diff --git a/CHANGELOG.md b/CHANGELOG.md
index 06e821a..7ef22a3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,18 @@ this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ## [Unreleased]
 
+## [3.16.0] - 2026-07-05
+
+### Added
+
+- **The scaffolded PR workflow prunes its own report branch, out of the box.**
+  `styleproof-init`'s `.github/workflows/styleproof.yml` now also runs on
+  `pull_request: closed`: when a PR closes, a `prune` job removes that PR's `pr-<n>/`
+  folder from the report branch (`styleproof-reports`), so the branch no longer grows
+  without bound as PRs come and go — no adopter has to remember to garbage-collect it.
+  The report job is unchanged, only guarded to skip the close event. Covered by the
+  `styleproof-init` workflow test.
+
 ## [3.15.0] - 2026-07-05
 
 ### Changed
diff --git a/action.yml b/action.yml
index f30bf29..c45a491 100644
--- a/action.yml
+++ b/action.yml
@@ -16,7 +16,7 @@ inputs:
     description: 'Directory with restored or freshly captured PR-head maps to compare (.json.gz + .png).'
     required: true
   report-branch:
-    description: 'Orphan branch that stores reports (created on first run). One pr-<n>/ folder per PR; never pruned.'
+    description: 'Orphan branch that stores reports (created on first run). One pr-<n>/ folder per PR; the styleproof-init workflow prunes each on PR close.'
     default: 'styleproof-reports'
   github-token:
     description: 'Token used to push the report branch and post the PR comment.'
diff --git a/bin/styleproof-init.mjs b/bin/styleproof-init.mjs
index e2fa311..98a6f91 100755
--- a/bin/styleproof-init.mjs
+++ b/bin/styleproof-init.mjs
@@ -345,7 +345,9 @@ const CI_WORKFLOW = `name: StyleProof
 #   report without a browser;
 # - on cache miss, CI recaptures both sides in one pinned environment so the
 #   comparison stays valid.
-on: pull_request
+on:
+  pull_request:
+    types: [opened, synchronize, reopened, closed]
 
 permissions:
   contents: write
@@ -355,6 +357,8 @@ permissions:
 
 jobs:
   styleproof:
+    # Report on open/update; the prune job below handles close.
+    if: github.event.action != 'closed'
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
@@ -408,6 +412,41 @@ ${PM.setup}
           baseline-dir: __stylemaps__/base
           fresh-dir: __stylemaps__/head
           require-approval: true
+
+  prune:
+    # PR closed: drop its pr-<n>/ folder from the report branch so the branch
+    # never grows without bound. Keep BRANCH in sync with the report-branch
+    # input above (default: styleproof-reports).
+    if: github.event.action == 'closed'
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    steps:
+      - name: Prune this PR's report folder
+        shell: bash
+        env:
+          GH_TOKEN: \${{ github.token }}
+          BRANCH: styleproof-reports
+          PR: \${{ github.event.pull_request.number }}
+        run: |
+          set -euo pipefail
+          REMOTE="https://x-access-token:\${GH_TOKEN}@github.com/\${{ github.repository }}.git"
+          if ! git ls-remote --exit-code "$REMOTE" "refs/heads/$BRANCH" >/dev/null 2>&1; then
+            echo "No $BRANCH branch yet — nothing to prune."; exit 0
+          fi
+          TMP="$(mktemp -d)"
+          # Blobless clone keeps this fast; a very large report branch may prefer
+          # a --no-checkout plumbing rewrite instead.
+          git clone --filter=blob:none --single-branch --branch "$BRANCH" "$REMOTE" "$TMP"
+          cd "$TMP"
+          if [ ! -d "pr-$PR" ]; then
+            echo "No pr-$PR/ folder — nothing to prune."; exit 0
+          fi
+          git config user.name  "github-actions[bot]"
+          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
+          git rm -r --quiet "pr-$PR"
+          git commit -m "chore(styleproof): prune report for closed PR #$PR"
+          git push origin "$BRANCH"
 `;
 
 function writeFileSafe(file, contents, { force: f } = {}) {
diff --git a/package.json b/package.json
index c64a884..b03b364 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "styleproof",
-  "version": "3.15.0",
+  "version": "3.16.0",
   "description": "Catch every CSS change before it ships — review PRs and certify refactors by the browser's computed styles, not pixels. Works with any styling system.",
   "keywords": [
     "playwright",
diff --git a/test/init.test.mjs b/test/init.test.mjs
index 649e05f..7929344 100644
--- a/test/init.test.mjs
+++ b/test/init.test.mjs
@@ -132,6 +132,13 @@ for (const manager of [
       const workflow = readFile(root, '.github/workflows/styleproof.yml');
       for (const pattern of manager.workflow) assert.match(workflow, pattern);
       for (const pattern of manager.absent ?? []) assert.doesNotMatch(workflow, pattern);
+
+      // Report branch self-prunes on PR close (out of the box) — manager-independent.
+      assert.match(workflow, /types: \[opened, synchronize, reopened, closed\]/);
+      assert.match(workflow, /if: github\.event\.action != 'closed'/); // report skips close
+      assert.match(workflow, /^\s{2}prune:/m);
+      assert.match(workflow, /if: github\.event\.action == 'closed'/);
+      assert.match(workflow, /git rm -r --quiet "pr-\$PR"/);
     } finally {
       rmTmp(root);
     }