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>
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# UseCaseCatalog
Status: **draft** · Date: 2026-06-08 · Updated: 2026-06-13
Status: **draft** · Date: 2026-06-08 · Updated: 2026-06-14
Promoted from `research/260608-c2-wiki-origins/`,
`research/260608-yawex-prior-art/`, `research/260608-federation-concepts/`,
`research/260608-wikiengines-overview/`, `research/260613-xwiki-deep-dive/`,
`research/260613-twiki-deep-dive/`, and `research/260613-foswiki-deep-dive/`.
`research/260613-twiki-deep-dive/`, `research/260613-foswiki-deep-dive/`, and
`research/260614-xanadu-deep-dive/`.
See InfoTechPrimers on coulomb.social for use-case catalog conventions.
## Conventions
@@ -116,7 +117,10 @@ and UC-03 (projection only). Fork vs overlay vs import decided in
authors without collapsing them into one canonical page.
**Source:** federation, intent
**Notes:** Fedwiki "chorus of voices"; INTENT union without erasure. Equivalent-
page identity model TBD (`SHARD-WP-0002`). Links UC-07 divergence detection.
page identity model TBD (`SHARD-WP-0002`) — Xanadu deep dive offers a path-independent
detection mechanism via content-identity / span-set intersection (UC-46,
`research/260614-xanadu-deep-dive/findings.md` §5, §8.2). Links UC-07 divergence
detection.
**Priority:** Later
### UC-28 — Carry forward pages from closed or archived shard
@@ -134,9 +138,13 @@ lifecycle policy. Complements UC-02 attach and UC-26 fork at scale.
**Actor:** Author
**Goal:** Reuse content across shards or spaces with attribution and edit
history intact, without manual copy-paste.
**Source:** federation, intent
**Source:** federation, intent, xanadu
**Notes:** Fedwiki journal travels with page; shard-wiki coordination journal +
per-shard history. Frictionless reuse principle (~15s not ~15min).
per-shard history. Frictionless reuse principle (~15s not ~15min). Xanadu
**transcopyright**: a reference carries provenance *and reuse terms* with it, so
attribution/permission travel with the span — but reuse policy stays configurable, not
baked into the substrate (`research/260614-xanadu-deep-dive/findings.md` §6); links the
authz-in-core L0→L4 ladder decision.
**Priority:** Later
### UC-30 — Time-bounded collaboration space
@@ -169,7 +177,11 @@ concrete push transport: an engine event bus (`ObservationManager`
refreshable content.
**Source:** federation, intent
**Notes:** Xanadu transclusion pattern; stronger than UC-03 whole-page
projection. Provenance and staleness must be explicit.
projection. Provenance and staleness must be explicit. Xanadu deep dive sharpens this:
transclusion should be **content-identity based and bidirectional** (content is "knowably
in more than one place" and aware of its appearances), not a one-way path fetch —
enables UC-45 reverse lookup (`research/260614-xanadu-deep-dive/findings.md` §4). See
UC-44 for the whole-page composition-manifest form.
**Priority:** Later
### UC-33 — Git-branch an information space
@@ -342,6 +354,49 @@ Relates to UC-40 (attach path) and UC-41 (history import) but is about *change u
live attachment*, not initial attach.
**Priority:** Later
### UC-44 — Compose a page by reference (xanadoc / EDL manifest)
**Actor:** Author
**Goal:** Author a page whose canonical body is an ordered list of spans pulled by
reference from one or more shards, stored as a composition manifest rather than a copy.
**Source:** xanadu, intent
**Notes:** Xanadu EDL/xanadoc — a document that contains no content, only span
references plus link tables, assembled by the client
(`research/260614-xanadu-deep-dive/findings.md` §2). The reference-not-copy embodiment
of INTENT "lazy projection over eager copying" and "union without erasure". Stronger
than UC-32 (single inline span): the *whole page* is a manifest. Requires the wiki page
model to admit a reference-list canonical form — flag for page-model spec. Open:
core vs. adapter vs. reference-UI; MVP vs. deferred with UC-32 (findings §11 Q2).
**Priority:** Later
### UC-45 — Reverse transclusion: find all appearances of a span
**Actor:** Reader or maintainer
**Goal:** Given a span (paragraph/section/page), find every page and shard where that
content appears or is transcluded.
**Source:** xanadu, intent
**Notes:** Xanadu content "remembers its identity and traces back to all its
appearances" (`research/260614-xanadu-deep-dive/findings.md` §4). Union BackLinks
generalized from page links to sub-page content identity. Depends on a content-identity
mechanism (UC-46) and on span addressing as an adapter capability (`SHARD-WP-0002`).
Open: exact-identity only vs. fuzzy/derived tracking (findings §11 Q4).
**Priority:** Later
### UC-46 — Detect content-identity equivalence across shards
**Actor:** Reader or orchestrator
**Goal:** Determine that two pages in different shards are the same or derived content
by content/span overlap, without relying on matching titles or paths.
**Source:** xanadu, intent
**Notes:** Xanadu compares documents by **span-set intersection** over an invariant
content pool (`research/260614-xanadu-deep-dive/findings.md` §5). Supplies the
equivalent-page identity model left open in UC-27 with a *path-independent* detection
mechanism — equivalence is detected, not enforced (parallel versions stay visible per
UC-27, not collapsed). Adapter advertises its content fingerprint (Git blob hash,
normalized-text hash, none). Open: core vs. adapter-index; cost at wiki scale without
enfilades (findings §11 Q3).
**Priority:** Later
---
## B. Knowledge work and collaboration
@@ -520,7 +575,10 @@ CommonMark wikilink + red-link extension.
edit count, and whether the page has local overlays or diverges elsewhere.
**Source:** yawex, c2, intent
**Notes:** yawex `Page::info`; c2 optional `UserName` signing. INTENT explicit
provenance principle.
provenance principle. Xanadu deep dive: provenance is *structural*, not decorative —
content remembers where it came from and where it is reused (UC-45), built into the
storage model rather than added after the fact
(`research/260614-xanadu-deep-dive/findings.md` §4, §8.1).
**Priority:** Later
### UC-25 — Collaborative glossary and precise naming
@@ -564,6 +622,9 @@ CamelCase and `[[free links]]`. Markdown-first link semantics TBD.
| UC-41 | | | | ✓ | ✓ |
| UC-42 | | | | ✓ | ✓ |
| UC-43 | | | | ✓ | ✓ |
| UC-44 | | | ✓† | | ✓ |
| UC-45 | | | ✓† | | ✓ |
| UC-46 | | | ✓† | | ✓ |
| UC-08 | ✓ | | |
| UC-09 | ✓ | | |
| UC-10 | ✓ | | |
@@ -654,6 +715,34 @@ which also enriched UC-39 (MetaDataPlugin multi-record), UC-40 (PlainFile store)
logged the `Foswiki::Store` versioned interface as **adapter-contract prior art** for
`SHARD-WP-0002` (no UC — architecture).
### xanadu mapping
(† UC-44UC-46 are placed in the **federation** matrix column as the nearest existing
source; their true lineage is the **Xanadu deep dive**,
`research/260614-xanadu-deep-dive/findings.md`.)
| Xanadu mechanism (findings §) | Catalog UC |
|-------------------------------|------------|
| EDL/xanadoc — document as a manifest of span references, not content (§2) | UC-44 |
| Content "knowably in more than one place," remembers its appearances (§4) | UC-45 |
| Version/document comparison by span-set intersection, content identity (§5) | UC-46 |
| Content-identity, bidirectional transclusion (§4) | UC-32 (enriched) |
| Path-independent equivalence detection for parallel versions (§5) | UC-27 (enriched) |
| Transcopyright — reuse terms travel with the reference (§6) | UC-29 (enriched) |
| Structural provenance — content remembers origin and reuse (§4, §8.1) | UC-24 (enriched) |
Note: Xanadu is **conceptual prior art, not a candidate shard backend** — it never
shipped at scale and there is nothing to attach. Its yield is *mechanism*:
**reference-not-copy** documents (validating projection + overlay + union),
content-identity transclusion, and the still-open **portable span-address** problem
(tumblers), logged as adapter-contract architecture for `SHARD-WP-0002` (span
addressing as an adapter capability; content fingerprint; composition manifests;
reuse-terms metadata — `research/260614-xanadu-deep-dive/findings.md` §10). The dive
also recorded **design-bug boundaries**: shard-wiki **rejects** Xanadu's
single-global-docuverse premise, single-canonical-instance model, and baked-in economic
policy (findings §8.2), as these violate shard sovereignty, parallel-version support
(UC-27), and mechanism-over-policy.
---
## Open questions