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/checklists/phase-6.md

@@ -24,10 +24,15 @@ The middle of each side wall and the top centre may be glass, to see the Pokémo
 
 ## In game (Prism instance)
 
-Creative mode gives the cores in the Functional Blocks tab; each has a recipe for survival.
+**The save "Machine Test (Phase 6)"** (2026-11-02): superflat, creative, cheats on, no wild Pokémon. You start between two rows; looking north, the first row has every machine working with a Pokémon inside (they belong to a "Showcase" owner, so you can watch but not take them out): Large Furnace with a furnace and a smoker fed by hoppers, Generator cabled to the Drop Synthesizer (gold shell, hopper and chest under its core), Sacrifice Altar, Rebirth Chamber. Behind you, the same machines empty, to try with your own Pokémon (`/pokegive`); further south, the bare cores. Signs say which is which.
+
+Elsewhere, creative mode gives the cores in the Functional Blocks tab; each has a recipe for survival.
+
+- [ ] Use a bare core (third row): ghost blocks show its shell for ten seconds, and chat lists what's missing. Place a new core anywhere: the same.
+- [ ] Hover a core in the inventory: the tooltip says what it does and what its shell is made of.
 
 - [ ] Build a Heat Core shell of bricks with glass in a side window, send out a Fire type and use the core: the Pokémon stands in the chamber, small enough to fit, and doesn't move. **Does it look right?** (the roadmap asks you to confirm this)
-- [ ] Put a furnace against the outside of that shell, a hopper with raw iron above it and a hopper with a chest below: the iron cooks without fuel, faster with a stronger Pokémon, and ends in the chest.
+- [ ] Put a furnace against the outside of that shell, a hopper with raw iron above it and a hopper with a chest below: the iron cooks without fuel, faster with a stronger Pokémon (speed doubled on 2026-11-02: 7.4× at Lv 50), and ends in the chest.
 - [ ] Build a Dynamo Core shell of copper with an Electric type, lay Poke Power cables from the core: sneak-use shows the energy made.
 - [ ] Put a Synthesis Core shell of gold blocks next to it (cables between), with a Pokémon inside and a hopper and chest under its core: its drops arrive in the chest. Swap the shell for diamond blocks: sneak-use shows looting 2.
 - [ ] Put a Lv 20+ Pokémon in an Altar Core shell: sneak-use shows the reward, sneak-use again within 5 seconds sacrifices it.