ci: comment Playwright shard-selection triage on PRs (#14347)

.github/scripts/pw-triage-comment.js

@@ -0,0 +1,65 @@
+#!/usr/bin/env node
+// Render the sticky PR shard-triage comment from $MATRIX + the select log (argv[2]) to stdout.
+const fs = require("fs");
+
+function readLog(path) {
+  if (!path) return "";
+  try {
+    return fs.readFileSync(path, "utf8").trim();
+  } catch {
+    return "";
+  }
+}
+
+const marker = process.env.MARKER || "<!-- playwright-shard-triage -->";
+const smokeActive = process.env.SMOKE_ACTIVE === "true";
+const headSha = (process.env.HEAD_SHA || "").slice(0, 9);
+const attempt = process.env.ATTEMPT || "1";
+const log = readLog(process.argv[2]);
+
+let matrix;
+try {
+  matrix = JSON.parse(process.env.MATRIX || "{}");
+} catch {
+  matrix = {};
+}
+const shards = Array.isArray(matrix.include) ? matrix.include : [];
+
+// smoke_active only says selection ran; a global_paths hit still returns the full
+// matrix, so infer the real mode from the log rather than the flag alone.
+const fellBackToFull = /falling back to full matrix|full matrix:/.test(log);
+const mode = smokeActive && !fellBackToFull ? "smoke (changed-path)" : "full matrix";
+
+const specsOf = (s) => (Array.isArray(s.run_files) ? s.run_files.length : 0);
+const totalSpecs = shards.reduce((n, s) => n + specsOf(s), 0);
+const shardList = shards
+  .map((s) => `${s.testfolder} (${specsOf(s)})`)
+  .join(" · ");
+
+const lines = [
+  marker,
+  "### 🎯 Playwright shard selection",
+  `Mode: **${mode}** · **${shards.length} shard${shards.length === 1 ? "" : "s"}** · **${totalSpecs} spec${totalSpecs === 1 ? "" : "s"}**`,
+  "",
+  shardList || "_no shards selected_",
+];
+
+if (log) {
+  lines.push(
+    "",
+    "<details><summary>Why these shards</summary>",
+    "",
+    "```",
+    log,
+    "```",
+    "",
+    "</details>"
+  );
+}
+
+lines.push(
+  "",
+  `<sub>Updated for \`${headSha}\` · attempt ${attempt} · updates in place on every push.</sub>`
+);
+
+process.stdout.write(lines.join("\n") + "\n");