Fix chat placeholder rotation during dictation

[meganrogge]

Fixes microsoft/vscode-internalbacklog#8615

Summary

• pause rotating chat prompts while dictation displays model download/preparation progress or the Listening… placeholder
• keep the regular chat prompt visible during microphone acquisition
• limit shimmer transitions to rotation-driven placeholder updates
• restore the regular chat prompt when dictation ends
• add regression coverage for placeholder ownership and the dictation placeholder lifecycle

[Copilot]

Pull request overview

Fixes conflicts between rotating chat prompts and dictation-owned placeholders.

Changes:

• Pauses rotation when another feature changes the placeholder.
• Restricts shimmer animation to rotation updates.
• Hides/restores placeholders across dictation and adds regression tests.

Show a summary per file

File	Description
chatInputPlaceholderRotation.ts	Adds placeholder ownership and animation controls.
dictationSession.ts	Manages placeholders throughout dictation.
chatInputPlaceholderRotation.test.ts	Tests placeholder ownership.
dictationSession.test.ts	Tests dictation placeholder lifecycle.

Review details

• Files reviewed: 4/4 changed files
• Comments generated: 1
• Review effort level: Medium

[Copilot]

Review details

Comments suppressed due to low confidence (1)

src/vs/workbench/contrib/chat/browser/widget/input/chatInputPlaceholderRotation.ts:76

• After a slow microphone acquisition, this guard can pause rotation permanently after dictation ends. startDictation snapshots the placeholder before awaiting microphone/backend setup, while rotation remains active during acquisition; if a tick advances the prompt, dictation later restores the older snapshot, which no longer equals expectedPlaceholder, so every future tick returns here. Capture the placeholder when dictation first takes ownership (or add an explicit pause/resume handoff), and cover acquisition spanning a rotation interval.

		if (editor.getOption(EditorOption.placeholder) !== expectedPlaceholder) {
			return;

• Files reviewed: 4/4 changed files
• Comments generated: 0 new
• Review effort level: Medium