Add evidence redaction and log integrity

[haasonsaas]

Summary

• redact common token/password/API-key shapes before evidence events are written to JSONL
• add per-event sequence numbers plus SHA-256 previous-hash/event-hash chaining
• surface log-integrity verification in proof JSON, Markdown, and HTML artifacts
• add regression tests for redaction, tamper detection, and proof-level integrity

Test plan

• git diff --check
• cargo test --test security_evidence -- --nocapture
• cargo fmt -- --check
• cargo clippy --all-targets --all-features -- -D warnings
• cargo test
• cargo build --release
• cargo test --test e2e_tmux -- --ignored --nocapture

Smoke coverage

• tmux-backed end-to-end run generated proof artifacts with Log integrity: verified
• HTML proof artifact includes the verified log-integrity badge/metadata
• process hygiene checked after tmux smoke; no lingering tmux sessions

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	sha2@​0.10.9

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[haasonsaas]

Review pass completed on the current PR head.

What I checked:

• Evidence writes now redact common secret-like values before JSONL persistence, including send keys, exec argv, policy command text, observations, and git snapshots.
• Event sequencing and previous-hash/event-hash chaining are computed while holding the append lock, so concurrent appenders cannot race the chain.
• Proof bundles surface log-integrity status in JSON, Markdown, and HTML, and the tmux smoke artifacts show Log integrity: verified.
• Regression coverage includes redaction, tamper detection, proof integrity, full cargo integration coverage, and the ignored tmux black-box harness.

Residual caveat: redaction is intentionally heuristic for common agent secret shapes, not a full DLP engine. That is documented by the wording in README and should be expanded later with configurable redaction policy.

Verification run:

• git diff --check
• cargo test --test security_evidence -- --nocapture
• cargo fmt -- --check
• cargo clippy --all-targets --all-features -- -D warnings
• cargo test
• cargo build --release
• cargo test --test e2e_tmux -- --ignored --nocapture
• gh pr checks 10 --repo evalops/agent-pty

No blocking findings.