fix(inbox): a segment title is declared, never marked derived

A segment's title comes from the plan, so a human adjudicated it. But
structure derivation runs over the segment body, finds no title key and
no usable heading, falls back to a stem, and adds "title" to derived.
The concept then emitted a stated fact under an inferred marker, and a
consumer that distrusts derived fields would distrust exactly the thing
a human decided. An over-marked field is the same defect class as an
unmarked heuristic: the marker is only worth something if it is
accurate in both directions.

Scoped to title alone, and pinned that way by test: number stays in
derived on a segment, because nothing about segmentation makes an
inferred document number declared. Without a segment a derived title is
still marked, so only a plan makes a title declared.

The SEGMENTED_V1 golden moves, which is the intended consequence and
the only golden that may. The four existing goldens are byte-identical
to baseline 770d8d4, measured against the sha rather than inspected.

Co-Authored-By: Claude <claude-opus-5>

src/llm_ingestion_okf/inbox.py

@@ -22,7 +22,7 @@ from __future__ import annotations
 import hashlib
 import unicodedata
 from collections.abc import Callable, Mapping
-from dataclasses import dataclass
+from dataclasses import dataclass, replace
 from pathlib import Path, PurePosixPath
 
 from .errors import IngestError, MaterializationError, SegmentationError, SourceError
@@ -168,6 +168,16 @@ def render_inbox_concept(
         "generated": "true",
     }
     if structure is not None and profile.index.facets is not None:
+        if segmented:
+            # A segment's title comes from the PLAN, so it is DECLARED by the
+            # adjudicator -- but derivation runs over the segment BODY, finds
+            # no title key and no usable heading, falls back, and marks it
+            # derived. The concept then emits a stated fact under an inferred
+            # marker, and a consumer that distrusts derived fields distrusts
+            # exactly the thing a human decided. Scoped to `title` alone: every
+            # other field here really was inferred from the body, and blunting
+            # the marker would be the opposite defect.
+            structure = replace(structure, derived=structure.derived - {"title"})
         frontmatter.update(structure_frontmatter(structure, profile.index.facets.keys))
     if segmented:
         assert segment is not None