[DYN-024] Durable adaptive workspace data and offline sync

[veryCrunchy]

Roadmap

• Task ID: DYN-024
• Priority: P0
• Parent epic: [EPIC] Adaptive Nextcloud apps #15
• Related foundations: [DYN-001] Contract cache performance #41, [SEC-002] Cache/account isolation #105, [UX-009] Loading and cache UX #156, [UX-010] Empty/error/offline state system #157, [DYN-021] Adaptive collection navigation and filtering #250

Scope

Provide one shared, account-isolated persistence and synchronization layer for semantic app workspaces. Mail is an important acceptance fixture, but the implementation must remain contract-driven and reusable by Pantry, Chores, Budget, and untested apps exposing equivalent resources and actions.

Acceptance criteria

• Persist bounded collection pages, detail records, relationship data, pagination checkpoints, and revalidation metadata by account, app, resource, parent scope, and request identity.
• Render cached collection and detail data immediately after navigation or process restart, then refresh non-blockingly when online.
• Keep previously loaded read-only workspace data available offline with clear freshness and connectivity state.
• Queue only fully verified mutations whose target identity, provenance, payload, and conflict strategy can be persisted safely.
• Replay queued mutations after connectivity returns only when the authoritative server state still satisfies the recorded precondition or has no conflict.
• Pause and surface a resolvable conflict instead of overwriting when ETags, versions, record identity, or authoritative postconditions diverge.
• Show pending, synced, stale, failed, and conflicted state consistently on Android and desktop without app-specific UI branches.
• Enforce account isolation, bounded storage, expiry/invalidation, sensitive-field policy, and logout/account-removal cleanup.
• Cover restart, offline read, offline mutation, reconnect, duplicate replay, conflict, pagination, and cache-eviction behavior with synthetic Mail, Pantry, Chores, and generic contract fixtures.
• Add cross-platform visual QA for immediate cached content, background refresh, offline state, pending writes, and conflict resolution.