# M03-RND-M2-PLACEMENT-GROUPER-001 — M2 placement grouper

<!-- OPENWC_CLAIM:M03-RND-M2-PLACEMENT-GROUPER-001:sindo-main-codex:2026-07-19 -->

## Ownership

- Target: M03
- Program: RND
- Owner/Agent ID: sindo-main-codex
- Branch: `work/sindo-main-codex/m03-m2-placement-grouper`
- Lease expires UTC: 2026-07-19
- Integrator: M03 milestone integrator

## Outcome

Extract pure ADT M2 placement validation, path normalization and local-transform
grouping from the worker callback into a scene-free service.

## Non-goals

- Change placement ordering, coordinate conversion, transform formulas or clamps.
- Move WorkerThreadPool tasks, mutex/result queues, tile state or retry behavior.
- Move build jobs, animation/mesh loading, caches, Nodes, MultiMesh or RIDs.
- Generalize grouping policy, change batching or add a dependency.
- Claim build-12340 placement or visual parity beyond preserved formulas.

## Paths

- Exclusive: `src/render/m2/m2_placement_grouper.gd`,
  `src/tools/verify_m2_placement_grouper.gd`,
  `docs/modules/m2-placement-grouper.md`, this claim
- Shared/hotspots: `src/scenes/streaming/streaming_world_loader.gd`,
  `docs/modules/m2-placement-transform-resolver.md`,
  `docs/modules/world-renderer.md`, `docs/modules/README.md`, `RENDER.md`,
  `targets/03-renderer-facade.md`
- Generated/ignored: `.godot`, native DLL, generated ADT resources, caches and
  proprietary renderer corpus

## Contracts and data

- Input: tile-local origin, MMDX name table and raw ADT M2 placement array
- Output: fresh Dictionary keyed by historically normalized relative M2 path;
  each value is a fresh ordered Array of tile-local `Transform3D` values
- Invalid variants, out-of-range name IDs and empty paths are skipped
- Backslashes become slashes; lowercase `.mdx/.mdl` suffixes become `.m2`
- Transform basis/origin delegates to `M2PlacementTransformResolver`; final basis
  scale retains the grouping-path clamp `max(scale, 0.0001)`
- Cache/schema/coordinate versions: unchanged

## Dependencies

- Requires: current master `c34e538`, `M2PlacementTransformResolver`
- Blocks: broader M2 worker/build decomposition
- External state: none; tests use synthetic names and placement dictionaries

## Verification

- Commands: dedicated invalid/name/path/group-order/default/transform/scale and
  bounded timing verifier; loader source boundary; resolver/registry/dedupe plus
  facade/internal-access/manifest/shutdown/documentation/coordination gates
- Fidelity evidence: exact loop rules and transform composition moved unchanged
- Performance budget: linear over placement count with fresh output containers;
  no Node, Resource, RID, task, mutex, cache or file access

## Documentation deliverables

- Inline grouper API documentation
- New module spec with inputs/outputs, data-flow, lifecycle, ownership, failure,
  performance, fidelity limitations and source map
- Transform resolver, renderer/module registry and `RENDER.md` updates

## Simplicity and naming

- Important name: `M2PlacementGrouper`
- Simplest solution: one stateless `group_placements` query
- Rejected complexity: group/result classes, strategy interfaces, callbacks,
  Resources, policies or generic spatial batching framework
- Unavoidable complexity: raw ADT dictionaries remain at the parser adapter
- Measured optimization evidence: bounded synthetic grouping loop

## Status

- State: claimed
- Done: boundary, exact preservation rules and ownership published
- Next: implement grouper, migrate worker callback, tests and docs
- Blocked by:

## Handoff

- Commit:
- Results:
- Remaining risks:
- Documentation updated: