The serializer escapes a leading asterisk the strong run beside it already leaves literal

[Azganoth]

Summary

The serializer escapes a leading * that the strong run beside it already keeps literal. ***text** parses as a literal asterisk followed by strong emphasis, and saving it writes \***text**. The backslash changes nothing: the unescaped form reparses to the same document, measured below.

This is the class #252, #256, #257, #258, #271, #289, #292, and #293 removed, reaching a run the pairing leaves over. It is also the serializer disagreeing with itself: the same save drops an unnecessary escape from a link destination and from a text run, then adds one here.

Steps to reproduce

1. Open a document containing ***text**.
2. Save it without editing.
3. Read the file.

Expected behavior

***text**. The three-asterisk run spells one literal asterisk and a two-asterisk opener, and the run itself is what keeps the leftover literal, so no backslash is needed to hold it.

Actual behavior

Measured against 83033d4b by driving the editor mount used by the plugin tests, on corpus/commonmark/emphasis.md line 59.

Document	Saved
***asterisk combination missing one closer**	\***asterisk combination missing one closer**

The escape is redundant, not merely cosmetic. Both spellings parse to the same document:

Source	Document
\***asterisk combination missing one closer**	literal * followed by strong asterisk combination missing one closer
***asterisk combination missing one closer**	literal * followed by strong asterisk combination missing one closer

Closure and convergence both hold today, so neither the corpus round-trip guard nor the document-preservation guard can see this. What it costs is byte identity for corpus/commonmark/emphasis.md.

The same save normalizes in the opposite direction elsewhere in the corpus, which is what makes this a defect rather than a house style: [Escaped](garden\(section\).md) is written back as [Escaped](garden(section).md), and a run of escaped ASCII punctuation is written back with only the escapes that carry weight.

Related context

• Related issues or pull requests: The serializer escapes characters that cannot be syntax where they sit #252 is the closest precedent and states the rule this breaks — the serializer escapes characters that cannot be syntax where they sit. The serializer escapes a construct it can only see one text node of #292 and The serializer escapes a bracket run whose link tail it never parses #293 narrowed the same pass. fix: pair a delimiter run typed into literal text with the run that text opens #346 established the pairing that leaves the surplus delimiter literal, which is the run this escape sits on. Preserve the authored form of a Markdown file on save #251 is the tracker whose byte-identity target this blocks for one file.
• Documentation, decisions, or prior investigation: docs/decisions.md under Preserve the form a file was written in; the escape rules under Offer the escape gesture only where the conversion exists, which record that nothing durable is stored for an escape and that it is derived from the text and the serializer's safety check.

Done when

• A surplus delimiter left literal by a pairing is written without an escape wherever the run beside it already keeps it literal.
• Regression coverage asserts the saved bytes and the document the saved file reopens as, since closure already holds and cannot catch this.
• The escapes the pass still needs are unchanged, including the cases The serializer escapes characters that cannot be syntax where they sit #252, The serializer escapes a construct it can only see one text node of #292, and The serializer escapes a bracket run whose link tail it never parses #293 were opened for.
• corpus/commonmark/emphasis.md loses this difference, or the reason it cannot is recorded.

Notes, logs, screenshots

Out of scope

• The underscore spelling, ___text__, which was not measured. Confirm whether it behaves the same before deciding whether the fix covers one delimiter or both.
• Escapes dropped from a link destination and from a text run, which follow from an escape being derived rather than owned and are not defects.