Add onDidReceiveChatDebugEvent API to send chat customization events

[vijayupadya]

Add a new proposed API event onDidReceiveChatDebugEvent on vscode.chat that fires when VS Code core logs a debug event (e.g., prompt discovery, skill/instruction loading). This enables extensions to capture core-originated events in real-time.

[Copilot]

Pull request overview

This PR adds a new proposed chatDebug API surface that streams VS Code core-originated chat debug events to extensions in real time, enabling extensions to capture core debug activity (e.g., prompt discovery / skill loading) as it happens.

Changes:

• Add proposed API vscode.chat.onDidReceiveChatDebugEvent (Event<ChatDebugEvent>).
• Forward core events from IChatDebugService.onDidAddEvent (main thread) to the extension host via a new ExtHost RPC method.
• Enrich prompt discovery debug log details payload with file/folder information.

Reviewed changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/vscode-dts/vscode.proposed.chatDebug.d.ts	Adds the new proposed vscode.chat.onDidReceiveChatDebugEvent event.
src/vs/workbench/contrib/chat/browser/promptsDebugContribution.ts	Expands prompt discovery log details to include file/folder paths to surface in forwarded event payloads.
src/vs/workbench/api/common/extHostChatDebug.ts	Adds an ExtHost emitter and RPC handler to receive and re-emit core debug events.
src/vs/workbench/api/common/extHost.protocol.ts	Extends the ExtHost shape with $onCoreDebugEvent for main-thread-to-ext-host forwarding.
src/vs/workbench/api/common/extHost.api.impl.ts	Wires the proposed vscode.chat.onDidReceiveChatDebugEvent API to the ExtHost event.
src/vs/workbench/api/browser/mainThreadChatDebug.ts	Forwards core debug events to the extension host in real time.

Comments suppressed due to low confidence (1)

src/vs/workbench/contrib/chat/browser/promptsDebugContribution.ts:62

• f.uri.path.split('/').pop() can return an empty string (e.g. when the path ends with /). Because ?? doesn’t treat '' as nullish, this would produce blank entries in the loaded/skipped arrays. Consider using a helper that guarantees a non-empty basename (or falling back when the basename is empty).

				const loaded = info.files.filter(f => f.status === 'loaded').map(f => f.name ?? f.uri.path.split('/').pop() ?? f.uri.toString());
				const skipped = info.files.filter(f => f.status === 'skipped').map(f => f.name ?? f.uri.path.split('/').pop() ?? f.uri.toString());
				const folders = info.sourceFolders?.map(sf => sf.uri.path) ?? [];

[Copilot]

The new details enrichment logic isn’t covered by existing tests (e.g. details undefined, formatting, and any truncation behavior you add). Adding a focused unit test in promptsDebugContribution.test.ts would help prevent regressions since this string is now part of the payload forwarded to extensions.

[pwang347]

since this is just for discovery events, maybe no need to truncate?