Keep the star visible at the distance that frames its system

Framing the whole system pushed the camera far enough back that the star
at the centre became a speck — about a pixel across for the Sun.

The cause is a constraint that cannot be tuned away. A star is sized
against its system's innermost orbit, because it must never swallow its
closest planet, while the camera is placed to frame the outermost ring.
In the solar system those differ by a factor of a hundred: at the distance
that fits Pluto in view, a disc that stays clear of Mercury is a pixel
across. No radius satisfies both, because the information genuinely does
not fit on one screen at that zoom.

So the disc stays honest to the orbits and the halo carries the
visibility. Light is not a surface: a glow that reaches past the innermost
orbit says the star is bright, not that it is large. Its extent is still a
multiple of the star — so a compact system keeps exactly the corona it had
— but floored against the framed radius, which is what the wide systems
needed.

The disc grows a little too: it may now reach 45% of the innermost orbit
rather than 35%, which still leaves clear space between the star's limb
and the closest orbit.

Also makes createGlowSprite take the extent it will draw rather than a
radius and a multiplier. The two were only ever multiplied together, and
how large a star's halo should be is not a property of the star — it
depends on how its system is framed, which is a decision that belongs with
the framing.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WaySiNst4HhDXBHnMy8p5G

src/app/features/galaxy-system/system-framing.ts

@@ -25,7 +25,25 @@ export const DEFAULT_STAR_MARKER_RADIUS_AU = 0.2;
  * space between the star's limb and the closest orbit, rather than the orbit grazing or
  * disappearing inside it.
  */
-const STAR_RADIUS_TO_INNERMOST_ORBIT = 0.35;
+const STAR_RADIUS_TO_INNERMOST_ORBIT = 0.45;
+
+/**
+ * Halo extent as a multiple of the star's own radius, and the floor on that extent as a
+ * fraction of the framed radius.
+ *
+ * The floor is what keeps a star visible. A system's star is sized against its *innermost*
+ * orbit — it must never swallow its closest planet — while the camera is placed to frame the
+ * *outermost* ring, and those differ by a factor of a hundred in the solar system. At the
+ * distance that fits Pluto in view, a disc that stays clear of Mercury is about one pixel
+ * across; there is no radius that satisfies both, because the information genuinely does not
+ * fit on one screen at that zoom.
+ *
+ * The halo resolves it, because light is not a surface: a glow that reaches past the innermost
+ * orbit does not claim the star is that large, it claims the star is bright. So the disc stays
+ * honest to the orbits and the halo is floored against the frame.
+ */
+const STAR_GLOW_TO_MARKER = 3.2;
+const MIN_STAR_GLOW_TO_FRAME = 0.035;
 
 /**
  * Clear space left around the framed radius, as a fraction of it. The camera backs off this
@@ -125,6 +143,20 @@ export function systemFrameRadiusAu(distanceAu: number, viewport: SystemViewport
   return distanceAu * tightHalfExtent(viewport);
 }
 
+/**
+ * Extent (AU) of the star's glow sprite — how wide it is drawn, not its radius.
+ *
+ * Normally a multiple of the star's own radius, so a compact system keeps the corona it has.
+ * Floored against the framed radius, so a star framed from far enough out to hold its whole
+ * system still reads as a bright point rather than disappearing into it. `glowScale` lets a
+ * caller dim the halo for stars drawn without a real photograph.
+ */
+export function starGlowExtentAu(markerRadiusAu: number, frameRadiusAu: number, glowScale = 1): number {
+  const fromStar = markerRadiusAu * STAR_GLOW_TO_MARKER * glowScale;
+  const fromFrame = Number.isFinite(frameRadiusAu) && frameRadiusAu > 0 ? frameRadiusAu * MIN_STAR_GLOW_TO_FRAME : 0;
+  return Math.max(fromStar, fromFrame);
+}
+
 /**
  * Distance (AU) to settle the camera at so that `framedRadiusAu` fits in view with a margin
  * around it.