chore(quality): baseline-headroom skips generated and vendored files in the fileSize worst-file signal

scripts/quality/baseline-headroom.mjs

@@ -63,17 +63,27 @@ export function sumTypecheckBaseline(json) {
   return n;
 }
 
+// Files whose size is not an editable-code signal: generated modules are frozen at
+// their emitter's exact output size (≈0% headroom by construction — growth is policed
+// by re-freezing, e.g. openapi.generated.ts in #12212), and vendored code is upstream's.
+// The GATE (check:file-size) still enforces both; only the monitor skips them so the
+// nightly headroom-alert reflects files a human can actually slim.
+export function isMonitorExemptFile(file) {
+  return file.includes(".generated.") || /(^|\/)vendor\//.test(file);
+}
+
 /**
  * Frozen-file headroom: the worst (most consumed) frozen file and how many sit within
  * `warnFraction` of their cap. `locOf(file)` returns the live line count or null.
+ * Generated/vendored files are excluded (see isMonitorExemptFile).
  */
 export function fileSizeHeadroom(frozen, locOf, warnFraction = 0.1) {
   let worst = null;
   let nearCap = 0;
   let over = 0;
   let measured = 0;
   for (const [file, capRaw] of Object.entries(frozen)) {
-    if (file.startsWith("_")) continue;
+    if (file.startsWith("_") || isMonitorExemptFile(file)) continue;
     const cap = Number(capRaw);
     const loc = locOf(file);
     if (!Number.isFinite(cap) || loc === null || loc === undefined) continue;

tests/unit/build/baseline-headroom.test.ts

@@ -4,6 +4,7 @@ import test from "node:test";
 import {
   fileSizeHeadroom,
   headroomOf,
+  isMonitorExemptFile,
   renderMarkdown,
   statusOf,
   sumTypecheckBaseline,
@@ -54,6 +55,30 @@ test("fileSizeHeadroom reports the worst frozen file and the near-cap / over cou
   assert.ok(r.worst!.headroom < 0);
 });
 
+test("fileSizeHeadroom skips generated and vendored files (monitor-only exemption)", () => {
+  assert.equal(isMonitorExemptFile("src/app/docs/lib/openapi.generated.ts"), true);
+  assert.equal(
+    isMonitorExemptFile("open-sse/vendor/codex-chatgpt-web/adapters/chatgpt-web/browser-worker.ts"),
+    true
+  );
+  assert.equal(isMonitorExemptFile("vendor/thing.ts"), true);
+  assert.equal(isMonitorExemptFile("src/lib/generatedReport.ts"), false);
+  assert.equal(isMonitorExemptFile("src/lib/vendorAdapter.ts"), false);
+
+  const frozen = {
+    "x.generated.ts": 100, // 0% headroom by construction — must not be the worst
+    "open-sse/vendor/lib/big.ts": 1000,
+    "real.ts": "1200",
+  };
+  const loc = (f: string) =>
+    ({ "x.generated.ts": 100, "open-sse/vendor/lib/big.ts": 999, "real.ts": 900 })[f] ?? null;
+  const r = fileSizeHeadroom(frozen, loc, 0.1);
+  assert.equal(r.measured, 1); // only real.ts counted
+  assert.equal(r.nearCap, 0);
+  assert.equal(r.over, 0);
+  assert.equal(r.worst?.file, "real.ts");
+});
+
 test("renderMarkdown lists every row with its status icon and flags the bad ones", () => {
   const md = renderMarkdown(
     [