fix(render): environment-aware atlas drift guard, pinned text scale, shipped-atlas coverage

tools/fonts/gen_atlas.py

@@ -617,9 +617,13 @@ def main(argv=None):
     if args.check:
         out = Path(args.out)
         committed = out.read_bytes() if out.is_file() else None
-        fresh, _ = generate(args.font, args.em, args.supersample)
+        # A missing committed file is drift whatever else is wrong with the
+        # machine, so it is reported before the font is read: otherwise a checkout
+        # with no atlas *and* no installed face would look like an environment
+        # gap (EXIT_BAD_FONT) instead of the failure it is.
         if committed is None:
             return _fail(EXIT_MISMATCH, f"{out} does not exist; run {SCRIPT} to generate it")
+        fresh, _ = generate(args.font, args.em, args.supersample)
         if committed != fresh.encode():
             return _fail(
                 EXIT_MISMATCH,