acdream/docs/research/2026-05-12-l2d-next-session-prompt.md

Copy-paste prompt — next session for L.2d brainstorm

This file is meant to be pasted verbatim into a new Claude Code session. It assumes the next session starts on a freshly-merged main with the L.2a-slice-1/2/3 work already landed.

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Prompt to paste

You are picking up Phase L.2d (Movement & Collision Conformance — Shape Fidelity: Sphere / CylSphere / Building Objects) for the acdream project.

The previous session shipped L.2a-slice-1/2/3 (resolver + cell-transit probes + entity attribution plumbing) and used the probes to settle the L.2d sub-direction call: the wall blocking us at building doorways is a landblock-baked static (0xA9B47900 for the Holtburg test building), NOT a door entity. The fix is to port CBuildingObj + per-cell walkability so the building's baked collision mesh has walkable openings where doorways are. Door-state-toggle is NOT the issue.

Before writing any code:

1. Read the handoff: docs/research/2026-05-12-l2a-shipped-l2d-handoff.md — full context, evidence, file pointers.
2. Read the plan-of-record: docs/plans/2026-04-29-movement-collision-conformance.md — focus on L.2d, and notice that L.2c already shipped most of its work + L.2a is now ~75% covered.
3. Read the named-retail anchors (grep docs/research/named-retail/acclient_2013_pseudo_c.txt by class::method):
   • CCellStruct::point_in_cell
   • CCellStruct::sphere_intersects_cell
   • CCellStruct::box_intersects_cell
   • CBuildingObj::find_building_collisions
   • CObjCell::find_cell_list
4. Read current code:
   • src/AcDream.Core/Physics/TransitionTypes.cs:1386 — FindObjCollisions (where building objects currently flow through generic BSP path).
   • src/AcDream.Core/Physics/PhysicsDataCache.cs — what building-specific data we already load vs ignore.
5. Cross-reference WorldBuilder at references/WorldBuilder/ for any building-cell handling we can crib.

Your deliverable for this session:

1. A brainstorm using superpowers:brainstorming if scope is unclear, then
2. A design spec at docs/superpowers/specs/2026-05-13-l2d-cbuildingobj-collision-design.md covering:
   • Named-retail anchors with line numbers from the PDB pseudo-C
   • Component breakdown (CObjCell port, CBuildingObj port, integration with FindObjCollisions)
   • Conformance test plan (synthetic + real-DAT fixtures at known Holtburg buildings)
   • Slice plan (3-5 commits, each conformance-cited)
   • Acceptance criteria
3. After spec approval, implement slice 1.

Before implementation, verify the L.2a probes still work — relaunch with ACDREAM_PROBE_RESOLVE=1 ACDREAM_PROBE_CELL=1 ACDREAM_DEVTOOLS=1, walk up to the Holtburg test doorway, confirm [resolve] lines still show obj=0xA9B4xxxx for the wall hits. (Reproduction recipe in the handoff doc's last section.)

Side note: 8 pre-existing test failures exist on main (verified by stash+rerun in the prior session, none from L.2a slice work). Most touch movement/physics code we're about to evolve. Triage them before sinking deep L.2d effort — a recent baseline regression in this area could waste hours of L.2d work.

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Reading order if you only have 10 minutes

1. docs/research/2026-05-12-l2a-shipped-l2d-handoff.md — TL;DR + Three findings sections (5 min).
2. docs/plans/2026-04-29-movement-collision-conformance.md §L.2d (2 min).
3. src/AcDream.Core/Physics/TransitionTypes.cs:1386-1543 — current FindObjCollisions body (3 min).

From there, decide whether to brainstorm or jump straight to the spec.