Problem

Agent<C> in crates/zeph-core/src/agent/mod.rs has 40+ fields and 9 #[allow(clippy::too_many_lines)] suppressions. While sub-structs (MemoryState, SkillState, McpState, IndexState, RuntimeConfig, SecurityState, DebugState) were extracted previously, many fields remain directly on the struct.

Proposed Changes

Extract additional sub-structs:

1. ProviderState — provider, summary_provider, judge_provider, judge_detector, server_compaction_active, provider_override
2. SessionState — messages, pending_image_parts, cached_prompt_tokens, message_queue
3. UiState — metrics_tx, cancel_signal, cancel_token, start_time, warmup_ready, cost_tracker
4. OrchestrationState — pending_graph, plan_cancel_token, subagent_manager, subagent_config, orchestration_config

Motivation

• Reduce cognitive load when reading the agent struct
• Enable isolated unit testing of sub-components
• Align with the established pattern already used for MemoryState, SecurityState, etc.
• Remove clippy::too_many_lines suppressions by making method bodies smaller

Acceptance Criteria

• Agent struct has <= 15 top-level fields (composed from sub-structs)
• No new #[allow(clippy::too_many_lines)] suppressions added
• All existing tests pass
• Builder API remains backward-compatible

Files

• crates/zeph-core/src/agent/mod.rs (3377 lines)
• crates/zeph-core/src/agent/builder.rs