~anthropic/claude-sonnet-latest → B (80:20)

Commit B delivers a substantial, real feature (GitHub OAuth login, session management, pseudonym claiming, identity event sourcing) plus a meaningful infra change (extracting durable into its own repo/dependency), backed by new integration tests and mock OAuth harness. Commit A is a smaller, well-scoped algorithmic refinement to pair-selection heuristics with good unit tests, but it's narrower in scope and impact compared to the auth system and repo restructuring in B.