Fix IME composition causing premature filtering in tree find widget

[Copilot]

Fixes #274958

During IME composition (e.g., typing ¨ + u → ü), the find widget filtered on intermediate characters, hiding content before composition completed.

Changes

FindInput (src/vs/base/browser/ui/findinput/findInput.ts)

• Gate onInput event with existing imeSessionInProgress flag
• Event fires after compositionend with final composed text

FindWidget (src/vs/base/browser/ui/tree/abstractTree.ts)

• Use findInput.onInput instead of findInput.onDidChange
• onInput respects IME composition boundaries; onDidChange continues firing on every keystroke

Behavior

Before: Input events during composition → premature filtering → content disappears
After: Composition blocks input events → single event on compositionend → correct filtering

Maintains backward compatibility. Consumers needing immediate updates can continue using onDidChange.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>During composition everything is filtered</issue_title>
<issue_description>Testing #274958

• open agents sessions view
• type to filter
• compose a character, like ¨ and u makes ü
• while the ¨ is there, everything gets filtered out already

Screen.Recording.2025-11-04.at.16.59.14.mov

(slightly bad sample because the PR doesn't have ü in its title but if so it would be hidden and reappear during composition)

fyi - the input element has composition events for this, compositionend and compositionstart</issue_description>

<agent_instructions>The find widget probably needs to make a change to FindWidget and only fire onDidChangeValue event in the following way:

  this._register(this.findInput.onInput(() => {
  	this._onDidChangeValue.fire(this.findInput.inputBox.value);
  }));

Maybe there is more to this such as checking isImeSessionInProgress</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@dineshc-msft The find functionality simply delegates to the underlying find widget. Handling composition is a good suggestion for the underlying widget.

@benibenj - Johannes mentioned you may be the owner of the underlying widget, so assigning to you. Please feel free to triage / re-assign to the right owner as appropriate.

• Fixes During composition everything is filtered #275152

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