Hold Io and Europa to their own track ceilings, and Hyperion's one-date ceiling to just above its offset

Io's and Europa's periapses turn backwards, held by the Laplace resonance (apsidesRegress), which
brings them to 0.07 and 0.23 degrees of Horizons from 1950 to 2100. Nothing guarded the flag: with it
dropped the ETL still passed, Io at 0.96 and Europa at 2.24 under the general 3-degree track
ceiling, their cards quietly rewriting themselves to "within 1.0" and "within 2.3". They now have
ceilings of 0.2 and 0.5, as Tethys has for the term it takes from its W. The comment on the
one-date check, which said it catches the periapsis run the wrong way, now says it does not
(0.904 against 2.5) and which check does.

Hyperion's one-date ceiling was 21 degrees, described as just above its offset on that date, where
it is 9.413: the 21 was its worst over twelve dates in an earlier check. It is now 10.

Measured on the real catalogue with the solar ETL: Io 0.07, Europa 0.23 at worst, Hyperion 9.413,
all passing. Guarded mutants, run through the solar ETL: apsidesRegress removed from both specs
fails with "Io's mean elements put it up to 0.96 degrees ... (at most 0.2 expected)"; Hyperion's row
misread by 6 degrees of node fails the one-date check at 15.41, which 21 let through.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

tools/etl/build.ts

@@ -142,9 +142,9 @@ function validateMerge(stars: StarRecord[]): void {
  * Measured on this catalogue: the planets at most 0.10 degrees (Uranus; Standish's own stated
  * error for his fit is 2 000 arcseconds, 0.56 degrees), the moons at most 1.41 (the Moon, whose
  * evection and variation, 1.27 and 0.66 degrees, no mean ellipse has). What this catches is a
- * table read wrongly: a moon read against the ecliptic instead of its Laplace plane, a precession
- * run the wrong way, or a column taken for its neighbour, which put Triton 26 degrees out and Io
- * 0.9.
+ * table read wrongly: a moon read against the ecliptic instead of its Laplace plane, a node run the
+ * wrong way, or a column taken for its neighbour, which put Triton 26 degrees out. Io's periapsis
+ * run forwards put it 0.9 out here, which passes; {@link TRACK_OFFSET_CEILINGS_DEG} catches that.
  */
 const MAX_PLANET_OFFSET_DEG = 0.25;
 /** Measured on this catalogue: at most 0.0151 (Phoebe and the Moon) once Hyperion prints its current 0.105. */
@@ -155,9 +155,11 @@ const DEG_TO_RAD = Math.PI / 180;
 
 /**
  * The moons whose table row cannot come within that on this one date, each with a ceiling just
- * above its offset here; see {@link TRACK_OFFSET_CEILINGS_DEG} for what they reach from 1950 to 2100.
+ * above its offset here (Hyperion 9.41, Iapetus 9.56, Nereid 2.58); see
+ * {@link TRACK_OFFSET_CEILINGS_DEG} for what they reach from 1950 to 2100. Hyperion's was 21, its
+ * worst over twelve dates, which let a row misread by twice its offset through.
  */
-const MOON_OFFSET_CEILINGS_DEG: Record<string, number> = { hyperion: 21, iapetus: 11, nereid: 3 };
+const MOON_OFFSET_CEILINGS_DEG: Record<string, number> = { hyperion: 10, iapetus: 11, nereid: 3 };
 
 /**
  * How far a moon's or dwarf planet's orbit may stray from Horizons from 1950 to 2100, sampled every
@@ -183,12 +185,17 @@ const MOON_OFFSET_CEILINGS_DEG: Record<string, number> = { hyperion: 21, iapetus
  * - Ceres, 7.12 (1953): the SBDB's elements are osculating, exact at 2026 Jun 9 and drifting
  *   either side; 1.9 by 2050, 5.3 by 2100, and 39 at 1600 on Horizons' own figures.
  *
- * And one is held tighter than the rest: Tethys, 0.28, which takes the other half of that
- * libration, 2.23 degrees, from its W. Without it Tethys strays 2.09 degrees, under the general
- * ceiling, and its card would quietly restate itself as "within 2.1".
+ * And three are held tighter than the rest, each where one reading of its row is all that keeps it
+ * close, and without it the card would quietly restate itself under the general ceiling:
+ *
+ * - Tethys, 0.28, which takes the other half of that libration, 2.23 degrees, from its W. Without
+ *   it Tethys strays 2.09.
+ * - Io, 0.07, and Europa, 0.23, whose periapses turn backwards, held by the Laplace resonance at
+ *   2n(Europa) - n(Io), -0.7395 degrees a day (`apsidesRegress`). Read as advancing, Io strays 0.96
+ *   and Europa 2.24, and their cards said "within 1.0" and "within 2.3".
  */
 const MAX_TRACK_OFFSET_DEG = 3;
-const TRACK_OFFSET_CEILINGS_DEG: Record<string, number> = { hyperion: 23, nereid: 12, iapetus: 11, mimas: 8, ceres: 8, tethys: 0.5 };
+const TRACK_OFFSET_CEILINGS_DEG: Record<string, number> = { hyperion: 23, nereid: 12, iapetus: 11, mimas: 8, ceres: 8, tethys: 0.5, io: 0.2, europa: 0.5 };
 
 /**
  * The bodies the IAU WGCCRE 2015 report gives no rotational elements for: Hyperion tumbles, and