docs: the lineage is broken at one link, and layer 4 is now the outlier

CLAUDE.md's lineage note said layers 3 and 4 are one chain -- Divinum
Officium, missalemeum, lectio, colitur -- and that a defect inherited at the
root is invisible to both. That is still true everywhere except on the days
lectio has now corrected.

lectio adopted eight corrections colitur argued from the Missal. On those days
the chain no longer runs DO to lectio: lectio follows the Missal, and
missalemeum is the only party still carrying the inherited error. C27, C28 and
C37 went to zero and are closed; C38 narrowed to a readings-only divergence
that cannot close without lectio gaining a Commons concept.

The practical consequence for layer 4 is a base rate, and it is worth stating
because it is easy to get backwards: on those days the oracle disagrees with
BOTH engines, so M29 and M30 should be read as "missalemeum is the outlier"
rather than "colitur is unusual". A fresh colitur-vs-missalemeum divergence is
no longer presumptively colitur's fault.

And the limit, stated so it is not over-read: everywhere else the two layers
remain one lineage, and lectio's sanctoral is still generated from missalemeum
by a script that would silently revert all four calendar corrections if
re-run. That warning now lives in lectio's two ini headers and the generator's
own doc comment as well as here.

1 files changed, 25 insertions, 0 deletions

diff --git a/CLAUDE.md b/CLAUDE.md
index 0c0272d..23dce0b 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -135,6 +135,31 @@ against missalemeum; layer 5 pins ~30 dates.
   Litanies, the RG 110 Peter companion, St Barbara). Not wired in as a layer —
   its PDF columns shift between pages and extraction is unreliable; a
   structured Ordo would be the only way to add a fourth *lineage*.
+- **THE CHAIN IS NOW BROKEN AT ONE LINK, AND LAYER 4 IS THE OUTLIER**
+  (2026-08-18). lectio has ADOPTED eight corrections colitur argued from the
+  Missal — `ubaldus`/`didacus` promoted to III-class feasts, both August
+  vigils recoloured violet under RG 128, and both Ember Saturdays' readings.
+  So on those days the lineage no longer runs Divinum Officium → lectio:
+  lectio now follows the Missal, and **missalemeum is the only party still
+  carrying the inherited error.** Layer 3's fixture was regenerated, and
+  **C27, C28 and C37 went to zero and are closed** (C38 narrowed to a
+  readings-only divergence, which cannot close without lectio gaining a
+  Commons concept). 227 of 16 801 rows changed; agreement 86.6% → 87.5%.
+  Read the percentage as the *least* interesting part: those 227 days now
+  agree BECAUSE BOTH ENGINES FOLLOW THE MISSAL, where before they agreed
+  because both inherited the same errors. This is the first time the project
+  has RESOLVED the lineage problem on a set of days rather than documenting
+  it.
+  **What this changes for layer 4, practically.** On those days the oracle
+  now disagrees with BOTH engines, and its allow-list entries (M29, M30, and
+  the Ember-reading classes) should be read as "missalemeum is the outlier",
+  not as "colitur is unusual". Do not treat a fresh colitur-vs-missalemeum
+  divergence as presumptively colitur's fault: the base rate has changed.
+  **What it does NOT change**: everywhere else, layers 3 and 4 remain one
+  lineage, and lectio's own data is still generated from missalemeum by
+  `scripts/gen-sanctoral-ef.go`. That generator would silently revert all
+  four calendar corrections if re-run, which is why lectio's ini headers and
+  the generator's own doc comment now each carry the list.
 - Layer 3 **never compares commemorations** (lectio has no RG 111 admission logic,
   so its "others" are losing candidates, not the admitted set) and never compares
   the week column. It also **shares colitur's own lineage**: colitur's data was