Rebuild n8n sandbox escape semantic annotations

[March-77]

Summary

• independently rebuild the six n8n semantic annotations requested by issue 【2026犀牛鸟】修正 n8n 沙箱逃逸样本的入口点和关键操作语义 #6
• move sources to workflow-controlled expression, header, and Python code inputs
• move critical operations from decorators/static declarations/intermediate lookup to evaluator execution, AST bypass, CSP decision, Python exec, native .apply, and writable sanitizer state
• retain only source-backed propagation/control-flow nodes
• include a reproducible source-slicing builder, six-entry patch JSONL, field diff, rationale report, and tests

Evidence

The analysis uses each entry's pinned vulnerable commit plus the corresponding security-fix behavior:

• reserved-variable and WithStatement guards for the Tournament expression escape
• Content-Type trimming for the CSP bypass
• __objclass__ denylisting for the Python runner escape
• unsafe extension-name rejection and immutable __sanitize for VM escapes

All six rows remain verify=0 for maintainer confirmation.

Validation

• 6 patch rows and 18 field-level diff rows
• 40/40 replacement nodes exactly match their pinned source file, line range, and code
• python -m unittest discover -s tests -p "test_n8n_semantic_fixes.py" -v (4 tests)
• python -m py_compile scripts/build_n8n_semantic_fixes.py
• git diff --check

Closes #6