Support PreCompact hook

[roblourens]

No description provided.

[Copilot]

Pull request overview

Adds a new PreCompact hook type to the chat prompt-syntax hooks system so it can be configured in hooks.json, displayed/validated via schema metadata, and parsed/collected from supported hook file formats.

Changes:

• Extend HookType/HOOK_TYPES/IChatRequestHooks and JSON schema to include PreCompact.
• Add Claude compatibility mapping for PreCompact.
• Ensure parsed hooks collection in PromptsService initializes storage for PreCompact.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/vs/workbench/contrib/chat/common/promptSyntax/service/promptsServiceImpl.ts	Initializes the per-hook-type collection map with a PreCompact bucket so parsed hooks can be retained.
src/vs/workbench/contrib/chat/common/promptSyntax/hookSchema.ts	Defines the new hook type and exposes it via metadata + schema so it can be authored/validated.
src/vs/workbench/contrib/chat/common/promptSyntax/hookClaudeCompat.ts	Maps Claude’s PreCompact hook identifier to the new HookType.PreCompact.

Comments suppressed due to low confidence (1)

src/vs/workbench/contrib/chat/common/promptSyntax/hookSchema.ts:25

• parseCopilotHooks supports Copilot CLI-style camelCase hook ids via resolveCopilotCliHookType(...), but hookCopilotCliCompat.ts does not map a preCompact id to HookType.PreCompact. That means a hooks.json authored in Copilot CLI format using preCompact will be silently ignored; consider adding the missing mapping so PreCompact works across supported formats.

	PreCompact = 'PreCompact',
	SubagentStart = 'SubagentStart',
	SubagentStop = 'SubagentStop',
	Stop = 'Stop',