docs(limits): tags and description block the whole OKF corpus before sources is even read

Measured 08-23 (order 20260823T161935Z): the line-flat frontmatter parser has
no sequence-value type at all, so tags rejects 53/53 upstream concepts
regardless of flow or block form, and description's folded-scalar continuation
misreads as a nested mapping in 29/53. Independent of both the mapping-form
gap and the sources block-form gap already documented here -- closing either
moves nothing on this corpus. 43 -> 44 items; README count moved with it. No
code change, no release.

README.md

@@ -269,7 +269,7 @@ a green scan means safe content. The highest-impact items:
   two of the three corpora are living, so the cells are not rewritten in place.
   Method and before/after: [`docs/rawhtml-census.py`](docs/rawhtml-census.py).
 
-**Full list — 43 items, each with the mechanism, plus the out-of-scope boundary:**
+**Full list — 44 items, each with the mechanism, plus the out-of-scope boundary:**
 [`docs/LIMITATIONS.md`](docs/LIMITATIONS.md). Several carry field measurements from
 consumer corpora, including the false positives the URL-shape rule actually produces.
 

docs/LIMITATIONS.md

@@ -98,6 +98,24 @@ items; this is the full list, each with the mechanism.
   A concept whose `sources` are flat strings, or absent, imports. The
   dangling-or-substituted `executor`/`attester` pointer question stays out of reach
   for the same reason: both are mappings whose payload key is `resource`.
+- **`tags` and `description` block the OKF import corpus universally, before the
+  trust layer is even reached.** The line-flat frontmatter parser has no
+  sequence-value type at all: `tags` is present in 53/53 upstream concept
+  documents — 9/53 as a flow sequence (`[a, b, c]`, rejected on the `[`
+  indicator) and 44/53 as a block sequence (`- a` / `- b`, rejected as
+  `"malformed frontmatter line"`) — 100% rejection regardless of form.
+  `description` is present in 53/53; 29/53 is a folded plain scalar continuing
+  on an indented second line, which the parser has no continuation-line model
+  for and misreads as `"nested mappings are not supported"` (the remaining
+  24/53 are single-line and parse fine). Measured directly on the upstream
+  reference bundles (`_okf-upstream/okf` @ `3fcbb9f`): removing `tags` alone
+  lets 4/53 documents pass; removing both `tags` and `description` together
+  (trust layer untouched) lets the same 4/53 pass, and all four then parse
+  `generated` correctly as a mapping. **Independent of both the mapping-form
+  gap and the `sources` block-form gap above:** closing either moves nothing
+  on this corpus, because `tags`/`description` reject before `sources` is ever
+  read. No sequence-value type or continuation-line model exists in the
+  stdlib-only parser to close this with.
 - **A persist gate cannot cover execution risk.** OKF v0.2 introduces concepts whose
   purpose is to *name code to be run* (`runtime`, `executor.resource`,
   `attester.resource`). This library answers "is this safe to **store**"; executable