diff --git a/.github/workflows/frontend-js-size-comment.yml b/.github/workflows/frontend-js-size-comment.yml
index 3f75abf6f9..4d40aa8946 100644
--- a/.github/workflows/frontend-js-size-comment.yml
+++ b/.github/workflows/frontend-js-size-comment.yml
@@ -6,6 +6,27 @@ on:
       - Frontend JS size
     types:
       - completed
+  pull_request_target:
+    types:
+      - opened
+      - synchronize
+      - reopened
+      - ready_for_review
+    paths:
+      - packages/frontend/**
+      - packages/frontend-shared/**
+      - packages/frontend-builder/**
+      - packages/i18n/**
+      - packages/icons-subsetter/**
+      - packages/misskey-js/**
+      - packages/misskey-reversi/**
+      - packages/misskey-bubble-game/**
+      - package.json
+      - pnpm-lock.yaml
+      - pnpm-workspace.yaml
+      - .node-version
+      - .github/workflows/frontend-js-size.yml
+      - .github/workflows/frontend-js-size-comment.yml
 
 permissions:
   actions: read
@@ -16,50 +37,148 @@ permissions:
 jobs:
   comment:
     name: Comment frontend JS size
-    if: github.event.workflow_run.event == 'pull_request' && github.event.workflow_run.conclusion == 'success'
+    if: github.event_name == 'pull_request_target' || (github.event.workflow_run.event == 'pull_request' && github.event.workflow_run.conclusion == 'success')
     runs-on: ubuntu-latest
+    concurrency:
+      group: frontend-js-size-comment-${{ github.event.pull_request.number || github.event.workflow_run.id }}
+      cancel-in-progress: true
     steps:
-      - name: Download size report
+      - name: Find size report run
+        if: github.event_name == 'pull_request_target'
+        id: find-report-run
+        uses: actions/github-script@v9
+        with:
+          script: |
+            const workflow_id = 'frontend-js-size.yml';
+            const artifactName = 'frontend-js-size-report';
+            const headSha = context.payload.pull_request.head.sha;
+            const prNumber = context.payload.pull_request.number;
+            const pollIntervalMs = 30_000;
+            const timeoutMs = 90 * 60_000;
+            const startedAt = Date.now();
+            const { owner, repo } = context.repo;
+
+            async function listSizeWorkflowRuns() {
+              const runsForHead = await github.paginate(github.rest.actions.listWorkflowRuns, {
+                owner,
+                repo,
+                workflow_id,
+                event: 'pull_request',
+                head_sha: headSha,
+                per_page: 100,
+              });
+
+              if (runsForHead.length > 0) {
+                return runsForHead;
+              }
+
+              const recentRuns = await github.paginate(github.rest.actions.listWorkflowRuns, {
+                owner,
+                repo,
+                workflow_id,
+                event: 'pull_request',
+                per_page: 100,
+              });
+              return recentRuns.filter((run) =>
+                run.pull_requests?.some((pullRequest) => pullRequest.number === prNumber));
+            }
+
+            async function findReportRun() {
+              const runs = (await listSizeWorkflowRuns())
+                .sort((a, b) => new Date(b.updated_at) - new Date(a.updated_at));
+
+              for (const run of runs) {
+                if (run.status !== 'completed') continue;
+                if (run.conclusion !== 'success') {
+                  core.warning(`Frontend JS size run ${run.id} completed with conclusion: ${run.conclusion}`);
+                  return { done: true, run: null };
+                }
+
+                const artifacts = await github.paginate(github.rest.actions.listWorkflowRunArtifacts, {
+                  owner,
+                  repo,
+                  run_id: run.id,
+                  per_page: 100,
+                });
+                const report = artifacts.find((artifact) => artifact.name === artifactName && !artifact.expired);
+                if (report) return { done: true, run };
+              }
+
+              return { done: false, run: null };
+            }
+
+            while (Date.now() - startedAt < timeoutMs) {
+              const { done, run } = await findReportRun();
+              if (run) {
+                core.info(`Found frontend JS size report on workflow run ${run.id}.`);
+                core.setOutput('run-id', String(run.id));
+                return;
+              }
+              if (done) {
+                return;
+              }
+
+              core.info('Waiting for frontend JS size report artifact...');
+              await new Promise((resolve) => setTimeout(resolve, pollIntervalMs));
+            }
+
+            core.warning(`Timed out waiting for ${artifactName} from ${workflow_id} for ${headSha}.`);
+
+      - name: Download size report from workflow_run
+        if: github.event_name == 'workflow_run'
         uses: actions/download-artifact@v8
         with:
           name: frontend-js-size-report
-          path: frontend-js-size-report
+          path: ${{ runner.temp }}/frontend-js-size-report
           github-token: ${{ github.token }}
           repository: ${{ github.repository }}
           run-id: ${{ github.event.workflow_run.id }}
 
+      - name: Download size report from pull_request_target
+        if: github.event_name == 'pull_request_target' && steps.find-report-run.outputs.run-id != ''
+        uses: actions/download-artifact@v8
+        with:
+          name: frontend-js-size-report
+          path: ${{ runner.temp }}/frontend-js-size-report
+          github-token: ${{ github.token }}
+          repository: ${{ github.repository }}
+          run-id: ${{ steps.find-report-run.outputs.run-id }}
+
       - name: Comment on pull request
+        if: github.event_name == 'workflow_run' || steps.find-report-run.outputs.run-id != ''
         uses: actions/github-script@v9
         with:
           script: |
             const fs = require('node:fs');
+            const path = require('node:path');
 
             const marker = '<!-- misskey-frontend-js-size -->';
-            const body = fs.readFileSync('frontend-js-size-report/frontend-js-size-report.md', 'utf8');
+            const reportDir = path.join(process.env.RUNNER_TEMP, 'frontend-js-size-report');
+            const reportPath = [
+              path.join(reportDir, 'report.md'),
+              path.join(reportDir, 'frontend-js-size-report.md'),
+            ].find((file) => fs.existsSync(file));
+            if (reportPath == null) {
+              core.setFailed('The frontend JS size report artifact does not contain a report markdown file.');
+              return;
+            }
+
+            const body = fs.readFileSync(reportPath, 'utf8');
+            const prNumberPath = path.join(reportDir, 'pr-number.txt');
+            let issue_number = fs.existsSync(prNumberPath)
+              ? Number(fs.readFileSync(prNumberPath, 'utf8').trim())
+              : context.payload.pull_request?.number;
             if (!body.includes(marker)) {
               core.setFailed('The frontend JS size report is missing the expected marker.');
               return;
             }
-
-            const { owner, repo } = context.repo;
-            const workflowRun = context.payload.workflow_run;
-            let issue_number = workflowRun.pull_requests?.[0]?.number;
-
-            if (issue_number == null) {
-              const { data: pullRequests } = await github.rest.repos.listPullRequestsAssociatedWithCommit({
-                owner,
-                repo,
-                commit_sha: workflowRun.head_sha,
-              });
-              issue_number = pullRequests.find((pr) => pr.head.sha === workflowRun.head_sha)?.number
-                ?? pullRequests[0]?.number;
-            }
-
-            if (issue_number == null) {
-              core.info(`No pull request found for workflow run ${workflowRun.id}.`);
+            if (!Number.isInteger(issue_number)) {
+              core.setFailed('The frontend JS size report is missing a valid pull request number.');
               return;
             }
 
+            const { owner, repo } = context.repo;
+
             const comments = await github.paginate(github.rest.issues.listComments, {
               owner,
               repo,
diff --git a/.github/workflows/frontend-js-size.yml b/.github/workflows/frontend-js-size.yml
index a511560a02..7d3641355b 100644
--- a/.github/workflows/frontend-js-size.yml
+++ b/.github/workflows/frontend-js-size.yml
@@ -330,14 +330,18 @@ jobs:
         env:
           BASE_SHA: ${{ github.event.pull_request.base.sha }}
           HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+          PR_NUMBER: ${{ github.event.pull_request.number }}
         run: |
+          mkdir -p frontend-js-size-report
           node .github/tmp/frontend-js-size-report.mjs before after frontend-js-size-report.md
-          cat frontend-js-size-report.md >> "$GITHUB_STEP_SUMMARY"
+          mv frontend-js-size-report.md frontend-js-size-report/report.md
+          printf '%s\n' "$PR_NUMBER" > frontend-js-size-report/pr-number.txt
+          cat frontend-js-size-report/report.md >> "$GITHUB_STEP_SUMMARY"
 
       - name: Upload size report
         uses: actions/upload-artifact@v7
         with:
           name: frontend-js-size-report
-          path: frontend-js-size-report.md
+          path: frontend-js-size-report/
           if-no-files-found: error
           retention-days: 1