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

Fix (reviewer findings)

Applied the reviewer correction for the trusted source endpoint contract:

In go/vehicle-gateway/internal/stats/source_mileage.go, projectDailyMileageSQL now writes trusted_source_endpoint from vehicle_data_source.latest_source_endpoint via COALESCE(NULLIF(ds.latest_source_endpoint, ''), s.source_endpoint) so latest connection metadata is authoritative with a simple fallback.
Replaced hardcoded quality predicate with the existing constant using s.quality_status = ' + QualityOK + ' in projectDailyMileageSQL.
Updated go/vehicle-gateway/internal/stats/source_mileage_test.go to assert both the endpoint expression and constant-based quality predicate.

Validation commands:

cd go/vehicle-gateway && go test ./internal/stats -run TestProjectDailyMileageSelectsCandidateAndMarksSource -count=1
# PASS: lingniu-vehicle-ingest/go/vehicle-gateway/internal/stats

cd go/vehicle-gateway && go test ./internal/stats -count=1
# PASS: lingniu-vehicle-ingest/go/vehicle-gateway/internal/stats

Fix (reviewer findings #2)

Corrected the remaining projectDailyMileageSQL contract issue so trusted_source_endpoint uses only vehicle_data_source.latest_source_endpoint:

In go/vehicle-gateway/internal/stats/source_mileage.go, changed the projection from: COALESCE(NULLIF(ds.latest_source_endpoint, ''), s.source_endpoint) to: ds.latest_source_endpoint.
In go/vehicle-gateway/internal/stats/source_mileage_test.go, extended TestProjectDailyMileageSelectsCandidateAndMarksSource assertions to:
- require ds.latest_source_endpoint is selected, and
- explicitly verify no fallback expression using s.source_endpoint remains.

This enforces the strict source-of-truth rule that endpoint data for final projection must come from latest connection metadata only, even when it is null/empty.

Fix (reviewer findings #3)

Addressed stale candidate selection re-flagging by narrowing source marking to the same eligibility rules used by projection:

In go/vehicle-gateway/internal/stats/source_mileage.go, markSelectedSourceSQL now:
- No longer joins vehicle_daily_mileage to discover the selected source.
- Selects the same single winning candidate directly from vehicle_daily_mileage_source, constrained by:
  - VIN/date/protocol
  - quality_status = QualityOK
  - mileage bounds (0..maxSelectedDailyMileageKM)
  - enabled source metadata
  - same trust/sample/time ordering
- Marks only that candidate as is_selected = 1.
In go/vehicle-gateway/internal/stats/source_mileage_test.go, TestProjectDailyMileageSelectsCandidateAndMarksSource now verifies:
- the mark query includes candidate filters and ordering, including s2.quality_status, s2.daily_mileage_km, and COALESCE(ds.enabled, 1) = 1.
- it no longer references vehicle_daily_mileage as a join source.
- it passes the selection window arg through to marking (maxSelectedDailyMileageKM) and uses seven bind args.