feat: Handle analyze retry with failure marker

When a previous analysis attempt fails and leaves a failure marker, the
retry mechanism now correctly identifies this state. It removes the
stale
input file, allowing the retry to proceed without a conflict error. This
ensures users can recover from analysis failures more gracefully.

server/tests/analyze_test.rs

@@ -272,6 +272,59 @@ async fn analyze_case_second_time_returns_409() {
     assert_eq!(second.status(), StatusCode::CONFLICT);
 }
 
+/// Bug regression (case c414cf52, 2026-05-03): a prior LLM run failed,
+/// leaving `analysis_input.json` AND `.analysis_failed.json` on disk.
+/// The user clicks "Erneut versuchen" — the handler must accept the
+/// retry instead of rejecting it as 409 Conflict ("Analyse läuft
+/// bereits"). The failure marker is the explicit "worker has given up"
+/// signal that legitimises overwriting the stale sentinel.
+#[tokio::test]
+async fn analyze_retry_after_failure_marker_overwrites_stale_input() {
+    let (cfg, settings) = cfg_llm("retry-after-fail");
+    let case_id = "11111111-1111-1111-1111-111111111111";
+    let case_dir = seed_case(&cfg.data_path, "dr_a", case_id);
+    seed_recording(&case_dir, "2026-04-15T10-00-00Z", Some("frischer Text"));
+
+    // Simulate the post-failure on-disk state: stale input from the
+    // attempt the worker gave up on, plus the matching failure marker.
+    std::fs::write(
+        case_dir.join(ANALYSIS_INPUT_FILE),
+        r#"{"last_recording_mtime":"2026-04-15T10:00:00Z","recordings":[{"recorded_at":"2026-04-15T10:00:00Z","text":"alter Text"}],"backend_id":""}"#,
+    )
+    .unwrap();
+    std::fs::write(
+        case_dir.join(".analysis_failed.json"),
+        r#"{"last_recording_mtime":"2026-04-15T10:00:00Z","reason":"llm: connect timeout","failed_at":"2026-04-15T10:05:00Z"}"#,
+    )
+    .unwrap();
+
+    let (app, store) = doctate_server::create_router_and_session_store_with_settings(cfg, settings);
+    let (cookie, csrf) = login_with_csrf(&app, &store, "dr_a", "s").await;
+
+    let resp = app
+        .oneshot(csrf_form_post(
+            paths::case_analyze(case_id),
+            &cookie,
+            &csrf,
+            "",
+        ))
+        .await
+        .unwrap();
+    assert_eq!(
+        resp.status(),
+        StatusCode::SEE_OTHER,
+        "retry with failure marker present must succeed, not 409"
+    );
+
+    // Input was rewritten with the fresh transcript — the stale "alter Text"
+    // must be gone.
+    let raw = std::fs::read_to_string(case_dir.join(ANALYSIS_INPUT_FILE)).unwrap();
+    let parsed: Value = serde_json::from_str(&raw).unwrap();
+    let recs = parsed["recordings"].as_array().unwrap();
+    assert_eq!(recs.len(), 1);
+    assert_eq!(recs[0]["text"], "frischer Text");
+}
+
 #[tokio::test]
 async fn analyze_case_skips_blank_transcript_from_recordings() {
     let (cfg, settings) = cfg_llm("i");