to check for any
`.m4a` files without a corresponding transcript, and the
`update_oneliner` logic now only proceeds if no pending recordings are
found.

server/src/transcribe/worker.rs

@@ -78,11 +78,16 @@ pub async fn run(
             "Transcript written"
         );
 
-        // Regenerate the oneliner from all transcripts of the case. Later
-        // recordings override earlier ones — symmetric to the analyze-LLM
-        // rule "Spätere Aufnahmen haben Vorrang". Silent / empty cases are
-        // no-ops; LLM errors leave any existing oneliner untouched.
-        if let Some(case_dir) = audio_path.parent() {
+        // Regenerate the oneliner, but only after the *last* pending
+        // recording in the batch — otherwise we'd burn LLM calls on
+        // incomplete inputs that the next job would redo. Later
+        // recordings still override earlier ones (symmetric to the
+        // analyze-LLM "Spätere Aufnahmen haben Vorrang" rule). Silent /
+        // empty cases are no-ops; LLM errors leave any existing
+        // oneliner untouched.
+        if let Some(case_dir) = audio_path.parent()
+            && !has_pending_recordings(case_dir).await
+        {
             update_oneliner(case_dir, &client, &config, &vocab).await;
         }
     }
@@ -157,6 +162,29 @@ pub(crate) async fn update_oneliner(
     }
 }
 
+/// Return true if `case_dir` contains at least one `.m4a` recording
+/// that has no corresponding `.transcript.txt`. Used to gate the
+/// oneliner-regenerate call: we only run it after the *last* pending
+/// transcription in a batch, not after every single one. `.m4a.failed`
+/// entries are skipped — they don't block the oneliner. Fail-open on
+/// read errors: if we can't scan, return false so the oneliner runs
+/// anyway (one redundant call beats never).
+pub(crate) async fn has_pending_recordings(case_dir: &Path) -> bool {
+    let Ok(mut entries) = tokio::fs::read_dir(case_dir).await else {
+        return false;
+    };
+    while let Ok(Some(entry)) = entries.next_entry().await {
+        let path = entry.path();
+        if path.extension().and_then(|s| s.to_str()) != Some("m4a") {
+            continue;
+        }
+        if !path.with_extension("transcript.txt").exists() {
+            return true;
+        }
+    }
+    false
+}
+
 /// Read every non-empty `*.transcript.txt` in `case_dir`, ordered
 /// chronologically (ISO-8601 filename sort equals chronological order), and
 /// join them with `\n\n---\n\n`. Empty / whitespace-only transcripts (silent
@@ -261,4 +289,61 @@ mod tests {
             .unwrap();
         assert!(all_transcripts_joined(dir.path()).await.is_none());
     }
+
+    #[tokio::test]
+    async fn has_pending_recordings_true_when_m4a_without_transcript() {
+        let dir = tempdir().unwrap();
+        tokio::fs::write(dir.path().join("2026-04-16T10-00-00Z.m4a"), b"a")
+            .await
+            .unwrap();
+        tokio::fs::write(
+            dir.path().join("2026-04-16T10-00-00Z.transcript.txt"),
+            "text",
+        )
+        .await
+        .unwrap();
+        tokio::fs::write(dir.path().join("2026-04-16T10-05-00Z.m4a"), b"b")
+            .await
+            .unwrap();
+        assert!(has_pending_recordings(dir.path()).await);
+    }
+
+    #[tokio::test]
+    async fn has_pending_recordings_false_when_all_transcribed() {
+        let dir = tempdir().unwrap();
+        tokio::fs::write(dir.path().join("2026-04-16T10-00-00Z.m4a"), b"a")
+            .await
+            .unwrap();
+        tokio::fs::write(
+            dir.path().join("2026-04-16T10-00-00Z.transcript.txt"),
+            "text1",
+        )
+        .await
+        .unwrap();
+        tokio::fs::write(dir.path().join("2026-04-16T10-05-00Z.m4a"), b"b")
+            .await
+            .unwrap();
+        tokio::fs::write(
+            dir.path().join("2026-04-16T10-05-00Z.transcript.txt"),
+            "text2",
+        )
+        .await
+        .unwrap();
+        assert!(!has_pending_recordings(dir.path()).await);
+    }
+
+    #[tokio::test]
+    async fn has_pending_recordings_ignores_failed() {
+        let dir = tempdir().unwrap();
+        tokio::fs::write(dir.path().join("2026-04-16T10-00-00Z.m4a.failed"), b"x")
+            .await
+            .unwrap();
+        assert!(!has_pending_recordings(dir.path()).await);
+    }
+
+    #[tokio::test]
+    async fn has_pending_recordings_false_for_empty_dir() {
+        let dir = tempdir().unwrap();
+        assert!(!has_pending_recordings(dir.path()).await);
+    }
 }