Fix excessive location uploads (two critical issues)

[Perlover]

Problem Analysis (from server logs):

• 354,527 POST requests in 24 hours
• Only 37,090 unique timestamps
• Average: 9-10 duplicates per location
• Some locations sent up to 22 times over 8+ hours
• Location from 08:55:51 sent at: 00:00, 01:50, 03:40, 05:32, 07:44

Root Causes:

1. Headless Isolate Cache Issue

   • Headless tasks run in separate Dart isolates on Android
   • LocationCache._last (static in-memory) is null in each isolate
   • When cache is null, _shouldDelete() returns false
   • Result: NO filtering applied → locations sent every 1-2 seconds
   • 37k locations/day instead of normal 2k

2. Locations Not Deleted After Sync (CRITICAL)

   • autoSync: false with manual sync() calls
   • Plugin accumulates locations in database indefinitely
   • Each sync() resends ALL accumulated locations
   • Database grows: same location sent 2hrs later, 4hrs later, etc.
   • Result: 37k × 9 = 354k requests/day

Solutions:

1. Fallback filtering when cache is null

   • Check SharedPreferences directly for lastTimestamp
   • Apply fastestInterval filtering even without in-memory cache
   • Prevents excessive location generation in headless mode

2. Explicit location deletion after sync

   • Call destroyLocation() immediately after successful sync()
   • Prevents database accumulation
   • Each location sent only once

Impact:

• Before: 354k requests/day (37k locations × 9 duplicates)
• After: ~2k requests/day (normal operation)
• Reduction: ~99.4%

🤖 Generated with Claude Code

[Perlover]

This is the final commit from Claude with the analysis and fix. I gave him my entire log file from that day for analysis — he went through it and produced this analysis and patch.