fix(EXPOSED_SECRETS): detect modern API key formats (OpenAI sk-proj/svcacct, Anthropic, GitHub, Google, Slack, Stripe)

[dmchaledev]

Summary

The CRITICAL EXPOSED_SECRETS rule (src/rules/runtime-rules.ts) only matched legacy secret formats:

/sk-[a-zA-Z0-9]{20,}/i,           // OpenAI API key
/ghp_[a-zA-Z0-9]{36}/i,            // GitHub PAT
/AKIA[0-9A-Z]{16}/i,               // AWS access key
/[Pp]assword\s*[=:]\s*\S{8,}/,     // Password assignment

It silently missed the secret formats most commonly found in AI/MCP configs today — including the LLM provider keys an MCP server is most likely to carry. Verified against the current patterns:

Secret	Before
Legacy OpenAI sk-…	✅ detected
OpenAI project sk-proj-…	❌ missed
OpenAI service-account sk-svcacct-…	❌ missed
Anthropic sk-ant-…	❌ missed
GitHub classic ghp_…	✅ detected
GitHub OAuth/app gho_/ghu_/ghs_/ghr_	❌ missed
GitHub fine-grained github_pat_…	❌ missed
AWS AKIA…	✅ detected
Google AIza…	❌ missed
Slack xoxb-…	❌ missed
Stripe sk_live_… / rk_live_…	❌ missed

Root cause for the OpenAI miss: modern keys (sk-proj-, sk-svcacct-, sk-ant-) contain hyphens/underscores, and the old [a-zA-Z0-9]-only run stops at the first -, so the {20,} length is never reached.

For a scanner whose CRITICAL rule is "Potential Secret Exposed in Configuration", missing current provider key formats is a meaningful false negative — and especially relevant for an AI/MCP scanner, since sk-proj-/sk-ant- keys are exactly what these servers tend to hold.

Changes

• Broaden SECRET_PATTERNS to cover modern OpenAI (project/service-account/admin), Anthropic, the full GitHub token family + fine-grained PATs, Google API keys, Slack tokens, and Stripe live/restricted keys. Legacy patterns are preserved.
• Add EXPOSED_SECRETS tests (the rule previously had zero test coverage): one positive case per supported format, plus negatives for benign config strings and a JWT-style bearer token (the kind used in examples/secure-config.json) to guard against false positives.

Verification

• npm run typecheck, npm run lint, npm test (113 passing) all green.
• CLI smoke test: examples/secure-config.json still passes (no new false positives); a config carrying an sk-proj-… key now correctly fails with a CRITICAL EXPOSED_SECRETS finding.
• Test fixtures are assembled from prefix + filler at runtime so no real-looking credential literal appears in source (keeps secret-scanning push protection happy).

Scope

Detection only. Redaction of matched secrets in finding evidence is tracked separately in #28, and the missed-password case in #14 — this PR is complementary and does not overlap with either.

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