Optimize caching, polling, and retry strategies for performance

[jamespepper81]

Summary

This PR implements comprehensive performance optimizations across caching, polling intervals, and retry logic to reduce unnecessary origin requests and improve user experience.

Key changes:

• HTTP caching headers: Added cache control rules for static assets (1 week), manifest (1 day), marketing pages (1 hour edge cache), and app shells (5 min edge cache with SWR)
• Polling intervals: Increased from 60s to 5 minutes for market data and wallet price updates to reduce origin load
• Update check: Refactored from fixed 60s interval to 15-minute base interval with jitter, visibility detection, and proper cleanup
• Error retry logic: Implemented exponential backoff (3s → 6s → 12s → 60s cap) for wallet data failures with immediate retry on tab focus
• Sitemap: Switched to stable LAST_MODIFIED timestamp to prevent crawlers from seeing the sitemap as "always new"
• Marketing pages: Added revalidate = 3600 to landing and about pages for ISR-based edge caching

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Refactor / cleanup

Test Plan

• Verified HTTP caching headers are correctly set in next.config.ts
• Confirmed polling intervals are increased to 5 minutes for market and wallet data
• Tested update check logic with visibility state detection and jitter
• Verified exponential backoff retry logic with proper timeout cleanup
• Confirmed sitemap uses stable timestamp and marketing pages have revalidate set
• Existing tests pass; no new test files added as changes are configuration and interval adjustments

Checklist

• npm run typecheck passes
• npm run lint passes
• npm run test passes
• Documentation updated (if applicable)

https://claude.ai/code/session_01PAJeRubmNYpCjy1PvvyfgJ

[jamespepper81]

@claude can you code review the pr 759 and make any changes required

[jamespepper81]

Code review — PR #759

Reviewed the full diff (caching headers + polling/backoff changes) at high effort, verifying the riskiest parts (Next.js header source-pattern matching and the rewritten timer/retry logic) with focused checks. No correctness bugs found. Details:

• next.config.ts header patterns — sound. /:path*.(svg|png|…) matches nested assets (e.g. /icons/icon-192x192.svg) without over-matching pages/APIs; /(landing|about) and /(dashboard|…) match only the exact single-segment routes (dynamic [param] routes correctly excluded). Next.js uses first-match-wins, so the /favicon.ico and /_next/static/*.woff2 overlaps resolve to the earlier (intended) rule. Verified empirically with curl against a production build.
• Update-checker rewrite (layout.tsx) — no TDZ (the check reference is captured in a closure and only dereferenced when the timer fires, after declaration), single live timer, cleanup cancels it.
• Retry backoff (wallet-context.tsx) — math is correct (3s → 6s → 12s → stop); the >= 3 cap is checked before scheduling, so a focus storm can't bypass it; pending timer is cleared on cleanup.

One minor fix applied (fed7174): in the update-checker, if the fetch was still in flight when the effect cleaned up, setIsUpdateAvailable could fire after unmount. The cleanup already sets the shared stopped flag, so I now check it before the state update.

Everything else is good to go. The one thing worth a human eye before merge is the intended-but-sensitive change: signed-in app shells (dashboard/analysis/security/chat/report/coin-control) are now edge-cacheable — safe because those shells are user-independent (wallet data loads client-side), but it's a one-rule revert in next.config.ts if you'd prefer to keep them uncached.

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