Metabolism M2.8: rock — inert resource the song drops and builders quarry, carry and build with; livelier metabolisms

metabolism/EVOLUTION.md

@@ -177,6 +177,36 @@ holds at 640×360 (~12 ms/frame sim+render). Songs still diverge ≫ seeds on
 the fingerprint (classMix now sorted — the seed permutes the casting, the
 song decides its shape).
 
+### M2.8 — rock: the world gains an inert resource ✔
+
+The films were alive but weightless: nothing on the map was *stuff*. Rock is
+the correction — an inert resource with mass, presence and consequence:
+
+- **the field** (`world.rock`) — a rock height per cell; above 0.55 the cell
+  is impassable (advection aims mass at stone and the mass stays, piling
+  against the wall; diffusion only crosses open edges). Food does not recharge
+  through rock: capped ground is barren until someone quarries it open.
+- **the song's weather** — the map is born with a deterministic scatter of
+  stone (7–15 blobs, from the seed). Strong low/mid hits DROP rock where they
+  land (and crush what they land on); strong high hits SHATTER it. The
+  section regimes gained `rockfall` and `erode` operators: drops rain stone,
+  breakdowns weather it away.
+- **the masons** — builders gained two VM actions: **dig** (a slow bite out
+  of the rock, which becomes carried burden — and grinding yields soil, a
+  little food, right where they dug) and **build** (the carried burden rises
+  as a wall where the ground is clear). The carry lives in per-block registers
+  of the world, so stone genuinely travels: quarries open, roads run from
+  them, walls rise where the colony loiters.
+- **livelier organisms** — slower metabolisms (longer lives off food), faster
+  strains, softer bare-ground starvation: agents travel farther between
+  wells, meet more, and work more.
+
+*Outcome:* 44 tests green, with new pins: the deterministic scatter; the
+song's rockfall outpacing a mute sky; a stone wall holding a crowd west of it
+for 10 s straight; quarries opening with soil and burden appearing; carried
+rock rising as walls. The strips read it directly: grey masses the colonies
+grow around, fronts grinding along them.
+
 ### M3 — the lens: travel, don't cut
 Replace the cut-to-a-point grammar with a **move grammar**: *track* (follow a
 moving front), *reveal* (pan along a coastline), *establish* (hold wide and