docs(conductor): ACVD remeshing feature plan

conductor/index.md

@@ -16,6 +16,7 @@ Navigation hub for project context.
 - [UVMap](./tracks/uv-map_20260323/index.md) — `uv-map_20260323` ✓ complete
 - [Mesh IO](./tracks/mesh-io_20260323/index.md) — `mesh-io_20260323` ✓ complete
 - [Multi-Chart PLY Write Support](./tracks/ply-multichart_20260624/index.md) — `ply-multichart_20260624` ⋯ pending
+- [ACVD Remeshing](./tracks/acvd_20260904/index.md) — `acvd_20260904` ⋯ pending
 
 ## Getting Started
 

conductor/tracks.md

@@ -6,5 +6,6 @@
 | [x] | uv-map_20260323 | UVMap | 2026-03-23 | 2026-03-24 |
 | [x] | mesh-io_20260323 | Mesh IO | 2026-03-23 | 2026-06-24 |
 | [ ] | ply-multichart_20260624 | Multi-Chart PLY Write Support | 2026-06-24 | 2026-06-24 |
+| [ ] | acvd_20260904 | ACVD Remeshing | 2026-09-04 | 2026-09-04 |
 
 <!-- Tracks registered by /conductor:new-track -->

conductor/tracks/acvd_20260904/index.md

@@ -0,0 +1,21 @@
+# Track: ACVD Remeshing
+
+**ID:** acvd_20260904
+**Status:** Pending
+
+## Documents
+
+- [Specification](./spec.md)
+- [Implementation Plan](./plan.md)
+
+## Progress
+
+- Phases: 0/7 complete
+- Tasks: 0/26 complete
+
+## Quick Links
+
+- [Back to Tracks](../../tracks.md)
+- [Product Context](../../product.md)
+- GitHub issue: educelab/libcore#22
+- Companion issue: educelab/OpenABF#62

conductor/tracks/acvd_20260904/metadata.json

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+{
+  "id": "acvd_20260904",
+  "title": "ACVD Remeshing",
+  "type": "feature",
+  "status": "pending",
+  "created": "2026-09-04T00:00:00Z",
+  "updated": "2026-09-04T00:00:00Z",
+  "issue": 22,
+  "phases": {
+    "total": 7,
+    "completed": 0
+  },
+  "tasks": {
+    "total": 26,
+    "completed": 0
+  }
+}

conductor/tracks/acvd_20260904/plan.md

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+# Implementation Plan: ACVD Remeshing
+
+**Track ID:** acvd_20260904
+**Spec:** [spec.md](./spec.md)
+**Created:** 2026-09-04
+**Status:** [ ] Not Started
+
+> Task detail is at planning granularity. Per-task test lists get filled in when
+> each phase starts, per the strict tests-first workflow. Design detail lives in
+> [spec.md](./spec.md) and [educelab/libcore#22](https://github.com/educelab/libcore/issues/22).
+
+## Overview
+
+One clustering engine, built in dependency order, with each layer a separate
+verifiable phase. **Phases 0–2 are the useful milestone** — they produce a
+working uniform remesher that stands alone; later phases add weight policies
+against the same engine. Header-only throughout, matching the rest of the
+library.
+
+## Checkpoints
+
+| Phase   | Checkpoint SHA | Date | Status  |
+| ------- | -------------- | ---- | ------- |
+| Phase 0 |                |      | pending |
+| Phase 1 |                |      | pending |
+| Phase 2 |                |      | pending |
+| Phase 3 |                |      | pending |
+| Phase 4 |                |      | pending |
+| Phase 5 |                |      | pending |
+| Phase 6 |                |      | pending |
+
+---
+
+## Phase 0: Design decisions
+
+Two decisions shape the rest of the code and are expensive to revisit. Settle
+both against the paper PDFs before the minimizer is written.
+
+### Tasks
+
+- [ ] **Task 0.1**: Decide the clustered item domain — mesh vertices (assumed
+      throughout the plan: cluster count equals output vertex count, triangles
+      fall out of the dual directly) or mesh faces. Record the decision and
+      rationale in `spec.md`.
+- [ ] **Task 0.2**: Decide open-mesh boundary treatment. A separate 1D
+      clustering along each boundary loop is the presumed approach. This matters
+      more for EduceLab meshes than for the papers' test cases — most are open
+      patches, where a shrinking or ragged boundary is disqualifying.
+- [ ] **Task 0.3**: Add the three reference papers to `docs/citations.bib`
+      (already wired into Doxygen via `CITE_BIB_FILES`, currently empty).
+
+### Verification
+
+- [ ] Both decisions recorded in `spec.md` with rationale
+- [ ] Doxygen builds with the new bib entries resolving
+
+---
+
+## Phase 1: Mesh topology
+
+Read-only CSR adjacency. ACVD never mutates topology, so no half-edge structure
+and no incremental maintenance.
+
+### Tasks
+
+- [ ] **Task 1.1**: Tests for `types/MeshTopology.hpp` in
+      `tests/src/TestMeshTopology.cpp`
+- [ ] **Task 1.2**: Implement CSR vertex→vertex, vertex→face and
+      face→face adjacency; edge table keyed on sorted vertex pairs;
+      boundary-loop extraction; crease flags by dihedral angle; a small
+      index-view type (C++17 has no `std::span`)
+- [ ] **Task 1.3**: Register the test in `tests/CMakeLists.txt` and the header
+      in `public_hdrs` and the `README.md` header-only list
+
+### Verification
+
+- [ ] Built in a single O(V+F) pass; no allocation per adjacency query
+- [ ] `ctest` passes with no regressions; Debug and Release both build
+
+---
+
+## Phase 2: Uniform ACVD (2004)
+
+### Tasks
+
+- [ ] **Task 2.1**: Tests for the energy bookkeeping — incremental accumulators
+      match a from-scratch recompute; the O(1) move test matches full energy
+      recomputation
+- [ ] **Task 2.2**: Item weights (lumped area) and `utils/MeshQuality.hpp`
+      (areas, angle bounds, edge-length statistics)
+- [ ] **Task 2.3**: Density-weighted seeding and multi-source BFS growth, with
+      every connected component guaranteed at least one seed
+- [ ] **Task 2.4**: Energy minimizer — boundary-item queue, the O(1)
+      reassignment test, `double` accumulators, mean-centered positions, guards
+      against emptying or disconnecting a cluster
+- [ ] **Task 2.5**: Cluster repair — reseed empty clusters by splitting the
+      highest-energy cluster, split disconnected clusters, re-minimize
+- [ ] **Task 2.6**: Dual construction, centroid placement, trait-aware
+      attribute transfer via `if constexpr`, and the result/statistics report
+- [ ] **Task 2.7**: End-to-end tests — identity case, uniformity on a grid patch
+      and subdivided icosphere, output topology validity, determinism,
+      degenerate inputs
+
+### Verification
+
+- [ ] Output vertex count is exactly as requested; output is manifold and
+      consistently oriented
+- [ ] Energy non-increasing across sweeps; converges within `maxSweeps`
+- [ ] Deterministic for a fixed seed across Debug and Release
+- [ ] Test runtime stays within the CI budget on all five OS images
+
+---
+
+## Phase 3: Adaptive weights and quadric placement (2008, scalar)
+
+### Tasks
+
+- [ ] **Task 3.1**: SPD 3×3 solve (Cholesky) added to
+      `utils/LinearAlgebra.hpp`, with tests
+- [ ] **Task 3.2**: `utils/Curvature.hpp` — per-item curvature estimate
+- [ ] **Task 3.3**: Gradation weights and the `WeightFn` overload;
+      `density_for_edge_length`
+- [ ] **Task 3.4**: Quadric (QEM) site placement regularized toward the
+      centroid; boundary line quadrics; crease-corner pinning
+
+### Verification
+
+- [ ] Gradation concentrates vertices in high-curvature regions, measured
+- [ ] Quadric placement preserves a known sharp edge better than centroid
+      placement
+- [ ] Open-mesh boundary vertices stay on the input boundary curve within
+      tolerance
+- [ ] A two-region density field achieves the predicted mean edge-length ratio,
+      validating the `ρ = h⁻⁴` exponent
+
+---
+
+## Phase 4: Anisotropic metrics (2008, full)
+
+Highest risk, least load-bearing for EduceLab meshes. Defer until something
+needs anisotropy.
+
+### Tasks
+
+- [ ] **Task 4.1**: Symmetric 3×3 eigensolve (Jacobi) in
+      `utils/LinearAlgebra.hpp`, with tests
+- [ ] **Task 4.2**: Curvature tensor estimation and metric tensor construction
+- [ ] **Task 4.3**: Tensor accumulators and the metric energy path, with the
+      scalar path kept as a specialization
+
+### Verification
+
+- [ ] `M = ρI` reproduces the scalar path's output exactly
+- [ ] Anisotropic metrics produce measurably elongated elements in the
+      prescribed direction
+
+---
+
+## Phase 5: Approach-guided density fields (2011)
+
+### Tasks
+
+- [ ] **Task 5.1**: ROI distance helpers (point, segment, polyline)
+- [ ] **Task 5.2**: Size↔density calibration helper and worked example
+- [ ] **Task 5.3**: Element quality report suitable for FE consumers
+
+### Verification
+
+- [ ] A corridor-proximity density field produces the prescribed element size
+      gradient, measured
+
+---
+
+## Phase 6: Optional extras
+
+Not required by any acceptance criterion; pull forward only on demand.
+
+### Tasks
+
+- [ ] **Task 6.1**: Subdivision pre-pass for inputs too coarse for the
+      requested cluster count
+- [ ] **Task 6.2**: Spatial index, enabling surface-projected site placement
+- [ ] **Task 6.3**: UV/attribute resampling onto the remeshed output
+
+### Verification
+
+- [ ] Each addition is independently tested and does not alter default behavior
+
+---
+
+## Final Verification
+
+- [ ] All acceptance criteria in `spec.md` and issue #22 met
+- [ ] All tests passing (`ctest`), Debug and Release
+- [ ] Doxygen builds cleanly for the new public API
+- [ ] New headers registered in `CMakeLists.txt` and `README.md`
+- [ ] Clean-room constraint upheld — no reference implementation consulted
+- [ ] Ready for PR review
+
+---
+
+_Generated by Conductor. Tasks will be marked [~] in progress and [x] complete._