chore: Add scheduled job to check for retrace spec changes (#90)

## Summary
- Adds a daily GHA workflow that checks if the upstream R8 retrace
mapping spec (`doc/retrace.md`) has been updated
- Mirrors the approach from
[sentry-java#5157](getsentry/sentry-java#5157)
for the tombstone proto schema
- Allows us to react to retrace format changes promptly

## Test plan
- [x] Verified the script runs successfully locally and reports "Spec is
up to date"

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

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: romtsn

.github/workflows/check-retrace-spec.yml

@@ -0,0 +1,16 @@
+name: Check Retrace Spec
+
+on:
+  schedule:
+    - cron: '0 9 * * *'
+  workflow_dispatch:
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Check for newer retrace spec
+        run: ./scripts/check-retrace-spec.sh

.github/workflows/ci.yml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - run: rustup toolchain install stable --profile minimal --component rustfmt --component clippy --no-self-update
       - uses: Swatinem/rust-cache@v2
@@ -35,7 +35,7 @@ jobs:
     runs-on: ${{ matrix.os }}
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - run: rustup toolchain install stable --profile minimal --no-self-update
       - uses: Swatinem/rust-cache@v2
@@ -48,7 +48,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - run: rustup toolchain install stable --profile minimal --component llvm-tools-preview --no-self-update
       - uses: Swatinem/rust-cache@v2

.github/workflows/release.yml

@@ -22,7 +22,7 @@ jobs:
         with:
           app-id: ${{ vars.SENTRY_RELEASE_BOT_CLIENT_ID }}
           private-key: ${{ secrets.SENTRY_RELEASE_BOT_PRIVATE_KEY }}
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           # Fetch all commits so we can determine previous version
           fetch-depth: 0

.github/workflows/weekly.yml

@@ -18,7 +18,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - run: |
           rustup toolchain install ${{ matrix.rust }} --profile minimal --component clippy --no-self-update

scripts/check-retrace-spec.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+TRACKED_COMMIT="e212426be84283876b6bb832630c0de25a2a7bc5"
+
+# tail -n +2 to remove the magic anti-XSSI prefix from the Gitiles JSON response
+LATEST_COMMIT=$(curl -sf \
+  'https://r8.googlesource.com/r8/+log/refs/heads/main/doc/retrace.md?format=JSON' \
+  | tail -n +2 \
+  | jq -r '.log[0].commit')
+
+if [ -z "$LATEST_COMMIT" ] || [ "$LATEST_COMMIT" = "null" ]; then
+  echo "ERROR: Failed to fetch latest commit from Gitiles" >&2
+  exit 1
+fi
+
+echo "Tracked commit: $TRACKED_COMMIT"
+echo "Latest commit:  $LATEST_COMMIT"
+
+if [ "$LATEST_COMMIT" != "$TRACKED_COMMIT" ]; then
+  echo "Spec has been updated! Latest: https://r8.googlesource.com/r8/+/${LATEST_COMMIT}/doc/retrace.md"
+  exit 1
+fi
+
+echo "Spec is up to date."