fix: resolve chat message fade persisting after teleport

[biotech77]

Prevent messages fading out if we are not in default chat state

Closes #4272

Pull Request Description

Prevent messages fading out when we teleport

Explanation:

1. Caller is EventBus - the async continuation from the MVC framework
2. 39 DOTween tweens actively playing when Kill is called - DOTween is mid-iteration
3. OnKill DEFERRED - correctly detected, field unchanged after Kill
4. Frame 5438: deferred OnKill fires, nulls seq#4
5. killed=False on seq#4 - proof it was never killed, ran full 13s fade

The sequence is still alive inside DOTween's internal update list, but we lost our reference to it (_fadeSequenceTween = null). Without the reference, StopChatEntriesFadeout() cannot call Kill() on it. Setting _fadeSequenceTween to null does NOT stop the tween it only removes our handle to it.

Fix:

• Remove _fadeSequenceTween = null from OnKill/OnComplete callbacks - callbacks no longer touch the field, so a deferred callback from an old sequence can never corrupt the reference to a newer one
• Null the field explicitly right after Kill() in Start/Stop methods - the caller manages the lifecycle, not the callback
• Build the Sequence into a local variable first, then assign to - _fadeSequenceTween after construction - no window where the field holds a partially-built sequence

From logs:

OnMvcViewClosed → PopState frame=5437
  DOTween active tweens: 38
  caller: EventBus

STOP frame=5437: Kill(seq#3 = 2120662738)
  seq IsActive=True IsPlaying=True
  DOTween total playing: 39
  field after Kill: 2120662738
  result: OnKill DEFERRED — field UNCHANGED, callback will fire later

START frame=5437: created seq#4 = -1328791714
>> seq#3 OnKill frame=5438: field points to -1328791714 ← nulls seq#4!

STOP frame=5726: field: null — NOTHING TO KILL ← seq#4 orphaned
>> seq#4 OnComplete frame=6419 (killed=False) ← ran full fade, never killed

Raw and full logs attached
logs_raw.txt
logs_formatted.txt

What does this PR change?

Properly disposes tween sequence

Test Steps

1. Go to friends panel and teleport to location of a friend
2. Wait scene to load
3. Observe if messages are not fading out

Quality Checklist

• Changes have been tested locally
• Documentation has been updated (if required)
• Performance impact has been considered
• For SDK features: Test scene is included

Code Review Reference

Please review our Code Review Standards before submitting.

[github-actions]

Windows and Mac build successful in Unity Cloud! You can find a link to the downloadable artifact below.

Name	Link
Commit	d318c49
Logs	https://github.com/decentraland/unity-explorer/actions/runs/23544400747
Download Windows	https://github.com/decentraland/unity-explorer/suites/61969221486/artifacts/6103448609
Download Windows S3	https://explorer-artifacts.decentraland.org/@dcl/unity-explorer/branch/fix/7596-fading-chat/pr-20229-d318c49/Decentraland_windows64.zip
Download Mac	https://github.com/decentraland/unity-explorer/suites/61969221486/artifacts/6103243484
Download Mac S3	https://explorer-artifacts.decentraland.org/@dcl/unity-explorer/branch/fix/7596-fading-chat/pr-20229-d318c49/Decentraland_macos.zip
Built on	2026-03-25T14:34:59Z

[DafGreco]

✔️ PR reviewed and approved by QA on both platforms following instructions playing both happy and un-happy path

Regressions for this ticket had been performed in order to verify that the normal flow is working as expected:

• [ ✔️] Backpack and wearables in world
• [✔️ ] Emotes in world and in backpack
• [✔️ ] Teleport with map/coordinates/Jump In
• [✔️ ] Chat and multiplayer
• [ ✔️] Skybox
• [ ✔️] Settings

Evidence:

20260320-1332-21.2950686.mp4

[dalkia]

@claude review

[claude]

Claude finished @dalkia's task in 1m 4s —— View job

---

Claude Code Review

• Gathering context and reading changed files
• Analyzing diff and reviewing code
• Posting review feedback

---

Review: ChatMessageFeedView.cs

The fix correctly addresses a well-documented DOTween deferred-kill race condition. The three changes work together as a coherent solution:

1. Null field immediately after Kill() — prevents callbacks from finding a stale reference
2. Remove null-assignment from OnComplete/OnKill callbacks — deferred callbacks can no longer corrupt the field with a newer sequence's reference
3. Build sequence in a local variable, then assign — no window where _fadeSequenceTween holds a partially-constructed sequence

One observation (non-blocking, pre-existing)

Dispose() at line 44 does not kill _fadeSequenceTween. If the view is disposed while a fade is in progress, the orphaned DOTween sequence will continue to tick and attempt to mutate a destroyed chatEntriesCanvasGroup. This is a pre-existing issue not introduced by this PR, but worth noting for a follow-up.

public void Dispose()
{
    fadeoutCts.SafeCancelAndDispose();
    _fadeSequenceTween?.Kill();   // missing — pre-existing issue
    _fadeSequenceTween = null;

    if (chatScrollToBottomView != null)
        chatScrollToBottomView.OnClicked -= ChatScrollToBottomToBottomClicked;
}

The fix is minimal, well-reasoned, and QA-verified. No blocking issues found.

---

REVIEW_RESULT: PASS ✅

[dalkia]

Approving due to the urgency of the release, but I do suggest to analyze if it can be done differently, considering the following:

• Removes code repetition
• Doesnt rely OnKill and OnComplete. Doesnt look like its needed like these, since you are always killing and setting to 1 the chateEntriesCanvasGroup values
• Doesnt require the extra seq (Im not sure its needed at all, I still dont understand the window part)
• Doesnt require nullification of _fadeSequenceTween

        internal void StartChatEntriesFadeout()
        {
            StopChatEntriesFadeout()
            float waitSeconds = chatEntriesWaitBeforeFading / 1000f;

            _fadeSequenceTween = DOTween.Sequence()
                .AppendInterval(waitSeconds)
                .Append(chatEntriesCanvasGroup.DOFade(0.4f, chatEntriesFadeTime))
        }

        internal void StopChatEntriesFadeout()
        {
            _fadeSequenceTween?.Kill();
            chatEntriesCanvasGroup.DOKill();
            chatEntriesCanvasGroup.alpha = 1f;
        }

[DafGreco]

✔️ PR reviewed and approved by QA on both platforms following instructions playing both happy and un-happy path

Regressions for this ticket had been performed in order to verify that the normal flow is working as expected:

• [✔️ ] Backpack and wearables in world
• [✔️ ] Emotes in world and in backpack
• [✔️ ] Teleport with map/coordinates/Jump In
• [✔️ ] Chat and multiplayer
• [✔️ ] Profile card
• [✔️ ] Settings

Evidence:

Screen.Recording.2026-03-25.at.08.40.47.mp4

More evidence on the following thread