docs(k3): round 13, and the two proposer rules between a reader and its ceiling [skip-docs]

The reader reaches the ceiling and the build does not, and the report separates
the two with denominators and a control for each: the orphan check removes 710
of 2 761 (710 of 710 removed headings are followed immediately by another
heading; 0 of 2 051 delivered ones are), and Arm F removes 2 066 more, swept
one flag at a time.

Both instrument forms on every row, because the pair key scores 28 of 2 761
here for a reason that has nothing to do with segmentation -- and the shipped
instrument turns out to carry the round-12 correction in NO block, not just in
the three the order named. That is proposed to the owning repository, never
applied there.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -9,6 +9,48 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- **`.xml` is a core file type, NISO-STS aware, with a generic fallback.** A
+  publisher's own viewer delivers a zip that holds 0 html, 1 xml and 109
+  images; `okf build` on it was **110 of 110 unreadable, 0 plans, exit 2**, and
+  the conservation identity `merged + coded rejections == N` was never written
+  because the run aborted earlier. The one xml file is the whole product: 7 715
+  `<sec>`, **2 761 with a `<title>`**, 4 954 lettered points, 10
+  `<table-wrap>`, and a `<sec>`-nesting depth distribution row-for-row
+  identical to the publisher's own structure fasit.
+  - The output grammar is MARKDOWN, the same the office and HTML rows reach the
+    proposer through: `propose.py` is untouched. `<label>` + `<title>` become
+    one ATX line at the section's own depth; a `<sec>` with only a `<label>` is
+    a body line and never a heading (**0 of 4 954** became concepts);
+    `<table-wrap>` becomes one markdown table (**10 of 10**, against 0 of 10 on
+    the PDF path).
+  - The reader emits **2 761 of 2 761** heading lines and preserves text
+    exactly -- 1 283 395 of 1 283 395 non-whitespace characters, ratio
+    **1.000000**. The BUILD reaches 2 065 of 2 761 with `--no-unit-fold` and 15
+    of 2 761 on the shipped defaults; the whole distance is two proposer rules,
+    decomposed with denominators in the report.
+  - hit@k over six questions, k=50: **3/6 · 5/6 · 6/6**, matching the PDF arm
+    row for row, with the known-positive moving from **rank 13 to rank 1**.
+    2 022 concept ids are shared between the two channels -- 96.8 % of the XML
+    bundle.
+  - **No new dependency:** `xml.etree.ElementTree` is stdlib and `uv.lock` is
+    untouched. A `<!DOCTYPE` is REFUSED unparsed with its own code, which is a
+    guarantee about this package rather than about the installed libexpat.
+  - `.xml` never routes through the converter, and it is measured about 12x
+    faster and about 30x smaller in peak memory than the PDF arm on the same
+    document and the same machine.
+  - Report: `docs/2026-09-11-k3-runde13-xml-sts.md`.
+
+### Fixed
+
+- **A PDF bookmark sharing a line with another left no trace.** `pdf_outline`
+  collected marks in a dict keyed on the destination line index, so a second
+  bookmark on a line was discarded by `setdefault` in silence: measured on a
+  701-page document, **2 763 nodes in, 2 762 marks out, `unresolved` = 0**.
+  `PdfOutline` now carries `collided`, and the identity `nodes in == marks +
+  unresolved + collided` holds. Keeping both nodes was measured and felled --
+  the two candidates then open at one offset and the first closes with an empty
+  span the orphan check deletes.
+
 - **`--pdf-outline` (OFF): cut a PDF at the boundaries its own `/Outlines`
   bookmark tree declares.** Measured outside this repository on one 701-page
   process code whose publisher also ships a NISO-STS structure for it: the