research: Trilium (TriliumNext) deep dive (note cloning/DAG hierarchy, attribute inheritance, HTML-native); UC-66/67

SQLite-local PKB whose standout is note cloning — a single note can sit in
multiple tree locations at once via the note (identity) vs branch
(placement) split, so the hierarchy is a DAG, not a tree, with no single
canonical path. The identity-not-equal-placement model is the clean way to
represent a page in multiple locations/shards and the namespace-level form
of the clone/reference primitive. Also: attributes (labels + typed
relations) are inherited + templated, so metadata is computed (own +
inherited + template), not a flat bag; content opacity is per-item
(per-note encryption / protected notes), refining the proposed 12th
spectrum; HTML-native (CKEditor, lossy to Markdown); dual extension
surface (scripting code notes + ETAPI token REST). TriliumNext is the
active community fork of zadam's Trilium (TWiki->Foswiki pattern). Added
UC-66 (DAG hierarchy / note cloning), UC-67 (inherited/templated
attributes, effective vs own); enriched UC-15/22/34/38/42/61. Catalog now
67 UCs. Architecture for SHARD-WP-0002 T11/T12/T14/T15/T16: DAG namespace
+ identity/placement split, computed/inherited metadata, per-item content
opacity, HTML source model, scripting + ETAPI host surfaces.

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

spec/UseCaseCatalog.md

@@ -9,8 +9,9 @@ Promoted from `research/260608-c2-wiki-origins/`,
 `research/260614-xanadu-deep-dive/`, `research/260614-zigzag-deep-dive/`,
 `research/260614-roam-deep-dive/`, `research/260614-obsidian-deep-dive/`,
 `research/260614-notion-deep-dive/`, `research/260614-joplin-deep-dive/`,
-`research/260614-logseq-deep-dive/`, and
-`research/260614-localfirst-workspaces-deep-dive/`.
+`research/260614-logseq-deep-dive/`,
+`research/260614-localfirst-workspaces-deep-dive/`, and
+`research/260614-trilium-deep-dive/`.
 See InfoTechPrimers on coulomb.social for use-case catalog conventions.
 
 ## Conventions
@@ -244,7 +245,9 @@ end: typed database properties with relations/rollups/formulas, lossy to Markdow
 see UC-58 (`research/260614-notion-deep-dive/findings.md` §2). **Logseq** sits between:
 `key:: value` block/page properties live in the Markdown text (git-diffable) yet are
 queried via a derived Datalog graph (`research/260614-logseq-deep-dive/findings.md` §2–§3)
-— in-text structure at block granularity.  
+— in-text structure at block granularity. **Trilium** adds **computed** structure: labels
++ typed relations that are **inherited + templated**, so effective metadata ≠ stored
+metadata — see UC-67 (`research/260614-trilium-deep-dive/findings.md` §3).  
 **Priority:** Later
 
 ### UC-35 — Attach a shard with coarse write granularity
@@ -326,7 +329,10 @@ client, so write-through requires in-engine hosting (findings §11 Q2). **Joplin
 *two* surfaces: an in-app plugin host (`joplin.data`/`workspace`/`contentScripts`) **and**
 a **local Data API** (REST on `localhost:41184`, token, app-running) — a local-REST attach
 sub-mode between in-engine host and external API (UC-57,
-`research/260614-joplin-deep-dive/findings.md` §4).  
+`research/260614-joplin-deep-dive/findings.md` §4). **Trilium** is the same dual pattern:
+**scripting** (frontend/backend code notes against a Script API) as the in-app host, plus
+**ETAPI** (token REST) as a designed external surface for a self-hosted server
+(`research/260614-trilium-deep-dive/findings.md` §5).  
 **Priority:** Later
 
 ### UC-39 — Attach a wiki-as-application-platform shard (pages as typed records)
@@ -399,7 +405,10 @@ as read-only.
 HTML→TML losslessly on save) (`research/260613-foswiki-deep-dive/findings.md` §5).
 Open: is round-trip lossless enough, or must overlays be stored in the shard's native
 syntax to be safe (findings §9 Q2)? Without this, non-Markdown shards degrade to
-read-only (UC-03) — a graceful-degradation floor, not the goal.  
+read-only (UC-03) — a graceful-degradation floor, not the goal. **Trilium** is the
+HTML-native case: text notes are HTML (CKEditor5), so participation needs HTML↔Markdown
+translation — more tractable than Notion's blocks but still lossy for some constructs
+(`research/260614-trilium-deep-dive/findings.md` §4, links UC-59).  
 **Priority:** Later
 
 ### UC-43 — Tolerate a shard's storage-backend swap without losing identity
@@ -739,7 +748,9 @@ undecryptable content. Open: does shard-wiki ever hold keys, or only treat such
 opaque backups (findings §9 Q1)? Ties [[shard-wiki-auth-in-core-decision]]. **Anytype**
 reinforces this: any-sync is **E2EE by default** — backup nodes hold ciphertext they
 cannot read (`research/260614-localfirst-workspaces-deep-dive/findings.md` §1), and it is
-**P2P** (UC-65).  
+**P2P** (UC-65). **Trilium** refines the dimension to **per-item**: protected (encrypted)
+notes coexist with plaintext notes in one shard, so opacity is per-note, not whole-shard
+(`research/260614-trilium-deep-dive/findings.md` §6).  
 **Priority:** Later
 
 ### UC-62 — Attach a block-graph-on-plain-files shard
@@ -811,6 +822,40 @@ file-store / in-engine-host / external-API (UC-40/38/57). Combines with **conten
 whether shard-wiki holds keys (findings §10 Q3–Q4). Ties [[shard-wiki-auth-in-core-decision]].  
 **Priority:** Later
 
+### UC-66 — Attach a shard with a DAG hierarchy (note cloning)
+
+**Actor:** Maintainer  
+**Goal:** Attach a shard where a page may occupy **multiple namespace locations at once**
+(Trilium note cloning) — representing the multi-location membership, with page identity
+separated from placement, without forcing a single canonical path.  
+**Source:** trilium, intent  
+**Notes:** Trilium models a **note** (identity, `noteId`) separately from its **branches**
+(placements, `branchId`); a note with several branches is **cloned** into several tree
+locations — so the hierarchy is a **DAG, not a tree**
+(`research/260614-trilium-deep-dive/findings.md` §2). Breaks UC-22's single-path
+assumption. shard-wiki should borrow the **identity ≠ placement** split (one page entity,
+N placements/paths/shards) — also the right model for a page appearing under multiple
+paths or across shards. The namespace-level form of the clone/reference primitive (T16;
+cf. Xanadu/ZigZag clone, UC-44/45). Open: model as one page with N placements vs
+transclusion into N locations (findings §11 Q1).  
+**Priority:** Later
+
+### UC-67 — Preserve inherited and templated attributes (effective vs own metadata)
+
+**Actor:** Reader or maintainer  
+**Goal:** Project a structured shard whose metadata is **computed** — a page's effective
+attributes derive from its own values plus inherited (ancestor) and templated values —
+distinguishing **effective vs own** with per-attribute provenance, not flattening.  
+**Source:** trilium, intent  
+**Notes:** Trilium attributes (labels `#tag`, typed relations `~relation`) can be
+**inherited down the subtree** and injected by **templates** (`~template`), so effective
+metadata = own + inherited + templated (`research/260614-trilium-deep-dive/findings.md`
+§3). Extends UC-34/UC-58 with a new wrinkle: **metadata is computed, not just stored** —
+record each attribute's provenance (own / inherited-from / template). Open: materialize
+effective values (snapshot) vs compute live from the shard's tree/templates (findings §11
+Q2). Templates also reinforce UC-15 (blueprints).  
+**Priority:** Later
+
 ---
 
 ## B. Knowledge work and collaboration
@@ -896,7 +941,9 @@ an agreed layout or subtree.
 **Notes:** yawex blueprint pages. Distinct from UC-08 (blank capture) and UC-10
 (refactoring existing discussion). Obsidian's popular **Templater** (4.6M) / **QuickAdd**
 (1.9M) plugins show templated creation is a top real-world need
-(`research/260614-obsidian-deep-dive/findings.md` §7).  
+(`research/260614-obsidian-deep-dive/findings.md` §7). **Trilium** templates (`~template`
+relation) inject an attribute set + structure into instances — blueprint-as-typed-template
+(`research/260614-trilium-deep-dive/findings.md` §3, links UC-67).  
 **Priority:** Later
 
 ### UC-16 — Append or comment without full edit
@@ -970,7 +1017,10 @@ inspiration only for federation design (not inherited as API). ZigZag deep dive:
 the namespace hierarchy as **one dimension among many** (encoded left-child/right-sibling
 as two zz-dimensions), not the privileged structure — consistent with mechanism over
 policy; navigate it as one axis via UC-47 (`research/260614-zigzag-deep-dive/findings.md`
-§4, §7.1).  
+§4, §7.1). **Trilium** pushes further: its hierarchy is a **DAG** — a note can sit in
+multiple locations (cloning), with **identity (note) separated from placement (branch)** —
+so there is no single canonical path (UC-66,
+`research/260614-trilium-deep-dive/findings.md` §2).  
 **Priority:** Later
 
 ### UC-23 — Soft topic creation via red link
@@ -1064,6 +1114,8 @@ CamelCase and `[[free links]]`. Markdown-first link semantics TBD.
 | UC-63 | | | | ※ | ✓ |
 | UC-64 | | | | ⌘ | ✓ |
 | UC-65 | | | | ⌘ | ✓ |
+| UC-66 | | | | ⊕ | ✓ |
+| UC-67 | | | | ⊕ | ✓ |
 | UC-08 | ✓ | | |
 | UC-09 | ✓ | | |
 | UC-10 | ✓ | | |
@@ -1408,6 +1460,37 @@ spectrum: `none / git / native-CRDT`), a **CRDT-replica** substrate + **P2P/no-c
 endpoint** attach mode, an **endpoint-model** capability, and MCP as an integration
 surface.
 
+### trilium mapping
+
+(⊕ UC-66–UC-67 are placed in the **wikiengines** matrix column as the nearest existing
+source — Trilium is a shipped tool — but their true lineage is the **Trilium deep dive**,
+`research/260614-trilium-deep-dive/findings.md`.)
+
+| Trilium mechanism (findings §) | Catalog UC |
+|--------------------------------|------------|
+| Note cloning → DAG hierarchy; note (identity) vs branch (placement) (§2) | UC-66 (new) |
+| Attributes inherited + templated → effective vs own metadata (§3) | UC-67 (new) |
+| DAG / multi-parent vs tree; identity ≠ placement (§2) | UC-22 (enriched) |
+| Labels (`#tag`) + typed relations (`~relation`), computed (§3) | UC-34 (enriched) |
+| Templates (`~template`) inject attribute sets (§3) | UC-15 (enriched) |
+| HTML-native (CKEditor) → HTML↔Markdown lossy translation (§4) | UC-42 (enriched; links UC-59) |
+| Per-note encryption (protected notes) = per-item opacity (§6) | UC-61 (enriched) |
+| Scripting (code notes) in-app host + ETAPI external REST (§5) | UC-38 (enriched; links UC-57) |
+| Render/script notes + attribute queries = dynamic content (§4–§5) | links UC-54 |
+| Typed relations = knowledge graph (§3) | links UC-58 |
+| `noteId`/`branchId` 12-char IDs (§1) | links UC-51 |
+
+Note: Trilium (active fork **TriliumNext**) is a SQLite-local PKB whose standout is **note
+cloning** — a **DAG hierarchy** with **note identity separated from placement** (note vs
+branch), the namespace-level form of the clone/reference primitive and the clean model for
+a page in multiple locations/shards. It also makes **metadata computed** (own + inherited +
+templated, UC-67) and refines **content opacity to be per-item** (per-note encryption,
+UC-61). HTML-native (lossy to Markdown), dual extension surface (scripting + ETAPI).
+**Boundary recorded:** one SQLite-local candidate shard, best attached via ETAPI; not a
+substrate and not the federation layer. Architecture logged for `SHARD-WP-0002`
+(T11/T12/T14/T15/T16): DAG namespace + identity/placement split, computed/inherited
+metadata, per-item content opacity, HTML source model, scripting + ETAPI host surfaces.
+
 ---
 
 ## Open questions
@@ -1452,4 +1535,9 @@ surface.
     patches? (Local-first workspaces dive §10.)
 19. For a **P2P shard** (UC-65), what is the shard's address (space ID + peer / replica
     path / invite-key), and does shard-wiki ever hold E2EE keys or only treat it as an
-    opaque replica? (UC-61.)
+    opaque replica? (UC-61.)
+20. For a **DAG/cloned page** (UC-66), is it one page with multiple path placements, or a
+    page transcluded into multiple locations? Does shard-wiki adopt Trilium's identity ≠
+    placement (note/branch) split as its own page model? (Trilium dive §11.)
+21. Are **inherited/templated attributes** (UC-67) materialized (snapshot) or computed
+    live from the shard's tree/templates, and how is per-attribute provenance recorded?