diff --git a/.github/workflows/upstream-sync.yml b/.github/workflows/upstream-sync.yml
new file mode 100644
index 0000000000..6d18bfc070
--- /dev/null
+++ b/.github/workflows/upstream-sync.yml
@@ -0,0 +1,418 @@
+name: Upstream Sync Monitor
+
+on:
+  schedule:
+    # Weekdays at 9am UTC
+    - cron: '0 9 * * 1-5'
+  workflow_dispatch:
+    inputs:
+      dry_run:
+        description: 'Skip push and PR creation (validate pipeline only)'
+        type: boolean
+        default: false
+
+jobs:
+  sync:
+    name: Sync upstream rrweb commits
+    runs-on: ubuntu-22.04
+    permissions:
+      contents: write
+      pull-requests: write
+      # Required by anthropics/claude-code-action for OIDC-based GitHub token setup
+      id-token: write
+
+    steps:
+      - name: Checkout amplitude/rrweb
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          token: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Configure git
+        run: |
+          git config user.name "github-actions[bot]"
+          git config user.email "github-actions[bot]@users.noreply.github.com"
+
+      - name: Add upstream remote
+        run: |
+          git remote add upstream https://github.com/rrweb-io/rrweb.git
+          git fetch upstream master --no-tags
+
+      - name: Determine last sync point
+        id: last_sync
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          FALLBACK="3e9e42fdfd6349087d7a0345af1b39dd56528502"
+
+          # Look for the most recent upstream-sync PR (open first, then merged)
+          # PR titles look like: chore: upstream rrweb sync 2026-04-16 (4 commits) [last: abc1234def]
+          LAST_HASH=""
+          for STATE in open closed; do
+            TITLE=$(gh pr list \
+              --label upstream-sync \
+              --state "$STATE" \
+              --limit 1 \
+              --sort updated \
+              --json title \
+              --jq '.[0].title // empty' 2>/dev/null || true)
+
+            if [ -n "$TITLE" ]; then
+              LAST_HASH=$(echo "$TITLE" | sed -n 's/.*\[last: \([0-9a-f]\{1,\}\)\].*/\1/p')
+              if [ -n "$LAST_HASH" ]; then
+                echo "Found last sync hash from $STATE PR: $LAST_HASH"
+                break
+              fi
+            fi
+          done
+
+          if [ -z "$LAST_HASH" ]; then
+            LAST_HASH="$FALLBACK"
+            echo "No previous sync PR found; using fallback: $LAST_HASH"
+          fi
+
+          echo "hash=$LAST_HASH" >> "$GITHUB_OUTPUT"
+
+      - name: Collect new upstream commits
+        id: collect
+        run: |
+          LAST_SYNC="${{ steps.last_sync.outputs.hash }}"
+
+          # Commits in upstream/master after the last sync point.
+          # Do not hand-build JSON from %s/%an: quotes and backslashes in subjects break jq.
+          # One line per commit: fields separated by US (\x1f); git's trailing newline separates records.
+          COMMITS=$(git log ${LAST_SYNC}..upstream/master --format='%H%x1f%h%x1f%s%x1f%an%x1f%ci' | jq -Rs '
+            split("\n")
+            | map(select(length > 0))
+            | map(split("\u001f"))
+            | map({
+                hash: .[0],
+                short: .[1],
+                subject: .[2],
+                author: .[3],
+                date: .[4]
+              })
+          ')
+
+          COUNT=$(echo "$COMMITS" | jq 'length')
+
+          # The newest commit in the range — this becomes the next sync point.
+          # git log outputs newest-first, so .[0] is the tip of upstream/master.
+          LAST_UPSTREAM_HASH=$(echo "$COMMITS" | jq -r '.[0].hash // empty')
+
+          echo "count=$COUNT" >> "$GITHUB_OUTPUT"
+          echo "commits<<EOF" >> "$GITHUB_OUTPUT"
+          echo "$COMMITS" >> "$GITHUB_OUTPUT"
+          echo "EOF" >> "$GITHUB_OUTPUT"
+          echo "last_upstream_hash=$LAST_UPSTREAM_HASH" >> "$GITHUB_OUTPUT"
+
+          echo "Found $COUNT new upstream commits since $LAST_SYNC"
+          echo "Last upstream commit: $LAST_UPSTREAM_HASH"
+
+      - name: Exit early if no new commits
+        if: steps.collect.outputs.count == '0'
+        run: |
+          echo "No new upstream commits. Nothing to do."
+          exit 0
+
+      - name: Create sync branch
+        id: branch
+        run: |
+          BRANCH="upstream-sync/$(date +%Y-%m-%d)"
+          git checkout -b "$BRANCH"
+          echo "branch=$BRANCH" >> "$GITHUB_OUTPUT"
+
+      - name: Analyze commits and cherry-pick with Claude
+        id: claude
+        uses: anthropics/claude-code-action@c7c8889b30499b4e46f4c32b892e43cd364bc2fe
+        with:
+          anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
+          claude_args: '--max-turns 3 --allowedTools Bash,Read,Edit'
+          prompt: |
+            You are helping maintain `amplitude/rrweb`, a fork of `rrweb-io/rrweb`.
+            Amplitude extends rrweb with custom functionality for Session Replay (background
+            capture, privacy masking, performance optimizations).
+
+            Your task is to triage the following upstream commits, cherry-pick the relevant
+            ones onto the current branch, and resolve any conflicts.
+
+            ## Upstream commits to evaluate
+            ```json
+            ${{ steps.collect.outputs.commits }}
+            ```
+
+            ## Instructions
+
+            For each commit, decide if it is RELEVANT or SKIP:
+
+            **Relevant** — cherry-pick it:
+            - Bug fixes in rrweb-snapshot, rrweb, or record packages
+            - Performance improvements
+            - Privacy or masking changes
+            - Browser compatibility fixes
+
+            **Skip** — do not cherry-pick:
+            - CI/CD, tooling, or release process changes
+            - Docs or example-only changes
+            - Features Amplitude has already implemented differently
+            - Changes to packages Amplitude doesn't use
+
+            Also assign a risk level to each relevant commit:
+            - `low` — isolated fix, minimal blast radius
+            - `medium` — touches shared logic, needs testing
+            - `high` — core serialization, replay, or snapshot changes
+
+            ## Cherry-pick process
+
+            For each RELEVANT commit (oldest first):
+            1. Run: `git cherry-pick <hash>`
+            2. If it succeeds, move on.
+            3. If it fails with conflicts:
+               a. Use the Read tool to read each conflicting file (they will have conflict markers).
+               b. Use the Edit tool to resolve the conflicts, preserving Amplitude's custom logic
+                  while incorporating the upstream fix.
+               c. Run: `git add <file>` for each resolved file.
+               d. Run: `git cherry-pick --continue --no-edit`
+               e. If the conflict is too complex to resolve safely, run:
+                  `git cherry-pick --abort`
+                  and mark the commit as `manual-required`.
+
+            ## Output
+
+            After processing all commits, write a JSON summary to `/tmp/sync-summary.json`:
+            ```json
+            {
+              "cherry_picked": [
+                {
+                  "hash": "abc1234",
+                  "subject": "fix: textarea serialization",
+                  "risk": "low",
+                  "summary": "One-line description of what the fix does",
+                  "conflict_resolved": false,
+                  "conflict_resolution_note": null
+                }
+              ],
+              "skipped": [
+                {
+                  "hash": "def5678",
+                  "subject": "chore: update CI config",
+                  "reason": "CI-only change, not relevant to Amplitude fork"
+                }
+              ],
+              "manual_required": [
+                {
+                  "hash": "ghi9012",
+                  "subject": "refactor: reorganize snapshot exports",
+                  "reason": "Structural reorganization conflicts with Amplitude's export overrides"
+                }
+              ]
+            }
+            ```
+
+            For any commit where you resolved a conflict, set `conflict_resolved: true` and
+            populate `conflict_resolution_note` with a brief explanation of what you decided
+            and why.
+
+            If a conflict was resolved but you are uncertain about the decision, prefix the
+            note with `[UNCERTAIN] `.
+
+      - name: Read Claude summary
+        id: summary
+        run: |
+          if [ ! -f /tmp/sync-summary.json ]; then
+            echo "ERROR: Claude did not produce /tmp/sync-summary.json"
+            exit 1
+          fi
+
+          cat /tmp/sync-summary.json
+
+          PICKED=$(jq '.cherry_picked | length' /tmp/sync-summary.json)
+          SKIPPED=$(jq '.skipped | length' /tmp/sync-summary.json)
+          MANUAL=$(jq '.manual_required | length' /tmp/sync-summary.json)
+          HIGH_RISK=$(jq '[.cherry_picked[] | select(.risk == "high")] | length' /tmp/sync-summary.json)
+
+          echo "picked=$PICKED" >> "$GITHUB_OUTPUT"
+          echo "skipped=$SKIPPED" >> "$GITHUB_OUTPUT"
+          echo "manual=$MANUAL" >> "$GITHUB_OUTPUT"
+          echo "high_risk=$HIGH_RISK" >> "$GITHUB_OUTPUT"
+
+      - name: Exit early if nothing was cherry-picked
+        if: steps.summary.outputs.picked == '0'
+        run: |
+          echo "No relevant commits to cherry-pick. Exiting."
+          exit 0
+
+      - name: Build PR body
+        id: pr_body
+        run: |
+          DATE=$(date +%Y-%m-%d)
+          PICKED=${{ steps.summary.outputs.picked }}
+          SUMMARY_JSON=$(cat /tmp/sync-summary.json)
+
+          # Build commit table rows
+          ROWS=$(echo "$SUMMARY_JSON" | jq -r '
+            .cherry_picked[] |
+            "| `\(.hash[0:7])` | \(.subject) | `\(.risk)` | \(if .conflict_resolved then "⚠️ " else "" end)\(.summary) |"
+          ')
+
+          SKIPPED_ROWS=$(echo "$SUMMARY_JSON" | jq -r '
+            .skipped[] |
+            "| `\(.hash[0:7])` | \(.subject) | \(.reason) |"
+          ')
+
+          MANUAL_ROWS=$(echo "$SUMMARY_JSON" | jq -r '
+            .manual_required[] |
+            "| `\(.hash[0:7])` | \(.subject) | \(.reason) |"
+          ')
+
+          CONFLICT_NOTES=$(echo "$SUMMARY_JSON" | jq -r '
+            .cherry_picked[] | select(.conflict_resolved == true) |
+            "- **`\(.hash[0:7])`** \(.subject)\n  \(.conflict_resolution_note)"
+          ')
+
+          LAST_SYNC="${{ steps.last_sync.outputs.hash }}"
+          LAST_UPSTREAM="${{ steps.collect.outputs.last_upstream_hash }}"
+
+          {
+            echo "body<<PRBODY"
+            echo "## Upstream rrweb sync — $DATE"
+            echo ""
+            echo "Automatically cherry-picked **$PICKED** upstream commit(s) from [rrweb-io/rrweb](https://github.com/rrweb-io/rrweb)."
+            echo ""
+            echo "**Sync range:** \`$LAST_SYNC\` → \`$LAST_UPSTREAM\`"
+            echo ""
+            echo "### Cherry-picked commits"
+            echo ""
+            echo "| Commit | Subject | Risk | Notes |"
+            echo "|--------|---------|------|-------|"
+            echo "$ROWS"
+            echo ""
+
+            if [ -n "$CONFLICT_NOTES" ]; then
+              echo "### ⚠️ Auto-resolved conflicts"
+              echo ""
+              echo "The following commits had conflicts that were resolved automatically."
+              echo "Give these extra scrutiny before merging."
+              echo ""
+              echo "$CONFLICT_NOTES"
+              echo ""
+            fi
+
+            MANUAL_COUNT=$(echo "$SUMMARY_JSON" | jq '.manual_required | length')
+            if [ "$MANUAL_COUNT" -gt 0 ]; then
+              echo "### 🔴 Manual cherry-pick required"
+              echo ""
+              echo "These commits could not be resolved automatically:"
+              echo ""
+              echo "| Commit | Subject | Reason |"
+              echo "|--------|---------|--------|"
+              echo "$MANUAL_ROWS"
+              echo ""
+              echo "To apply manually:"
+              echo "\`\`\`bash"
+              echo "git fetch upstream"
+              echo "git cherry-pick <commit-hash>"
+              echo "# Resolve conflicts in your editor"
+              echo "git add ."
+              echo "git cherry-pick --continue"
+              echo "\`\`\`"
+              echo ""
+            fi
+
+            SKIPPED_COUNT=$(echo "$SUMMARY_JSON" | jq '.skipped | length')
+            if [ "$SKIPPED_COUNT" -gt 0 ]; then
+              echo "<details>"
+              echo "<summary>Skipped commits ($SKIPPED_COUNT)</summary>"
+              echo ""
+              echo "| Commit | Subject | Reason |"
+              echo "|--------|---------|--------|"
+              echo "$SKIPPED_ROWS"
+              echo ""
+              echo "</details>"
+            fi
+
+            echo ""
+            echo "---"
+            echo "_Generated by [Upstream Sync Monitor](/.github/workflows/upstream-sync.yml)_"
+            echo "PRBODY"
+          } >> "$GITHUB_OUTPUT"
+
+      - name: Push branch
+        if: inputs.dry_run != true
+        run: git push origin ${{ steps.branch.outputs.branch }}
+
+      - name: Create draft PR
+        id: pr
+        if: inputs.dry_run != true
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          PICKED=${{ steps.summary.outputs.picked }}
+          DATE=$(date +%Y-%m-%d)
+          LAST_HASH="${{ steps.collect.outputs.last_upstream_hash }}"
+          TITLE="chore: upstream rrweb sync $DATE ($PICKED commit(s)) [last: $LAST_HASH]"
+
+          PR_URL=$(gh pr create \
+            --title "$TITLE" \
+            --body "${{ steps.pr_body.outputs.body }}" \
+            --base master \
+            --head ${{ steps.branch.outputs.branch }} \
+            --draft \
+            --label upstream-sync)
+
+          echo "pr_url=$PR_URL" >> "$GITHUB_OUTPUT"
+          echo "Created PR: $PR_URL"
+
+      - name: Post Slack digest
+        if: inputs.dry_run != true
+        env:
+          SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK_URL }}
+        run: |
+          PICKED=${{ steps.summary.outputs.picked }}
+          SKIPPED=${{ steps.summary.outputs.skipped }}
+          MANUAL=${{ steps.summary.outputs.manual }}
+          HIGH_RISK=${{ steps.summary.outputs.high_risk }}
+          PR_URL="${{ steps.pr.outputs.pr_url }}"
+          DATE=$(date +%Y-%m-%d)
+
+          HIGH_RISK_NOTE=""
+          if [ "$HIGH_RISK" -gt 0 ]; then
+            HIGH_RISK_NOTE="\n:warning: *$HIGH_RISK high-risk commit(s) included — review carefully.*"
+          fi
+
+          MANUAL_NOTE=""
+          if [ "$MANUAL" -gt 0 ]; then
+            MANUAL_NOTE="\n:red_circle: *$MANUAL commit(s) need manual cherry-pick.*"
+          fi
+
+          PAYLOAD=$(jq -n \
+            --arg date "$DATE" \
+            --arg picked "$PICKED" \
+            --arg skipped "$SKIPPED" \
+            --arg high_risk_note "$HIGH_RISK_NOTE" \
+            --arg manual_note "$MANUAL_NOTE" \
+            --arg pr_url "$PR_URL" \
+            '{
+              text: ("*Upstream rrweb sync — " + $date + "*\n" +
+                     "• " + $picked + " commit(s) cherry-picked\n" +
+                     "• " + $skipped + " commit(s) skipped\n" +
+                     $high_risk_note +
+                     $manual_note + "\n" +
+                     "<" + $pr_url + "|View draft PR>")
+            }')
+
+          curl -s -X POST -H 'Content-type: application/json' \
+            --data "$PAYLOAD" \
+            "$SLACK_WEBHOOK_URL"
+
+      - name: Dry run summary
+        if: inputs.dry_run == true
+        run: |
+          echo "=== DRY RUN COMPLETE ==="
+          echo "Branch: ${{ steps.branch.outputs.branch }}"
+          echo "Commits cherry-picked: ${{ steps.summary.outputs.picked }}"
+          echo "Commits skipped: ${{ steps.summary.outputs.skipped }}"
+          echo "Manual required: ${{ steps.summary.outputs.manual }}"
+          echo ""
+          echo "--- PR body preview ---"
+          echo "${{ steps.pr_body.outputs.body }}"
diff --git a/.gitignore b/.gitignore
index 7384b1a8ab..6b80b5f937 100644
--- a/.gitignore
+++ b/.gitignore
@@ -35,3 +35,6 @@ dist
 # for vite
 vite.config.js.timestamp-*
 vite.config.ts.timestamp-*
+
+# upstream sync test output
+tools/upstream-sync-output/
diff --git a/tools/test-upstream-sync.sh b/tools/test-upstream-sync.sh
new file mode 100755
index 0000000000..ead3c5f7ab
--- /dev/null
+++ b/tools/test-upstream-sync.sh
@@ -0,0 +1,429 @@
+#!/usr/bin/env bash
+#
+# Local end-to-end test for the upstream sync workflow.
+# Mirrors .github/workflows/upstream-sync.yml but runs entirely locally
+# using the Claude CLI instead of claude-code-action.
+#
+# Usage:
+#   bash tools/test-upstream-sync.sh          # test with 5 oldest commits
+#   bash tools/test-upstream-sync.sh 1        # test with 1 oldest commit
+#   bash tools/test-upstream-sync.sh --all    # test with all commits
+#
+# Prerequisites:
+#   - Claude CLI installed (claude)
+#   - gh CLI authenticated
+#   - jq installed
+#   - upstream remote configured (script will add it if missing)
+
+set -euo pipefail
+
+REPO_ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+cd "$REPO_ROOT"
+
+MAX_COMMITS=5
+if [ "${1:-}" = "--all" ]; then
+  MAX_COMMITS=0
+elif [ -n "${1:-}" ] && [[ "${1:-}" =~ ^[0-9]+$ ]]; then
+  MAX_COMMITS="$1"
+fi
+
+ORIGINAL_BRANCH=$(git branch --show-current || git rev-parse --short HEAD)
+TEST_BRANCH="upstream-sync/test-$(date +%s)"
+OUTPUT_DIR="$REPO_ROOT/tools/upstream-sync-output"
+mkdir -p "$OUTPUT_DIR"
+LOG_FILE="$OUTPUT_DIR/test-run.log"
+SUMMARY_FILE="$OUTPUT_DIR/sync-summary.json"
+PROMPT_FILE="$OUTPUT_DIR/prompt.txt"
+PR_TITLE_FILE="$OUTPUT_DIR/pr-title.txt"
+PR_BODY_FILE="$OUTPUT_DIR/pr-body.md"
+
+# Log all output to file AND terminal
+exec > >(tee -a "$LOG_FILE") 2>&1
+echo "Test started at $(date)"
+
+cleanup() {
+  echo ""
+  echo "=== Cleanup ==="
+  git cherry-pick --abort 2>/dev/null || true
+  git checkout "$ORIGINAL_BRANCH" 2>/dev/null || true
+  git branch -D "$TEST_BRANCH" 2>/dev/null || true
+  rm -f "$PROMPT_FILE"
+  echo "Restored branch: $ORIGINAL_BRANCH"
+  echo "Test branch $TEST_BRANCH deleted."
+  echo "Output files preserved in: $OUTPUT_DIR"
+}
+trap cleanup EXIT
+
+header() {
+  echo ""
+  echo "========================================"
+  echo "  $1"
+  echo "========================================"
+}
+
+# ── Step 1: Prerequisites ────────────────────────────────────────────
+
+header "Step 1: Check prerequisites"
+
+for cmd in claude gh jq git; do
+  if ! command -v "$cmd" &>/dev/null; then
+    echo "ERROR: $cmd is not installed or not in PATH."
+    exit 1
+  fi
+done
+echo "  All tools available."
+
+# ── Step 2: Fetch upstream ───────────────────────────────────────────
+
+header "Step 2: Fetch upstream master"
+
+if ! git remote get-url upstream &>/dev/null; then
+  echo "  Adding upstream remote..."
+  git remote add upstream https://github.com/rrweb-io/rrweb.git
+fi
+git fetch upstream master --no-tags
+echo "  Done."
+
+# ── Step 3: Determine last sync point ────────────────────────────────
+
+header "Step 3: Determine last sync point"
+
+FALLBACK="3e9e42fdfd6349087d7a0345af1b39dd56528502"
+LAST_SYNC=""
+
+for STATE in open closed; do
+  TITLE=$(gh pr list \
+    --label upstream-sync \
+    --state "$STATE" \
+    --limit 1 \
+    --sort updated \
+    --json title \
+    --jq '.[0].title // empty' 2>/dev/null || true)
+
+  echo "  Checked $STATE PRs — title: '${TITLE:-<none>}'"
+
+  if [ -n "$TITLE" ]; then
+    LAST_SYNC=$(echo "$TITLE" | sed -n 's/.*\[last: \([0-9a-f]\{1,\}\)\].*/\1/p')
+    if [ -n "$LAST_SYNC" ]; then
+      echo "  Found last sync hash from $STATE PR: $LAST_SYNC"
+      break
+    fi
+  fi
+done
+
+if [ -z "$LAST_SYNC" ]; then
+  LAST_SYNC="$FALLBACK"
+  echo "  No previous sync PR found; using fallback: $LAST_SYNC"
+fi
+
+# ── Step 4: Collect upstream commits ─────────────────────────────────
+
+header "Step 4: Collect upstream commits"
+
+ALL_COMMITS=$(git log "${LAST_SYNC}..upstream/master" \
+  --format='%H%x1f%h%x1f%s%x1f%an%x1f%ci' | jq -Rs '
+  split("\n")
+  | map(select(length > 0))
+  | map(split("\u001f"))
+  | map({
+      hash: .[0],
+      short: .[1],
+      subject: .[2],
+      author: .[3],
+      date: .[4]
+    })
+')
+
+TOTAL_COUNT=$(echo "$ALL_COMMITS" | jq 'length')
+LAST_UPSTREAM_HASH=$(echo "$ALL_COMMITS" | jq -r '.[0].hash // empty')
+
+echo "  Found $TOTAL_COUNT total commits since $LAST_SYNC"
+echo "  Newest upstream commit: $LAST_UPSTREAM_HASH"
+
+if [ "$TOTAL_COUNT" -eq 0 ]; then
+  echo "  No new upstream commits. Nothing to test."
+  exit 0
+fi
+
+if [ "$MAX_COMMITS" -gt 0 ] && [ "$TOTAL_COUNT" -gt "$MAX_COMMITS" ]; then
+  # Take the N oldest commits (they appear last in git log's newest-first output)
+  COMMITS=$(echo "$ALL_COMMITS" | jq ".[- $MAX_COMMITS:]")
+  SUBSET_COUNT=$(echo "$COMMITS" | jq 'length')
+  # The "last upstream hash" for the subset is the newest in the subset (first element)
+  LAST_UPSTREAM_HASH=$(echo "$COMMITS" | jq -r '.[0].hash // empty')
+  echo "  Scoped to $SUBSET_COUNT oldest commits for testing (use --all for full run)."
+else
+  COMMITS="$ALL_COMMITS"
+  SUBSET_COUNT="$TOTAL_COUNT"
+fi
+
+echo ""
+echo "  Commits to process:"
+echo "$COMMITS" | jq -r '.[] | "    \(.short) — \(.subject)"'
+
+# ── Step 5: Create test branch ───────────────────────────────────────
+
+header "Step 5: Create test branch"
+
+git checkout -b "$TEST_BRANCH" origin/master
+git config user.name "test-upstream-sync"
+git config user.email "test@localhost"
+echo "  Branch: $TEST_BRANCH"
+
+# ── Step 6: Invoke Claude CLI ────────────────────────────────────────
+
+header "Step 6: Invoke Claude CLI for cherry-pick + triage"
+
+rm -f "$SUMMARY_FILE"
+
+cat > "$PROMPT_FILE" <<PROMPT_EOF
+You are helping maintain \`amplitude/rrweb\`, a fork of \`rrweb-io/rrweb\`.
+Amplitude extends rrweb with custom functionality for Session Replay (background
+capture, privacy masking, performance optimizations).
+
+Your task is to triage the following upstream commits, cherry-pick the relevant
+ones onto the current branch, and resolve any conflicts.
+
+## Upstream commits to evaluate
+\`\`\`json
+$COMMITS
+\`\`\`
+
+## Instructions
+
+For each commit, decide if it is RELEVANT or SKIP:
+
+**Relevant** — cherry-pick it:
+- Bug fixes in rrweb-snapshot, rrweb, or record packages
+- Performance improvements
+- Privacy or masking changes
+- Browser compatibility fixes
+
+**Skip** — do not cherry-pick:
+- CI/CD, tooling, or release process changes
+- Docs or example-only changes
+- Features Amplitude has already implemented differently
+- Changes to packages Amplitude doesn't use
+
+Also assign a risk level to each relevant commit:
+- \`low\` — isolated fix, minimal blast radius
+- \`medium\` — touches shared logic, needs testing
+- \`high\` — core serialization, replay, or snapshot changes
+
+## Cherry-pick process
+
+For each RELEVANT commit (oldest first):
+1. Run: \`git cherry-pick <hash>\`
+2. If it succeeds, move on.
+3. If it fails with conflicts:
+   a. Use the Read tool to read each conflicting file (they will have conflict markers).
+   b. Use the Edit tool to resolve the conflicts, preserving Amplitude's custom logic
+      while incorporating the upstream fix.
+   c. Run: \`git add <file>\` for each resolved file.
+   d. Run: \`git cherry-pick --continue --no-edit\`
+   e. If the conflict is too complex to resolve safely, run:
+      \`git cherry-pick --abort\`
+      and mark the commit as \`manual-required\`.
+
+## Output
+
+After processing all commits, write a JSON summary to \`$SUMMARY_FILE\`:
+\`\`\`json
+{
+  "cherry_picked": [
+    {
+      "hash": "abc1234",
+      "subject": "fix: textarea serialization",
+      "risk": "low",
+      "summary": "One-line description of what the fix does",
+      "conflict_resolved": false,
+      "conflict_resolution_note": null
+    }
+  ],
+  "skipped": [
+    {
+      "hash": "def5678",
+      "subject": "chore: update CI config",
+      "reason": "CI-only change, not relevant to Amplitude fork"
+    }
+  ],
+  "manual_required": [
+    {
+      "hash": "ghi9012",
+      "subject": "refactor: reorganize snapshot exports",
+      "reason": "Structural reorganization conflicts with Amplitude's export overrides"
+    }
+  ]
+}
+\`\`\`
+
+For any commit where you resolved a conflict, set \`conflict_resolved: true\` and
+populate \`conflict_resolution_note\` with a brief explanation of what you decided
+and why.
+
+If a conflict was resolved but you are uncertain about the decision, prefix the
+note with \`[UNCERTAIN] \`.
+PROMPT_EOF
+
+echo "  Prompt written to $PROMPT_FILE ($(wc -l < "$PROMPT_FILE") lines)"
+echo "  Running Claude CLI... (this may take a minute)"
+echo ""
+
+claude -p "$(cat "$PROMPT_FILE")" \
+  --allowedTools Bash,Read,Edit
+
+# ── Step 7: Validate summary ────────────────────────────────────────
+
+header "Step 7: Validate sync summary"
+
+if [ ! -f "$SUMMARY_FILE" ]; then
+  echo "  ERROR: Claude did not produce $SUMMARY_FILE"
+  echo "  The Claude step may have failed. Check output above."
+  exit 1
+fi
+
+echo "  Summary file exists."
+echo ""
+cat "$SUMMARY_FILE"
+echo ""
+
+PICKED=$(jq '.cherry_picked | length' "$SUMMARY_FILE")
+SKIPPED=$(jq '.skipped | length' "$SUMMARY_FILE")
+MANUAL=$(jq '.manual_required | length' "$SUMMARY_FILE")
+HIGH_RISK=$(jq '[.cherry_picked[] | select(.risk == "high")] | length' "$SUMMARY_FILE")
+
+echo "  Cherry-picked: $PICKED"
+echo "  Skipped:       $SKIPPED"
+echo "  Manual:        $MANUAL"
+echo "  High-risk:     $HIGH_RISK"
+
+# Validate schema
+for field in cherry_picked skipped manual_required; do
+  if ! echo "$(cat "$SUMMARY_FILE")" | jq -e ".$field" >/dev/null 2>&1; then
+    echo "  ERROR: Missing required field: $field"
+    exit 1
+  fi
+done
+echo "  Schema valid."
+
+# ── Step 8: Build PR title and body ─────────────────────────────────
+
+header "Step 8: Build PR title and body"
+
+DATE=$(date +%Y-%m-%d)
+TITLE="chore: upstream rrweb sync $DATE ($PICKED commit(s)) [last: $LAST_UPSTREAM_HASH]"
+
+echo "$TITLE" > "$PR_TITLE_FILE"
+echo "  PR title written to: $PR_TITLE_FILE"
+
+# Verify round-trip
+PARSED_HASH=$(echo "$TITLE" | sed -n 's/.*\[last: \([0-9a-f]\{1,\}\)\].*/\1/p')
+if [ "$PARSED_HASH" = "$LAST_UPSTREAM_HASH" ]; then
+  echo "  Round-trip parse: PASS"
+else
+  echo "  Round-trip parse: FAIL ($PARSED_HASH != $LAST_UPSTREAM_HASH)"
+fi
+
+SUMMARY_JSON=$(cat "$SUMMARY_FILE")
+
+ROWS=$(echo "$SUMMARY_JSON" | jq -r '
+  .cherry_picked[] |
+  "| `\(.hash[0:7])` | \(.subject) | `\(.risk)` | \(if .conflict_resolved then "⚠️ " else "" end)\(.summary) |"
+')
+
+SKIPPED_ROWS=$(echo "$SUMMARY_JSON" | jq -r '
+  .skipped[] |
+  "| `\(.hash[0:7])` | \(.subject) | \(.reason) |"
+')
+
+MANUAL_ROWS=$(echo "$SUMMARY_JSON" | jq -r '
+  .manual_required[] |
+  "| `\(.hash[0:7])` | \(.subject) | \(.reason) |"
+')
+
+CONFLICT_NOTES=$(echo "$SUMMARY_JSON" | jq -r '
+  .cherry_picked[] | select(.conflict_resolved == true) |
+  "- **`\(.hash[0:7])`** \(.subject)\n  \(.conflict_resolution_note)"
+')
+
+{
+  echo "## Upstream rrweb sync — $DATE"
+  echo ""
+  echo "Automatically cherry-picked **$PICKED** upstream commit(s) from [rrweb-io/rrweb](https://github.com/rrweb-io/rrweb)."
+  echo ""
+  echo "**Sync range:** \`$LAST_SYNC\` → \`$LAST_UPSTREAM_HASH\`"
+  echo ""
+  echo "### Cherry-picked commits"
+  echo ""
+  echo "| Commit | Subject | Risk | Notes |"
+  echo "|--------|---------|------|-------|"
+  echo "$ROWS"
+  echo ""
+
+  if [ -n "$CONFLICT_NOTES" ]; then
+    echo "### ⚠️ Auto-resolved conflicts"
+    echo ""
+    echo "The following commits had conflicts that were resolved automatically."
+    echo "Give these extra scrutiny before merging."
+    echo ""
+    echo -e "$CONFLICT_NOTES"
+    echo ""
+  fi
+
+  MANUAL_COUNT=$(echo "$SUMMARY_JSON" | jq '.manual_required | length')
+  if [ "$MANUAL_COUNT" -gt 0 ]; then
+    echo "### Manual cherry-pick required"
+    echo ""
+    echo "| Commit | Subject | Reason |"
+    echo "|--------|---------|--------|"
+    echo "$MANUAL_ROWS"
+    echo ""
+  fi
+
+  SKIPPED_COUNT=$(echo "$SUMMARY_JSON" | jq '.skipped | length')
+  if [ "$SKIPPED_COUNT" -gt 0 ]; then
+    echo "<details>"
+    echo "<summary>Skipped commits ($SKIPPED_COUNT)</summary>"
+    echo ""
+    echo "| Commit | Subject | Reason |"
+    echo "|--------|---------|--------|"
+    echo "$SKIPPED_ROWS"
+    echo ""
+    echo "</details>"
+  fi
+
+  echo ""
+  echo "---"
+  echo "_Generated by [Upstream Sync Monitor](/.github/workflows/upstream-sync.yml)_"
+} > "$PR_BODY_FILE"
+
+echo "  PR body written to:  $PR_BODY_FILE"
+
+# ── Step 9: Git log of cherry-picked commits on the branch ──────────
+
+header "Step 9: Verify git history"
+
+echo "  Commits on test branch (beyond origin/master):"
+git log origin/master..HEAD --oneline | while read -r line; do
+  echo "    $line"
+done
+
+# ── Done ─────────────────────────────────────────────────────────────
+
+header "Test complete"
+
+echo "  Results:"
+echo "    Commits evaluated:  $SUBSET_COUNT"
+echo "    Cherry-picked:      $PICKED"
+echo "    Skipped:            $SKIPPED"
+echo "    Manual required:    $MANUAL"
+echo "    High-risk:          $HIGH_RISK"
+echo "    Last upstream hash: $LAST_UPSTREAM_HASH"
+echo "    Round-trip parse:   $([ "$PARSED_HASH" = "$LAST_UPSTREAM_HASH" ] && echo PASS || echo FAIL)"
+echo ""
+echo "  Output files:"
+echo "    $SUMMARY_FILE"
+echo "    $PR_TITLE_FILE"
+echo "    $PR_BODY_FILE"
+echo ""
+echo "  Cleanup will run automatically..."