feat(types): add PostCompact hook event support

[husniadil]

Summary

Adds PostCompact hook event support to the Python SDK, matching the Claude Code CLI v2.1.76+ specification.

PostCompact fires after a compact operation completes, providing the trigger type (manual/auto) and compact_summary (the generated conversation summary).

Changes

• Add "PostCompact" to HookEvent union type
• Add PostCompactHookInput with trigger and compact_summary fields
• Add PostCompactHookSpecificOutput with additionalContext field
• Add to HookInput and HookSpecificOutput union types
• Export new types from __init__.py

Tests

• Type construction tests for PostCompactHookInput (auto + manual trigger)
• Type construction test for PostCompactHookSpecificOutput
• Behavioral callback test verifying end-to-end hook execution via MockTransport

Verified against Claude Code hooks docs and tested with live CLI v2.1.77.

[km-anthropic]

@claude review

[claude]

LGTM — straightforward addition of PostCompact hook event types following the established pattern.

Extended reasoning...

Overview

This PR adds PostCompact hook event support across four files: new PostCompactHookInput and PostCompactHookSpecificOutput TypedDict classes in types.py, their addition to the HookEvent, HookInput, and HookSpecificOutput union types, exports in __init__.py, and corresponding tests in test_types.py and test_tool_callbacks.py.

Security risks

None. The changes are purely additive type definitions and test code. No auth, crypto, or permission logic is modified.

Level of scrutiny

Low scrutiny is appropriate. The new types follow the exact same pattern as the existing hook events (PreCompact, Notification, SubagentStart, PermissionRequest). The PostCompactHookInput has hook_event_name, trigger, and compact_summary fields — mirroring PreCompactHookInput which has trigger and custom_instructions. The output type follows the standard hookEventName + additionalContext pattern.

Other factors

Tests are thorough: type construction tests for both auto and manual triggers, output type construction, and a behavioral callback test using MockTransport that verifies the full hook execution flow. No CODEOWNERS concerns, no outstanding reviewer comments, and no bugs found by the automated bug hunting system.