diff --git a/.machine_readable/6a2/ECOSYSTEM.a2ml b/.machine_readable/6a2/ECOSYSTEM.a2ml
index a8f8a48..794abf6 100644
--- a/.machine_readable/6a2/ECOSYSTEM.a2ml
+++ b/.machine_readable/6a2/ECOSYSTEM.a2ml
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: MPL-2.0
 # ECOSYSTEM.a2ml — Ecosystem position
 # Converted from ECOSYSTEM.scm on 2026-03-15
+# Boundary aligned to D142 write-back on 2026-10-10; prose canon in docs/ecosystem/ECOSYSTEM.adoc
 
 [metadata]
 project = "universal-language-server-plugin"
@@ -8,3 +9,19 @@ ecosystem = "hyperpolymath"
 
 [position]
 type = "component"
+
+[boundary]
+# Owner ruling D142 (2026-09-30T14:10Z, scope: repo): this repo embeds its OWN
+# document converter (server/src/core.rs + server/src/formats/); no docmatrix dependency.
+converter = "embedded"
+docmatrix_dependency = false
+ruling = "D142"
+ruling_surface = "https://github.com/hyperpolymath/standards/issues/787#issuecomment-5912989503"
+ruling_issue = "https://github.com/hyperpolymath/universal-language-server-plugin/issues/96"
+canon = "docs/ecosystem/ECOSYSTEM.adoc"
+
+[suite]
+docmatrix = "https://github.com/hyperpolymath/docmatrix"
+docmatrix_contract = "https://github.com/hyperpolymath/docmatrix/issues/71"
+formatrix_docs = "https://github.com/hyperpolymath/formatrix-docs"
+blocky_writer = "https://github.com/hyperpolymath/blocky-writer"
diff --git a/README.adoc b/README.adoc
index aec5573..a55e096 100644
--- a/README.adoc
+++ b/README.adoc
@@ -14,6 +14,35 @@ image:https://img.shields.io/badge/License-MPL_2.0-blue.svg[License: MPL-2.0,lin
 [![Rust](https://img.shields.io/badge/Rust-1.75+-orange.svg)](https://www.rust-lang.org/)
 [![LSP 3.17](https://img.shields.io/badge/LSP-3.17-green.svg)](https://microsoft.github.io/language-server-protocol/)
 
+== Ecosystem boundary (D142, binding)
+
+This repository embeds its *own* document converter
+(`server/src/core.rs` + `server/src/formats/` for Markdown, HTML, JSON,
+YAML, XML, TOML). Per owner ruling *D142* (2026-09-30T14:10Z, scope:
+repo, via `standards#787`), this project has *no docmatrix dependency* —
+the owner explicitly overrode the sharing recommendation.
+
+* *Conversion here* means editor-delivered conversion over LSP 3.17
+(stdio), HTTP REST, and WebSocket, plus the bundled web dashboard.
+* *Suite precision infrastructure* (multi-format conversion coordination,
+versioned interchange contracts, provenance/evidence chains) belongs to
+https://github.com/hyperpolymath/docmatrix[docmatrix] (see
+https://github.com/hyperpolymath/docmatrix/issues/71[docmatrix#71] for
+the suite's composition contract).
+* Sibling components, each useful standalone and composed only by
+explicit user choice: tabbed multi-format viewing/editing in
+https://github.com/hyperpolymath/formatrix-docs[formatrix-docs],
+fixed-layout PDF / application-form placement in
+https://github.com/hyperpolymath/blocky-writer[blocky-writer].
+ForthWall remains a proposed, optional capability — not a dependency.
+
+Non-goals for this repo: suite-wide precision coordination, shared
+interchange-contract implementation, and any mandatory Word-hub
+pipeline. Anything that would introduce a docmatrix dependency or a
+shared converter call-out requires a fresh owner ruling superseding
+D142 — see `docs/ecosystem/ECOSYSTEM.adoc` for the full boundary record
+(requested by https://github.com/hyperpolymath/universal-language-server-plugin/issues/96[#96]).
+
 == Features
 
 🚀 *Universal Editor Support* - One server powers plugins for VS Code, Neovim, Emacs, JetBrains, Sublime, Zed, and Helix
diff --git a/TOPOLOGY.adoc b/TOPOLOGY.adoc
index d626a09..56749cd 100644
--- a/TOPOLOGY.adoc
+++ b/TOPOLOGY.adoc
@@ -38,6 +38,15 @@
                         └─────────────────────────────────────────┘
 ....
 
+=== Ecosystem boundary (D142 — pointer, not a second truth)
+
+Per owner ruling *D142* (2026-09-30, scope: repo) this repo's Conversion
+Core is *embedded and self-contained* — there is no docmatrix
+dependency and no shared-converter call-out. The conversion box in the
+diagram above is `server/src/core.rs` + `server/src/formats/` only.
+Canon: `docs/ecosystem/ECOSYSTEM.adoc` and the `README.adoc` boundary
+section (see https://github.com/hyperpolymath/universal-language-server-plugin/issues/96[#96]).
+
 === Completion Dashboard
 
 ....
diff --git a/docs/ecosystem/ECOSYSTEM.adoc b/docs/ecosystem/ECOSYSTEM.adoc
new file mode 100644
index 0000000..184cdab
--- /dev/null
+++ b/docs/ecosystem/ECOSYSTEM.adoc
@@ -0,0 +1,120 @@
+// SPDX-License-Identifier: CC-BY-SA-4.0
+// Copyright (c) Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
+= Ecosystem boundary — universal-language-server-plugin
+:toc:
+
+This file is the F3a write-back surface for owner ruling *D142*. It
+exists because https://github.com/hyperpolymath/universal-language-server-plugin/issues/96[#96]
+asked for the conversion-boundary decision to be recorded where the
+next person can find it, instead of being quietly resolved by whoever
+writes code first.
+
+== The ruling (D142)
+
+[quote]
+____
+OWNER OVERRODE recommendation: the LSP plugin embeds its OWN document
+converter; no docmatrix dependency
+____
+
+* *Provenance (F10a):* asked in `standards#787` decision harvest as the
+`universal-language-server-plugin#96` row; answered by the owner via
+AskUserQuestion selector (direct answer, not applied-unless-struck).
+* *Clock time:* 2026-09-30T14:10Z (harvest table), mirrored to `#96` at
+2026-09-30T14:12Z.
+* *Scope:* repo — binds this repository fully.
+* *Surfaces:*
+https://github.com/hyperpolymath/standards/issues/787#issuecomment-5912989503[standards#787 D127–D156 table]
+and
+https://github.com/hyperpolymath/universal-language-server-plugin/issues/96#issuecomment-5913038149[#96 ruling comment].
+* *Instruction to future agents:* the open question in `#96` is answered
+by this ruling; act on it rather than re-asking.
+
+== What D142 means here
+
+. The converter in `server/src/core.rs` plus
+`server/src/formats/{yaml,xml,toml}.rs` is *self-contained and stays
+that way*. No `docmatrix` crate, binary, submodule, service call-out,
+or shared-converter client may be introduced without a fresh owner
+ruling that supersedes D142 by name.
+. "`Universal document conversion`" in this repo's tagline means
+*editor-delivered* conversion: LSP 3.17 over stdio for the seven thin
+editor clients, plus the HTTP REST API, WebSocket events, and web
+dashboard served by the same Rust server.
+. Boundary *documentation and links* are required and are not
+dependencies. This file, the `README.adoc` boundary section, and
+`.machine_readable/6a2/ECOSYSTEM.a2ml` carry the same truth in three
+renderings; if they ever disagree, this file governs and the others
+must be re-aligned to it.
+
+== Suite map (docmatrix#71, summarised — canon lives there)
+
+The authoritative suite contract is
+https://github.com/hyperpolymath/docmatrix/issues/71[docmatrix#71]. What
+follows is a pointer summary, not a restatement of canon:
+
+[cols="1,3",options="header"]
+|===
+| Component | Boundary
+
+| *This repo* (`universal-language-server-plugin`)
+| One server, all editors. Own embedded converter; LSP/HTTP/WebSocket
+delivery. No docmatrix dependency (D142).
+
+| https://github.com/hyperpolymath/docmatrix[docmatrix]
+| Multi-format conversion and precision infrastructure for the document
+suite; owns the versioned interchange contract and precision
+coordination.
+
+| https://github.com/hyperpolymath/formatrix-docs[formatrix-docs]
+| Tabbed views of one logical document across TXT,
+delimiter-selected tabular text, Markdown, AsciiDoc, Djot, and A2ML;
+synchronised editing is the intended progression.
+
+| https://github.com/hyperpolymath/blocky-writer[blocky-writer]
+| Fitting and placement into fixed-layout PDF and application-form
+boxes, baselines, and per-character cells designed for hand spacing.
+Not in the conversion business at all (their words, `#96`).
+
+| ForthWall (proposed)
+| Optional, capability-bounded execution layer for critical operations;
+never a mandatory end-user product or runtime.
+|===
+
+Composition rules we inherit from `docmatrix#71` and honour:
+
+* Each component remains useful standalone; composition is explicit and
+user-selected.
+* No supported workflow requires Microsoft Word (or any other mandatory
+hub format) as an intermediate.
+* The user's native input stays authoritative unless they explicitly
+select another representation; lossy or ambiguous transformations are
+proposals requiring approval, never silent normalisation.
+* Proof obligations do not transfer: our conversion round-trip tests
+prove our converter, nothing else.
+
+== What would require re-ruling
+
+Any of the following re-opens the boundary question and must be raised
+as a new row on the standing decision surface (`standards#787`
+successor) rather than implemented directly:
+
+* Adding a docmatrix dependency (library, service, submodule, or
+interchange-client).
+* Implementing the suite's versioned interchange contract as a
+*mandatory* path instead of an opt-in composition.
+* Routing any supported workflow through a mandatory hub format.
+* Changing this repo's tagline or description in a way that claims the
+suite precision-infrastructure remit.
+
+== History
+
+* 2026-09-27 — `#96` filed (boundary overlap flagged, `ECOSYSTEM.adoc`
+recording requested).
+* 2026-09-30 — D142 ruled by owner; ruling mirrored to `#96`.
+* 2026-10-10 — F3a write-back executed on session
+`arena/dee33dad`: README boundary section, this file,
+`.machine_readable/6a2/ECOSYSTEM.a2ml` alignment, `TOPOLOGY.adoc`
+pointer. (Sandbox token lacks issue-comment scope, so the F5a claim and
+`#96` close-out comment are recorded here and in the landing PR
+instead of as issue comments.)