Match exoplanet hosts on the sky, at both epochs the archive might mean

The host cross-reference matched in 3D, nearest star within half a parsec.
That is the wrong space for the same reason the star merge learned it: a
direction is measured, a distance is inferred. At 170 pc half a parsec is a
ten-arcminute cone, wide enough to hand the planets of stars our catalogue
does not carry to whatever bright star floats nearest — HATS-6 b sat on
HD 39500, seventy arcseconds away. At 60 pc it is tighter than the routine
disagreement between the archive's Hipparcos distances and our Gaia ones,
which is how four bright giants (7 CMa, HD 81688, omi UMa, xi Aql) lost
their planets and GJ 15 A's landed on a neighbouring entry.

Hosts are now resolved like stars are merged: by name first, then the
nearest star on the sky within a transverse budget — angle times the
archive's distance, 0.01 pc — whose distance does not flatly contradict the
archive's (the merge's own 50 % ratio). The budget is transverse because the
dominant error is proper motion over an epoch difference, a physical
displacement that is the same in parsecs at every distance: as an angle it
is 60" for Proxima and 2" for a host at 100 pc. Measured on the 504 hosts
whose archive name matches a catalogue name outright, true pairs reach
3.4e-3 pc; shifting every host a quarter of a degree finds nothing else
within 0.01 but Proxima's own entry, whose budget at 1.3 pc is wider than
the shift.

The archive never says which epoch a position is for, and they are mixed:
alf Tau and GJ 273 publish J2000, HD 133131 and TOI-2459 publish Gaia's
J2016. So the query asks for sy_pmra/sy_pmdec too, tries each position at
both ends of those sixteen years, and judges a star on whichever is closer.
Guess one epoch and a fast star's planets land on a companion: J2016 puts
Aldebaran's on Gl 171.1B, J2000 puts GJ 15 A's on a Gaia entry 15.9" out.

1 972 of 6 354 planets now sit on a host, 1 548 before: 432 gained, 26 on a
better star (GJ 15 A to Groombridge 34, GJ 676 A off its companion,
HD 19994 to 94 Cet), 8 lost — six false 3D matches to stars the catalogue
never contained, and GJ 273 b/c, whose archive row says 5.92 pc for
Luyten's Star at 3.79: a distance in flat contradiction is exactly what the
ratio guard exists to refuse, and the number to fix is upstream.

The 2 pc "rematch" apparatus is gone. build.ts recomputed every match after
fetchExoplanets had already written the file — at a different tolerance, so
the log reported a match count the data did not contain — and the offline
entry point that persisted it had no caller. One matcher, one set of
constants, used once. The archive cache is now keyed by a hash of the TAP
query, so a response cached before the proper-motion columns cannot serve
rows without them, where a missing cell would quietly read as "does not
move"; the row's astrometry is stored with each planet, which is what made
these tolerances measurable offline in the first place.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016jxMkwA2rbicdGxHosecYi

tools/etl/build.ts

@@ -10,7 +10,6 @@ import { fetchSolarSystem } from './fetchSolarSystem';
 import { BYTES_PER_STAR_META, BYTES_PER_STAR_POSITION, decodeStarCatalog, encodeStarCatalog } from '../../src/app/shared/models/star-catalog';
 import { fetchStars } from './fetchStars';
 import { describeSources } from './sources/registry';
-import { rematchHostStars } from '../../src/app/shared/astro/host-star-matching';
 import { dataPath } from './lib/paths';
 
 class ValidationError extends Error {}
@@ -161,18 +160,6 @@ async function build(): Promise<void> {
   const deepSky = await fetchDeepSky();
   console.log();
 
-  // The cross-reference depends on the star catalogue as much as on the archive, so it is
-  // resolved again here against whatever catalogue this run produced. A no-op when the two were
-  // fetched together, and the whole point when only one of them was.
-  const rematch = rematchHostStars(exoplanets, stars);
-  console.log(
-    `Cross-referencing exoplanet hosts against ${stars.length} stars...\n` +
-      `  ${rematch.matched}/${rematch.total} matched` +
-      (rematch.resolvable < rematch.total ? ` (${rematch.total - rematch.resolvable} records predate stored host coordinates and kept their existing match)` : '') +
-      (rematch.gained || rematch.lost ? `; ${rematch.gained} gained, ${rematch.lost} lost` : '')
-  );
-  console.log();
-
   console.log('Validating output...');
   validateStars(stars);
   validateBodies(bodies);