platformer: finish Phase E — the goo serpent (L6) + the serpent generalized

CHANGELOG.md

@@ -10,16 +10,30 @@ The native shim's ABI is tracked separately by `b2Version()` (currently `4`).
 
 ### Added
 
+- **Platformer: the GOO SERPENT in a slime-pool beat + the serpent generalized
+  (asset-expansion Phase E, continued).** L6's PIT2 spike chasm becomes a **toxic
+  GOO POOL** (new `pfMakeSlimePool` — a green goo rect over a knockback hurt
+  sensor, the slime-biome twin of `pfMakeLava`) where a rearing **`snakeSlime`
+  serpent** rises out of the goo, arcs across and sinks back in, peaking at
+  jump-arc height so you time your double-jump for when it has sunk (a mistimed
+  leap or a slip into the goo is a recoverable knockback). The L4 lava serpent's
+  maker is generalized to `pfMakeSerpent pL,pR,pSurfY,pPeakY,pFrame,pAnim` (tick
+  `pfTickSerpent`), driving both the lava (`snakeLava`) and goo (`snakeSlime`)
+  skins from one code path (single-instance — one serpent per level, reset on each
+  build). Plus two more plain **snake** placements for variety: a meadow snake on
+  L1 and a sand snake on L5. Self-gates on `gSpooksOK`; static gates clean, audit
+  0 findings.
 - **Platformer: the LAVA SERPENT + a widened L4 lava pit (asset-expansion Phase
   E).** L4's old collapsing bridge (which never read right) is **gone**; in its
   place the lava pit is widened to a **512px chasm** (2944..3456, up from a 192px
   strip) crossed in **two ~160px hops** over a middle **stepping-stone**, and a
   rearing **LAVA SERPENT** (`snakeLava` art, bodiless) rises OUT of the lava, arcs
   ACROSS it and sinks back in on a sine path, **peaking at the stepping-stone** so
   it contests the very rock you must land on (time your hops between its rises).
-  New `pfMakeLavaSerpent` / `pfTickLavaSerpent`: a pure sprite created BEFORE the
-  lava tiles so the y576 tile row occludes its submerged lower body (it reads as
-  rising from / sinking into the lava), with a visibility toggle backing the
+  `pfMakeSerpent` / `pfTickSerpent` (the generic serpent maker/tick): a pure
+  sprite created BEFORE the lava tiles so the y576 tile row occludes its submerged
+  lower body (it reads as rising from / sinking into the lava), with a visibility
+  toggle backing the
   no-tile fallback; the head's strike zone is a proximity-poll knockback (the saw
   rule, gotcha 16), never a stomp. The collapsing-bridge maker/tick/globals were
   removed wholesale. Self-gates on `gSpooksOK` - absent the spooks sheet the pit is

CLAUDE.md

@@ -250,6 +250,16 @@ OXT's compiler is **stricter than LiveCode's**. These are the recurring footguns
    real half-height (a build-time global), never a hardcoded constant. The
    platformer's brick-smash gap (round 7) was exactly this: an 88px capsule
    over a ~76px visible character.
+29. **A `constant` must be declared BEFORE its first use, lexically.** OXT resolves
+   `constant` names by their position in the file, so a handler that references a
+   constant declared *later* gets an UNRESOLVED name: it compiles with no error,
+   then evaluates to nothing at runtime, silently zeroing the expression. The L4
+   lava serpent shipped broken this way — `pfTickLavaSerpent` used `sin(kPI * tP)`
+   while `kPI` was declared ~900 lines below, so the term collapsed to 0 every
+   frame and the serpent never rose (it stayed in its "submerged, hidden" branch
+   forever). Fix: declare the constant above its first use, or inline the literal
+   value. Distinct from gotcha 6 (constant *values* must be literals) — this is
+   about the *order* of declaration vs use. (Confirmed in OXT.)
 
 ## The single-threaded performance playbook
 

docs/asset-expansion-plan.md

@@ -226,30 +226,35 @@ needs an OXT eye.
   `spooks`, via `pfMakeCritter`'s new optional sheet param, `gSpooksOK`-gated) and
   the **ring worm** (`worm_ring`, native foes). Phase D essentially complete.
 
-### Phase E — Snakes & the slither biome beat  (M)  — BEGUN
+### Phase E — Snakes & the slither biome beat  (M)  — DONE (pending OXT)
 - **Assets:** `snake(.png)/_walk/_hit/_dead`, `snakeLava*`, `snakeSlime*`.
 - **New movement type:** **slither** — a ground crawler that hugs the floor and
   reverses at edges/walls (slime-family kind `snake`, animated `_walk`). The LOW
   `snake.png` is the crawler; the TALL rearing `snakeLava`/`snakeSlime` art is the
-  rising **lava serpent** (a separate bodiless mover, not a floor crawler).
-- Woven into L4 and the new biomes (no dedicated level needed).
+  rising **serpent** (a separate bodiless mover, not a floor crawler).
+- Woven into L4 (lava), L6 (goo), and across the biomes (no dedicated level needed).
 - **Done (pending OXT):**
   - The `snake` kind + slither tick (floor-probe edge/wall reversal) +
     `pfMakeSnake pIdx,pX,pMinX,pMaxX,pTopY` — the plain low crawler, `gSpooksOK`-
-    gated, via `pfMakeCritter`'s sheet param. Deployed: L3's ice platform (turns at
-    the spike pit) and L4's lava-pit approach (turns at the entry pit + lava lip).
-  - **The "serpent pit" beat (`pfMakeLavaSerpent`/`pfTickLavaSerpent`):** L4's old
-    collapsing bridge is removed; the lava pit is widened to a 512px chasm crossed
-    in two hops over a middle stepping-stone, and a rearing `snakeLava` serpent
-    rises out / arcs across / sinks back in on a sine path, peaking at the stone
-    (a proximity-poll knockback, the saw rule). Created under the lava tiles so its
-    submerged body is occluded.
+    gated, via `pfMakeCritter`'s sheet param. Deployed: L1 meadow, L3 ice, L4
+    lava-approach, L5 desert — the slither type across four biomes.
+  - **The serpent (`pfMakeSerpent`/`pfTickSerpent`, generic):** a rearing snake
+    that rises out of a hazard pool, arcs across on a sine path and sinks back in,
+    peaking high so it contests the crossing (a proximity-poll knockback, the saw
+    rule). Created under the pool surface so its submerged body is occluded.
+    Single-instance (one per level). Two homes:
+    - **L4 lava** (`snakeLava`): the old collapsing bridge is gone; the pit is a
+      512px chasm crossed in two hops over a middle stepping-stone the serpent
+      peaks at.
+    - **L6 goo** (`snakeSlime`): PIT2's spike chasm becomes a toxic **goo pool**
+      (`pfMakeSlimePool`, the slime-biome twin of `pfMakeLava`); the serpent peaks
+      at jump-arc height, so you time the double-jump for when it has sunk.
   - **Sprite grounding fix:** the spook skins fill their frames edge-to-edge (no
     transparent padding, measured), so their bind offset is the plain geometric
     `pFullH/2 - frameH*0.9/2`, not the FOES soft-bottom sink that floated them ~9px.
-- **TODO:** a `snakeSlime` home (a slime-pool beat) and more snake placements;
-  optionally teach `audit-platformer.py` the `pfMakeSnake`/`pfMakeLavaSerpent`
-  makers (currently ignored — harmless, the pit isn't gap-checked).
+- **TODO (optional):** more snake placements if wanted; `audit-platformer.py` now
+  tracks `pfMakeSlimePool` as a hazard but still ignores `pfMakeSnake`/`pfMakeSerpent`
+  (harmless — the pools aren't gap-checked and the snakes self-reverse).
 
 ### Phase F — Collectibles & a health model  (M)
 - **Assets:** `coin_bronze/silver(_side)`, `star`, `heart`, `hud_heart(_half/