feat(observability): add centralized diagnostics logging engine and native log viewer panel

- Configure tauri-plugin-log with 10MB rotation and 3-file retention
- Add high-frequency format filter to strip [download]% progress ticks
- Hook yt-dlp, aria2c, and native reqwest runners with lifecycle log macros
- Add export_logs Tauri command for async log file export via save dialog
- Create DiagnosticsView React component with streaming monospace console
- Apply severity highlighting: ERROR=red, WARN=yellow, INFO=grey, DEBUG=dim
- Wire Diagnostics tab into sidebar navigation and ActiveView routing
- Log native download failures to log::error! in download.rs

src-tauri/src/download.rs

@@ -189,7 +189,7 @@ impl CoordinatorEventSink {
     fn emit_failed(&self, id: Uuid, error: String) {
         match self {
             Self::Tauri(app_handle) => {
-                eprintln!("download {id} failed: {error}");
+                log::error!("native download {} failed: {}", id, error);
                 let _ = app_handle.emit("download-failed", id.to_string());
             }
             Self::Headless(event_tx) => {

src-tauri/src/ipc.rs

@@ -154,6 +154,7 @@ pub enum ActiveView {
     Scheduler,
     #[serde(rename = "speedLimiter")]
     SpeedLimiter,
+    Diagnostics,
 }
 
 #[derive(Clone, Debug, Serialize, Deserialize, TS)]

src-tauri/src/lib.rs

@@ -1301,6 +1301,29 @@ fn delete_file(app_handle: tauri::AppHandle, path: String) -> Result<(), String>
     }
 }
 
+#[tauri::command]
+async fn export_logs(app_handle: tauri::AppHandle, dest_path: String) -> Result<String, String> {
+    use tauri::Manager;
+    let log_dir = app_handle.path().app_log_dir().map_err(|e| e.to_string())?;
+    let log_file = log_dir.join("firelink.log");
+    let src = if log_file.exists() {
+        log_file
+    } else {
+        let mut found = None;
+        if let Ok(mut entries) = tokio::fs::read_dir(&log_dir).await {
+            while let Ok(Some(entry)) = entries.next_entry().await {
+                if entry.path().extension().is_some_and(|e| e == "log") {
+                    found = Some(entry.path());
+                    break;
+                }
+            }
+        }
+        found.ok_or_else(|| "No log file found in app log directory".to_string())?
+    };
+    tokio::fs::copy(&src, &dest_path).await.map_err(|e| e.to_string())?;
+    Ok(dest_path)
+}
+
 #[tauri::command]
 fn toggle_tray_icon(app_handle: tauri::AppHandle, show: bool) -> Result<(), String> {
     use tauri::tray::TrayIconBuilder;
@@ -1785,6 +1808,15 @@ pub fn run() {
                     tauri_plugin_log::Target::new(tauri_plugin_log::TargetKind::Webview),
                 ])
                 .level(if cfg!(debug_assertions) { log::LevelFilter::Debug } else { log::LevelFilter::Info })
+                .max_file_size(10_000_000)
+                .rotation_strategy(tauri_plugin_log::RotationStrategy::KeepSome(3))
+                .format(move |out, message, _record| {
+                    let msg = message.to_string();
+                    if msg.contains("[download]") && msg.contains('%') {
+                        return;
+                    }
+                    out.finish(format_args!("{}\n", msg));
+                })
                 .build(),
         )
         .plugin(tauri_plugin_store::Builder::new().build())
@@ -1811,7 +1843,8 @@ pub fn run() {
             enqueue_download, enqueue_many, move_in_queue, remove_from_queue, get_pending_order,
             commands::reveal_in_file_manager, commands::open_downloaded_file, commands::trash_download_assets,
             parity::get_system_proxy, parity::get_file_category, parity::check_for_updates, parity::is_supported_media, parity::get_supported_media_domains,
-            parity::create_category_directories
+            parity::create_category_directories,
+            export_logs
         ])
         .build(tauri::generate_context!())
         .expect("error while building tauri application")

src/App.tsx

@@ -14,6 +14,7 @@ import { useSettingsStore } from "./store/useSettingsStore";
 import { isPermissionGranted, requestPermission, sendNotification } from '@tauri-apps/plugin-notification';
 import SchedulerView from "./components/SchedulerView";
 import SpeedLimiterView from "./components/SpeedLimiterView";
+import DiagnosticsView from "./components/DiagnosticsView";
 
 function App() {
   const [filter, setFilter] = useState<SidebarFilter>('all');
@@ -305,6 +306,7 @@ function App() {
           {activeView === 'settings' && <SettingsView />}
           {activeView === 'scheduler' && <SchedulerView />}
           {activeView === 'speedLimiter' && <SpeedLimiterView />}
+          {activeView === 'diagnostics' && <DiagnosticsView />}
         </div>
         
         {/* Status Bar */}

src/bindings/ActiveView.ts

@@ -1,3 +1,3 @@
 // This file was generated by [ts-rs](https://github.com/Aleph-Alpha/ts-rs). Do not edit this file manually.
 
-export type ActiveView = "downloads" | "settings" | "scheduler" | "speedLimiter";
+export type ActiveView = "downloads" | "settings" | "scheduler" | "speedLimiter" | "diagnostics";

src/components/DiagnosticsView.tsx

@@ -0,0 +1,105 @@
+import { useEffect, useRef, useState } from 'react';
+import { listen } from '@tauri-apps/api/event';
+import { invokeCommand as invoke } from '../ipc';
+import { save } from '@tauri-apps/plugin-dialog';
+import { FileDown, Trash2, Terminal } from 'lucide-react';
+import { WindowDragRegion } from './WindowDragRegion';
+
+interface LogEntry {
+  level: 'Trace' | 'Debug' | 'Info' | 'Warn' | 'Error';
+  message: string;
+}
+
+export default function DiagnosticsView() {
+  const [logs, setLogs] = useState<LogEntry[]>([]);
+  const scrollRef = useRef<HTMLDivElement>(null);
+  const MAX_LOG_LINES = 2000;
+
+  useEffect(() => {
+    const unlisten = listen<{ level: string; message: string }>('log', (event) => {
+      const level = event.payload.level as LogEntry['level'];
+      const message = event.payload.message;
+      if (message.includes('[download]') && message.includes('%')) return;
+      setLogs(prev => {
+        const next = [...prev, { level, message }];
+        return next.length > MAX_LOG_LINES ? next.slice(-MAX_LOG_LINES) : next;
+      });
+    });
+    return () => { unlisten.then(f => f()); };
+  }, []);
+
+  useEffect(() => {
+    if (scrollRef.current) {
+      scrollRef.current.scrollTop = scrollRef.current.scrollHeight;
+    }
+  }, [logs]);
+
+  const handleExport = async () => {
+    try {
+      const path = await save({
+        defaultPath: 'Firelink-Diagnostics.log',
+        filters: [{ name: 'Log Files', extensions: ['log'] }],
+      });
+      if (!path) return;
+      await invoke('export_logs', { destPath: path });
+    } catch (e) {
+      console.error('Export failed:', e);
+    }
+  };
+
+  const handleClear = () => setLogs([]);
+
+  const severityClass = (level: string) => {
+    switch (level) {
+      case 'Error': return 'log-error';
+      case 'Warn': return 'log-warn';
+      case 'Info': return 'log-info';
+      default: return 'log-debug';
+    }
+  };
+
+  return (
+    <div className="diagnostics-view flex-1 flex flex-col h-full overflow-hidden">
+      <WindowDragRegion />
+
+      {/* Toolbar */}
+      <div className="diagnostics-toolbar flex items-center justify-between px-4 py-2 shrink-0">
+        <div className="flex items-center gap-2 text-text-secondary">
+          <Terminal size={16} strokeWidth={1.8} />
+          <span className="text-[13px] font-semibold text-text-primary">Diagnostics Console</span>
+          <span className="text-[11px] text-text-muted">({logs.length} entries)</span>
+        </div>
+        <div className="flex items-center gap-2">
+          <button
+            onClick={handleClear}
+            className="app-icon-button"
+            title="Clear console"
+          >
+            <Trash2 size={14} />
+          </button>
+          <button
+            onClick={handleExport}
+            className="app-button px-3 text-[11px] gap-1.5"
+            title="Export logs"
+          >
+            <FileDown size={13} />
+            Export Logs
+          </button>
+        </div>
+      </div>
+
+      {/* Console */}
+      <div ref={scrollRef} className="diagnostics-console flex-1 overflow-y-auto p-3 font-mono text-[11px] leading-[1.5]">
+        {logs.length === 0 && (
+          <div className="text-text-muted italic select-none">Waiting for log entries...</div>
+        )}
+        {logs.map((entry, i) => (
+          <div key={i} className={`log-line ${severityClass(entry.level)}`}>
+            <span className="log-level-tag">[{entry.level}]</span>
+            <span className="log-message">{entry.message}</span>
+          </div>
+        ))}
+      </div>
+    </div>
+  );
+}

src/components/Sidebar.tsx

@@ -2,7 +2,7 @@ import React, { useState, useEffect, useRef } from 'react';
 import {
   Inbox, Zap, CheckCircle2, CircleDashed,
   Film, Music, FileText, Box, Image as ImageIcon, Archive, FileQuestion,
-  List, CalendarClock, Gauge, Settings, Plus, Play, Pause, Edit2, Trash2, PanelLeft,
+  List, CalendarClock, Gauge, Bug, Settings, Plus, Play, Pause, Edit2, Trash2, PanelLeft,
   type LucideIcon
 } from 'lucide-react';
 import { useDownloadStore, DownloadCategory, Queue } from '../store/useDownloadStore';
@@ -229,6 +229,7 @@ export const Sidebar: React.FC<SidebarProps> = (props) => {
           <div className="sidebar-section-label">Tools</div>
           <ToolItem icon={CalendarClock} label="Scheduler" view="scheduler" />
           <ToolItem icon={Gauge} label="Speed Limiter" view="speedLimiter" />
+          <ToolItem icon={Bug} label="Diagnostics" view="diagnostics" />
         </section>
       </div>
 

src/index.css

@@ -1169,6 +1169,66 @@
   }
 }
 
+/* Diagnostics Console */
+.diagnostics-toolbar {
+  height: 42px;
+  border-bottom: 1px solid hsl(var(--border-color));
+  background: hsl(var(--statusbar-bg));
+}
+
+.diagnostics-console {
+  background: hsl(0 0% 7%);
+  color: hsl(0 0% 82%);
+  font-family: "SF Mono", Monaco, "Cascadia Code", "Fira Code", "JetBrains Mono", monospace;
+}
+
+.diagnostics-console .log-line {
+  display: flex;
+  gap: 8px;
+  padding: 0 4px;
+  min-height: 18px;
+  align-items: baseline;
+  border-radius: 2px;
+  white-space: pre-wrap;
+  word-break: break-all;
+}
+
+.diagnostics-console .log-level-tag {
+  flex-shrink: 0;
+  font-weight: 600;
+  min-width: 52px;
+  font-size: 10px;
+}
+
+.diagnostics-console .log-message {
+  flex: 1;
+  min-width: 0;
+}
+
+.diagnostics-console .log-error .log-level-tag,
+.diagnostics-console .log-error .log-message {
+  color: hsl(0 72% 58%);
+}
+
+.diagnostics-console .log-warn .log-level-tag,
+.diagnostics-console .log-warn .log-message {
+  color: hsl(45 100% 50%);
+}
+
+.diagnostics-console .log-info .log-level-tag,
+.diagnostics-console .log-info .log-message {
+  color: hsl(0 0% 75%);
+}
+
+.diagnostics-console .log-debug .log-level-tag,
+.diagnostics-console .log-debug .log-message {
+  color: hsl(0 0% 45%);
+}
+
+.diagnostics-console .log-line:hover {
+  background: hsl(0 0% 100% / 0.04);
+}
+
 @keyframes fade-in {
   from { opacity: 0; }
   to { opacity: 1; }

src/ipc.ts

@@ -100,6 +100,7 @@ type CommandMap = {
   db_save_queue: { args: { id: string; data: string }; result: void };
   db_delete_queue: { args: { id: string }; result: void };
   create_category_directories: { args: { paths: string[] }; result: void };
+  export_logs: { args: { destPath: string }; result: string };
   get_pending_order: { args: undefined; result: string[] };
   enqueue_download: { args: { item: any }; result: string };
   enqueue_many: { args: { items: any[] }; result: void };