Root cause: update_from_state() used visible_tiles (always empty in live
server mode) instead of visible_positions for bounds calculation. Bounds
never grew beyond 64x64, so tiles outside that area rendered as solid
unexplored black.
Fix: new _grow_bounds_from_positions() method reads visible_positions
(always populated from server snapshots). Shader fix: removed the
(explored < 0.01 && vis_raw < 0.01) guard that cut off the Gaussian
gradient at unexplored tile boundaries. Doubled blur step size for
D-066 compliant 6-8 tile soft gradient. Added debug_exploration mode
for diagnostic rendering of the exploration texture.
19 acceptance tests covering exploration persistence, bounds grow-only
invariant, gradient margin, Forward-only visibility writes, and
exploration data surviving texture resize.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>