docs(skills): objectstack-formula eval case 4 names the refused date forms without spelling its own must_not_contain strings

Case 4's expected_output carried both strings its own must_not_contain
refuses (`new Date(` and `today() + `), so a reference-grade answer was
graded wrong. The reference now says "never a JS `Date` / `Date.now()`"
and "never date arithmetic on `today()` (it faults)"; every assertion and
fact stays, the file keeps its 5407 bytes, and a per-case cross-check of
all seven cases reports 0 failures. Patch changeset for @objectstack/skills.

Claude-Session: https://claude.ai/code/session_01ADHkmPQ8p3cVKear7Mchi2
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

.changeset/26814-formula-eval-case4-self-consistent.md

@@ -0,0 +1,12 @@
+---
+'@objectstack/skills': patch
+---
+
+docs(skills): objectstack-formula eval case 4's reference answer names the refused date forms without spelling its own `must_not_contain` strings
+
+Clause-②: no
+Metadata-protocol: none
+
+- **Before.** Case 4 of `skills/objectstack-formula/evals/cel-predicates-formulas.json` refuses `new Date(` and `today() + ` in an answer, yet its own `expected_output` spelled both (`` `new Date()` `` and `` `today() + 45` ``), so a reference-grade answer was graded wrong.
+- **Now.** The reference answer says "never a JS `Date` / `Date.now()`" and "never date arithmetic on `today()` (it faults)", as case 7 names "the `label` macro". Every assertion and every fact stays: the CEL envelope seed, the determinism gate, `daysBetween(today(), record.close_date)`, the `{}` duration trap. A per-case cross-check (no `must_not_contain` string inside its own `expected_output`, every `must_contain` string present) reports 0 failures over all 7 cases; the file keeps its byte size, so its token-ratchet row does not move.
+- No schema, key or behaviour changes.

skills/objectstack-formula/evals/cel-predicates-formulas.json

@@ -34,7 +34,7 @@
     {
       "id": 4,
       "prompt": "Demo opportunities should close 45 days after the package is installed, and a formula should show how many days remain until close.",
-      "expected_output": "Seed value as a CEL envelope, `close_date: cel`daysFromNow(45)``, never `new Date()` / `Date.now()` (the determinism gate: two `os build` runs must be byte-identical). Days remaining is `daysBetween(today(), record.close_date)` — never `record.close_date - today()` (a duration stored as `{}`) and never `today() + 45` (date arithmetic faults).",
+      "expected_output": "Seed value as a CEL envelope, `close_date: cel`daysFromNow(45)``, never a JS `Date` / `Date.now()` (the determinism gate: two `os build` runs must be byte-identical). Days remaining is `daysBetween(today(), record.close_date)` — never `record.close_date - today()` (a duration stored as `{}`) and never date arithmetic on `today()` (it faults).",
       "files": [],
       "assertions": {
         "must_contain": ["cel`", "daysFromNow(", "daysBetween("],