fix: harden media handoff and live logs

Reject stale extension media cookie headers before yt-dlp metadata work, preserve ordinary capture cookies, and advance the companion extension.

Stream redacted diagnostic logs only while the visible Logs view is active, with bounded batched updates and race-safe snapshot handoff.

src-tauri/src/extension_server.rs

@@ -315,10 +315,15 @@ fn normalize_download(payload: ExtensionRequest) -> Option<ExtensionDownload> {
         silent: payload.silent,
         filename,
         headers: payload.headers.filter(|value| !value.trim().is_empty()),
-        // Keep the exact tab/container cookie context. The Add modal may retry
-        // public media without this header when an upstream rejects its size,
-        // but authenticated and container-scoped media must not lose it here.
-        cookies: payload.cookies.filter(|value| !value.trim().is_empty()),
+        // Explicit media is resolved by yt-dlp, which must use Firelink's
+        // configured browser-cookie source. Forwarding a browser's complete
+        // Cookie header can exceed upstream limits and makes old extension
+        // builds pay for a doomed metadata request before retrying. Ordinary
+        // captured downloads still need their exact request cookies.
+        cookies: (!payload.media)
+            .then_some(payload.cookies)
+            .flatten()
+            .filter(|value| !value.trim().is_empty()),
         media: payload.media,
     })
 }
@@ -496,24 +501,41 @@ mod tests {
     }
 
     #[test]
-    fn explicit_media_preserves_the_extension_cookie_header() {
+    fn explicit_media_drops_the_extension_cookie_header() {
         let download = normalize_download(ExtensionRequest {
             urls: vec!["https://www.youtube.com/watch?v=example".to_string()],
             referer: None,
             silent: false,
             filename: None,
             headers: Some("User-Agent: Firefox".to_string()),
-            cookies: Some("large=browser-cookie-header".to_string()),
+            cookies: Some(format!("large={}", "x".repeat(64 * 1024))),
             media: true,
         })
         .expect("valid media handoff");
 
         assert!(download.media);
+        assert!(download.cookies.is_none());
+        assert_eq!(download.headers.as_deref(), Some("User-Agent: Firefox"));
+    }
+
+    #[test]
+    fn regular_capture_preserves_the_extension_cookie_header() {
+        let download = normalize_download(ExtensionRequest {
+            urls: vec!["https://example.com/private.zip".to_string()],
+            referer: None,
+            silent: true,
+            filename: None,
+            headers: None,
+            cookies: Some("session=browser-cookie-header".to_string()),
+            media: false,
+        })
+        .expect("valid download handoff");
+
+        assert!(!download.media);
         assert_eq!(
             download.cookies.as_deref(),
-            Some("large=browser-cookie-header")
+            Some("session=browser-cookie-header")
         );
-        assert_eq!(download.headers.as_deref(), Some("User-Agent: Firefox"));
     }
 
     #[test]

src-tauri/src/lib.rs

@@ -4542,6 +4542,27 @@ fn redact_log_line(line: &str) -> String {
     query.replace_all(&redacted, "$1?[redacted]").into_owned()
 }
 
+fn redact_log_line_for_output(line: &str) -> String {
+    static HOME_PATHS: OnceLock<(String, String)> = OnceLock::new();
+    let (home, escaped_home) = HOME_PATHS.get_or_init(|| {
+        let home = std::env::var("USERPROFILE")
+            .or_else(|_| std::env::var("HOME"))
+            .unwrap_or_default();
+        let home = if home.len() > 3 { home } else { String::new() };
+        let escaped_home = home.replace('\\', "\\\\");
+        (home, escaped_home)
+    });
+
+    let mut redacted = line.to_string();
+    if !home.is_empty() {
+        redacted = redacted.replace(home, "<HOME>");
+    }
+    if !escaped_home.is_empty() && escaped_home != home {
+        redacted = redacted.replace(escaped_home, "<HOME>");
+    }
+    redact_log_line(&redacted)
+}
+
 fn redact_log_line_for_app(line: &str, app_handle: &tauri::AppHandle) -> String {
     use tauri::Manager;
     let without_home = app_handle
@@ -4780,8 +4801,9 @@ mod tests {
         media_output_template, media_progress_args, media_progress_speed,
         normalize_speed_limit_for_aria2,
         parse_firelink_deep_link, parse_ffmpeg_version, parse_media_progress_line,
-        redact_log_line, sanitize_ytdlp_config_value, should_cleanup_media_artifacts_after_failure,
-        FirelinkDeepLink, MediaProgress, MediaSpeedSampler, MEDIA_PROGRESS_PREFIX,
+        redact_log_line, redact_log_line_for_output, sanitize_ytdlp_config_value,
+        should_cleanup_media_artifacts_after_failure, FirelinkDeepLink, MediaProgress,
+        MediaSpeedSampler, MEDIA_PROGRESS_PREFIX,
     };
     use serde_json::json;
     use std::time::{Duration, Instant};
@@ -4979,6 +5001,15 @@ mod tests {
         assert!(redacted.contains("[redacted]"));
     }
 
+    #[test]
+    fn redacts_live_log_output_before_webview_delivery() {
+        let line = "Cookie: session=abc https://example.com/file?signature=secret";
+        let redacted = redact_log_line_for_output(line);
+        assert!(!redacted.contains("session=abc"));
+        assert!(!redacted.contains("signature=secret"));
+        assert!(redacted.contains("[redacted]"));
+    }
+
     #[test]
     fn collects_primary_url_and_unique_mirrors_in_order() {
         let uris = collect_download_uris(
@@ -5459,6 +5490,7 @@ mod tests {
 }
 
 static LOG_PAUSED: std::sync::atomic::AtomicBool = std::sync::atomic::AtomicBool::new(true);
+static LOG_STREAM_ACTIVE: std::sync::atomic::AtomicBool = std::sync::atomic::AtomicBool::new(false);
 
 #[tauri::command]
 fn toggle_log_pause(pause: bool) {
@@ -5470,6 +5502,11 @@ fn is_log_paused() -> bool {
     LOG_PAUSED.load(std::sync::atomic::Ordering::Relaxed)
 }
 
+#[tauri::command]
+fn set_log_stream_active(active: bool) {
+    LOG_STREAM_ACTIVE.store(active, std::sync::atomic::Ordering::Release);
+}
+
 #[cfg_attr(mobile, tauri::mobile_entry_point)]
 pub fn run() {
     ensure_reqwest_crypto_provider();
@@ -5881,7 +5918,13 @@ pub fn run() {
             tauri_plugin_log::Builder::new()
                 .targets([
                     tauri_plugin_log::Target::new(tauri_plugin_log::TargetKind::Stdout),
-                    tauri_plugin_log::Target::new(tauri_plugin_log::TargetKind::LogDir { file_name: None }),
+                    tauri_plugin_log::Target::new(tauri_plugin_log::TargetKind::LogDir {
+                        file_name: None,
+                    }),
+                    tauri_plugin_log::Target::new(tauri_plugin_log::TargetKind::Webview)
+                        .filter(|_| {
+                            LOG_STREAM_ACTIVE.load(std::sync::atomic::Ordering::Acquire)
+                        }),
                 ])
                 .level(if cfg!(debug_assertions) { log::LevelFilter::Debug } else { log::LevelFilter::Info })
                 .filter(|metadata| {
@@ -5899,21 +5942,8 @@ pub fn run() {
                 .max_file_size(10_000_000)
                 .rotation_strategy(tauri_plugin_log::RotationStrategy::KeepSome(3))
                 .timezone_strategy(tauri_plugin_log::TimezoneStrategy::UseLocal)
-                .format({
-                    let home_dir = std::env::var("USERPROFILE").or_else(|_| std::env::var("HOME")).unwrap_or_default();
-                    let home_dir = if home_dir.len() > 3 { home_dir } else { String::new() };
-                    let escaped_home_dir = home_dir.replace("\\", "\\\\");
-                    move |out, message, record| {
-                        let msg = message.to_string();
-                        let redacted = if !home_dir.is_empty() {
-                            let mut s = msg.replace(&home_dir, "<HOME>");
-                            if !escaped_home_dir.is_empty() && escaped_home_dir != home_dir {
-                                s = s.replace(&escaped_home_dir, "<HOME>");
-                            }
-                            s
-                        } else {
-                            msg
-                        };
+                .format(|out, message, record| {
+                    let redacted = redact_log_line_for_output(&message.to_string());
                     out.finish(format_args!(
                         "[{}][{}][{}] {}",
                         chrono::Local::now().format("%Y-%m-%d][%H:%M:%S"),
@@ -5921,7 +5951,6 @@ pub fn run() {
                         record.target(),
                         redacted
                     ))
-                    }
                 })
                 .build(),
         )
@@ -5955,7 +5984,8 @@ pub fn run() {
             parity::create_category_directories,
             db_save_settings, db_load_settings, db_get_all_downloads, db_replace_downloads,
             db_get_all_queues, db_replace_queues,
-            read_logs, export_logs, toggle_log_pause, is_log_paused, clear_logs
+            read_logs, export_logs, toggle_log_pause, is_log_paused, clear_logs,
+            set_log_stream_active
         ])
         .build(tauri::generate_context!())
         .expect("error while building tauri application")

src/App.tsx

@@ -397,6 +397,12 @@ function App() {
     invoke('toggle_log_pause', { pause: !logsEnabled }).catch(console.error);
   }, [logsEnabled]);
 
+  useEffect(() => {
+    if (activeView !== 'logs') {
+      invoke('set_log_stream_active', { active: false }).catch(console.error);
+    }
+  }, [activeView]);
+
   useEffect(() => {
     if (!extensionPairingToken) return;
     invoke('set_extension_pairing_token', { token: extensionPairingToken }).catch(error => {

src/components/AddDownloadsModal.tsx

@@ -120,9 +120,8 @@ export const AddDownloadsModal = () => {
     if (context) return extensionHeaders(context).trim();
     return hasExtensionRequestContext ? '' : headers.trim();
   };
-  const cookiesForRow = (sourceUrl: string, omitRequestCookies = false) => {
+  const cookiesForRow = (sourceUrl: string) => {
     if (cookiesManuallyEditedRef.current) return cookies.trim();
-    if (omitRequestCookies) return '';
     const context = requestContextForUrl(sourceUrl);
     if (context) return context.cookies.trim();
     return hasExtensionRequestContext ? '' : cookies.trim();
@@ -303,25 +302,7 @@ export const AddDownloadsModal = () => {
               cookies: rowCookies || null,
               proxy
             };
-            let requestCookiesOmitted = false;
-            let mediaData;
-            try {
-              mediaData = await fetchMediaMetadataDeduped(mediaMetadataArgs);
-            } catch (error) {
-              const capturedCookies = requestContextForUrl(row.sourceUrl)?.cookies.trim();
-              if (!rowCookies || !capturedCookies || cookiesManuallyEditedRef.current) {
-                throw error;
-              }
-              console.warn(
-                'Media metadata rejected the captured Cookie header; retrying without request cookies',
-                error
-              );
-              mediaData = await fetchMediaMetadataDeduped({
-                ...mediaMetadataArgs,
-                cookies: null
-              });
-              requestCookiesOmitted = true;
-            }
+            const mediaData = await fetchMediaMetadataDeduped(mediaMetadataArgs);
             if (mediaData && mediaData.formats.length > 0) {
               const mappedFormats = mediaData.formats.map(f => {
                 const quality = f.resolution || 'Video';
@@ -353,7 +334,6 @@ export const AddDownloadsModal = () => {
                   size: mappedFormats[0].bytes ? mappedFormats[0].detail : undefined,
                   sizeBytes: mappedFormats[0].bytes || undefined,
                   status: 'ready',
-                  requestCookiesOmitted,
                   formats: mappedFormats,
                   selectedFormat: 0
                 })
@@ -729,7 +709,7 @@ export const AddDownloadsModal = () => {
           checksum: checksumEnabled && checksumValue.trim()
             ? `${checksumAlgo}=${checksumValue.trim()}`
             : undefined,
-          cookies: cookiesForRow(item.sourceUrl, item.requestCookiesOmitted) || undefined,
+          cookies: cookiesForRow(item.sourceUrl) || undefined,
           mirrors: mirrors.trim() || undefined,
           destination: useSharedDestination
             ? finalLocation
@@ -1148,11 +1128,6 @@ export const AddDownloadsModal = () => {
                         className="add-download-control w-full px-3 py-1.5 text-xs font-mono"
                         aria-label="Cookies"
                       />
-                      {!cookiesManuallyEditedRef.current && parsedItems.some(item => item.requestCookiesOmitted) && (
-                        <p className="mt-1 text-[10px] text-amber-400">
-                          Media metadata only worked without the captured cookies, so they will be omitted for affected rows. Edit this field to force a manual value.
-                        </p>
-                      )}
                     </div>
                     <div>
                       <label className="block text-[10px] uppercase font-bold tracking-wider text-text-muted mb-1">Mirrors</label>

src/components/LogsView.tsx

@@ -7,11 +7,15 @@ import { FileDown, Trash2, Terminal, Filter, Play, Pause, Info, Copy } from 'luc
 import { WindowDragRegion } from './WindowDragRegion';
 import { useToast } from '../contexts/ToastContext';
 import { useSettingsStore } from '../store/useSettingsStore';
-
-interface LogEntry {
-  level: 'Trace' | 'Debug' | 'Info' | 'Warn' | 'Error';
-  message: string;
-}
+import {
+  MAX_LOG_LINES,
+  appendBoundedLogEntries,
+  liveLogEntry,
+  mergeLogSnapshotAndLiveEntries,
+  persistedLogEntry,
+  pushBoundedLogEntry,
+  type LogEntry
+} from '../utils/logEntries';
 
 export default function LogsView() {
   const { addToast } = useToast();
@@ -20,56 +24,75 @@ export default function LogsView() {
   const [logs, setLogs] = useState<LogEntry[]>([]);
   const [levelFilter, setLevelFilter] = useState<LogEntry['level'] | 'All'>('All');
   const [contextMenu, setContextMenu] = useState<{ x: number; y: number; text: string } | null>(null);
+  const [pageVisible, setPageVisible] = useState(() => document.visibilityState !== 'hidden');
   const scrollRef = useRef<HTMLDivElement>(null);
-  const rawLineCountRef = useRef(0);
-
-  const MAX_LOG_LINES = 2000;
+  const liveBatchRef = useRef<LogEntry[]>([]);
+  const liveFrameRef = useRef<number | null>(null);
 
   useEffect(() => {
+    const handleVisibilityChange = () => setPageVisible(document.visibilityState !== 'hidden');
+    document.addEventListener('visibilitychange', handleVisibilityChange);
+    return () => document.removeEventListener('visibilitychange', handleVisibilityChange);
+  }, []);
+
+  useEffect(() => {
+    if (!pageVisible) {
+      void invoke('set_log_stream_active', { active: false }).catch(console.error);
+      return;
+    }
+
+    if (!logsEnabled) {
+      void invoke('set_log_stream_active', { active: false }).catch(console.error);
+    }
+
     let active = true;
-    let unlisten: (() => void) | undefined;
+    let initialized = false;
+    let pendingLiveEntries: LogEntry[] = [];
+    let unlistenPromise: Promise<() => void> | undefined;
+
+    const scheduleLiveEntry = (entry: LogEntry) => {
+      if (!initialized) {
+        pushBoundedLogEntry(pendingLiveEntries, entry);
+        return;
+      }
+
+      pushBoundedLogEntry(liveBatchRef.current, entry);
+      if (liveFrameRef.current !== null) return;
+      liveFrameRef.current = window.requestAnimationFrame(() => {
+        liveFrameRef.current = null;
+        if (!active || liveBatchRef.current.length === 0) return;
+        const batch = liveBatchRef.current;
+        liveBatchRef.current = [];
+        setLogs(current => appendBoundedLogEntries(current, batch));
+      });
+    };
 
     const init = async () => {
       try {
         await initLogger();
-        const [lines] = await Promise.all([
-          invoke('read_logs', { limit: MAX_LOG_LINES })
-        ]);
         if (!active) return;
-        const initialLogs = lines.map(message => {
-          const level: LogEntry['level'] = message.includes('[ERROR]') ? 'Error'
-            : message.includes('[WARN]') ? 'Warn'
-              : message.includes('[INFO]') ? 'Info'
-                : message.includes('[TRACE]') ? 'Trace'
-                  : 'Debug';
-          return { level, message };
-        });
-        
-        setLogs(initialLogs);
-        rawLineCountRef.current = initialLogs.length;
 
         if (logsEnabled) {
-          unlisten = await attachLogger((log) => {
+          unlistenPromise = attachLogger((log) => {
             if (!active) return;
-            const levelStr: LogEntry['level'] = log.level === 5 ? 'Error'
-              : log.level === 4 ? 'Warn'
-                : log.level === 3 ? 'Info'
-                  : log.level === 1 ? 'Trace'
-                    : 'Debug';
-
-            const timeStr = new Date().toISOString().replace('T', ' ').substring(0, 19);
-            const formattedMsg = `[${timeStr}] [${levelStr.toUpperCase()}] ${log.message}`;
-
-            setLogs(prev => {
-              const newLogs = [...prev, { level: levelStr, message: formattedMsg }];
-              rawLineCountRef.current = newLogs.length;
-              if (newLogs.length > MAX_LOG_LINES + 500) {
-                return newLogs.slice(newLogs.length - MAX_LOG_LINES);
-              }
-              return newLogs;
-            });
+            scheduleLiveEntry(liveLogEntry(log.level, log.message));
           });
+          await unlistenPromise;
+          if (!active) return;
+          await invoke('set_log_stream_active', { active: true });
+          if (!active) {
+            await invoke('set_log_stream_active', { active: false }).catch(console.error);
+            return;
           }
+        }
+
+        const lines = await invoke('read_logs', { limit: MAX_LOG_LINES });
+        if (!active) return;
+        const snapshot = lines.map(persistedLogEntry);
+        initialized = true;
+        const caughtUpLogs = mergeLogSnapshotAndLiveEntries(snapshot, pendingLiveEntries);
+        pendingLiveEntries = [];
+        setLogs(caughtUpLogs);
       } catch (e) {
         console.error('Failed to init logs:', e);
       }
@@ -78,9 +101,19 @@ export default function LogsView() {
     
     return () => {
       active = false;
-      if (unlisten) unlisten();
+      liveBatchRef.current = [];
+      if (liveFrameRef.current !== null) {
+        window.cancelAnimationFrame(liveFrameRef.current);
+        liveFrameRef.current = null;
+      }
+      if (logsEnabled) {
+        void invoke('set_log_stream_active', { active: false }).catch(console.error);
+      }
+      if (unlistenPromise) {
+        void unlistenPromise.then(unlisten => unlisten()).catch(console.error);
+      }
     };
-  }, [logsEnabled]);
+  }, [logsEnabled, pageVisible]);
 
   useEffect(() => {
     if (scrollRef.current) {
@@ -139,6 +172,11 @@ export default function LogsView() {
   };
 
   const handleClear = async () => {
+    liveBatchRef.current = [];
+    if (liveFrameRef.current !== null) {
+      window.cancelAnimationFrame(liveFrameRef.current);
+      liveFrameRef.current = null;
+    }
     setLogs([]);
     await invoke('clear_logs').catch(console.error);
   };

src/ipc.ts

@@ -76,6 +76,7 @@ type CommandMap = {
   clear_logs: { args: undefined; result: void };
   toggle_log_pause: { args: { pause: boolean }; result: void };
   is_log_paused: { args: undefined; result: boolean };
+  set_log_stream_active: { args: { active: boolean }; result: void };
   get_pending_order: { args: { queueId: string | null }; result: string[] };
   enqueue_download: { args: { item: EnqueueItem }; result: EnqueueAccepted };
   cancel_enqueue_generation: { args: { id: string; generation: string }; result: void };

src/store/useDownloadStore.test.ts

@@ -819,7 +819,7 @@ describe('useDownloadStore', () => {
       silent: false,
       filename: null,
       headers: 'User-Agent: Firefox Test',
-      cookies: 'session=secret',
+      cookies: `oversized=${'x'.repeat(64 * 1024)}`,
       media: true
     });
 
@@ -827,7 +827,21 @@ describe('useDownloadStore', () => {
     expect(state.isAddModalOpen).toBe(true);
     expect(state.pendingAddUrls).toBe('https://adult.example/watch/123');
     expect(state.pendingAddMediaUrls).toEqual(['https://adult.example/watch/123']);
-    expect(state.pendingAddCookies).toBe('session=secret');
+    expect(state.pendingAddCookies).toBe('');
+  });
+
+  it('preserves extension cookies for ordinary captured downloads', async () => {
+    await useDownloadStore.getState().handleExtensionDownload({
+      urls: ['https://example.com/private.zip'],
+      referer: 'https://example.com/downloads',
+      silent: true,
+      filename: 'private.zip',
+      headers: null,
+      cookies: 'session=secret',
+      media: false
+    });
+
+    expect(useDownloadStore.getState().pendingAddCookies).toBe('session=secret');
   });
 
   it('clears stale request context when the same URL is captured without it later', async () => {

src/store/useDownloadStore.ts

@@ -551,12 +551,17 @@ export const useDownloadStore = create<DownloadState>((set, get) => ({
     const urls = [...new Set(request.urls.map(url => url.trim()).filter(Boolean))];
     if (urls.length === 0) return;
 
+    // Explicit media authentication belongs to yt-dlp's configured browser
+    // cookie source. Keep this frontend guard for events from older desktop or
+    // extension builds; ordinary captured downloads retain their cookies.
+    const cookies = request.media === true ? null : request.cookies;
+
     get().openAddModalWithUrls(
       urls.join('\n'),
       request.referer,
       urls.length === 1 ? request.filename : null,
       request.headers,
-      request.cookies,
+      cookies,
       request.media === true
     );
   },

src/utils/addDownloadMetadata.test.ts

@@ -94,7 +94,6 @@ describe('add download metadata workflow', () => {
       status: 'ready',
       generation: 4,
       requestContextVersion: 1,
-      requestCookiesOmitted: true,
       formats: [{
         name: '1080p MP4',
         selector: '137+140',
@@ -121,7 +120,6 @@ describe('add download metadata workflow', () => {
       status: 'loading',
       generation: 5,
       requestContextVersion: 2,
-      requestCookiesOmitted: false,
       formats: undefined,
       selectedFormat: undefined
     });

src/utils/addDownloadMetadata.ts

@@ -27,7 +27,6 @@ export interface AddDownloadDraftRow {
   status: MetadataStatus;
   generation: number;
   requestContextVersion?: number;
-  requestCookiesOmitted?: boolean;
   isMedia: boolean;
   resumable?: boolean;
   formats?: AddMediaFormat[];
@@ -94,7 +93,6 @@ export const reconcileDownloadRows = (
           status: 'loading',
           generation: preserved.generation + 1,
           requestContextVersion,
-          requestCookiesOmitted: false,
           isMedia: preserved.isMedia || forcedMedia,
           formats: preserved.isMedia || forcedMedia ? undefined : preserved.formats,
           selectedFormat: preserved.isMedia || forcedMedia ? undefined : preserved.selectedFormat

src/utils/logEntries.test.ts

@@ -0,0 +1,55 @@
+import { describe, expect, it } from 'vitest';
+import {
+  appendBoundedLogEntries,
+  liveLogEntry,
+  mergeLogSnapshotAndLiveEntries,
+  persistedLogEntry,
+  pushBoundedLogEntry,
+  type LogEntry
+} from './logEntries';
+
+const entry = (message: string): LogEntry => ({ level: 'Info', message });
+
+describe('log entry streaming', () => {
+  it('derives levels from persisted formatted lines', () => {
+    expect(persistedLogEntry('[2026-07-10][18:00:00][ERROR][firelink] failed')).toEqual({
+      level: 'Error',
+      message: '[2026-07-10][18:00:00][ERROR][firelink] failed'
+    });
+  });
+
+  it('does not double-format backend Webview log lines', () => {
+    const message = '[2026-07-10][18:00:00][WARN][firelink] retrying';
+    expect(liveLogEntry(4, message).message).toBe(message);
+  });
+
+  it('formats an unformatted plugin event with its numeric level', () => {
+    expect(liveLogEntry(3, 'download started', new Date('2026-07-10T14:30:00Z'))).toEqual({
+      level: 'Info',
+      message: '[2026-07-10 14:30:00] [INFO] download started'
+    });
+  });
+
+  it('merges only the ordered snapshot-to-stream overlap', () => {
+    expect(mergeLogSnapshotAndLiveEntries(
+      [entry('one'), entry('repeat'), entry('three')],
+      [entry('three'), entry('repeat'), entry('four')]
+    ).map(item => item.message)).toEqual(['one', 'repeat', 'three', 'repeat', 'four']);
+  });
+
+  it('bounds burst updates to the newest entries', () => {
+    expect(appendBoundedLogEntries(
+      [entry('old')],
+      Array.from({ length: 5 }, (_, index) => entry(`new-${index}`)),
+      3
+    ).map(item => item.message)).toEqual(['new-2', 'new-3', 'new-4']);
+  });
+
+  it('bounds the mutable pre-render queue without copying on every event', () => {
+    const queue = [entry('old')];
+    for (let index = 0; index < 5; index += 1) {
+      pushBoundedLogEntry(queue, entry(`new-${index}`), 3);
+    }
+    expect(queue.map(item => item.message)).toEqual(['new-2', 'new-3', 'new-4']);
+  });
+});

src/utils/logEntries.ts

@@ -0,0 +1,92 @@
+export type LogLevel = 'Trace' | 'Debug' | 'Info' | 'Warn' | 'Error';
+
+export interface LogEntry {
+  level: LogLevel;
+  message: string;
+}
+
+export const MAX_LOG_LINES = 2000;
+
+const LEVEL_NAMES: LogLevel[] = ['Trace', 'Debug', 'Info', 'Warn', 'Error'];
+const LIVE_LEVELS: Record<number, LogLevel> = {
+  1: 'Trace',
+  2: 'Debug',
+  3: 'Info',
+  4: 'Warn',
+  5: 'Error'
+};
+
+const levelFromMessage = (message: string): LogLevel | undefined =>
+  LEVEL_NAMES.find(level => message.includes(`[${level.toUpperCase()}]`));
+
+export const persistedLogEntry = (message: string): LogEntry => ({
+  level: levelFromMessage(message) || 'Debug',
+  message
+});
+
+export const liveLogEntry = (
+  numericLevel: number,
+  message: string,
+  now: Date = new Date()
+): LogEntry => {
+  const level = levelFromMessage(message) || LIVE_LEVELS[numericLevel] || 'Debug';
+  const alreadyFormatted = /^\[\d{4}-\d{2}-\d{2}\]\[\d{2}:\d{2}:\d{2}\]\[(TRACE|DEBUG|INFO|WARN|ERROR)\]/.test(message);
+
+  return {
+    level,
+    message: alreadyFormatted
+      ? message
+      : `[${now.toISOString().replace('T', ' ').substring(0, 19)}] [${level.toUpperCase()}] ${message}`
+  };
+};
+
+export const appendBoundedLogEntries = (
+  current: LogEntry[],
+  additions: LogEntry[],
+  limit = MAX_LOG_LINES
+): LogEntry[] => {
+  if (additions.length === 0) return current;
+  const combined = [...current, ...additions];
+  return combined.length > limit ? combined.slice(combined.length - limit) : combined;
+};
+
+export const pushBoundedLogEntry = (
+  queue: LogEntry[],
+  entry: LogEntry,
+  limit = MAX_LOG_LINES
+): void => {
+  queue.push(entry);
+  if (queue.length > limit) {
+    queue.splice(0, queue.length - limit);
+  }
+};
+
+// The live target writes after the file target, so entries received while the
+// initial disk snapshot is loading can also appear at the snapshot's tail.
+// Remove only the exact ordered overlap; global message de-duplication would
+// incorrectly hide legitimate repeated log lines.
+export const mergeLogSnapshotAndLiveEntries = (
+  snapshot: LogEntry[],
+  liveEntries: LogEntry[],
+  limit = MAX_LOG_LINES
+): LogEntry[] => {
+  const maxOverlap = Math.min(snapshot.length, liveEntries.length);
+  let overlap = 0;
+
+  for (let candidate = maxOverlap; candidate > 0; candidate -= 1) {
+    const snapshotStart = snapshot.length - candidate;
+    let matches = true;
+    for (let index = 0; index < candidate; index += 1) {
+      if (snapshot[snapshotStart + index].message !== liveEntries[index].message) {
+        matches = false;
+        break;
+      }
+    }
+    if (matches) {
+      overlap = candidate;
+      break;
+    }
+  }
+
+  return appendBoundedLogEntries(snapshot, liveEntries.slice(overlap), limit);
+};