feat: Tool Script Safety Guard — pre-execution safety scanner

[DNKYr]

Summary

Implements #90 — a pre-execution script safety scanner for Python/Bash tool scripts with pluggable filter integration, audit logging, and OpenTelemetry span attributes.

What's included

• trpc_agent_sdk/tools/safety/ — 7 modules: types, policy (YAML), rules (13 pattern + 3 AST), scanner, filter (BaseFilter), audit logger (JSONL), telemetry (OTel)
• 6 risk categories: dangerous file ops, network access, system commands, dependency install, resource abuse, sensitive info leak
• ToolSafetyFilter — plugs into existing BaseFilter chain via FilterType.TOOL, blocks execution on deny
• Configurable policy — tool_safety_policy.yaml supports whitelist/blocklist domains, commands, paths; per-rule enable/disable/severity/decision overrides
• 40 tests covering all 12 sample scripts + edge cases + policy validation + filter integration + audit + telemetry
• Performance: 500-line script scanned in 0.08ms (threshold: 1s)
• Documentation: design docs (EN/ZH), test plan, README with integration guide, example outputs

Acceptance criteria (#90)

• 12 sample scripts produce structured reports
• High-risk detection: critical types (delete, read-secrets, non-whitelisted network) at 100%
• 500-line scan ≤ 1 second
• Reports contain decision, risk_level, rule_id, evidence, recommendation
• Policy YAML changes without code changes
• Filter blocks before execution + audit event
• README explains sandbox/filter/telemetry/CodeExecutor relationship

Known limitations (documented)

• Pattern-based detection bypassable via obfuscation
• Bash scanning is pattern-only (no Bash AST)
• No data flow analysis
• Not a replacement for runtime sandboxing

[codecov]

Codecov Report

❌ Patch coverage is 83.74656% with 59 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@4336564). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
trpc_agent_sdk/tools/safety/_rules.py	58.57143%	29 Missing ⚠️
trpc_agent_sdk/tools/safety/_scanner.py	77.96610%	26 Missing ⚠️
trpc_agent_sdk/tools/safety/_filter.py	91.11111%	4 Missing ⚠️

Additional details and impacted files

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  Hits            ?       38913           
  Misses          ?        5553           
  Partials        ?           0           

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