Record production tree v2 decisions and resource deposit rules

progression_design.md: rewrite the resource phases around the four
decided inputs (two mined everywhere, one deposit-gated mid resource,
one scrap-only late input), add the Resource deposits rule set
(freedom first / geography later, deposits only in expansions, patch
area as throughput cap, deterministic content, binary mining), note
the dual gating of the mid resource, and add the deposit-layer action
item.

content_design.md: mark the first-pass tree as superseded and record
the v2 decisions — iron/copper/quartz/voidsteel with their fiction
(M-type asteroid, quartz geodes, battle-forged voidsteel), titanium
dropped with its gating role moved to electronics and possibly a
quality-steel step, the material palette fingerprints, and the
laser-to-railgun rename with lasers reserved as a future weapon type.
Update the balancing target phase boundaries accordingly.

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

docs/progression_design.md

@@ -27,20 +27,55 @@ adapts later (see Refactorability).
 ## Resource phases
 
 - A run has exactly **four base inputs**:
-  1. Two mined ores available from the start.
-  2. A third mined ore unlocked mid-game (slower to mine than the starting
-     ores).
+  1. Two mined resources available from the start, minable on **every**
+     asteroid tile.
+  2. A third mined resource unlocked mid-game, minable **only on deposit
+     patches** found in expansion territory (see Resource deposits).
   3. A fourth input unlocked late-game, obtainable **only** from
      reprocessing salvaged scrap.
 - The fourth input is the core loop hook: capital ship production requires
   fighting (salvaging and reprocessing), not just mining.
+- Every gating has a fictional reason (concrete fiction in
+  `content_design.md`): the asteroid is a metal-rich body, so its bulk
+  rock is minable anywhere; the mid resource sits in rare pockets; the
+  late input is battle-forged — created only in the violence of ship
+  destruction, which is why any wreck (including the player's own)
+  yields it and no foundry can make it.
+- The mid resource is **dual-gated**: schematics (knowledge, via drops)
+  and territory (deposits, via expansions). Tuning must guarantee the
+  deposit-bearing expansion is comfortably affordable by the time the
+  first mid-tier schematics drop, or those drops are dead picks.
 - There is no direct "resource unlock" mechanism. Miner recipes unlock
   **implicitly** (REQ-LOCK-IMPLICIT) when some unlocked schematic's material
-  chain reaches that ore. Resource pacing is therefore controlled entirely
+  chain reaches that resource. Resource pacing is therefore controlled
   through the `unlock_at_station_level` values of ships, modules, and
   assembler recipe schematics — and the content must guarantee that the
   chains actually connect (a mid-game schematic must require an item whose
-  chain reaches the third ore, or the ore never unlocks).
+  chain reaches the mid resource, or it never unlocks).
+
+### Resource deposits
+
+- **Rule: freedom first, geography later.** The starting resources are
+  minable everywhere, so the player has full layout freedom while
+  learning. Later mined resources are bound to deposit patches — fixed
+  geography as a layout puzzle, introduced once the player is competent.
+- **Rule: deposits exist only in expansion territory.** Expansions buy
+  space *and* access to resource tiers — the second leg of the growth
+  curve (see Building block economy).
+- **Rule: patch area is the throughput cap.** Deposits never deplete but
+  are finite in area; the number of deposit tiles caps how many miners
+  the chain supports. Buying deeper expansions raises the throughput
+  ceiling of high-tier chains.
+- **Rule: no empty expansions.** Deposit content per expansion is
+  deterministic and config-defined; only the placement within the new
+  columns is randomized. Buying an expansion never rolls "nothing".
+- **Rule: mining is binary.** A miner whose footprint overlaps at least
+  one deposit tile of a resource can select that resource's recipe; no
+  partial-coverage rate scaling.
+- Deposits arrive at the periphery (expansions add columns on the left),
+  so each new chain starts in fresh space — supporting the
+  refactorability property — and high-tier chains have the longest belt
+  runs to the shipyards, escalating the logistics puzzle with tier.
 
 ## Production tree rules
 
@@ -48,11 +83,11 @@ adapts later (see Refactorability).
 
 - **Each phase transition adds exactly one new base input chain.** A base
   input is a bottom-level resource entering the factory from outside — a
-  mined ore or the scrap-only input. The early game starts with two ores
-  as the baseline; the transition to mid adds one (the third ore), the
-  transition to late adds one (the scrap-only input). No transition ever
-  introduces more than one unfamiliar bottom-level chain, so the factory
-  grows in one direction at a time.
+  mined resource or the scrap-only input. The early game starts with two
+  ores as the baseline; the transition to mid adds one (the deposit-bound
+  mid resource), the transition to late adds one (the scrap-only input).
+  No transition ever introduces more than one unfamiliar bottom-level
+  chain, so the factory grows in one direction at a time.
 - **Intermediates are generic shared parts.** Keep the item count low —
   modules and hulls of a tier draw from a shared pool of that tier's and
   lower tiers' intermediates rather than each having bespoke inputs.
@@ -330,3 +365,11 @@ in `requirements.md` and the git history). Still open:
    number of expansions already purchased (x = expansions bought so
    far), so expansion costs can escalate per the block economy rules.
    Update REQ-EXP-COST and wherever the UI displays the expansion cost.
+5. **Resource deposits.** Add a terrain deposit layer per the Resource
+   deposits rules: deposit patches generated in expansion columns
+   (deterministic content per expansion, randomized placement within the
+   new columns), deposit rendering, and a miner condition (a resource
+   recipe is selectable only if the miner's footprint overlaps at least
+   one matching deposit tile). Touches REQ-BLD-MINER ("every asteroid
+   tile is equivalent" no longer holds), REQ-GW-ASTEROID-EXPAND /
+   REQ-EXP-*, `world.toml`, and `visuals.toml`.