EPIC: Code Duplication Consolidation (DRY)

[bug-ops]

Problem

8 significant duplication patterns across the codebase, primarily in the LLM provider layer:

• Usage/cache tracking (Mutex pattern) duplicated in 4 providers
• set_status_tx boilerplate in 6 providers
• type_name schema generation in 3 providers
• ChannelError::Other mapping in 14+ locations
• BoxFuture type alias in 3 files

Goal

Consolidate duplicated patterns into shared utilities, reducing maintenance burden.

Audit Reference

.local/audit/003-duplication-analysis.md

Key Issues

• DRY-01: Extract UsageTracker struct for LLM providers (60 lines, 4 providers)
• DRY-02: Consolidate set_status_tx (18 lines, 6 providers)
• DRY-03: Shared type_name schema helper (30 lines, 3 providers)
• DRY-04: ChannelError::Other helper method (14+ sites)
• DRY-05: Single BoxFuture alias in zeph-memory
• DRY-06: Provider Clone via UsageTracker
• DRY-07: Model context window lookup table
• DRY-08: Error::Other extension trait

Acceptance Criteria

• UsageTracker extracted and used by all 4 LLM providers
• ChannelError helper method reduces .map_err boilerplate
• Single BoxFuture definition
• All tests pass
• No behavioral changes

Estimated Effort

~7 hours total