Whole-block segments cover paired formatting (strong/em/s), not just links

The model mangles Markdown it can see (Seed-X dropped the ** and the
glued-on colon in '**Pagerite**: ...'), so emphasis now crosses stripped,
inline in its sentence, and the syntax is weight-mapped back like links.
Also fix _place_marks swallowing trailing punctuation into the inner text
(end at the slice's last unit) — same-language round trips are now exact.

docs/localization.md

@@ -376,13 +376,14 @@ fragment is parsed with the project's own markdown-it setup
 tasklist label wrapping, so token text stays byte-identical to the source)
 and split into the runs a model may touch: paragraph/heading/table-cell text
 (merged across soft line breaks), image alt texts and captions, footnote
-bodies. A block of plain text and inline **links stays whole** — link texts
-cross inline, in sentence context (see below). Everything else never leaves
-the server: code spans and
+bodies. A block of plain text, inline **links and paired text formatting**
+(strong/em/s) **stays whole** — link and formatted texts cross inline, in
+sentence context, with the Markdown stripped (see below). Everything else
+never leaves the server: code spans and
 fences, URLs and autolinks, link/image *destinations*, `{...}` spans
 (placeholders like `{dates}` as well as attrs), reference and footnote
-labels, container fences, GFM alert markers (`[!NOTE]`), raw HTML — and all
-markup punctuation (`*`, `|`, `[]()`, `:::`), which is a run boundary.
+labels, container fences, GFM alert markers (`[!NOTE]`), raw HTML — and the
+remaining markup punctuation (`|`, `:::`), which is a run boundary.
 Chunks with no segments (a lone `{dates}`, container fences, pure
 code/HTML) are never dispatched at all (`needs_translation`); every
 language renders them from the original chunk. Each segment is accompanied
@@ -404,24 +405,29 @@ near-deterministic, so an immediate retry would re-fail; the fragment stays
 pending and gets another chance on restart or `DELETE /_api/translations`).
 `Data.trans` therefore only ever holds clean translated Markdown.
 
-Link-carrying blocks are the one place a segment is not spliced verbatim:
-a label translated apart from its sentence comes back grammatically
-incompatible with it (case government, particles, word order), so the
-block crosses whole and the server re-inserts the link markdown into the
-translated block. The boundaries are found by **text processing alone** —
+Link- and formatting-carrying blocks are the one place a segment is not
+spliced verbatim: a label translated apart from its sentence comes back
+grammatically incompatible with it (case government, particles, word
+order), and shown the Markdown the model mangles it (Seed-X dropped the
+`**` and the glued-on colon in `**Pagerite**: …`), so the block crosses
+whole — all Markdown stripped — and the server re-inserts the link and
+formatting syntax into the translated block. The boundaries are found by
+**text processing alone** —
 markers on the wire are hopeless (an earlier sentinel-masking design let
 the model see and mangle exactly that punctuation: Seed-X renumbered the
-tokens and turned `![` into `¡¡…!!`). Each link's weight ratio in the
+tokens and turned `![` into `¡¡…!!`). Each mark's weight ratio in the
 source block (word units before its text boundaries over the block total;
 CJK ideographs count as one unit each, kana runs as one — no spaces to
-count words by) is applied to the translation's units. Placement is
-approximate and drift accumulates across several links in one block — the
+count words by) is applied to the translation's units; the inner text ends
+at its last unit, so punctuation and whitespace between the mark and the
+next word stay outside it. Placement is
+approximate and drift accumulates across several marks in one block — the
 accepted trade: better a coherent sentence with a slightly shifted link
 than separately translated snippets that don't fit together. A boundary
-that maps to an empty slice degrades to the source link text rather than
-emitting a broken `[](url)`. Blocks mixing in any other inline markup
-(emphasis, code spans, images) don't qualify and still split into runs at
-those boundaries.
+that maps to an empty slice degrades to the source text rather than
+emitting a broken `[](url)` or `**`. Blocks mixing in any other inline
+markup (code spans, images, raw HTML) don't qualify and still split into
+runs at those boundaries.
 
 Punctuation is the translator's own job: Seed-X tends to "finish" short
 labels (titles, nav items) with a comma or period the source never had.