chore: Update btrace skill with release builds and sound cues

Use release builds for accurate profiling, add ProGuard keep rules
for btrace and Sentry class names, increase trace duration to 30s,
and play a Ping sound synced to the actual trace start.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: romtsn

.claude/skills/btrace-perfetto/SKILL.md

@@ -28,7 +28,7 @@ Before starting, verify:
 |----------|---------|-------------|
 | branch1 | current branch | First branch to trace |
 | branch2 | `main` | Second branch to compare against |
-| duration | `20` | Trace duration in seconds |
+| duration | `30` | Trace duration in seconds |
 | sql-query | see below | SQL query to prefill in Perfetto UI |
 
 If no arguments are provided, ask the user what they want to trace and which branches to compare. If only one branch is given, capture only that branch (no comparison).
@@ -73,10 +73,23 @@ protected void attachBaseContext(Context base) {
 
 **Important**: The package is `com.bytedance.rheatrace`, not `com.bytedance.btrace`.
 
+### 2d: Add ProGuard keep rule for release builds
+
+In `sentry-samples/sentry-samples-android/proguard-rules.pro`, add:
+
+```
+-keep class com.bytedance.rheatrace.** { *; }
+-keepnames class io.sentry.** { *; }
+```
+
+The first rule prevents R8 from stripping btrace's HTTP server classes (fails with `SocketException` otherwise). The second preserves Sentry class and method names so they appear readable in the Perfetto trace instead of obfuscated single-letter names.
+
 ## Step 3: Build and Install
 
+Always use release builds for tracing — debug builds have StrictMode, debuggable overhead, and no R8 optimizations, which skew results.
+
 ```bash
-./gradlew :sentry-samples:sentry-samples-android:installDebug
+./gradlew :sentry-samples:sentry-samples-android:installRelease
 ```
 
 ## Step 4: Capture Trace
@@ -95,7 +108,20 @@ adb shell am start -n io.sentry.samples.android/.MainActivity
 
 The app must be started AFTER `debug.rhea3.startWhenAppLaunch` is set, otherwise the trace server won't initialize.
 
-### 4b: Tell the user to interact with the app, then capture
+### 4b: Play a sound to signal the user, then capture
+
+Play a sound when tracing actually starts so the user knows to begin interacting. Pipe btrace output through a loop that triggers the sound on the "start tracing" line:
+
+```bash
+java -jar tools/btrace/rhea-trace-shell.jar ... 2>&1 | while IFS= read -r line; do
+  echo "$line"
+  if [[ "$line" == *"start tracing"* ]]; then
+    afplay -v 1.5 /System/Library/Sounds/Ping.aiff &
+  fi
+done
+```
+
+This ensures the sound is synchronized with the actual trace start, not an estimated delay.
 
 ```bash
 java -jar tools/btrace/rhea-trace-shell.jar \
@@ -116,11 +142,12 @@ When capturing a second branch:
    ```bash
    git stash push -m "btrace integration" -- \
      sentry-samples/sentry-samples-android/build.gradle.kts \
-     sentry-samples/sentry-samples-android/src/main/java/io/sentry/samples/android/MyApplication.java
+     sentry-samples/sentry-samples-android/src/main/java/io/sentry/samples/android/MyApplication.java \
+     sentry-samples/sentry-samples-android/proguard-rules.pro
    ```
 2. Checkout the other branch
 3. Pop the stash: `git stash pop`
-4. Rebuild and install: `./gradlew :sentry-samples:sentry-samples-android:installDebug`
+4. Rebuild and install: `./gradlew :sentry-samples:sentry-samples-android:installRelease`
 5. Repeat steps 4a and 4b with a different output filename
 6. Switch back to the original branch and restore files
 
@@ -172,3 +199,4 @@ After tracing is complete, remind the user that the btrace integration changes t
 | `wait for trace ready timeout` on download | Set `debug.rhea3.startWhenAppLaunch=1` BEFORE launching the app, and use `-waitTraceTimeout 60` |
 | Empty jar file (0 bytes) | Download from Maven Central (`repo1.maven.org`), not `oss.sonatype.org` |
 | `FileNotFoundException` on sampling download | App was already running when properties were set; force-stop and relaunch |
+| `SocketException: Unexpected end of file` in release builds | R8 stripped btrace classes; add `-keep class com.bytedance.rheatrace.** { *; }` to proguard-rules.pro |