AnthropicProvider sanitizeMessages rejects empty strings but also rejects whitespace-only valid messages; resolveModel uses untyped 'effort in MODELS'

Opus finding

AnthropicProvider sanitizeMessages rejects empty strings but also rejects whitespace-only valid messages; resolveModel uses untyped 'effort in MODELS'

• src/providers/anthropic.ts:51-65
• src/providers/anthropic.ts:68-71

(1) `effort in MODELS` permits any object-prototype key like 'toString' or 'constructor' which would return a non-model string. Use Object.prototype.hasOwnProperty.call(MODELS, effort) or a switch. (2) Trimming user messages mutates input invisibly; an assistant message of literally ' ' is rejected but a code-fenced message with leading whitespace gets stripped of its formatting. Minor but inconsistent with non-Anthropic provider which does no sanitization.