Browser sync runs the native coordinator logic inside the storage worker

Context

The browser runtime (ADR-0027) is local-only: the OPFS-backed SQLite worker has no sync, checkpoint, or hydration path, while the desktop coordinator (skriuw-sync) already proves ordering, idempotency, local-echo, convergence, chunked content, and checkpoint behavior against the v2 Worker API (ADR-0026). Reimplementing that protocol logic in TypeScript would create a second source of truth for replication behavior that could drift from native. The skriuw-sync cycle, hydration, checkpoint, and content modules are pure synchronous orchestration over &dyn ports; only the coordinator's thread and timer scheduling and the reqwest transport are native-only.

Decision

The storage worker owns the entire browser sync lifecycle. skriuw-sync compiles to wasm32 with its thread-based coordinator and system clock gated out; run_sync_cycle, checkpoint hydration/publication, and asset externalization/resolution run unchanged inside the worker against the same durable WorkspaceSyncQueue port.

• Transport: a synchronous XHR bridge in the worker script implements the crate's synchronous SyncTransport boundary — dedicated workers permit synchronous XHR, and each call is one bounded request with its own deadline. URLs and HTTP status classification live in the shared skriuw_sync::http module used by both the desktop reqwest transport and the browser bridge.
• Scheduling: apps/workspace/src/bridge/browser-sync.ts replaces the coordinator thread. It submits one bounded sync_cycle worker request at a time and derives the next wake from the reported outcome, coalescing local commits, focus, and reconnect events like the coordinator's wake flag.
• Assets: replicated image bytes persist in a dedicated OPFS-backed SQLite asset store outside the canonical workspace schema, because the browser has no filesystem blob store and asset durability must hold before pulled operations apply.
• Progress: the worker posts out-of-band notifications (requestId 0) during multi-chunk transfers so checkpoint hydration stays visible while a worker request is in flight.
• Trust: the worker re-validates the cloud origin and session-token shape before creating a transport; a missing credential surfaces as authenticationRequired and is never bypassed.

Consequences

• Browser and native replication behavior come from one Rust implementation; parity is enforced by crates/skriuw-sqlite-wasm/tests/browser_sync_scenarios.rs over the same fake transport used by the coordinator tests.
• Sync cycles serialize with persistence requests inside the single storage worker. Cycle work is therefore bounded (four push batches / four pull pages per cycle) so a renderer save acknowledgement waits at most one bounded cycle; renderer state updates synchronously and never waits on either.
• A long first-connect hydration executes inside one worker request with per-chunk (1 MiB) bounded transfers, a dedicated long client deadline, and visible progress; interruption leaves durable state untouched and the next cycle restarts hydration.
• The browser session token persists in localStorage under a versioned key (apps/workspace/src/features/auth/session-store.ts) so a reload of a linked workspace resumes sync without interactive sign-in. Cookies are not an option because the cloud Worker is cross-origin and the auth client already runs the Bearer token flow, so localStorage is the least-novel fit; the accepted tradeoff is that an XSS compromise of the app origin could read the token, which the strict CSP and absence of third-party scripts mitigate. Hard lifecycle rules: the stored value is validated on load and cleared when malformed; explicit sign-out and any server session rejection (provision 401 or a cycle reporting authenticationRequired) clear it; the token is never logged. The server stays the authority on expiry — the client performs no expiry guessing, and a rejected persisted session degrades to authenticationRequired.
• The Worker API must allow PUT in CORS preflight for chunk uploads from browser origins.