render3d: stream_capture runs the game's own fill for a chunk outside any frame, for the bake

stream_capture(s, cx, cz, band) points the stream at a chunk of its own (made on the first capture),
calls the registered r3d_stream_fill for that cell and band, and returns how many instances it
emitted; stream_captured(i, k) reads them from stream_scratch. Build-time only; nothing in a frame
calls it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.render3d/env.ludic

@@ -829,6 +829,7 @@ export state Render3dState {
   ter_ortho_tex: int = 0            # a photograph of the same window, draped with distance
   ter_carpet: int = 0               # the distant-grass carpet (carpet_bake), 0 = none
   ter_shadow_tex: int = 0           # height-field sun shadow: R32F, the lowest lit height
+  stream_capture_c: Chunk = null    # the bake's capture chunk (stream_baked.ludic)
   sb_rec: floats = floats(8)        # one decoded baked record, reused (stream_baked.ludic)
   tt_dir: string = ""               # terrain_tiles_to: where a map's tiles are written ("" keeps the whole copies)
   tt_key: string = ""