CLAUDE.md: phase 2 gets clock-drift correction and AirPlay 1

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CLAUDE.md

@@ -53,7 +53,7 @@ Repo: https://gitea.apointless.space/bsncubed/aes67-ESP32-P4
 - [ ] 4. AES67 TX with a 1 kHz test tone, PTP-paced; /stream.sdp. Verify: import SDP on a Riedel Artist 4-wire AES67 port, and check packets/timestamps in Wireshark.
   Done and checked with a receiver script (all ptimes, L16/L24, tone phase-locked to PTP); still open: the Riedel import and a Wireshark capture.
 - [x] 5. SAP discovery, then syslog, then health/temperatures (one at a time). VLAN split moved to phase 2.
-- [x] 6. PTP TimeTransmitter: BMCA roles (auto/master), hybrid mode.
+- [x] 6. PTP TimeTransmitter: BMCA roles (slave/auto; the separate "master" role was dropped later, auto with a low priority1 does the same), hybrid mode.
 - [ ] 7. Sources: HLS player, then cspot (Spotify Connect), then failover + /api/player.
   - [x] 7.1-7.4 HLS plays on AES67 (PSRAM ring, TS demux + AAC, 44.1 -> 48 kHz). Tested with Triple J Hottest (TS, AAC-LC 44.1k).
   - [ ] Come back to HLS (open items):
@@ -73,8 +73,18 @@ Repo: https://gitea.apointless.space/bsncubed/aes67-ESP32-P4
     - Open: `aes67_tx resync` (TX 20-27 ms late) ~11 s after each switch to Spotify (seen 3 times); clicks at switches not yet checked in a recording; HLS start sometimes hits CDN read timeouts.
   - [x] /api/player: GET, transport, seek, volume (the app follows), source override and url (runtime, not saved); web UI progress bar.
 - [ ] 8. Mono sum, gain, polish.
+  - [x] Mono sum: stereo source mapped to a 1-channel stream in the core ((L+R)/2, 64 bit). Checked: 156 B packets, SDP L24/48000/1.
+  - [x] Gain: source.gain_db as a trim on top of the volume, saturating. Checked: -12 dB = -12 dB peak, +12 dB clips at 0 dBFS.
+  - [x] Pink noise source (-18 dBFS RMS, octaves flat within 0.4 dB 63 Hz-4 kHz).
+  - [x] 48 kHz only (96 kHz dropped: all sources are 48 kHz).
+  - [x] Network: status mask/gw/dns, UI shows the lease; static IP (reboot on change, validation).
+  - [x] Web UI: sticky save bar, dark default + light toggle, progress bar, PTP panel (2 min average offset, details), uptime d/h/m/s, VLAN option hidden, no hw_ts / preferred-TimeTransmitter options.
+  - [x] Versioning `<version.txt>-<git hash>`; tools/flash_board.py (tested on this board); docs/user-guide.md.
+  - [ ] Mute at 0 % volume: confirm on the board.
 
 ## Phase 2 (parked)
+- [ ] Clock-drift correction (do before AirPlay): steer the 44.1 -> 48 kHz converter by a few ppm from the ring level / distance to the live edge, so push sources that run on the sender's clock don't slowly over- or underrun. Closes the HLS clock-drift item in step 7; AirPlay needs the same.
+- [ ] AirPlay 1 (RAOP) as a source: `_raop._tcp` via our mDNS, RTSP control, AES (mbedTLS), ALAC decode, RTP audio + timing, 44.1 kHz into the existing converter, uses the clock-drift correction. Start from philippe44's RAOP code in squeezelite-esp32 (check its licence first). Covers iPhone/iPad/Mac (incl. Tidal and Apple Music apps) and Windows via AirPlay senders (TuneBlade, Airfoil). Not AirPlay 2 (HomeKit pairing, its own PTP on ports 319/320 clashes with ours). Then: auto mode as a priority list (whichever source plays wins, HLS as fallback). Check internal heap with Spotify + AirPlay sessions (buffers to PSRAM).
 - [ ] VLAN split: AES67 untagged + internet tagged (inet.vlan_id/pcp), per aes67-core-base.md "Network". Needs a tagged VLAN with DHCP on the switch port. Config group `inet` and the UI fields exist already; nothing is applied yet. The "VLAN split" checkbox is hidden in web/index.html (`<label hidden>`); unhide it when this is done.
 - [ ] NTP (SNTP): servers as hostnames or IPs (e.g. `pool.ntp.org`, several allowed; names resolved via DNS, re-resolved on failure). Uses: seed the PTP clock with real time before becoming GM (today it starts at 1970), syslog timestamps. Needs a `time` config group + UI fields (change doc and page together).