fix(email): keep trailing combining marks and variation selectors

[adhyaay-karnwal]

Fixes #5705.

remove_trailing_special_chars treated the combining-mark ranges and variation selectors as invisible, then truncated everything after the last character outside those ranges. A trailing decomposed accent (e + U+0301) lost its accent, and an emoji variation selector could be stripped.

The trailing-noise predicate is now limited to whitespace and formatting controls (zero-width spaces/joiners, BOM, NBSP, word joiner, and the existing general-punctuation format ranges). Combining marks and variation selectors are preserved.

U+034F COMBINING GRAPHEME JOINER stays in the noise set: it is a joiner/format control, not a meaning-bearing accent, which matches the issue's request to keep joiner cleanup intact.

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Note

Low Risk
Narrow change to subject/snippet trailing cleanup with added regression tests; improves display correctness without touching auth or data paths.

Overview
Fixes incorrect truncation of email subjects/snippets that end with decomposed accents or emoji variation selectors.

is_invisible_char in clean_subject_snippet.rs no longer treats combining diacritical marks or variation selectors as trailing noise, so remove_trailing_special_chars stops before those characters instead of stripping them. Zero-width spaces, BOM, NBSP, word joiner, U+034F grapheme joiner, and the existing general-punctuation format ranges are still removed from the end.

New unit tests cover preserved café/naïve-style trailing marks, emoji with U+FE0F, and format controls still stripped after a combining mark.

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Reviewing files that changed from the base of the PR and between e00d041 and cc63e46.

📒 Files selected for processing (1)

• services/email_service/src/util/process_pre_insert/clean_message/clean_subject_snippet.rs

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📝 Summary

Summary by CodeRabbit

• Bug Fixes
  • Preserved combining marks and variation selectors at the end of email subject snippets.
  • Continued removing trailing zero-width and formatting control characters for cleaner message display.

Walkthrough

The change updates is_invisible_char so remove_trailing_special_chars preserves trailing combining marks and variation selectors. Tests cover decomposed accented characters, emoji variation selectors, and trailing zero-width or format controls after combining marks.

Priority: ➖ Normal

Severity of issue fixed: Medium

Merge Risk: ⚪ Minimal · up to cc63e

The change preserves trailing combining marks and variation selectors while continuing to remove the intended trailing formatting noise.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title uses the conventional commits format with the valid fix(email): prefix. It clearly describes the change and is 65 characters long, which is under the 72-character limit.
Description check	✅ Passed	The description directly explains the subject and snippet cleanup change, the preserved Unicode characters, the retained formatting controls, and the regression tests.
Linked Issues check	✅ Passed	The changes satisfy the coding requirements in #5705. is_invisible_char no longer classifies combining-mark ranges or U+FE00–U+FE0F variation selectors as trailing noise. The existing cleanup remain…
Out of Scope Changes check	✅ Passed	The reviewed changes are limited to the email subject and snippet trailing-cleanup predicate and focused regression tests. These changes directly support #5705. No unrelated implementation or test cha…

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

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