Problem

• Agent struct fields all pub(super) — no encapsulation within 30-file module tree
• AgentSessionConfig exposes 25+ internal implementation detail fields
• MessagePart serialization includes internal variants (ThinkingBlock, Compaction)
• zeph-tools re-exports nearly everything (40+ types)
• LLM providers have inconsistent constructor patterns
• Error enums all have Other(String) catch-alls

Goal

Tighten abstraction boundaries, reduce public API surface, and improve encapsulation.

Audit Reference

.local/audit/005-abstraction-violations.md

Key Issues

• ABS-01: AgentSessionConfig field visibility
• ABS-02: Sanitizer types at zeph-core root
• ABS-03: zeph-tools re-export surface too wide
• ABS-04: Agent pub(super) field encapsulation
• ABS-05: MessagePart internal variant exposure
• ABS-06: AgentSessionConfig leaks implementation details
• ABS-07: Agent builder required field validation
• ABS-08: LLM provider constructor consistency
• ABS-09: Error Other(String) catch-all reduction

Acceptance Criteria

• Agent state accessed via accessor methods (not direct field access)
• MessagePart internal variants hidden behind serde attribute
• At least 2 LLM providers use consistent builder pattern
• All tests pass