Sync progression_design.md with implemented action items

Prune completed action items 1-4 and 8 (scrap-from-threat, schematic
upgrade and ship level removal, balancing tool cleanup, unlock
prerequisites), renumber the remaining three, and update stale
cross-references: cite REQ-LOCK-PREREQ and unlock_requires, reflect
that REQ-THREAT-SCRAP is now the 1/scrap_per_threat constant, and
drop the obsolete level-up wording from the artifact rule.

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

docs/progression_design.md

@@ -153,7 +153,7 @@ supporting different fleet doctrines feel structurally different to build.
 - **All time scaling lives in the threat rate** — waves get bigger, ships
   of a given schematic never get individually stronger. There is no ship
   level dimension: stat formulas are plain values, and per-ship level
-  scaling (`ship_level_formula`) does not exist (see Action items). Push
+  scaling does not exist. Push
   scaling on enemy defence stations is the separate, player-triggered
   difficulty axis and keeps its level formulas.
 
@@ -169,9 +169,10 @@ supporting different fleet doctrines feel structurally different to build.
   its materials need can be unlocked alongside it.
 - **Schematics can require other schematics.** Beyond the station-level
   gate, a schematic (ship, module, or assembler recipe) may list
-  prerequisite schematics that must already be unlocked before it enters
-  the drop pool — e.g. the medium laser requires the small laser; a
-  future Mk2 requires its base version. Station level gates the earliest
+  prerequisite schematics (`unlock_requires`, REQ-LOCK-PREREQ) that must
+  already be unlocked before it enters the drop pool — e.g. the medium
+  laser requires the small laser; a future Mk2 requires its base version.
+  Station level gates the earliest
   *when*; prerequisites gate the *order*, keeping drop offers coherent
   with what the player already owns.
 - **No duplicate drops.** Ship and module schematics leave the drop pool
@@ -184,8 +185,8 @@ supporting different fleet doctrines feel structurally different to build.
   tasks), never as free level-ups.
 - **Artifacts trade power for progress.** Artifact options compete with
   schematic picks in the same choice dialog; the artifact chance must be
-  tuned so that taking one is a real decision (giving up a level-up or
-  unlock), not automatic in either direction.
+  tuned so that taking one is a real decision (giving up an unlock), not
+  automatic in either direction.
 
 ## Scrap & reprocessing economy
 
@@ -206,8 +207,8 @@ supporting different fleet doctrines feel structurally different to build.
   the exception: they keep authored `scrap_drop_formula`s, because pushing
   rewards are tuned independently of ship production costs.
 - Consequence: the threat value of scrap is the constant
-  `1 / scrap_per_threat`. The min-`scrap_drop` schematic derivation
-  (REQ-THREAT-SCRAP) and its potential circularity disappear.
+  `1 / scrap_per_threat` (REQ-THREAT-SCRAP). The former min-`scrap_drop`
+  schematic derivation and its potential circularity are gone.
 - **Rule:** the late-game input's income rate meaningfully gates capital
   production — unlocking a capital hull must not mean spamming it; the
   input trickles in slowly enough that every capital ship is a noticeable
@@ -272,47 +273,22 @@ Constraints that every recipe must respect, independent of tuning:
 ## Action items — changes beyond this document
 
 Agreed changes that require edits to `requirements.md`, the code, and the
-configs:
+configs. Completed items are removed from this list (their outcomes live
+in `requirements.md` and the git history). Still open:
 
-1. **Derive ship scrap from threat.** Add `scrap_per_threat` to
-   `world.toml`; remove `[ship.loot].scrap_drop` from `ships.toml`; update
-   REQ-RES-SCRAP-DROP; replace REQ-THREAT-SCRAP with the constant
-   `1 / scrap_per_threat`. Station `scrap_drop_formula`s stay.
-2. **Remove schematic upgrades.** Owned ship/module schematics leave the
-   drop pool (REQ-DEF-SCHEMATIC-DROP); drop the new-unlock/level-up
-   annotation from the choice dialog; remove `player_production_level`
-   from `ships.toml`, `modules.toml`, and the code paths that increment
-   and evaluate it (REQ-BLD-SHIPYARD, REQ-MOD-CONFIG).
-3. **Remove ship levels entirely.** Delete `ship_level_formula`
-   (REQ-WAV-SHIP-LEVEL); replace all stat formulas in `ships.toml` and
-   `modules.toml` with plain values (REQ-SHP-STATS, REQ-MOD-CONFIG,
-   REQ-MOD-STAT-CALC evaluation rules). Enemy defence stations keep their
-   station-level formulas — push scaling is unaffected.
-4. **Balancing tool follow-up.** Remove the per-ship-entry `level` from
-   `balancing.toml` and the `L<level>` display format (REQ-BAL-TEAM,
-   REQ-BAL-CONFIG-GAME, REQ-BAL-UI-WIDGET, REQ-BAL-UI-INSPECT-WINDOW);
-   station entries keep their level. Ship stats panels no longer evaluate
-   at a level (REQ-MOD-UI-STATS-PANEL, REQ-UI-SHIP-STATS-PANEL).
-5. **Fill unfillable schematic slots with artifacts.** With duplicates
+1. **Fill unfillable schematic slots with artifacts.** With duplicates
    removed, the schematic drop pool can run dry — previously unreachable.
    Decision: every slot in the choice dialog that cannot be filled with a
    schematic because the eligible pool is exhausted is filled with an
    artifact option instead (in addition to any artifact option granted by
    the regular artifact roll). A push therefore always awards a full
    dialog. Update REQ-DEF-SCHEMATIC-DROP.
-6. **Confirm wave scaling carries alone.** With per-ship level scaling
-   gone, `threat_rate_formula` is the only time-scaling axis; verify the
-   current `world.toml` values still produce the intended difficulty
-   curve (the config reportedly already runs with a flat ship level, so
-   this is likely a review, not a retune).
-7. **Gate shortcut-recipe drops on their inputs.** Extend the assembler
+2. **Confirm wave scaling carries alone.** With per-ship level scaling
+   removed, `threat_rate_formula` is the only time-scaling axis; verify
+   the current `world.toml` values still produce the intended difficulty
+   curve (likely a review, not a retune, since the config already ran
+   with a flat ship level before the removal).
+3. **Gate shortcut-recipe drops on their inputs.** Extend the assembler
    recipe schematic pool eligibility in REQ-DEF-SCHEMATIC-DROP: in
    addition to the existing station-level and output-item checks, all of
    the recipe's input item types must be implicitly unlocked as well.
-8. **Schematic prerequisites.** Add an optional prerequisite list to
-   ship, module, and assembler recipe schematic entries (e.g.
-   `unlock_requires = ["laser_cannon_s"]`): a schematic enters the drop
-   pool only when every listed schematic is already unlocked, in addition
-   to the station-level check. Update REQ-DEF-SCHEMATIC-DROP and
-   REQ-LOCK-EXPLICIT. This is also the mechanism the future Mk2 design
-   builds on (`*_mk2` requires the base schematic).