feat: Show LLM failure banner and retry button

When an LLM analysis fails, a `.analysis_failed.json` marker is created.
If no document exists yet and the auto-trigger is blocked by this
marker,
the case page must display a banner. This banner provides the failure
reason and a button to retry the analysis, ensuring users are not left
in a dead-end state.

The `read_failure_marker` function is made public to allow the web layer
to access this failure information. The `CasePageTemplate` is updated to
include `analysis_failed` data, which conditionally renders the new
`.failure-banner` HTML.

This change prevents cases from becoming unrecoverable due to transient
LLM errors.

server/tests/case_page_test.rs

@@ -109,6 +109,79 @@ async fn case_page_shows_analyze_button_when_transcribed_without_document() {
     );
 }
 
+/// Bug regression: a previous LLM run that failed (e.g. transient HTTP
+/// transport error to the inference endpoint) leaves a `.analysis_failed.json`
+/// marker on disk. With no `document.md` yet, the existing "Neu analysieren"
+/// button — which lives inside the document-rendered branch — is invisible,
+/// and the auto-trigger refuses to retry as long as the marker matches the
+/// current input. The case page must therefore surface a recovery banner
+/// that exposes the reason and a retry form, otherwise the user is stuck.
+#[tokio::test]
+async fn case_page_shows_failure_banner_with_retry_when_marker_present() {
+    let (cfg, settings) = TestConfig::new()
+        .with_label("cp-fail-banner")
+        .with_user(test_user("dr_a"))
+        .with_llm("http://unused")
+        .build_pair();
+    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("transkribierter Text"),
+    );
+
+    // Seed the marker exactly as the analyze worker would on a transport
+    // failure. `last_recording_mtime` is intentionally close to (but not
+    // exactly equal to) the freshly-seeded recording's mtime — the banner
+    // path reads the marker unconditionally, so equality is irrelevant
+    // here; we only need the file to exist and parse.
+    std::fs::write(
+        case_dir.join(".analysis_failed.json"),
+        r#"{"last_recording_mtime":"2026-04-15T10:00:00Z","reason":"llm: connect timeout to https://example.invalid/v1/chat/completions","failed_at":"2026-04-15T10:05:00Z"}"#,
+    )
+    .unwrap();
+
+    let app = doctate_server::create_router_with_settings(cfg, settings);
+    let cookie = login_dr_a(&app).await;
+
+    let resp = app
+        .oneshot(get_with_cookie(paths::case_detail(case_id), &cookie))
+        .await
+        .unwrap();
+    assert_eq!(resp.status(), StatusCode::OK);
+    let body = body_string(resp).await;
+
+    assert!(
+        body.contains(r#"class="failure-banner""#),
+        "failure-banner div missing"
+    );
+    assert!(
+        body.contains("Analyse fehlgeschlagen"),
+        "user-facing failure title missing"
+    );
+    assert!(
+        body.contains("connect timeout"),
+        "raw reason text not surfaced (expected inside <details>)"
+    );
+    assert!(
+        body.contains(r#"datetime="2026-04-15T10:05:00Z""#),
+        "failed_at not rendered as <time datetime=...> for browser locale formatting"
+    );
+    assert!(
+        body.contains(&format!(r#"action="{}""#, paths::case_analyze(case_id))),
+        "retry form must POST to the analyze endpoint"
+    );
+    assert!(
+        body.contains("Erneut analysieren"),
+        "retry button label missing"
+    );
+    assert!(
+        !body.contains("Wird analysiert"),
+        "the analyzing placeholder must not coexist with the failure banner"
+    );
+}
+
 #[tokio::test]
 async fn case_page_shows_llm_missing_hint_without_llm() {
     let cfg = TestConfig::new()