Draft the v2 production tree structure

Add the tree structure draft to the v2 decisions section: mined and
smelted items, reprocessing pool, intermediates per tier with ratio
classes and archetypes, hull and module recipes as input lists, the
resolved m+ hull gate (hardened_steel plus control_chip), shortcut
recipe candidates, and a refactorability spot-check. Quantities and
durations are deferred to the numbers pass against the threat ladder.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DyCu8vwChKMbLJQ3xosYEN

docs/content_design.md

@@ -229,6 +229,116 @@ refactorability). Decisions fixed so far:
   arriving with quartz optics. More weapon types are planned; railguns
   are simply the baseline tech that ships with v1.
 
+### Tree structure — draft
+
+Recipes are sketched as input lists only; quantities and durations come
+in the numbers pass, tuned so every chain sums to its threat-ladder
+value and follows the ratio curve (t1 nice → t4 strange). Glass/optics
+are cut from v1 — their only consumers would be lasers, which are
+deferred; the silicon family ships as silicon + ceramics.
+
+**Mined (miner):** `iron_ore`, `copper_ore` (every tile), `quartz`
+(geode deposits in expansion territory).
+
+**Smelted (smelter — exactly one recipe per input item):**
+
+| output | input | ratio class |
+|---|---|---|
+| iron_ingot | iron_ore | nice (1:1 or 1:2) |
+| copper_ingot | copper_ore | nice |
+| silicon | quartz | mid entry |
+| iron_ingot | scrap | the safe, boring scrap sink |
+
+**Reprocessing pool (scrap):** `iron_ingot`, `copper_ingot`, `silicon`,
+`voidsteel` — the only source of voidsteel. Weights authored for the
+fully unlocked pool state.
+
+**Tier 2 — early intermediates (clean ratios, ~2:3):**
+
+| item | inputs | role |
+|---|---|---|
+| steel_plate | iron_ingot | structure backbone, highest volume |
+| copper_wire | copper_ingot | conductors |
+| copper_coil | copper_wire | electromagnets: railguns, thrusters |
+| building_block | steel_plate | depth-3 chain = the doubling-time knob |
+
+**Tier 3 — mid intermediates (strange ratios begin, need quartz):**
+
+| item | inputs | role |
+|---|---|---|
+| control_chip | silicon + copper_wire | electronics gate for m+ hulls |
+| capacitor_bank | copper_coil + silicon | power for railgun m/l |
+| hardened_steel | steel_plate (long cycle) | quality gate for m+ hulls; time-heavy |
+| ceramic_plate | quartz | heat shielding: drives, l guns, capitals |
+| drive_unit | steel_plate + copper_coil + control_chip | propulsion for m+ hulls |
+
+**Tier 4 — late intermediates (need voidsteel):**
+
+| item | inputs | role |
+|---|---|---|
+| voidsteel_plate | voidsteel + hardened_steel | capital structure |
+| capital_core | voidsteel + capacitor_bank + control_chip | capital heart |
+
+**Hull items** (`<ship>_hull`, assembler-made; the shipyard consumes the
+hull item plus module materials). The m+ hull gate is resolved as
+**both** of the open-question options: hardened_steel (quality steel, a
+deliberately long-running recipe — the time-heavy step) *and*
+control_chip (electronics):
+
+| hull | inputs |
+|---|---|
+| drone_hull | steel_plate |
+| frigate_hull | steel_plate + copper_wire |
+| destroyer_hull | steel_plate + copper_coil |
+| cruiser_hull | hardened_steel + control_chip |
+| battlecruiser_hull | hardened_steel + control_chip + drive_unit |
+| battleship_hull | voidsteel_plate + drive_unit + control_chip |
+| dreadnought_hull | voidsteel_plate + capital_core + drive_unit |
+| carrier_hull | voidsteel_plate + capital_core + drive_unit |
+
+**Module items** (`<module>_module`, assembler-made prefabs — kept as
+items so shipyard belt inputs stay simple and module production can be
+stockpiled):
+
+| module | inputs | archetype |
+|---|---|---|
+| railgun_s | steel_plate + copper_coil | balanced |
+| salvager | steel_plate + copper_wire | balanced |
+| repair_tool | steel_plate + copper_wire | balanced |
+| armor_plates | steel_plate (many) | material-heavy, fast |
+| maneuvering_thrusters | steel_plate + copper_coil | balanced |
+| sensor_booster | copper_wire + copper_coil | lean (an antenna, no chip) |
+| afterburner | copper_coil + steel_plate | balanced |
+| weapon_stabilizer | steel_plate + copper_coil | balanced |
+| weapon_primer | capacitor_bank + copper_coil | mid; time-heavy |
+| weapon_upgrade | control_chip + copper_coil | mid; time-heavy |
+| railgun_m | capacitor_bank + steel_plate + copper_coil | mid |
+| drone_bay | control_chip + steel_plate + copper_coil | mid |
+| railgun_l | capacitor_bank + hardened_steel + ceramic_plate | late |
+| drone_hangar | voidsteel_plate + control_chip + drive_unit | late (carrier only) |
+
+Refactorability check (the default technique holds): railgun_s → m
+introduces capacitor_bank, built from a subset of the small gun's
+inputs (copper_coil) plus the new base resource (silicon); the m gun
+otherwise reuses the small gun's inputs. Hulls likewise: cruiser adds
+hardening (fed by the existing steel line) and chips (fed by the new
+quartz territory) without touching the iron/copper core.
+
+**Shortcut recipe candidates** (drop-only assembler schematics; not
+every strange chain gets one):
+
+- `iron_ore → steel_plate` — skips the ingot step on the highest-volume
+  chain in the game.
+- `quartz → control_chip` — skips silicon on the electronics chain.
+- `iron_ingot → hardened_steel` — a nicer-ratio route past the
+  deliberately awkward hardening step.
+
+Item count: 3 mined + scrap + 3 smelted + 4 t2 + 5 t3 + 3 t4 (incl.
+voidsteel) + 8 hulls + 14 modules ≈ 41 item types — same scale as the
+first-pass tree. `verify_recipes.py` must be re-run once this lands in
+recipes.toml; the numbers pass should add a threat-report tool that
+prints per-item threat values and producer:consumer ratio tables.
+
 ## Balancing targets (first pass, July 2026)
 
 The six root numbers for the balancing pass. Every derived value (threat