Determinism issues possibly due to frontend issues

This is a lot of tickets, and by gathering them all together here I'm not stating with certainty that all of them are the same issue, or even that all of them are frontend issues. The truth is always more nuanced than that. But this is a lot of issues, all of them recently created. A small number of users reported most of them, suggesting that those users may inadvertently "trigger" things with their style of usage. Some of the referenced cores haven't seen any major work in a long time, so it seems unlikely that those cores are broken.

I want to investigate and fix core determinism issues, but the water is very muddy right now.

Possible desyncs caused by frontend:

• #3417
  • REPRO'D AND FIXED!
• #2738
  • REPRO'D AND FIXED!
• #2560
  • REPRO'D AND FIXED!
• #2523
  • not enough detail
• #2496
  • not enough detail, leaving open because there might be a real bug in MAME core
• #2473
  • mGBA in 2.4.2, waiting on user outdated build
• #2469
  • movie uses autofire, but leaving open due to 'randomizeinitialstate' discussion new issue opened for randomize, this one is closed
• #2470
  • many NES + 2 SNES + 1 PSX, user is adamant repro is easy and never provided a video recording when asked movies used autofire in effected builds, fixed
• #2438
  • NesHawk in 2.6, not TAStudio but "Record From: Now" autofire and SRAM issues in effected builds, fixed
• #2406, #2452
  • GBHawk movies used autofire in effected builds, fixed
• #2388
  • REPRO'D AND FIXED!
• #2384
  • adelikat said no-one uses this feature anyway Fixed
• Octoshock
  • #3090
    • 2.8 dev, w/ TAStudio
  • #2849
    • 2.6.3 dev, w/ TAStudio
  • #2830
    • 2.6.2, w/o TAStudio
  • #2743
    • w/ TAStudio
  • #2598
    • maybe w/o TAStudio
  • #2540
    • w/ TAStudio
  • #2214
    • maybe w/o TAStudio

Planned improvements to file management in frontend:

• #2484
• #2437
• #3061

Desyncs through unrelated, but known, causes:

• #2498

No files, tests, or entry points are identified. Start by narrowing the listed desync reports to a reproducible frontend or core cause, then confirm a specific fix with a deterministic reproduction; the issue provides no concrete completion test.