fix: count distinct districts/IPs instead of total rows in reportValidation.service.ts (#1967)

[nimkarprachi17]

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📋 PR Summary & Link

• Closes [BUG] reportValidation.service.ts counts total rows instead of distinct values in geographic spread and Sybil checks #1967
• Summary: Fixes apps/api/src/services/reportValidation.service.ts where the geographic spread check and both Sybil detection checks used select(column, { count: "exact", head: true }), which returns the total row count matching the filter, not a distinct count. This meant 5 duplicate reports from the same IP/district were incorrectly counted as 5 distinct districts/reporters. Fixed by fetching the actual rows and computing distinct counts in JavaScript with a Set, since the lookback window (burstDeadline, last hour) keeps the result set small. Added unit tests in apps/api/tests/reportValidation.service.test.ts verifying duplicate reports from the same IP/district do not trigger the distinct-value thresholds, while genuinely distinct districts/IPs still correctly trigger them.

📸 Proof of Work (Screenshots / Logs)

🏷️ PR Type

• 🐛 type: bug
• 🧪 type: testing

✅ Checklist

• My PR has a linked issue (Closes #1967)
• I have pulled the latest main and resolved any conflicts

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Files changed:

• apps/api/src/services/reportValidation.service.ts — fixed 3 distinct-count queries (geographic spread, Sybil-by-district, Sybil-by-medicine) to use Set-based distinct counting instead of count: "exact" row counts
• apps/api/tests/reportValidation.service.test.ts — new file, 4 unit tests covering both the bug scenario (duplicate reports not over-counted) and the correct-detection scenario (genuinely distinct districts/IPs still flagged)

[github-actions]

🎉 Congratulations @nimkarprachi17! Your Pull Request "fix: count distinct districts/IPs instead of total rows in reportValidation.service.ts (#1967)" has been successfully merged by @dipexplorer.

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