ROADMAP-16 — P2 — retry.py ships two retry mechanisms; collapse to one #108

Series: ROADMAP — filed from the 2026-10-27 whole-project assessment · Backlog task: M16-T03 · Priority: P2 · Effort: extra small

Problem

retry.py ships two retry mechanisms: a generic decorator (retry_with_backoff) and a class wrapper (RetryingLLMClient) whose only consumer for the decorator is the wrapper itself. Maintaining both costs: aclose delegation, a __getattr__ proxy, and ~40 lines guarding a partial-init state that cannot occur (self._client is assigned first; the chained construction cannot realistically raise between the two).

Evidence

• agentkit/llm/retry.py:91–130 — decorator (production consumer: the wrapper only, :153–159)
• agentkit/llm/retry.py:133–191 — wrapper + delegations + guard

Suggested fix / acceptance criteria

• Keep exactly one mechanism (wrapper recommended: it is what the factory injects and what aclose forwarding requires)
• The impossible-state __getattr__ guard removed or justified in a comment with the concrete failure it prevents
• Suite (incl. test_llm_retry.py) green

Suggested branch / commit

refactor/llm-retry-single-mechanism · refactor(llm): collapse retry.py to a single mechanism