Bead bf-3mx7: Document winner badge fix completion

The code fix was already applied in commit 6fe778b. This commit
adds documentation noting that the index builder needs to be run
to regenerate static JSON with correct winner badges.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.needle-predispatch-sha

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notes/bf-3mx7.md

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+# Bug Fix bf-3mx7: Match Index Winner Badge
+
+## Problem
+The match index winner badge was never showing because the `Won` field was incorrectly set using `p.BotID == m.WinnerID`. The issue: `m.WinnerID` is a player-slot integer as string (e.g. "2"), not a bot_id. The SQL query already computed the correct winner status in the `p.Won` field.
+
+## Fix Applied
+Fixed in commit `6fe778b` - Changed all occurrences from comparing `p.BotID == m.WinnerID` to using `p.Won` directly:
+
+1. **matchToSummary** (line ~355): Changed `Won: p.BotID == m.WinnerID` to `Won: p.Won`
+2. **buildPlaylistMatch** (line ~982): Changed `Won: p.BotID == m.WinnerID` to `Won: p.Won`
+3. **ratingUpsetMagnitude**: Use `p.Won` to identify winner instead of comparing with `m.WinnerID`
+4. **maxScoreDiff**: Use `p.Won` to identify winner instead of comparing with `m.WinnerID`
+5. **isEvolutionBreakthrough**: Find winner using `p.Won` before checking if evolved
+
+## Next Steps
+To apply the fix to production data:
+- Run the index builder to regenerate static JSON files with correct winner badges
+- This requires database access and running: `go run cmd/acb-index-builder/main.go`
+
+## Impact
+This fixes the issue where 984/1000 production matches had `winner_id` set but all participants showed `won: false`.