WIP: стабилизация звонков и E2EE + инструменты сборки WebRTC

tools/webrtc-custom/README.md

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+# Custom WebRTC for Rosetta Android (Audio E2EE Timestamp)
+
+This setup builds a custom `libwebrtc.aar` for Android and patches audio E2EE so
+`FrameEncryptor/FrameDecryptor` receive non-empty `additional_data` with RTP timestamp bytes.
+
+## Why
+
+Stock `io.github.webrtc-sdk:android:125.6422.07` can call audio frame encryptor with empty
+`additional_data` (`ad=0`), so nonce derivation based on timestamp is unavailable.
+
+Desktop uses frame timestamp for nonce. This patch aligns Android with that approach by passing
+an 8-byte big-endian timestamp payload in `additional_data`:
+
+- bytes `0..3` = `0`
+- bytes `4..7` = RTP timestamp (big-endian)
+
+## Files
+
+- `build_custom_webrtc.sh` — reproducible build script
+- `patches/0001-audio-e2ee-pass-rtp-timestamp-as-additional-data.patch` — WebRTC patch
+
+## Build
+
+Recommended on Linux (macOS can work but is less predictable for long WebRTC builds).
+
+Bootstrap `depot_tools` first:
+
+```bash
+cd /path/to/rosetta-android/tools/webrtc-custom
+./bootstrap_depot_tools.sh
+```
+
+Then run:
+
+```bash
+cd /path/to/rosetta-android/tools/webrtc-custom
+./build_custom_webrtc.sh
+```
+
+Optional env vars:
+
+- `WEBRTC_ROOT` — checkout root (default: `$HOME/webrtc_android`)
+- `WEBRTC_SRC` — direct path to `src/`
+- `WEBRTC_BRANCH` — default `branch-heads/6422`
+- `WEBRTC_TAG` — use a specific tag/commit instead of branch
+- `OUT_AAR` — output AAR path (default: `app/libs/libwebrtc-custom.aar`)
+- `SYNC_JOBS` — `gclient sync` jobs (default: `1`, safer for googlesource limits)
+- `SYNC_RETRIES` — sync retry attempts (default: `8`)
+- `SYNC_RETRY_BASE_SEC` — base retry delay in seconds (default: `20`)
+
+## Troubleshooting (HTTP 429 / RESOURCE_EXHAUSTED)
+
+If build fails with:
+
+- `The requested URL returned error: 429`
+- `RESOURCE_EXHAUSTED`
+- `Short term server-time rate limit exceeded`
+
+run with conservative sync settings:
+
+```bash
+SYNC_JOBS=1 SYNC_RETRIES=12 SYNC_RETRY_BASE_SEC=30 ./build_custom_webrtc.sh
+```
+
+The script now retries `fetch`, `git fetch`, and `gclient sync` with backoff.
+
+## Integration in app
+
+`app/build.gradle.kts` already prefers local `app/libs/libwebrtc-custom.aar` if present.
+If file exists, Maven WebRTC dependency is not used.
+
+## Maintenance policy
+
+- Keep patch small and isolated to `audio/channel_send.cc` + `audio/channel_receive.cc`.
+- Pin WebRTC branch/tag for releases.
+- Rebuild AAR on version bumps and verify `e2ee_diag.txt` shows `ad=8` (or non-zero).