settingsd contract changes

Mirrored from services/settingsd/CHANGELOG.md, where releases update it. The component's page is settingsd. This page describes the current main branch of MixOS.

0.1.0

Serve describe/get/validate/apply/reset/status through native ABP; durable changed/no-op receipts, target/revision fencing, exclusive writer, recoverable replacement and complete scoped retained publication. Package the service unit. Before initial release: add explicit idempotent first-run session seed, preserving established missing-primary failure, and session wants/upholds wiring without making GUI startup wait for authority readiness. Authority verbs/schema unchanged. First creation requires installer-only --allow-create; the automatic unit uses plain seed and cannot recreate a wholly lost profile directory or mount.

Before initial release: pin package source and verify stored content digest; bind storage to the held directory/lock; fence validation; add bounded pending publication retries and preserve missing-store failure visibility. Fence effective compiler interpretation; distinguish intact unsupported/I/O failures from corruption; keep pending publication backoff capped at 30 seconds until success. Inline capacity refusal has a distinct snapshot_too_large status.