Umbrella for the concurrency/responsiveness work deliberately deferred from the #403/#404 Phase A push. None of these gate the format freeze or the explicit-save model; they harden it.
- Worker ZIP: build/extract containers in a module Worker against OPFS handles (sync access handles are Worker-only). Pass handles/Files, never main-thread media ArrayBuffers. Generation checks on completion.
- Streaming: Worker-hosted JSZip fixes stalls, not peak memory — evaluate a streaming ZIP writer (incremental STORED media, CRC in Worker, chunked output) and streaming extraction into OPFS. Safari lacks a reliable streamed save sink; the fallback may still materialize a Blob.
- Per-project work directories (
work/<projectId>/) with a work index, recovery discovery/chooser for multiple dirty projects, and GC of stale snapshots/orphan media under locks.
- BroadcastChannel advisory coordination and the focus/read-only/fork second-tab UX (upgrade of the Phase A single-lock guard).
- Quota and environment handling:
navigator.storage.estimate() UI, OPFS-unavailable Private Browsing fallback, suspended/killed-tab behavior, iOS memory pressure (don't rely on navigator.deviceMemory).
- Cross-browser/iOS test matrix: Private Browsing, low storage, backgrounded tabs, large media, interrupted downloads.
Umbrella for the concurrency/responsiveness work deliberately deferred from the #403/#404 Phase A push. None of these gate the format freeze or the explicit-save model; they harden it.
work/<projectId>/) with a work index, recovery discovery/chooser for multiple dirty projects, and GC of stale snapshots/orphan media under locks.navigator.storage.estimate()UI, OPFS-unavailable Private Browsing fallback, suspended/killed-tab behavior, iOS memory pressure (don't rely onnavigator.deviceMemory).