Task 3 Report: Final Mileage Election Projector

Outcome

Implemented ProjectDailyMileage in go/vehicle-gateway/internal/stats/source_mileage.go and added focused projector coverage in go/vehicle-gateway/internal/stats/source_mileage_test.go.

RED

Before implementation, the new projector test failed as expected because the function did not exist yet:

internal/stats/source_mileage_test.go:87:9: undefined: ProjectDailyMileage

That confirmed the test was exercising the missing task-3 surface rather than passing accidentally.

GREEN

After implementation:

go test ./internal/stats -run TestProjectDailyMileageSelectsCandidateAndMarksSource -count=1
go test ./internal/stats -count=1

Both passed.

What Changed

Added maxSelectedDailyMileageKM = 1000.
Added ProjectDailyMileage(...) with three SQL steps:
- clear is_selected for the VIN/date/protocol slice,
- project the elected row from vehicle_daily_mileage_source into vehicle_daily_mileage,
- mark the winning source row as selected.
Kept the candidate identity intact: source_key still carries protocol + phone/device + source IP, while the data-source join uses protocol + source IP.
Added a focused test that asserts the clear/project/mark sequence and the key SQL fragments.

Files Changed

go/vehicle-gateway/internal/stats/source_mileage.go
go/vehicle-gateway/internal/stats/source_mileage_test.go

Self-Review

The projector stays aligned with the existing stats schema and helper conventions.
The SQL ordering and join logic preserve the intended source identity split; there is no IP-only simplification.
I did not add an unrelated schema migration because the current repository state already contained the needed vehicle_daily_mileage_source and vehicle_daily_mileage columns/indexes for this projector.
The only notable follow-up risk is that the final selection query relies on MySQL-style INSERT ... SELECT ... LIMIT 1 ON DUPLICATE KEY UPDATE behavior, which matches the rest of the stats package but should still be exercised against the target DB in an integration run.

Commit

aa12317b5 - feat(stats): project elected mileage source

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