fix: block autoplay before any frame renders (#1461)

[jiangyj545]

Summary

Fixes #1461 — Disabled autoplay was pausing ~1 second into playback instead of preventing it entirely.

Root Cause

The original autoplay-disable code:

1. Intercepted HTMLMediaElement.prototype.play() (worked)
2. Called player.pauseVideo() then returned Promise.resolve() (worked)
3. BUT: YouTube's player found other paths to start playback (internal API, retry logic, etc.)
4. The setTimeout(100ms) fallback allowed ~6 frames to render before pausing

Changes

File: js&css/web-accessible/functions.js (1 file, +22/-7)

Change	Before	After
Pause logic	Inline try/catch	Extracted blockAutoplay() helper
Safety net	None	playing event listener (once:true) catches escaped playback
setTimeout delay	100ms	0ms (next tick)
currentTime reset	None	Resets to 0 so watch history gets no progress

How the safety net works

play() called → blockAutoplay() pauses + resets time → return Promise.resolve()
                                                    ↓ (if YouTube retries)
                              'playing' fires → blockAutoplay() again → listener removes itself

The once:true ensures normal user-initiated playback is never affected.

Test Results

Test Suites: 16 passed, 1 failed (pre-existing)
Tests:       66 passed, 3 failed (pre-existing, from sidebar-transcript PR)

No new test failures introduced.

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Bounty claim: This PR addresses issue #1461 (Bounty label). Requesting review.

[ImprovedTube2]

hi! @jiangyj545
did you consider to make your (automated) process look at the timeline / edit history?
thanks