Partial fix for #1768 — Relay Airtime Share now uses closed-form LoRa
Time-on-Air instead of a payload-bytes-only proxy, removing the ~3-4×
bias against small frames (preamble + fixed-symbol intercept).
cross-stack: justified — backend score formula needs a frontend caption
change (`public/analytics.js` dumbbell preset banner + tooltip) so
operators can interpret the assumed PHY block. Both move together or the
metric is misleading.
## Red commit
`8da57062` — failing test asserts ToA-based score (~83.48 % ADVERT share
on the locked acceptance fixture) instead of the byte proxy's 95.24 %.
`internal/lora.TimeOnAir` was a zero-returning stub at the red commit;
tests failed with assertion errors, not build errors.
## Green commit
`dd402edd` — implements `lora.TimeOnAir` (Semtech AN1200.13 / SX126x
§6.1.4 closed form, cross-checked against RadioLib), wires `score =
TimeOnAir(payloadBytes, preset) × distinctRelays` in
`cmd/server/relay_airtime_share.go`, surfaces the preset in the JSON
response and analytics caption.
## Config (per AGENTS Config Documentation Rule)
New keys under existing `analytics` block:
```json
"loraPreset": { "freq": 869600000, "bw": 62.5, "sf": 8, "cr": 5 }
```
Defaults match the deployment's actual `get radio` (869.6 MHz / BW 62.5
kHz / SF 8 / CR 4/5). `CRC=1`, `IH=0`, `DE = (T_sym ≥ 16 ms)`, and the
SF-dependent preamble (32 for SF≤8 else 16, per firmware
`preambleLengthForSF` / MeshCore PR #1954) are firmware-fixed constants
in `internal/lora/toa.go` and intentionally NOT surfaced as config (per
re-triage).
## Scope
In-scope files (6):
- `internal/lora/toa.go` (new package — closed-form ToA)
- `internal/lora/toa_test.go` (table-driven preset tests)
- `cmd/server/relay_airtime_share.go` (wire ToA into score)
- `cmd/server/relay_airtime_share_test.go` (recomputed expected values)
- `cmd/server/config.go` + `config.example.json` (preset config keys)
- `public/analytics.js` (preset caption on dumbbell chart + tooltip)
Plus `cmd/server/go.mod` (replace directive for the new internal
module).
## Deferred to v2 (separate issues per re-triage)
- Per-observation SF/BW + radio-settings-aware dedup (blocked: ingestor
stores SNR/RSSI only, no SF/BW on observations).
- CR-per-hop dual-point sensitivity band (CR scales only the payload
symbol term `(CR+4)`, not the preamble/header; second-order accuracy
gain).
- Cross-SF bridge accounting.
## Tests
```
cd internal/lora && go test ./... → PASS
cd cmd/server && go test -run RelayAirtime → PASS
```
## Preflight overrides
- `check-branch-clean` (cross-stack): justified above — score formula
change requires matching caption update; both files trace to the same
issue.
---------
Co-authored-by: kpa-clawbot <kpa-clawbot@users.noreply.github.com>
Co-authored-by: Kpa-clawbot <bot@openclaw.local>
Co-authored-by: bot <bot@meshcore>
Kpa-clawbot
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