Harden routing boundaries for 0.4.0

[ictechgy]

Summary

• isolate optional Claude triage with safe mode, no tools/MCP, an empty private cwd, strict output parsing, and whole-process-group teardown
• fail Codex optional triage closed until its CLI documents an all-tools-disabled contract, without changing native Codex routes
• unify native/V2 JSON loading behind bounded regular-file, strict UTF-8, duplicate-key-safe parsing
• split narrow risk floors from broad complexity signals, fix multiline harmful outcomes, and harden dispatch/fingerprint/provider invariants
• add blocking macOS Python 3.10/3.13 boundary jobs and prepare source version 0.4.0

Breaking changes

• classification policy metadata is now version 2
• broad high-tier signals report high.complexity_signal
• --source-vendor codex --ask-vendor now fails closed with triage_unavailable

Verification

• PYTHONPATH=src python3 -W error::ResourceWarning -m unittest discover -s tests (177 passed)
• python3 -m compileall -q src tests
• ruff check src tests
• ruff format --check src tests
• mypy
• workflow YAML parse and git diff --check
• offline sdist/wheel build
• twine check --strict on both distributions
• clean --no-index wheel install, version/metadata/default-output smoke tests