fix: non-convergence when an empty heading has attachments

[QuadnucYard]

Summary

Fixes #441

Changes

Checklist

Before submitting, please ensure you've done the following:

• Updated CHANGELOG.md: Added your changes with examples to the changelog
• Updated documentation: Updated relevant docs, examples, or README
• Added tests: Added tests for new features or bug fixes

Testing

Additional Notes

[github-actions]

📊 Benchmark Performance Report

group                               base                                   pr
-----                               ----                                   --
pretty-ai-comprehensive-showcase    1.02   901.2±11.13µs        ? ?/sec    1.00    882.3±8.25µs        ? ?/sec
pretty-cetz-manual                  1.02   759.7±26.39µs        ? ?/sec    1.00    744.5±6.70µs        ? ?/sec
pretty-codly                        1.00  1787.5±13.79µs        ? ?/sec    1.00  1780.4±19.69µs        ? ?/sec
pretty-cpe                          1.12     13.7±0.96ms        ? ?/sec    1.00     12.2±0.44ms        ? ?/sec
pretty-deep-nested-args             1.02     17.2±0.12µs        ? ?/sec    1.00     16.9±0.12µs        ? ?/sec
pretty-fletcher-diagram             1.00   519.2±12.44µs        ? ?/sec    1.00    520.0±9.72µs        ? ?/sec
pretty-fletcher-draw                1.02  1272.7±31.01µs        ? ?/sec    1.00  1248.5±10.35µs        ? ?/sec
pretty-tablex                       1.02      3.4±0.01ms        ? ?/sec    1.00      3.3±0.01ms        ? ?/sec
pretty-touying-core                 1.00      2.1±0.01ms        ? ?/sec    1.00      2.1±0.02ms        ? ?/sec
pretty-touying-utils                1.01  1210.5±20.13µs        ? ?/sec    1.00  1199.2±12.20µs        ? ?/sec
pretty-undergraduate-math           1.03   886.3±28.97µs        ? ?/sec    1.00   859.3±17.86µs        ? ?/sec

📏 Binary Size Comparison

Metric	Base	PR	Change
File Size	5.8 MB	5.8 MB	📈 +336 B (+0.01%)
Text Section	1.4 MB	1.4 MB	📈 +400 B (+0.03%)

📦 Detailed Crate Size Diff (cargo-bloat)

Note: Numbers above are a result of guesswork. They are not 100% correct and never will be.

@@ -1,10 +1,10 @@
 std                       395.9 kB
 clap_builder              342.7 kB
-typstyle_core             216.6 kB
+typstyle_core             216.9 kB
 clap_complete             131.6 kB
-typst_syntax              120.2 kB
+typst_syntax              120.3 kB
 typstyle                  54.4 kB
 similar                   33.7 kB
 walkdir                   19.8 kB
 colored                   9.0 kB
 toml_edit                 8.7 kB

Generated by GitHub Actions on 2025-10-16 07:43:58 UTC