AetherSDR PR #3502 moved the TCI VOLUME command to dB (-60..0) on the wire.
Two breaks for this plugin, which models volume as 0-100 percent:

1. Read: AE now echoes volume in dB (negative). The parser stored that dB
   value as if it were percent, corrupting the local mirror and breaking the
   dial's first-step tracking (exactly the concern raised in #3502).
2. Write: stepping AF gain to the bottom sent `volume:0`, which AE now reads
   as 0 dB = FULL volume (was 0% mute) - turning the dial down jumped to max.

Fix (internal model stays percent; convert only at the wire):
- Read: an echoed value <=0 is dB -> dbToPercent(); >=1 stays legacy percent.
  Handles both old (percent-echo) and new (dB-echo) AetherSDR.
- Write: emit -60 dB for the silence floor instead of 0; 1-100 still go as
  legacy percent, which AE's compat shim accepts.

Follow-up to the hardware re-verification flagged in aethersdr/AetherSDR#3502.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

…aethersdr#3502)

## Problem

TCI Protocol v2.0 defines `VOLUME` as the main (master AF) volume **in
dB, range −60..0, where −60 dB is silence** — real ExpertSDR3 sends e.g.
`VOLUME:-12;`. AetherSDR has been sending and parsing it as our internal
**0–100 percent** amplitude instead. Two concrete breakages:

1. **Outbound:** every `volume:` we emit — the connect init-burst seed
(aethersdr#3245), GET replies, SET echoes, and the title-bar-slider broadcast —
carries a 0–100 percent value (`volume:33;`, visible in Yuri UT4LW's
init-burst capture from the aethersdr#3498 report). To a spec-conforming client
that's an out-of-range value on a −60..0 scale.
2. **Inbound (worse):** a spec-conforming client setting `volume:-12;`
(a normal listening level) got clamped to 0 percent — i.e. **we muted
the operator's audio** instead of setting −12 dB.

This only affects the local monitor volume path (`applyMasterVolume` →
PC audio RX volume or radio lineout gain). The TCI audio streams
themselves (TciRxGain/TciTxGain) and TX levels (`drive`/`mic_level`) are
unrelated and untouched.

## Fix

Convert at the wire; everything inboard stays 0–100 percent (the
`pendingMasterVolume()` → `masterVolumeRequested` → `applyMasterVolume`
contract is unchanged).

**Emit in dB** — `cmdVolume` GET, SET echo, the init-burst seed, and
`TciServer::broadcastMasterVolume()` all now send
`volumeDbFromPercent(pct)`:

| internal % | wire dB |
|---|---|
| 100 | 0 |
| 50 | −6 |
| 25 | −12 |
| 10 | −20 |
| 0 | −60 |

**Parse SET dual-scale** — the spec range is non-positive, so positive
values are unambiguous:
- `value ≤ 0` → spec dB, amplitude mapping `10^(dB/20)`; −60 → mute;
values between −59 and −41 floor at 1 % so only the spec's explicit
silence point (−60) mutes.
- `value ≥ 1` → **legacy AetherSDR percent, still accepted** — existing
percent senders keep working unchanged.
- `volume:0` now means 0 dB = full volume per spec (previously: percent
mute). Muting is the job of the TCI `mute:` command.

The SET echo is round-tripped through the percent store so it always
matches what a subsequent GET returns.

## Precision note (honest limits)

The internal store is integer percent, so dB→%→dB round-trip is **exact
from −24 dB up to 0 dB**, within ±1 dB down to −36 dB, and floors at 1 %
(≈−40 dB) below that. This affects only whisper-quiet settings; the
practical knob range is unaffected.

## Client compatibility

- **WSJT-X / JTDX**: recognize `volume` and explicitly ignore it (`case
Cmd_Volume: break;` in `Transceiver/TCITransceiver.cpp`), and never send
it. Unaffected.
- **Spec-conforming clients** (ExpertSDR-native panels, SDC ecosystem):
now see correct dB values and their dB SETs take effect instead of
muting. This is the population the fix targets.
- **Value-mirroring gain steppers** (Ulanzi D100H / Elgato /
StreamController, the aethersdr#3245 clients): these mirror whatever value we
seed and step it (aethersdr#3245 verified one happily mirroring `volume:87`).
With a dB seed they now step in dB space; if a given plugin clamps its
mirror to 0..100, its percent SETs still work via the legacy parse path.
⚠️ **Hardware re-verification of the Ulanzi D100H first-step behavior is
the one open test** — flagged below.
- **eesdr-tci-based parsers** (RF2K-S): `VOLUME` is a known command name
with no client-side range validation on the float; no parse risk.

## Testing

- Builds clean (RelWithDebInfo, Ninja, macOS).
- Conversion table + round-trip stability verified numerically (above).
- [ ] Live check: spec client SET `volume:-12;` → audible level drop,
GET returns `-12`
- [ ] Live check: Ulanzi D100H AF-gain step still tracks from the seeded
value (aethersdr#3245 regression check)

## Related / follow-ups

- `rx_volume` and `mon_volume` have the same percent-vs-dB mismatch per
spec (`RX_VOLUME`/`MON_VOLUME`: dB −60..0). They're **not** bundled here
because `rx_volume` also has an argument-shape divergence (spec is 3-arg
`trx,channel,dB`, and the spec's 2-arg GET `trx,channel` collides with
our documented legacy 2-arg SET `trx,value` from aethersdr#1764) that needs its
own design decision.
- Complements aethersdr#3498 (init-burst `ready;` ordering) — together they make
the connect handshake read correctly to spec-conforming clients.

💻 Generated with Claude Code (Fable 5.0) with architecture by @jensenpat

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Codex <noreply@openai.com>