fix(extract): a declared section's outline mark keeps its depth; only the heading clips

K3-21 D. `_StsReader._walk` computed `level = min(depth, _ATX_MAX_LEVEL)`
once and wrote it into BOTH the ATX heading and the `OutlineMark`. The
heading keeps the clip -- markdown has six levels and `#######` matches
nothing -- and the mark now carries the declared `depth`: it is no heading,
the declared route builds `Candidate(level=mark.level)` from it, and
`OutlineMark`'s own docstring says the level is what the tree declares,
"reported rather than fixed up". The extracted text does not move one
character; only the mark's level does.

On one standard 9 of 2 761 titled sections sit at depth 7; `--shell-parent`
gave its two depth-7 shells (`36.73211`, `36.73212`) the ancestor one level
too high. The gate -- plan otherwise unchanged, concept count, goldens, the
regression bundles, hit@k and the other 708 pointers -- is measured in a
frozen export of this commit.

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

src/llm_ingestion_okf/extract.py

@@ -322,10 +322,10 @@ _XML_INLINE_TAGS = frozenset(
 # stops at for the same reason. STS nesting goes DEEPER: 9 of the 2 761 titled
 # sections in that document sit at depth 7, and `#######` matches nothing at
 # all. The depth is CLIPPED rather than dropped -- a clipped heading still sets
-# its boundary and states its nesting one level too shallow, where a dropped
-# one loses the section entirely. The cost shows up in frontmatter nesting, not
-# in the depth row, because that row is the source's own depth and not the ATX
-# level we emitted.
+# its boundary, where a dropped one loses the section entirely. The clip is the
+# HEADING's alone (K3-21): the `OutlineMark` beside it carries the declared
+# depth, because the declared route builds its plan from the mark and a plan
+# reading 7 as 6 gave a depth-7 section the ancestor one level too high.
 _ATX_MAX_LEVEL = 6
 
 
@@ -590,7 +590,10 @@ class _XmlTextExtractor:
                 self.marks.append(
                     OutlineMark(
                         line=len(self._lines) - 1,
-                        level=level,
+                        # The DECLARED depth, never the clipped one: the mark
+                        # is not a markdown heading, and the plan the declared
+                        # route builds from it reads nesting off this level.
+                        level=depth,
                         title=heading,
                         description=self._spec_point(element),
                     )