feat: support additionalContext in PreCompact hook

[abwuge]

Allow PreCompact hook to inject additional context into the summarization prompt, matching the pattern used by other hooks (PreToolUse, PostToolUse, SessionStart, SubagentStart, UserPromptSubmit).

Changes:

• Add IPreCompactHookSpecificCommandOutput type in hookCommandTypes.ts
• Add PreCompactHookOutput interface in chatHookService.ts
• Modify executePreCompactHook() to collect additionalContext from hook results
• Merge hook additionalContext into summarizationInstructions in summarizeHistory()
• Add unit tests for prompt rendering with summarizationInstructions
• Add integration tests for PreCompact hook flow in preCompactHook.spec.tsx

[abwuge]

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[Copilot]

Pull request overview

This PR extends the PreCompact hook flow so hook scripts can inject additionalContext into the conversation compaction/summarization prompt, aligning PreCompact with other hook types that can contribute extra prompt context.

Changes:

• Added PreCompact hook-specific output typing (additionalContext) and exposed it via PreCompactHookOutput.
• Updated summarization flow to execute PreCompact hooks and merge returned additionalContext into summarization instructions.
• Added unit + integration tests to validate prompt rendering and end-to-end PreCompact hook behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/platform/chat/common/hookCommandTypes.ts	Defines PreCompact hook-specific command output shape (additionalContext).
src/platform/chat/common/chatHookService.ts	Adds PreCompactHookOutput type to represent hook output contract.
src/extension/prompts/node/agent/summarizedConversationHistory.tsx	Executes PreCompact hook before summarization and merges returned additionalContext into summarization instructions.
src/extension/prompts/node/agent/test/summarization.spec.tsx	Adds unit coverage for rendering summarizationInstructions in the summarization prompt.
src/extension/prompts/node/agent/test/preCompactHook.spec.tsx	Adds integration coverage for PreCompact hook invocation and additionalContext injection into LLM prompt.

[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated no new comments.

[roblourens]

Can you open an issue with a description of what you want to add and why?

[roblourens]

Superseded by microsoft/vscode#308297

[roblourens]

Actually if you want to be sure that your PR is attributed to your account, you could open the new PR on vscode yourself. We are moving copilot-chat sources to the vscode repo.

[abwuge]

Actually if you want to be sure that your PR is attributed to your account, you could open the new PR on vscode yourself. We are moving copilot-chat sources to the vscode repo.

Thank you. PR attribution isn’t a big concern for me.