fix(okf): top-level frontmatter title survives a nested sources: title

P15 (order 20260912T220951Z). okf._frontmatter_from_text was linewise
last-write-wins over EVERY line regardless of indentation, so a curated
concept's own top-level `title:` got silently overwritten by the nested
`sources:\n  - title: ...` block's title. Fix: a top-level (unindented)
key always wins over an indented one of the same name; a nested line
with no top-level counterpart is still preserved (SPEC §4).

Red-before/green-after: new test
test_parse_frontmatter_top_level_title_survives_nested_sources_title
(tests/test_okf.py) failed on 45edbf5 (fm["title"] == "N500:2024",
expected the concept's own), green after the fix.

Re-measured on all four vegnormal-okf bases (concept files / distinct
titles): n100-2023 446/446 (was 1) - n200-2024 1133/1133 (was 1) -
n500-2024 270/270 (was 1) - r761-2025 2756/2407 (genuine repeated
process names, not a collapse). directory_listing on krav/N500:
269 documents / 269 distinct titles (was 1).

tests/test_context_sets_loadbearing.py:
- The P14 tripwire test (asserting parse_frontmatter DID collapse
  titles) is INVERTED, not deleted, per the order: it now asserts the
  fix holds, as a live regression guard.
- own_frontmatter() stays (not replaced by parse_frontmatter): measured
  29,500 field reads (type/title/req_number/prosessnr, all four bases)
  agree exactly except for quote-stripping (2,728/29,500, zero value
  mismatches) - own_frontmatter unquotes for fasit comparison,
  parse_frontmatter deliberately doesn't (D1/(a)/(i): unquote_scalar is
  the ONE unquoting rule).

docs/2026-09-12-p14-kontekstsett.md Part B correction: the "22 of 22
cost words absent from n100/n200/n500" claim was false - n500-2024
carries `kroner` as a false positive (substring match inside
"borkroner", drill bits, not money). The original 22-word list was
never persisted, so only ~9 of the 22 survive named. Replaced with a
newly named, persisted 22-word list and the actual re-measured count:
n100 22/22 absent - n200 22/22 - n500 21/22 (kroner via borkroner) -
r761 18/22 (4 genuine cost words). No gate touched (no fasit anchor is
`kroner`).

Verification: full suite 1643 passed / 5 skipped (was 1642/5 on
45edbf5, +1 new test, 0 removed) - `uv run pytest -q`. ruff check +
ruff format --check clean on the three changed source/test files.
Golden transcripts byte-unchanged: shasum -a 1
tests/golden/demo-transcript.stdout = ea8c534773acdbe41ae68f2c55724d69aaf8be4f,
demo-transcript.stderr = ede3e2f685ce6a14ad9888e9de421d1a66f6c611.
No version bump, no push (both forbidden by the order).

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

src/portfolio_optimiser/okf.py

@@ -105,13 +105,34 @@ def _split_frontmatter(text: str) -> tuple[list[str], str, bool]:
 
 def _frontmatter_from_text(text: str) -> dict[str, str]:
     """``parse_frontmatter``'s rule, applied to already-read text: every frontmatter line that
-    carries a colon becomes one ``key: value`` pair, last write winning. Unterminated blocks are
-    parsed as if closed — the pre-split behaviour, preserved deliberately."""
+    carries a colon becomes one ``key: value`` pair, last write winning AMONG LINES AT THE SAME
+    LEVEL. Unterminated blocks are parsed as if closed — the pre-split behaviour, preserved
+    deliberately.
+
+    A TOP-LEVEL key (no leading whitespace — ``_split_frontmatter`` preserves indentation
+    verbatim, so this is a real structural signal, not a guess) always wins over an indented one
+    of the same name: a nested line is a block-sequence/-mapping entry under some OTHER top-level
+    key (``sources:\\n  - title: …`` names the SOURCE, not the concept) and must never overwrite
+    the concept's own field, however late it appears in the scan. Measured 2026-09-13 on
+    vegnormal-okf concepts: without this, every ``sources:``-bearing file's nested ``title``
+    replaced its own, collapsing 4605 concepts to 4 distinct titles. A nested line with no
+    top-level counterpart is still preserved (OKF SPEC §4, "unknown fields are preserved")."""
     fm: dict[str, str] = {}
+    top_level: set[str] = set()
     for line in _split_frontmatter(text)[0]:
+        if not line:
+            continue
         key, sep, val = line.partition(":")
-        if sep:
-            fm[key.strip()] = val.strip()
+        if not sep:
+            continue
+        key = key.strip()
+        if line[0].isspace():
+            if key in top_level:
+                continue
+            fm[key] = val.strip()
+        else:
+            fm[key] = val.strip()
+            top_level.add(key)
     return fm