research: Project Xanadu deep dive (EDL/reference-not-copy, transclusion, addressing); UC-44/45/46

Xanadu studied as conceptual ancestor, not a candidate shard. Yield:
reference-not-copy EDL/xanadoc validates projection+overlay+union;
content-identity bidirectional transclusion; portable span-address
(tumbler) problem logged as adapter-contract architecture for
SHARD-WP-0002. Recorded design-bug boundaries: reject
single-global-docuverse, single-canonical-instance, baked-in economic
policy. Added UC-44/45/46; enriched UC-24/27/29/32.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

research/260614-xanadu-deep-dive/README.md

@@ -0,0 +1,47 @@
+# 260614 — Project Xanadu deep dive (the docuverse, the EDL, reference-not-copy)
+
+Date: 2026-06-14
+
+## What this is
+
+A focused study of **Project Xanadu** (Ted Nelson) read through shard-wiki's lens.
+Unlike the engine dives (`xwiki`, `twiki`, `foswiki`), Xanadu is **not a candidate
+shard backend** — it never shipped at scale and there is nothing to attach. It is
+studied as the **deepest conceptual ancestor** of shard-wiki's own model: several
+shard-wiki primitives turn out to be Xanadu mechanisms under different names.
+
+The distinctive material:
+- the **EDL / xanadoc** — a document that contains *no content*, only an ordered list
+  of **spans** (content references) plus **xanalinks** (separate link tables); the
+  client assembles the page by reference → this is shard-wiki **projection** + **union**
+- the storage substrate — **tumblers** (stable fine-grained addresses), **istream**
+  (invariant content pool), **enfilades / spanfilade** (virtual↔content mapping,
+  version comparison by span-set intersection)
+- **content-identity, bidirectional transclusion** — content "knowably in more than
+  one place" that remembers all its appearances → stronger than UC-32
+- **transcopyright / micropayment** — a baked-in rights policy shard-wiki must keep
+  *configurable*, not inherit
+
+Goes deliberately **underneath** the surface pattern table in
+`research/260608-federation-concepts/findings.md` §3.3, which it extends rather than
+repeats.
+
+## Contents
+
+| Path | Role |
+|------|------|
+| `findings.md` | EDL/xanadoc, addressing substrate, transclusion, versioning, rights, INTENT mapping (reinforcements + design-bug divergences), UC seeds, architecture notes, sources |
+
+## Status
+
+Initial deep dive complete. Three new use cases promoted to `spec/UseCaseCatalog.md`
+(UC-44 compose-by-reference, UC-45 reverse transclusion, UC-46 content-identity
+equivalence); UC-24/27/29/32 enriched. Span-addressing as an adapter capability,
+content identity, composition manifests, and reuse-terms metadata logged as
+architecture for `workplans/SHARD-WP-0002-federation-architecture.md`.
+
+Key boundary recorded: shard-wiki inherits Xanadu's **reference-not-copy** mechanisms
+but **rejects** the single-global-docuverse premise, the single-canonical-instance
+model, and the baked-in economic policy — those would violate shard sovereignty,
+parallel-version support (UC-27), and mechanism-over-policy.
+</content>