Issue 21: Grace Period Policy Resolution Engine

[laraibg786]

Goal

Build a reusable policy resolution engine that resolves grace period and offline timeout settings from a hierarchy: per-license override → vendor default → global platform default.

Requirements

Functional

• Implement resolve_policy(license_id, vendor_id) → PolicySnapshot.
• Policy hierarchy: license.grace_override > vendor.default_grace > global default (60 min).
• Resolve max_offline_hours: license override > vendor default > global (24 hours).
• Resolve heartbeat_interval_seconds: vendor default > global (300 seconds).
• Snapshot Immutability: Policy is snapshotted at session creation time; subsequent changes don't affect active sessions.

Technical

• Location: app/services/policy_service.py.
• DB Migration: Create vendor_policies, license_policies, and platform_defaults tables.
• Resolution: Single SQL query with LEFT JOIN chain and COALESCE.
• Store policy snapshot in activation_sessions.policy_snapshot (JSONB column).

Acceptance Criteria

• Per-license override takes precedence over vendor default.
• Per-vendor override takes precedence over global default.
• Global defaults: grace=60, offline=24, heartbeat=300.
• Policy snapshot is immutable after session creation.
• RLS enforced: vendors can only resolve policies for their own licenses.

Dependencies

• Blocked by: Issue 03: PostgreSQL Schema and Migrations #3.
• Blocks: Issue 18: Activation Session Creation and Device Binding #18, Issue 20: Heartbeat Grace Period Enforcement #20.