feat(workspace): snapshot secret scrubber (closes #823)
Sub-issue of #799, security condition C4. Standalone module in
workspace/lib/snapshot_scrub.py with three public functions:
- scrub_content(str) → str: regex-based redaction of secret patterns
- is_sandbox_content(str) → bool: detect run_code tool output markers
- scrub_snapshot(dict) → dict: walk memories, scrub each, drop sandbox entries
Patterns covered: sk-ant-/sk-proj-, ghp_/ghs_/github_pat_, AKIA,
cfut_, mol_pk_, ctx7_, Bearer, env-var assignments, base64 blobs ≥33 chars.
21 unit tests, 100% coverage on new code.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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