diff --git a/.github/workflows/build-frontend.yml b/.github/workflows/build-frontend.yml
index b8170100..317cfc85 100644
--- a/.github/workflows/build-frontend.yml
+++ b/.github/workflows/build-frontend.yml
@@ -2,6 +2,12 @@ name: Build Frontend
 
 on:
   workflow_call:
+    inputs:
+      ref:
+        description: 'Git ref to checkout (branch, tag, or SHA). Defaults to github.ref_name.'
+        type: string
+        required: false
+        default: ''
 
 jobs:
   build-frontend:
@@ -22,7 +28,7 @@ jobs:
         timeout-minutes: 1
         with:
           repository: ${{ github.repository }}
-          ref: ${{ github.ref_name }}
+          ref: ${{ inputs.ref || github.ref_name }}
           token: ${{ env.REPO_READONLY_PAT }}
 
       - name: Setup Node.js
diff --git a/.github/workflows/build-windows-installer.yml b/.github/workflows/build-windows-installer.yml
index 69d3a513..61eea5c0 100644
--- a/.github/workflows/build-windows-installer.yml
+++ b/.github/workflows/build-windows-installer.yml
@@ -8,6 +8,11 @@ on:
         type: string
         required: false
         default: ''
+      ref:
+        description: 'Git ref to checkout (branch, tag, or SHA). Defaults to github.ref_name.'
+        type: string
+        required: false
+        default: ''
 
 jobs:
   build-windows-installer:
@@ -58,7 +63,7 @@ jobs:
         uses: actions/checkout@v4
         with:
           repository: ${{ env.githubRepository }}
-          ref: ${{ github.ref_name }}
+          ref: ${{ inputs.ref || github.ref_name }}
           token: ${{ env.REPO_READONLY_PAT }}
 
       - name: Download frontend artifact
diff --git a/.github/workflows/pr-build.yml b/.github/workflows/pr-build.yml
new file mode 100644
index 00000000..6b2c7272
--- /dev/null
+++ b/.github/workflows/pr-build.yml
@@ -0,0 +1,181 @@
+name: PR Build (Comment Triggered)
+
+on:
+  issue_comment:
+    types: [created]
+
+concurrency:
+  group: pr-build-${{ github.event.issue.number }}
+  cancel-in-progress: true
+
+permissions:
+  issues: write
+  pull-requests: read
+  actions: read
+
+jobs:
+  validate:
+    runs-on: ubuntu-latest
+    if: github.event.issue.pull_request != null
+    outputs:
+      build_windows: ${{ steps.parse.outputs.build_windows }}
+      pr_ref: ${{ steps.parse.outputs.pr_ref }}
+      pr_sha: ${{ steps.parse.outputs.pr_sha }}
+      pr_number: ${{ steps.parse.outputs.pr_number }}
+
+    steps:
+      - name: React to comment
+        uses: actions/github-script@v7
+        with:
+          script: |
+            await github.rest.reactions.createForIssueComment({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              comment_id: context.payload.comment.id,
+              content: 'eyes'
+            });
+
+      - name: Parse command and check permissions
+        id: parse
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const comment = context.payload.comment.body.trim();
+
+            // Parse supported commands
+            const commands = {
+              '/build-windows': 'build_windows'
+            };
+
+            const command = commands[comment];
+            if (!command) {
+              console.log(`Comment "${comment}" is not a recognized build command, skipping.`);
+              core.setOutput('build_windows', 'false');
+              return;
+            }
+
+            // Fetch PR details
+            const pr = await github.rest.pulls.get({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              pull_number: context.issue.number
+            });
+
+            // Verify PR is open
+            if (pr.data.state !== 'open') {
+              console.log('PR is not open, skipping.');
+              core.setOutput('build_windows', 'false');
+              return;
+            }
+
+            // Block fork PRs — fork code should not run with access to secrets
+            const isFork = pr.data.head.repo.full_name !== context.repo.owner + '/' + context.repo.repo;
+            if (isFork) {
+              console.log(`PR is from fork ${pr.data.head.repo.full_name}, blocking build.`);
+              await github.rest.issues.createComment({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                issue_number: context.issue.number,
+                body: 'On-demand builds are not available for PRs from forks.'
+              });
+              core.setOutput('build_windows', 'false');
+              return;
+            }
+
+            // Verify commenter has write access
+            let permission = 'none';
+            try {
+              const resp = await github.rest.repos.getCollaboratorPermissionLevel({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                username: context.payload.comment.user.login
+              });
+              permission = resp.data.permission;
+            } catch (_) {}
+
+            if (!['admin', 'write'].includes(permission)) {
+              console.log(`User ${context.payload.comment.user.login} has '${permission}' permission — insufficient.`);
+              await github.rest.issues.createComment({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                issue_number: context.issue.number,
+                body: `@${context.payload.comment.user.login} Only collaborators with write access can trigger builds.`
+              });
+              core.setOutput('build_windows', 'false');
+              return;
+            }
+
+            console.log(`User ${context.payload.comment.user.login} has '${permission}' permission — proceeding with ${command}.`);
+            core.setOutput(command, 'true');
+
+            // Export PR details for downstream jobs
+            core.setOutput('pr_ref', pr.data.head.ref);
+            core.setOutput('pr_sha', pr.data.head.sha);
+            core.setOutput('pr_number', String(pr.data.number));
+
+  build-frontend:
+    needs: validate
+    if: needs.validate.outputs.build_windows == 'true'
+    uses: ./.github/workflows/build-frontend.yml
+    with:
+      ref: ${{ needs.validate.outputs.pr_ref }}
+    secrets: inherit
+
+  build-windows:
+    needs: [validate, build-frontend]
+    if: needs.validate.outputs.build_windows == 'true'
+    uses: ./.github/workflows/build-windows-installer.yml
+    with:
+      ref: ${{ needs.validate.outputs.pr_ref }}
+    secrets: inherit
+
+  post-result:
+    needs: [validate, build-windows]
+    if: always() && needs.validate.outputs.build_windows == 'true'
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Post result comment
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const buildResult = '${{ needs.build-windows.result }}';
+            const runUrl = `https://github.com/${context.repo.owner}/${context.repo.repo}/actions/runs/${context.runId}`;
+            const prRef = '${{ needs.validate.outputs.pr_ref }}';
+            const prSha = '${{ needs.validate.outputs.pr_sha }}';
+            const shortSha = prSha.substring(0, 7);
+
+            // Skip comment for skipped builds
+            if (buildResult === 'skipped') {
+              console.log('Build was skipped, no comment needed.');
+              return;
+            }
+
+            let body;
+            if (buildResult === 'success') {
+              body = [
+                `Windows installer build **succeeded** for \`${prRef}\` (\`${shortSha}\`).`,
+                ``,
+                `**Download:** open the [workflow run](${runUrl}), scroll to the **Artifacts** section at the bottom.`,
+                `The artifact \`Cleanuparr-windows-installer\` is retained for 30 days.`
+              ].join('\n');
+            } else if (buildResult === 'cancelled') {
+              body = [
+                `Windows installer build was **cancelled** for \`${prRef}\` (\`${shortSha}\`).`,
+                ``,
+                `See the [workflow run](${runUrl}) for details.`
+              ].join('\n');
+            } else {
+              body = [
+                `Windows installer build **failed** for \`${prRef}\` (\`${shortSha}\`).`,
+                ``,
+                `See the [workflow run](${runUrl}) for details.`
+              ].join('\n');
+            }
+
+            await github.rest.issues.createComment({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number: parseInt('${{ needs.validate.outputs.pr_number }}'),
+              body
+            });