refactor: move TLE text parsing into a portable source module

The satellites layer parsed catalog text inside its Cesium-backed orbit
owner. Move the parser unchanged to src/sources/tle.js, add a catalog
number helper, and have the layer delegate to it so code outside the
layer can read TLE text without loading rendering.

scripts/package-boundaries.json

@@ -922,6 +922,7 @@
       "src/data/issPass.js",
       "src/data/satelliteClass.js",
       "src/data/satellitePass.js",
+      "src/sources/tle.js",
       "src/layers/satellites/catalog.js",
       "src/layers/satellites/controls.js",
       "src/layers/satellites/index.js",
@@ -1659,6 +1660,7 @@
       "src/layers/satellites/labels.js",
       "src/layers/satellites/lifecycle.js",
       "src/layers/satellites/orbits.js",
+      "src/sources/tle.js",
       "src/layers/satellites/records.js",
       "src/layers/satellites/policy.js",
       "src/layers/satellites/rendering.js",
@@ -2323,6 +2325,7 @@
       "src/layers/satellites/labels.js",
       "src/layers/satellites/lifecycle.js",
       "src/layers/satellites/orbits.js",
+      "src/sources/tle.js",
       "src/layers/satellites/records.js",
       "src/layers/satellites/policy.js",
       "src/layers/satellites/rendering.js",

src/layers/satellites/orbits.js

@@ -8,6 +8,7 @@ import {
   twoline2satrec,
 } from 'satellite.js';
 import { findNextSatellitePass } from '../../data/satellitePass.js';
+import { parseTleText } from '../../sources/tle.js';
 import { ORBIT_PATH_STEPS, ISS_NORAD } from './policy.js';
 
 export function createOrbits({ state: layerState, services, parts, source }) {
@@ -40,24 +41,7 @@ export function createOrbits({ state: layerState, services, parts, source }) {
   /**
    * Parse TLE text into array of { name, line1, line2 } objects.
    */
-
-  function parseTLE(text) {
-    const lines = text
-      .trim()
-      .split('\n')
-      .map((l) => l.trim())
-      .filter((l) => l.length > 0);
-    const result = [];
-    for (let i = 0; i < lines.length - 2; i += 3) {
-      const name = lines[i];
-      const line1 = lines[i + 1];
-      const line2 = lines[i + 2];
-      if (line1.startsWith('1 ') && line2.startsWith('2 ')) {
-        result.push({ name, line1, line2 });
-      }
-    }
-    return result;
-  }
+  const parseTLE = parseTleText;
 
   /**
    * Propagate satellite position at a given JS Date.

src/sources/tle.js

@@ -0,0 +1,27 @@
+/**
+ * Parse three-line TLE catalog text into `{ name, line1, line2 }` entries.
+ * Blocks whose second and third lines are not TLE lines 1 and 2 are skipped.
+ */
+export function parseTleText(text) {
+  const lines = String(text)
+    .trim()
+    .split('\n')
+    .map((line) => line.trim())
+    .filter((line) => line.length > 0);
+  const result = [];
+  for (let i = 0; i < lines.length - 2; i += 3) {
+    const name = lines[i];
+    const line1 = lines[i + 1];
+    const line2 = lines[i + 2];
+    if (line1.startsWith('1 ') && line2.startsWith('2 ')) {
+      result.push({ name, line1, line2 });
+    }
+  }
+  return result;
+}
+
+/** The NORAD catalog number from TLE line 1, or null. */
+export function tleCatalogNumber(line1) {
+  const number = Number.parseInt(String(line1).slice(2, 7), 10);
+  return Number.isInteger(number) ? number : null;
+}