fix: preserve latest tool result batch during compaction

[123456wda]

Summary

• Preserve every result from the newest tool-result batch during micro-compaction.
• Continue preserving the latest three results from earlier batches.
• Add a four-tool-batch regression test and align the chapter documentation.
• Normalize generated content line endings so metadata remains stable across Windows and Linux.

Validation

• python -m py_compile s08_context_compact/code.py s15_integrated_harness/code.py
• tests.test_compaction_tool_pairs (7 tests passed; Windows test run injects a no-op fcntl stub because fcntl is Unix-only)
• tests/test_web_scenarios.py::test_generated_s16_metadata_extends_s15_without_registry_false_positives (passed)
• The complete Python suite is validated by the PR's Ubuntu workflow. Local Windows runs cannot execute Unix-dependent lesson tests (fcntl, SIGKILL) and one README test also relies on the default UTF-8 locale.

[123456wda]

Superseded by shareAI-lab#523.