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/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']);
+  });
+});