Investigate Docker Build - Domain Identity: @requireCapability already exists in schema

Surfaced by workflow-noise Phase 2 survey (memory/2026-05-19-workflow-noise-phase2.md). Docker Build - Domain Identity job apollo-schema-publish/publish-subgraph fails with: Error: Directive @requireCapability already exists in this schema (at domains/identity/src/graphql/schema.ts:17:21). 4 failures in 30d window, deterministic on push to main. Likely cause: directive defined directly AND imported (e.g. via federation @link). Requires identity-domain context to diagnose + fix safely. Repro: gh run view 25876805349 --repo TextureHQ/mono --log-failed. Estimated 1-3h.