fix(agent-interface): preserve absent profile resources

[drewstone]

Problem

Applying an empty AgentProfileDiff materialized five absent resource arrays. This made a no-op profile change appear distinct and polluted candidate comparison.

Solution

Use the existing optional-array merge helper for resource lists so absent lists stay absent while explicit and populated lists retain append semantics.

Verification

• pnpm build
• pnpm check-types
• pnpm test (all workspace tests pass; agent-interface 105/105, agent-core 419/419, provider packages 10/10)

[tangletools]

✅ Auto-approved drewstone PR — da3e1431

This PR was opened by the trusted drewstone account.
The full PR reviewer audit still runs separately and will publish findings if it detects issues.

_{tangletools · auto-approval · reason: drewstone_author · 2026-07-12T02:47:37Z}