docs(phys L.2g): design spec for dynamic PhysicsState toggling (doors)

L.2d slice 1.5 ship identified the Holtburg doorway blocker as a closed
Door entity (Setup 0x020019FF) whose PhysicsState.Ethereal bit flips
when the player Uses the door. The L.2d shape-fidelity work doesn't
cover this — the door's collision shape is correct; what's missing is
honoring the *runtime* state change.

L.2g is the new sub-phase that handles it. Scope is narrow:

  * Parse inbound GameMessageSetState (0xF74B).
  * Plumb the new PhysicsState value into ShadowObjectRegistry's
    cached per-entity state so the existing CollisionExemption.IsExempt
    already-in-place short-circuit sees up-to-date bits.
  * Verify the Holtburg inn-door scenario: walk in blocked, Use door,
    walk through, auto-close blocks again after 30s.
  * Confirm UpdateMotion (NonCombat, On/Off) drives non-creature
    entities (door swing animation).

Why a new L.2 sub-letter (and not B.4 or Door-special-case): the wire
mechanism (SetState flipping Ethereal) is also how ACE handles activated
traps, opened chests, spell projectiles becoming ethereal. Generic
infrastructure with doors as the verification scenario; lane is the
informal sixth "dynamic state."

Roadmap state:
  * L.2 plan-of-record adds the L.2g section after L.2f.
  * Milestones doc M1 phase list extended `a-f` -> `a-g`.
  * CLAUDE.md status pointer + "next phase candidates" list updated to
    name L.2g slice 1 implementation as the natural next step.

Risk: low. Wire-byte width has a hex-dump fallback path in slice 1
(holtburger says 12 bytes, ACE writes 16, capture settles it). ETHEREAL
plumbing already exists; we feed it new data. No resolver changes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -618,10 +618,16 @@ acdream's plan lives in two files committed to the repo:
   approval.
 
 **Currently in Phase L.2 (Movement & Collision Conformance).** L.2a slices
-1+2+3 shipped 2026-05-12 (this evening); the natural next step is the
-L.2d slice 1 brainstorm / design spec. Cold-start prompt for the next
-session: [`docs/research/2026-05-12-l2d-next-session-prompt.md`](docs/research/2026-05-12-l2d-next-session-prompt.md).
-Full handoff: [`docs/research/2026-05-12-l2a-shipped-l2d-handoff.md`](docs/research/2026-05-12-l2a-shipped-l2d-handoff.md).
+1+2+3 + L.2d slice 1+1.5 shipped 2026-05-12. L.2d closed at the Holtburg
+site ("watch-and-wait" — no more slices until a new shape-fidelity bug
+shows up elsewhere); doorway blocker identified as a Door entity, not
+building BSP. L.2g (dynamic PhysicsState toggling — doors) brainstormed
+and design-spec'd 2026-05-12 evening; **the natural next step is the
+L.2g slice 1 implementation** (parse `SetState` 0xF74B, plumb new
+PhysicsState into ShadowObjectRegistry, verify Holtburg inn doorway).
+Design spec: [`docs/superpowers/specs/2026-05-12-l2g-dynamic-physicsstate-design.md`](docs/superpowers/specs/2026-05-12-l2g-dynamic-physicsstate-design.md).
+L.2d ship handoff: [`docs/research/2026-05-13-l2d-slice1-shipped-handoff.md`](docs/research/2026-05-13-l2d-slice1-shipped-handoff.md).
+L.2a→L.2d handoff (now superseded by the L.2d ship): [`docs/research/2026-05-12-l2a-shipped-l2d-handoff.md`](docs/research/2026-05-12-l2a-shipped-l2d-handoff.md).
 
 **Phase L.2a (Truth & Diagnostics) slices 1-3 shipped 2026-05-12.**
 Three commits land the L.2 "make every bad movement outcome explainable"
@@ -699,13 +705,18 @@ together comprise the streaming + rendering perf foundation for the
 project.
 
 **Next phase candidates (in rough preference order):**
-- **L.2d slice 1 brainstorm + spec** (`docs/research/2026-05-12-l2d-next-session-prompt.md`).
-  Direct continuation of tonight's L.2a evidence: port `CBuildingObj` collision
-  + per-cell walkability so doorway gaps are walkable. Unblocks "walk into a
-  building" + sets up G.3 dungeon streaming. **Note:** triage the 8 pre-existing
-  test failures first (none introduced by L.2a slices — verified by stash + rerun
-  — but most touch movement/physics code L.2d will evolve). See the handoff doc's
-  "Open concerns" section.
+- **L.2g slice 1 implementation — dynamic PhysicsState toggling for doors.**
+  Direct continuation of tonight's L.2d slice 1.5 evidence: parse inbound
+  `SetState (0xF74B)` wire message, plumb the new `PhysicsState` value into
+  `ShadowObjectRegistry`'s cached entity state so the existing
+  `CollisionExemption.IsExempt(...)` check sees up-to-date bits, and verify
+  the Holtburg inn-door scenario walks through cleanly when the server flips
+  Ethereal. Unblocks the M1 demo's *"open the inn door"* line. Spec:
+  [`docs/superpowers/specs/2026-05-12-l2g-dynamic-physicsstate-design.md`](docs/superpowers/specs/2026-05-12-l2g-dynamic-physicsstate-design.md).
+  **Note:** triage the 8 pre-existing test failures still hanging over the
+  physics modules first (none introduced by L.2a/L.2d slices — verified by
+  stash + rerun — but most touch code adjacent to where L.2g will plumb the
+  new state mutator).
 - **Triage the chronic open-issue list** in `docs/ISSUES.md` — #2 (lightning),
   #4 (sky horizon-glow), #28 (aurora), #29 (cloud thinness), #37 (humanoid
   coat), #50 (stray tree), #41 (remote-motion blips) have been open since