Phase 6: shell preview, core tooltips, machine test world, faster furnace

Adrian (2026-11-02): double the furnace speed; there must be a way in
game to see how a machine is built; a test world with the machines.

- Large Furnace speed doubled (2 + 0.08 x level + 0.02 x SpA).
- Ghost preview: placing a core, using it with an incomplete shell, or
  sneak-using it empty shows every wrong spot as a small glowing block
  display for 10 s (never saved), in the core's orientation, with a
  chat line counting what's missing.
- Core tooltips: what the machine does, what its shell is made of.
- /cobblesurvival machines showcase builds every machine three times
  (working with a Showcase-owned Pokemon, empty, bare core) with signs,
  hoppers, chests and cables; tools/make_machine_world.py makes a
  superflat creative world from it (level.dat via tools/nbtfile.py)
  and --prism installs it as "Machine Test (Phase 6)".
- Self-tests machine_preview_shows_the_shell and
  machine_showcase_builds_every_machine; docs and checklist.

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

docs/balance.md

@@ -31,7 +31,7 @@ Every tunable lives in a config file or in this table. **Placeholder** means gue
 | Breeding (Cobbreeding) | mod defaults: an egg every 8,000–14,000 ticks per breeding pasture, hatch multiplier 1.0 (about 10 min for 20 egg cycles), Masuda shiny boost ×4, no random eggs from two Dittos, no gate | Placeholder | `config/cobbreeding/main.json` (written by the mod; the pack ships none) | Adrian, 2026-10-31: breeding without a gate |
 | Machine shells | 3×3×3, core in a wall, chamber in the centre; casing: Heat bricks/mud bricks/deepslate bricks; Dynamo copper blocks; Synthesis iron/gold/diamond/netherite blocks; Altar obsidian/crying obsidian/blackstone/polished blackstone bricks; Rebirth amethyst/quartz/calcite; glass allowed at the window spots | Placeholder | `datapacks/core/data/cobblesurvival/machines/*.json`, `tags/block/*_casing.json` | Adrian, 2026-10-31 (Phase 6) |
 | Core recipes | Heat: 4 bricks, 4 iron ingots, blast furnace; Dynamo: 4 copper blocks, 4 redstone, thunder stone; Synthesis: 4 iron blocks, 2 redstone blocks, 2 hoppers, crafter; Altar: 4 obsidian, 4 gold blocks, echo shard; Rebirth: 4 amethyst blocks, 4 diamonds, shiny stone | Placeholder | `datapacks/core/data/cobblesurvival/recipe/*_core.json` | |
-| Large Furnace | furnaces heated: 1 + level/15 (max 8); cooking speed 1 + 0.04 × level + 0.01 × Special Attack (e.g. Lv 50, SpA 70: 3.7×); no fuel | Placeholder | `machines/heat_core.json` | |
+| Large Furnace | furnaces heated: 1 + level/15 (max 8); cooking speed 2 + 0.08 × level + 0.02 × Special Attack (e.g. Lv 50, SpA 70: 7.4×; doubled, Adrian 2026-11-02); no fuel | Placeholder | `machines/heat_core.json` | |
 | Generator | 50 FE/t per level × (1 + 0.005 × Special Attack) (Lv 30, SpA 50: 1,875 FE/t); stores 200,000 FE, pushes up to 16,000 FE/t | Placeholder | `machines/dynamo_core.json` | After Poke Power's 50 FE per level |
 | Drop Synthesizer | 2,000,000 FE per drop roll, takes up to 32,000 FE/t (one roll a minute at most), stores 4,000,000 FE; looting by casing tier: iron 0, gold I, diamond II, netherite III (+0–1 per drop per level; 25 % per level for a second roll); 9 output stacks | Placeholder | `machines/synthesis_core.json` | |
 | Sacrifice Altar | from Lv 20: 3 Exp. Candy S; 35: 3 M; 50: 3 L; 65: 2 XL + Ability Capsule; 80: 3 rare candies + 2 XL; 90: 5 rare candies + Ability Patch; 100: 8 rare candies + Ability Patch + nether star; Lv 100 Dragon type: + dragon egg; confirm within 5 s | Placeholder | `machines/altar_core.json` | Rare candies above the highest natural level (Lv 75 guardians) |