[rejoicetukura-blip]

Summary

• Add an SSE Fallback Transport for Clients Where WebSockets Are Unavailable #206: `Transport` interface, `WebSocketTransport`, new `SseTransport`; client falls back to SSE if the socket never opens and exposes `activeTransport`/`getStatus()`. Outbound control msgs go via REST POST (SSE is read-only); token via query param.
• Handle Message Ordering, Gap Detection, and Backpressure in the Realtime Client #209: per-topic `TopicSequencer` (gap detection → `resync`, bounded reorder window, dedupe) and `Coalescer` (replace = latest wins, append = never dropped).
• Deduplicate Realtime Connections Across Browser Tabs #202: `TabLeader` (BroadcastChannel) — one tab holds the connection, others receive fan-out; heartbeat failover; topic subscriptions ref-counted across tabs.
• Stream Pool Stats into the LP Provision Views #199: `usePoolStats` subscribes to `pool.stats` behind new `realtime-pool-stats` flag; only full snapshots applied, drift guard vs REST, REST fallback + `isStale` on disconnect.

Closes #199
Closes #202
Closes #206
Closes #209

Validation

• `tsc --noEmit`: no errors in changed files
• `vitest` on new unit tests: 5 passed

Notes / not done

• Deduplicate Realtime Connections Across Browser Tabs #202: SharedWorker, Playwright two-tab test and `.size-limit.json` check not done; BroadcastChannel leadership only.
• Stream Pool Stats into the LP Provision Views #199: Playwright/mock-server tests not added.
• Add an SSE Fallback Transport for Clients Where WebSockets Are Unavailable #206/Handle Message Ordering, Gap Detection, and Backpressure in the Realtime Client #209: integration/stress tests beyond unit tests not added.
• Pre-existing on main: feat: live countdowns, multi-wallet adapters, idle re-confirmation, on-chain read fallback #191 blanked ~43 files (incl. `usePoolStats.ts`, which I rebuilt here); no eslint config; `@testing-library/react` missing so `dataSourceFallback.test.ts` can't run.

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