docs(conductor): register PLY Binary IO and write_mesh options tracks

conductor/tracks.md

@@ -7,5 +7,7 @@
 | [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 |
+| [ ] | ply-binary-io_20260904 | PLY Binary IO | 2026-09-04 | 2026-09-04 |
+| [ ] | mesh-io-options_20260904 | write_mesh Options Struct | 2026-09-04 | 2026-09-04 |
 
 <!-- Tracks registered by /conductor:new-track -->

conductor/tracks/mesh-io-options_20260904/index.md

@@ -0,0 +1,30 @@
+# Track: write_mesh Options Struct
+
+**ID:** mesh-io-options_20260904
+**Status:** Pending
+
+## Documents
+
+- Specification — not yet written
+- Implementation Plan — not yet written
+
+## Summary
+
+Let callers control backend-specific writer behavior through `write_mesh`
+without dropping to the format-specific entry points and losing extension
+dispatch.
+
+Deferred from [ply-binary-io_20260904](../ply-binary-io_20260904/index.md),
+where `PLYFormat` lands on `write_ply` only: a PLY-only value is meaningless for
+half of `write_mesh`'s inputs, and there is no good answer to what
+`write_mesh("out.obj", mesh, PLYFormat::Binary)` should do.
+
+Not scoped or scheduled — registered so the intention is discoverable rather
+than living only in a design conversation. Open questions are listed on the
+GitHub issue.
+
+## Quick Links
+
+- [Back to Tracks](../../tracks.md)
+- [Product Context](../../product.md)
+- GitHub issue: educelab/libcore#26

conductor/tracks/mesh-io-options_20260904/metadata.json

@@ -0,0 +1,17 @@
+{
+  "id": "mesh-io-options_20260904",
+  "title": "write_mesh Options Struct",
+  "type": "feature",
+  "status": "pending",
+  "created": "2026-09-04T00:00:00+0200",
+  "updated": "2026-09-04T00:00:00+0200",
+  "issue": 26,
+  "phases": {
+    "total": 0,
+    "completed": 0
+  },
+  "tasks": {
+    "total": 0,
+    "completed": 0
+  }
+}

conductor/tracks/ply-binary-io_20260904/index.md

@@ -0,0 +1,49 @@
+# Track: PLY Binary IO
+
+**ID:** ply-binary-io_20260904
+**Status:** Pending
+
+## Documents
+
+- Specification — not yet written
+- Implementation Plan — not yet written
+
+## Summary
+
+Add binary PLY write support, and make `read_ply` honor the endianness declared
+in the file header rather than reinterpreting raw bytes as native. These are one
+contract and land together: a writer that can emit binary must not produce files
+the reader refuses or silently misreads.
+
+Design decisions are recorded on the GitHub issue. In brief:
+
+- Public `educelab::PLYFormat { ASCII, Binary }` on all three `write_ply` tiers,
+  defaulting to `ASCII`. Kept separate from `detail::PLYHeader::Format`.
+- `Binary` writes native-endian and labels the header accordingly; scalars are
+  always `float32` regardless of the mesh's `T`.
+- The writer mirrors the reader's record batching — precomputed offsets, one
+  `write` per vertex.
+- Read swaps bytes when file order differs from host order, at the two choke
+  points every binary scalar passes through. The swap applies to the raw
+  fixed-width value *before* the cast to the destination type.
+- Faces exceeding the `uchar` list-count limits throw: 255 corners for
+  `vertex_indices`, 127 for `texcoord` (which writes `2*N`).
+
+Round-trip tests do not anchor this work. The sized-alias bug in #24 survived
+because the suite only ever read what libcore wrote; a byte-order mistake shared
+by reader and writer round-trips just as happily. The reader gets a hand-crafted
+big-endian fixture, the writer a byte-level assertion against hand-derived bytes.
+
+## Sequencing
+
+Lands before [ply-multichart_20260624](../ply-multichart_20260624/index.md)
+(#19) — both rewrite `write_ply_header` and `write_ply_data`, multichart is
+Pending at 0/15, and this is the live need.
+
+Depends on #24 (sized PLY type aliases).
+
+## Quick Links
+
+- [Back to Tracks](../../tracks.md)
+- [Product Context](../../product.md)
+- GitHub issue: educelab/libcore#25

conductor/tracks/ply-binary-io_20260904/metadata.json

@@ -0,0 +1,17 @@
+{
+  "id": "ply-binary-io_20260904",
+  "title": "PLY Binary IO",
+  "type": "feature",
+  "status": "pending",
+  "created": "2026-09-04T00:00:00+0200",
+  "updated": "2026-09-04T00:00:00+0200",
+  "issue": 25,
+  "phases": {
+    "total": 0,
+    "completed": 0
+  },
+  "tasks": {
+    "total": 0,
+    "completed": 0
+  }
+}