[milestone Milestone 2] Implement `computeRiskScore(events, runId)` with configurable risk weights.

[telleroutlook]

🤖 Auto-filed from milestone doc bullet.

Repo: WasmAgent/open-agent-audit
Milestone: Milestone 2: Audit Core Pipeline
Bullet:

Implement computeRiskScore(events, runId) with configurable risk weights.

Problem

The computeRiskScore(events, runId) function is not yet implemented. This function is needed to calculate a risk score based on audit events, which is a core component of the audit pipeline.

Approach

Implement the computeRiskScore function that:

1. Takes events (array of audit events) and runId (audit run identifier) as parameters
2. Calculates a risk score based on configurable risk weights for different event types/severities
3. Returns a numeric risk score (likely 0-100 or similar normalized scale)

The function should be implemented in packages/core/src/drift-guard/index.ts, following the existing module patterns. Risk weights should be configurable (likely via a config parameter or environment-based configuration) to allow different weightings for:

• Event severity levels (critical, high, medium, low, info)
• Event types/categories
• Frequency factors

Files expected to change

• packages/core/src/drift-guard/index.ts — Add computeRiskScore function implementation
• packages/core/src/drift-guard/index.test.ts — Add tests for computeRiskScore function

Acceptance criteria

• Command bun install --frozen-lockfile && bun run build && bun run test passes
• computeRiskScore(events, runId) function is implemented and accepts the specified parameters
• Risk weights are configurable (not hardcoded)
• Tests cover basic functionality including different event scenarios
• No unrelated files touched (git status --short output limited to the intended changes)

Notes for the implementer

This issue was auto-created by SweepMilestoneBulletToIssue. The bullet text is verbatim from the milestone doc. The function should integrate with the existing drift-guard module and follow the codebase's patterns for configuration and error handling.