fix(session): WebSocket auto-reconnect with exponential backoff (#18)

[angelTomo9]

Closes #18

Summary of Changes

Implements automatic WebSocket reconnection with exponential backoff and network/visibility recovery in frontend/components/game/session/useGameSession.ts.

Features & Improvements

• Exponential Backoff Reconnect: When a socket drops unexpectedly, schedules up to 5 progressive retries with delays starting at 1.0s up to 10.0s.
• UI State Feedback: Emits error: "Reconectando (N/5)..." with connecting: true so players are visually informed of ongoing recovery attempts.
• Mobile & Background Recovery: Subscribes to visibilitychange (returning from background / screen lock) and online events to trigger immediate connection verification if closed.
• Full Handshake Preservation: Preserves character and ticket parameters during re-connect without requiring a manual page refresh.

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Summary by Gitar

• API data files:
  • Added seed npcs.json without UTF-8 BOM to unblock CI and market tests

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[gitar-bot]

Code Review ✅ Approved 3 resolved / 3 findings

Implements WebSocket auto-reconnect with exponential backoff and visibility recovery, addressing the missing close code check, retry counter reset, and 10s backoff scaling findings. No issues found.

✅ 3 resolved

✅ Edge Case: Reconnect fires on every close, ignoring close code/reason

📄 frontend/components/game/session/useGameSession.ts:521-535
socket.onclose schedules a reconnect whenever activeSessionKeyRef still matches, without inspecting CloseEvent.code/wasClean. Intentional server-side terminations (kick, ban, duplicate login, auth/ticket rejection) will therefore be auto-reconnected up to 5 times, re-sending the same connection.ticket; if the ticket is single-use this just burns retries and leaves the user stuck, and for kick/ban cases it fights the server's intent. Consider skipping reconnect for clean closures (e.g. event.code === 1000) or specific app-level close codes.

✅ Bug: Visibility/online recovery doesn't reset exhausted retry counter

📄 frontend/components/game/session/useGameSession.ts:566-578
After the 5 reconnect attempts are exhausted, reconnectAttempt stays at 5. When handleVisibilityOrOnline later fires (returning from background / network back), it calls connectSocket() but never resets reconnectAttempt, so onclose sees reconnectAttempt < maxReconnectAttempts as false and performs a single connect with no further retries — undermining the mobile/background recovery feature. Reset reconnectAttempt = 0 before calling connectSocket() here.

✅ Quality: Backoff never reaches the documented 10s maximum

📄 frontend/components/game/session/useGameSession.ts:530-535
The PR describes delays up to 10.0s, but with maxReconnectAttempts = 5 the delay 1000 * 1.5^(attempt-1) peaks at attempt 5 = ~5062ms, so the Math.min(10000, ...) cap is never hit. Either raise the base/multiplier/attempt count to actually reach the intended ceiling, or correct the description to reflect the real ~5s max.

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