Fix deferred tool query termination

[jordanchendev]

Summary

• Treat PreToolUse hooks returning permissionDecision: "defer" as an end-of-query signal for one-shot query stdin closure.
• Suppress assistant/user/stream_event messages after a deferred tool decision until the deferred result arrives.
• Add regression coverage for early input closure and dropping the extra wrap-up assistant message.

Fixes #1060

Test Plan

• .venv/bin/python -m ruff check src/ tests/ --fix
• .venv/bin/python -m ruff format src/ tests/
• .venv/bin/python -m mypy src/
• .venv/bin/python -m pytest tests/
• git diff --check

Notes

• E2E tests were not run because they require a live Anthropic API key and make real API calls.