feat: add auto-reconnect with exponential backoff to admin webhook SSE stream (Closes #300) [fj4WqyCCw3C5ShR1RfB7MoBPTpkRrBFYP1uT35g3MvT]

[waterWang]

Summary

Closes #300

Adds automatic reconnection with capped exponential backoff to the subscribeWebhookEvents() SSE stream in lib/api/live.ts.

Changes

Core reconnect logic (lib/api/live.ts)

• Replaced the single fetch + .then() call with an async tryConnect() loop that auto-reconnects on failure
• Added SSE-specific backoff constants (lazy functions for testability) with separate env vars:
  • NEXT_PUBLIC_SSE_RECONNECT_MAX_ATTEMPTS (default: 10)
  • NEXT_PUBLIC_SSE_RECONNECT_BASE_DELAY_MS (default: 100ms)
  • NEXT_PUBLIC_SSE_RECONNECT_MAX_DELAY_MS (default: 10s)
  • NEXT_PUBLIC_SSE_STABILITY_WINDOW_MS (default: 30s)
• Added sseBackoffDelayMs() — capped exponential backoff with jitter (same pattern as REST backoffDelayMs)
• Added onReconnecting callback parameter to notify callers of reconnect attempts
• Backoff counter resets on successful connection, and after a stability window of successful frames
• unsubscribe() now properly cleans up: sets stopped flag, clears pending reconnect timeout, aborts the controller

API surface (lib/api/types.ts, lib/api/mock.ts)

• Added onReconnecting?: (attempt: number, delayMs: number) => void to the AdminAccessApi interface
• Updated MockAccessApi to accept the new parameter (no-op)

Bug fixes

• Fixed pre-existing syntax error in lib/wallet/connectors.ts (missing = [ in array literal)
• Fixed pre-existing duplicate declaration in lib/api/mock.ts (duplicate analytics property)

Tests (test/webhook-stream-reconnect.test.ts)

• 6 comprehensive tests using real timers (no mock timer issues):
  • Healthy stream delivers events without reconnecting
  • Dropped stream (reader done) triggers reconnect after backoff
  • HTTP error triggers reconnect after backoff
  • Unsubscribe stops all further reconnect attempts
  • Stops retrying after max attempts and gives up
  • onError is still invoked so polling fallback works