feat: before_install → POST /install-scan (terminal, fail-closed)

[olivrg]

Implements before_install → POST /install-scan — the last unimplemented adapter hook (issue #11, Part B). Maps the OpenClaw install event to the scan endpoint and enforces the decision, fail-closed.

Behavior

• allow → {} (proceed)
• deny → { block: true, blockReason: feedback.message ?? reason ?? 'Blocked by Helio' }
• client { ok: false } (unreachable / timeout / 5xx / malformed) → fail closed (block)
• Terminal: no /audit follow-up, no correlation/evaluation_id threading.

Request-body mapping (per plan §B.2)

Field	Source
package.source	normalized request.kind (npm/git/archive/file/dir/skill) — not targetType (kind ≠ provenance; supply-chain rules match on origin)
package.name	plugin?.packageName ?? targetName (true package identity, universal fallback)
package.version	plugin?.version (omitted when absent)
package.spec	request.requestedSpecifier (omitted when absent)
metadata	mode, target_type, builtin_scan { critical, warn, info } (OpenClaw's own scan summary, forwarded as context)

Optional fields are conditionally spread, not set to undefined (exactOptionalPropertyTypes).

Notes

• A default switch arm with a never binding turns any future decision-enum drift into a compile error, while staying fail-closed at runtime.
• Re-exports PluginInstallRequestKind from the SDK types barrel.
• Independently reviewed against the contract and plan §B.2 — no blocking findings; both non-blocking suggestions (exhaustiveness guard + edge-case tests) applied.

Verification

pnpm verify green: format ✓, lint ✓, typecheck (0 errors) ✓, 185 tests pass, build ✓. 14 new unit tests cover the happy path, all six kind→source mappings, packageName fallback, deny via feedback/reason/default, update-mode + errored-scan metadata forwarding, and fail-closed unavailability.