---
id: SHARD-WP-0002
type: workplan
title: "federation architecture design"
domain: whynot
repo: shard-wiki
status: active
owner: tegwick
topic_slug: whynot
created: "2026-06-08"
updated: "2026-06-14"
depends_on:
  - SHARD-WP-0001
state_hub_workstream_id: "2af4c46d-cbfd-40ea-a94b-d9e60b0f9945"
---

# SHARD-WP-0002 — Federation architecture design

## Goal

Produce a **federation architecture specification** for shard-wiki: positioning
against prior art (Federated Wiki, git-backed wikis, ActivityPub), documented
**decisions and tradeoffs**, and ADR-ready design notes that resolve the open
questions raised by `research/260608-federation-concepts/` and UseCaseCatalog
UC-26–UC-33.

Primary deliverable: `spec/FederationArchitecture.md` (created and filled by
this workplan's tasks).

Secondary deliverable (T11–T16): the **shard adapter contract** constraints distilled
from the engine deep dives (T11–T15, added 2026-06-13) and the modern-tool dives +
cross-dive synthesis (T16 and scope extensions, added 2026-06-14), feeding
`spec/TechnicalSpecificationDocument.md`. Federation architecture decides *what the
union does*; the adapter contract decides *what a backend must expose to participate*.
The two are co-dependent (the capability matrix T10 consumes the contract vocabulary
T11 defines), so they live in one workplan.

The cross-dive synthesis (`research/260614-shard-spectrum-synthesis/findings.md`, **v2
2026-06-14** — extended to the full dive set incl. Joplin, Logseq, the CRDT cohort
Anytype/AFFiNE/AppFlowy, and Trilium) reframes the contract around **thirteen capability
spectra** (addressing, content identity, **identity-vs-placement**, structure, history,
**merge model**, native query, translation, attachment mode, operational envelope, access
grant, **content opacity**, write granularity) — positions on a spectrum anchored at both
ends by a real system, with federation ops degrading by position — rather than a flat verb
checklist.

## Context

- Federation research: `research/260608-federation-concepts/findings.md`
- Engine deep dives (adapter-contract inputs, T11–T15):
  - `research/260608-wikiengines-overview/findings.md` (landscape; capability
    heterogeneity, write granularity)
  - `research/260613-xwiki-deep-dive/findings.md` (DB/component app-platform)
  - `research/260613-twiki-deep-dive/findings.md` (file+RCS app-platform)
  - `research/260613-foswiki-deep-dive/findings.md` (`Foswiki::Store` versioned
    store interface = adapter-contract prior art)
- Conceptual + modern-tool dives (T16 + scope extensions, 2026-06-14):
  - `research/260614-xanadu-deep-dive/findings.md` (reference-not-copy, transclusion,
    tumbler span addressing — ideal)
  - `research/260614-zigzag-deep-dive/findings.md` (information space as co-equal
    dimensions; clone = transclusion — ideal)
  - `research/260614-roam-deep-dive/findings.md` (block-DB, store UUIDs, Datalog,
    in-app host)
  - `research/260614-obsidian-deep-dive/findings.md` (file-over-app, in-file `^id`,
    MetadataCache derived index, dual attach, ecosystem popularity)
  - `research/260614-notion-deep-dive/findings.md` (closed SaaS, external-API-only,
    DB schema+relations, operational envelope, scoped grant)
  - `research/260614-joplin-deep-dive/findings.md` (SQLite-local, interchange/sync-mirror
    attach, E2EE content opacity, local-REST)
  - `research/260614-logseq-deep-dive/findings.md` (block-graph on plain files, in-file
    `id::`, derived Datalog index, file→SQLite substrate migration)
  - `research/260614-localfirst-workspaces-deep-dive/findings.md` (Anytype/AFFiNE/AppFlowy:
    CRDT substrate, native merge, P2P/E2EE, CRDT-replica attach)
  - `research/260614-trilium-deep-dive/findings.md` (note cloning → DAG / identity≠placement,
    inherited+templated computed metadata, HTML-native, scripting+ETAPI, per-item opacity)
  - `research/260614-shard-spectrum-synthesis/findings.md` (**synthesis v2**: the thirteen
    capability spectra, shard family matrix, UC→task fold-in)
- Use cases: `spec/UseCaseCatalog.md` § A (UC-26–UC-67; UC-34–UC-43 are the
  engine-attachment cases, UC-44–UC-67 the conceptual + modern-tool cases)
- Aspiration: `INTENT.md` (orchestrator, not engine; mechanism over policy;
  capability-aware adapters; Markdown-first, backend-neutral)
- Related workplan: `SHARD-WP-0001` (page resolution, namespaces, overlays,
  provenance — federation architecture must align with, not duplicate, those
  outputs)

**Non-goal:** Implement federation. This workplan produces architecture and
decision records only.

## Decision topics (overview)

| Topic | Key tradeoff | Primary UCs |
|-------|--------------|-------------|
| Orchestrator positioning | Adapter layer vs fedwiki-style homogeneous network | UC-02, UC-26 |
| Remix primitives | Fork vs overlay vs import vs link-only | UC-04, UC-26, UC-29 |
| Equivalent page identity | Title/path/alias/graph matching; chorus vs canonical | UC-27, UC-07 |
| History model | Per-shard journal vs Git coordination journal vs both | UC-29, UC-33 |
| Union composition | Server orchestrator vs client composition | UC-05, UC-27 |
| Change notification | Git ping, ActivityPub, poll — adapter transports | UC-31 |
| Space lifecycle | Permanent vs ephemeral; archive and carry-forward | UC-28, UC-30 |
| Transclusion depth | Whole-page projection vs inline span | UC-03, UC-32 |
| Consensus presets | Spread, merge, designated canonical — policy not core | UC-07, UC-27 |
| Capability matrix | Which federation ops require which adapter capabilities | UC-02–UC-07 |

### Adapter-contract topics (T11–T16, from engine + modern-tool dives)

| Topic | Key tradeoff | Primary UCs |
|-------|--------------|-------------|
| Adapter contract & capabilities | **Thirteen spectra** (not flat verbs); write granularity; operational envelope; access grant; **merge model**; **content opacity** | UC-02, UC-35, UC-38, UC-57, UC-61, UC-64 |
| Structured page model | Typed frontmatter vs sidecar vs blob; bodiless / multi-record; DB schema+relations; **computed (inherited/templated) metadata**; non-Markdown assets; query-defined pages; **multi-placement (DAG) identity** | UC-34, UC-39, UC-55, UC-58, UC-54, UC-66, UC-67 |
| History portability | Supplement (DB-internal incl. Notion/Joplin/Trilium; **CRDT-log**) vs import (open file history) | UC-36, UC-41 |
| Adapter binding | **Full mode taxonomy**: file-store (native *or* interchange/sync-mirror) / in-engine-host / local-REST / external-API / **CRDT-replica** / **P2P-no-central-endpoint**; per-binding choice; backend-swap / substrate-migration | UC-38, UC-40, UC-43, UC-50, UC-57, UC-60, UC-62, UC-64, UC-65 |
| Syntax translation | Lossless round-trip vs **lossy-with-fidelity-report** (HTML/blocks/CRDT) vs read-only degradation | UC-42, UC-59, UC-03 |
| Addressing, identity & navigation (T16) | Span addressing; content identity; **identity≠placement**; transclusion-as-reference; **derived query index**; dimensional/query views | UC-44, UC-45, UC-46, UC-47, UC-48, UC-51, UC-52, UC-54, UC-63, UC-66 |

---

## Architecture positioning and boundaries

```task
id: SHARD-WP-0002-T1
status: todo
priority: high
state_hub_task_id: "ea8fdb22-6c7f-4ac1-9799-1346abf3c3b7"
```

Write the opening sections of `spec/FederationArchitecture.md`:

- shard-wiki as **orchestration layer** over heterogeneous shards (contrast
  Federated Wiki homogeneous JSON sites, ikiwiki homogeneous git wikis,
  ActivityPub activity streams).
- Explicit **compare, do not equate** mapping from federation research §6.
- Architectural boundaries: what core owns vs adapters vs UI vs policy config.
- Relationship to `SHARD-WP-0001` outputs (resolution, namespaces, overlays).

**Tradeoffs to document:** Central Git coordination journal vs fully
decentralized peer sync; browser-composed union vs server-side orchestrator for
agents/CLI.

---

## Remix primitives: fork, overlay, import, reference

```task
id: SHARD-WP-0002-T2
status: todo
priority: high
state_hub_task_id: "fb7d4bce-5d2e-4602-9b63-85934d90e82d"
```

Define when each remix primitive applies and how they interact:

| Primitive | Typical trigger | Writes to remote? |
|-----------|-----------------|-------------------|
| **Reference** | Link only | No |
| **Projection** | Read remote page | No (cache optional) |
| **Overlay** | Edit read-only shard | No until explicit apply |
| **Import / fork** | Copy into writable shard | Source unchanged |

Resolve federation research open question #1. Cover capability-limited shards
(read-only, no diff/merge). Map to UC-26, UC-04, UC-29.

**Tradeoffs:** Fedwiki fork-as-default vs overlay-before-mutation; copy cost
and attribution portability vs link-only federation.

---

## Equivalent page identity and multi-version presentation

```task
id: SHARD-WP-0002-T3
status: todo
priority: high
state_hub_task_id: "8f2a333d-ddcc-4cc6-b6ed-1ba9b178eee3"
```

Specify how shard-wiki identifies "the same topic" across shards:

- Matching signals: normalized title, path, explicit alias table, link-graph
  equivalence, manual curator binding.
- Presentation: chorus-of-voices (UC-27) vs designated canonical (policy).
- Link to UC-07 divergence detection and reconciliation triggers.

**Tradeoffs:** Automatic matching false positives vs manual curation burden;
showing all versions vs default canonical with alternates visible.

---

## History, attribution, and coordination journal

```task
id: SHARD-WP-0002-T4
status: todo
priority: high
state_hub_task_id: "5f39f48d-5142-4078-a84f-3245ec1add7e"
```

Define how edit history and attribution flow across federation operations:

- Per-shard revision model (Git commit, engine history, fedwiki-style journal
  where applicable).
- Information-space **coordination journal** role for cross-shard operations
  (fork, import, reconcile, space branch).
- Portable attribution requirements for UC-29 (frictionless remix).

**Tradeoffs:** Fedwiki journal-per-page vs Git-only; duplication of history vs
reconstructibility from coordination journal; storage cost of embedded media on
import.

---

## Union composition layer

```task
id: SHARD-WP-0002-T5
status: todo
priority: medium
state_hub_task_id: "3ff71e11-d0e9-4fda-b916-d6c34c51aa51"
```

Decide where the **union view** is assembled:

- Orchestrator API (server-side graph for agents, CI, non-browser clients).
- Optional client-side composition (fedwiki-style browser pull) as a consumer
  pattern, not the only path.
- Caching, freshness, and invalidation interaction with UC-03, UC-05, UC-31.

**Tradeoffs:** Single composition point (simpler provenance) vs distributed
composition (fedwiki resilience); cache staleness vs live-pull latency.

---

## Change notification and subscription transports

```task
id: SHARD-WP-0002-T6
status: todo
priority: medium
state_hub_task_id: "9596e5e8-8d6b-4ed4-bcbc-ebb45e3168be"
```

Specify change-notification as an **optional adapter capability**:

- Transports: git hook / pinger (ikiwiki), ActivityPub Create/Update (XWiki),
  WebDAV ETag, polling fallback.
- What a subscription triggers: projection refresh, reconciliation queue,
  RecentChanges union entry (UC-31, UC-17).
- Out-of-scope vs in-scope for v1.

**Tradeoffs:** Push freshness vs implementation complexity; ActivityPub as
notification-only vs content-bearing share; dependency on external fediverse
infrastructure.

---

## Information space lifecycle

```task
id: SHARD-WP-0002-T7
status: todo
priority: medium
state_hub_task_id: "38134064-51ce-4f5a-80bf-b2cfbe381c59"
```

Model lifecycle states for root entities / information spaces:

- Active, read-only archived, retired (detached), merged-into-successor.
- Carry-forward workflow (UC-28, UC-30): selective import from archived shard.
- Space-level fork / branch (UC-33): coordination journal + shard config branch.

**Tradeoffs:** First-class ephemeral "happenings" vs permanent spaces only;
automatic archive vs manual; whether retirement deletes projections or preserves
read-only union entries.

---

## Transclusion and projection depth

```task
id: SHARD-WP-0002-T8
status: todo
priority: medium
state_hub_task_id: "5607732b-612a-4550-bb17-b8cd34979cf4"
```

Distinguish projection levels:

| Level | UC | Behavior |
|-------|-----|----------|
| Whole-page projection | UC-03 | Lazy full page from remote shard |
| Block/span transclusion | UC-32 | Inline embed with origin + freshness |
| Link reference | UC-08 | Pointer only |

Define provenance display requirements and staleness semantics for UC-32.
Reference Xanadu transclusion patterns without adopting unbuilt Xanadu scope.

**Tradeoffs:** Live transclusion fragility (link rot, remote down) vs snapshot
on import; core orchestrator support vs Markdown extension + adapter.

---

## Consensus and reconciliation policy catalog

```task
id: SHARD-WP-0002-T9
status: todo
priority: medium
state_hub_task_id: "adfca8b3-eb21-497d-9f51-65dc9269c810"
```

Document **configurable policy presets** (mechanism over policy):

- Fedwiki-spread (versions coexist; popularity implicit).
- Designated canonical shard (explicit write target).
- Git-merge reconciliation (ikiwiki-style).
- Overlay-only (no destructive merge on read-only sources).
- Vote-to-merge / editorial gate (optional, UI-layer).

Map presets to UC-07, UC-27. Core provides primitives; policy selects preset.

**Tradeoffs:** Default policy for L0 open mode vs team mode; exposing conflicts
vs auto-merge when backends support it.

---

## Federation operations capability matrix

```task
id: SHARD-WP-0002-T10
status: todo
priority: medium
state_hub_task_id: "c7a93d06-8631-43b4-bc7f-1b0a1cd1436f"
```

Produce a capability matrix: which federation operations require which adapter
capabilities (read, write, diff, merge, lock, version, publish, notify,
transclude-source).

Cross-check against INTENT capability-aware adapters principle. Identify
graceful degradation paths for limited backends (read-only participant,
projection-only, patch target).

This matrix **consumes the capability vocabulary defined in T11** — keep the two
in sync. Feeds `spec/TechnicalSpecificationDocument.md` adapter contract section.

---

# Shard adapter contract (folded from engine deep dives, 2026-06-13)

These tasks distill the cross-cutting **adapter-contract constraints** surfaced by
the four engine deep dives (wiki-engines landscape, XWiki, TWiki, Foswiki). They
answer *what a backend must expose to participate as a shard*, complementing the
federation tasks above (which answer *what the union does*). Output target:
`spec/TechnicalSpecificationDocument.md` (adapter contract section), cross-linked
from `spec/FederationArchitecture.md`.

Recurring cross-engine insight to honor: **structure and history in text files
federate far more easily than in a database**, and **Foswiki::Store already proves
the versioned-interface-with-swappable-backends pattern** the contract should adopt.

## Adapter contract: capability model & versioned interface

```task
id: SHARD-WP-0002-T11
status: todo
priority: high
state_hub_task_id: "a7379621-6694-488b-94ca-846b8e27e745"
```

Define the **capability-aware shard adapter contract** as a *versioned* interface,
taking `Foswiki::Store` + `Foswiki::Meta` as direct prior art (a real engine that
already separates store backend from core behind a stable interface).

- **Operation verbs:** `read, write, diff, merge, lock, version, publish, notify,
  transclude-source, translate-syntax, structured-payload` (reconcile with T10).
- **Capability profile = the thirteen spectra** (synthesis v2 §2), each a *position* not a
  boolean, so federation ops degrade by position:
  1. addressing granularity (none → path → page-level store id → in-file span → in-file
     block `id::` → store-UUID → portable tumbler)
  2. content identity (none → path/title → fingerprint → span-set)
  3. identity vs placement (path=identity → **identity separated from placement**:
     Trilium note/branch; a page in many locations = a DAG)
  4. structure (flat MD → frontmatter/`key::` → %META% → typed objects → DB
     schema+relations → object-graph/ontology → **computed: inherited+templated**)
  5. history (none → internal-only / **CRDT-log** → open-file → git-native)
  6. **merge model** (none → git/text → conflict-notes/keep-both → **native-CRDT**)
  7. native query (none → text → **build-your-own derived index** → datalog/graph → DB query)
  8. translation (native → lossless → lossy-with-fidelity-report; incl. HTML)
  9. attachment mode (file-store [native *or* interchange/sync-mirror] → in-engine-host →
     local-REST → external-API → CRDT-replica → P2P/no-central-endpoint)
  10. operational envelope (local/unbounded → realtime CRDT/WebSocket → rate-limited/
      eventually-consistent/paginated)
  11. access grant (open → token → OAuth scoped+revocable → P2P key/invite)
  12. **content opacity** (plaintext → encrypted-at-rest whole-shard → **per-item**)
  13. write granularity (whole-file → per-page/note → per-block)
- Versioning/compatibility rules for the contract itself; capability discovery
  (static profile vs runtime negotiation).

**Inputs:** `260608-wikiengines-overview` §3, §5; `260613-foswiki-deep-dive` §2, §6;
`260614-shard-spectrum-synthesis` §2, §5 (v2). **Provides** the vocabulary T10's matrix
consumes. **UCs:** UC-02, UC-35, UC-38, UC-57, UC-61, UC-64.

**Tradeoffs:** Rich capability set (precise degradation) vs contract complexity;
static profile vs runtime capability negotiation.

---

## Page model: structured / typed payload representation

```task
id: SHARD-WP-0002-T12
status: todo
priority: high
state_hub_task_id: "7334a4a4-ba75-4fac-a8b4-8350d342b299"
```

Decide how the **backend-neutral, Markdown-first page model carries structured data
without flattening**:

The model must stretch **many ways at once** (synthesis v2 §3): prose Markdown, typed
*and computed* records, non-Markdown assets, reference/query-defined pages, and
**multi-placement (DAG) identity**.

- Source shapes: XWiki XObjects against an XClass; TWiki/Foswiki DataForms stored as
  `%META:FIELD%` in text; Foswiki MetaDataPlugin **multiple records per topic**;
  Semantic MediaWiki annotations; **Notion databases** (schema + typed properties +
  inter-record **relations** + rollups/formulas) — the apex of database-as-pages.
- Representation choice: typed frontmatter vs sidecar file vs opaque provenance blob.
  Prefer **in-text structure** (frontmatter/`%META%`, git-diffable); tolerate DB
  structure via sidecar + fidelity report (T15).
- **Bodiless pages** (UC-39): may a page be purely structured, no Markdown body?
- **N typed records per page** (not one form) must be representable.
- **Non-Markdown content types** (UC-55): drawings (Excalidraw), spatial canvases
  (JSON Canvas), images, attachments — typed asset vs opaque blob vs content-type
  registry, with provenance, not flattened away.
- **Inter-record relations** (UC-58): represented as typed links in the union link
  graph, a separate relation index (cf. ZigZag many-to-many), or both (T16).
- **Query-defined / reference pages** (UC-44, UC-54): a page whose canonical form is a
  span manifest (Xanadu EDL) or a saved query (Dataview/Notion linked DB) — coordinate
  with T16.
- **Computed metadata** (UC-67): Trilium attributes are **inherited (down the tree) +
  templated**, so effective metadata = own + inherited + templated. Represent
  **effective-vs-own with per-attribute provenance** (own / inherited-from / template);
  decide materialize (snapshot) vs compute-live.
- **Multi-placement / DAG identity** (UC-66): Trilium **note (identity) vs branch
  (placement)** — a page may occupy several locations at once. Separate **page identity
  from placement** (one entity, N placements/paths/shards); no single canonical path —
  coordinate with T16 (the namespace-level clone/reference primitive).

**Inputs:** `xwiki` §2.3; `twiki` §2.3; `foswiki` §4; `notion` §2–§3; `obsidian` §3;
`trilium` §2–§3; `localfirst-workspaces` §1–§3; `shard-spectrum-synthesis` §3 (v2).
**UCs:** UC-34, UC-39, UC-55, UC-58, UC-54, UC-44, UC-66, UC-67.

**Tradeoffs:** Lossless fidelity vs a uniform queryable model; diff/search over
structured fields vs prose; one coherent model vs many content shapes; effective-vs-own
metadata snapshot vs live computation.

---

## History portability: supplement vs import

```task
id: SHARD-WP-0002-T13
status: todo
priority: high
state_hub_task_id: "6837862a-8f57-410d-9200-a6a5dcf1a7b9"
```

Define how the **coordination journal** relates to an engine's native history (aligns
with and refines T4):

History is a spectrum (synthesis v2 §2): `none → internal-only / CRDT-log → open-file →
git-native`.

- **Adopt** — already git-native (Git folder/repo, Obsidian-with-Git, Logseq files): use
  as-is.
- **Supplement** — engine history is non-portable: DB-internal (Confluence, MediaWiki,
  XWiki `xwikircs`, **Notion**, **Joplin/Trilium** revisions) or a **CRDT update log**
  (Anytype/AFFiNE/AppFlowy): the journal begins now / mirrors forward / snapshots the
  replica (UC-36).
- **Import** — engine history is an open file format (TWiki/yawex RCS `.txt,v`,
  Foswiki PlainFile timestamped copies): backfill into Git preserving author/timestamp
  (UC-41).
- Authoritative journal vs mirror-reconciled-back; one-time vs continuous.

**Inputs:** `xwiki` §2.4; `twiki` §2.1; `foswiki` §2.2; `notion` §4; `joplin` §1;
`trilium` §1; `localfirst-workspaces` §4. **UCs:** UC-36, UC-41.

**Tradeoffs:** Import fidelity vs effort; duplicated history vs single source of truth.

---

## Adapter binding: attach path, hosting, backend-swap

```task
id: SHARD-WP-0002-T14
status: todo
priority: medium
state_hub_task_id: "f8835969-d118-4738-952a-5e67e5209f3d"
```

Decide **how and where an adapter binds to a backend**:

**Full attachment-mode taxonomy** (synthesis v2 §2, §3), with a backend possibly
offering more than one — so attach mode is a **per-binding, capability-gated choice**,
not a fixed property:

- **File-store direct** — read the on-disk store as a folder shard, in two sub-kinds:
  - *native store* — Obsidian vault, **Logseq** `pages/`+`journals/` (with a format
    profile parsing `id::`/`key::`), TWiki `data/`, Git repo: offline, git-native, but
    risks inconsistent reads under a running engine (UC-40, UC-53, UC-62).
  - *interchange / sync mirror* — a tool's documented sync representation on a third-party
    target (**Joplin** items on WebDAV/Nextcloud/S3): app-independent, read/projection/
    overlay-mostly (the tool owns the format; never re-sync) (UC-60).
- **In-engine hosted adapter** — adapter runs *inside* the app via its extension API
  (XWiki components; TWiki/Foswiki handlers; **Roam Depot** over `roamAlphaAPI`;
  **Obsidian plugin** over `App.vault`; **Logseq** plugin; **Trilium** scripting code
  notes): high fidelity, needs deploy access (UC-38, UC-50).
- **Local-REST** — a localhost API served by the running app (**Joplin** Data API;
  **Trilium** ETAPI): app-must-run, token auth (UC-38, links UC-57).
- **External-API only** — attach from outside via a remote REST API, no in-engine
  hosting (**Notion**): full write-through without deploy access, but bounded by the
  **operational envelope** (rate limit, eventual consistency, payload caps) and a
  **scoped, revocable access grant** that enforces no-silent-mutation (UC-57).
- **CRDT replica** — hold a local CRDT replica (**Anytype/AFFiNE/AppFlowy**: any-sync/
  Yjs/Yrs): the backend merges natively — respect CRDT semantics, don't git-merge; or a
  self-host sync endpoint (AFFiNE/AppFlowy Cloud) (UC-64).
- **P2P / no-central-endpoint** — bind a replica or a named peer/node, not a URL
  (**Anytype** any-sync), content possibly E2EE (UC-65).
- **Dual / multi attach** — a backend offering several modes (Obsidian/Logseq: file *or*
  plugin; TWiki: file *or* API; Joplin: mirror *or* Data API): pick per binding; declare
  which is authoritative (UC-53).
- **Backend-swap / substrate-migration tolerance** — shard identity/provenance survives a
  storage change (Foswiki RCS↔PlainFile; folder→Git; **Logseq file→SQLite DB-graph**) —
  bind to capabilities, not to "it's files" (UC-43).

**Inputs:** `twiki` §5–§6; `xwiki` §3; `foswiki` §2; `roam` §5; `obsidian` §4;
`notion` §4, §6; `joplin` §2, §4; `logseq` §4–§5; `localfirst-workspaces` §4; `trilium`
§5; `shard-spectrum-synthesis` §3 (v2). **UCs:** UC-38, UC-40, UC-43, UC-50, UC-53,
UC-57, UC-60, UC-62, UC-64, UC-65.

**Tradeoffs:** Fidelity vs deploy access; consistency vs offline capability; external
write-through vs rate-limit/eventual-consistency ceiling; CRDT-replica liveness vs
snapshot simplicity.

---

## Syntax translation & content fidelity

```task
id: SHARD-WP-0002-T15
status: todo
priority: medium
state_hub_task_id: "22b57b3a-b06b-4ff0-a34a-667a0386bf25"
```

Specify how **non-Markdown shards** participate in the Markdown-first model:

Translation is a spectrum (synthesis §2): `native → lossless → lossy-with-fidelity-report`.

- Read native markup (TWiki/Foswiki TML, XWiki syntax) into the page model and accept
  Markdown overlays back via **bidirectional, lossless translation** (UC-42).
- Feasibility proof: Foswiki **WysiwygPlugin** (TML→HTML for editing, HTML→TML
  losslessly on save).
- **Lossy-with-fidelity-report** (UC-59) — for models that do *not* round-trip: **Notion**
  blocks/rich-text/databases (export is lossy); **Trilium** **HTML** (CKEditor — more
  tractable than blocks but still lossy); CRDT/object models. Translate lossily but **make
  fidelity loss visible** — a per-shard/per-page report of what projects cleanly vs.
  degrades, with non-mappable elements preserved as provenance/sidecar. Fidelity becomes
  data (union without erasure). Distinct from the lossless case (UC-42).
- **HTML as a source model** (Trilium) joins TML/Notion-blocks/CRDT in the translation
  capability — HTML↔Markdown, lossy-aware.
- **Graceful degradation:** when neither lossless nor acceptable lossy translation is
  available, the shard is a read-only/projection participant (UC-03), never silently
  corrupted.
- Open: may overlays be stored in Markdown, or must they round-trip in native syntax?

**Inputs:** `foswiki` §5; `twiki` §2.4; `xwiki` §2.5; `notion` §3; `trilium` §4.
**UCs:** UC-42, UC-59, UC-03.

**Tradeoffs:** Translation coverage vs read-only floor; Markdown overlays (portable)
vs native-syntax overlays (safe round-trip); lossy-but-usable vs read-only-but-faithful.

---

## Addressing, content identity, and dimensional / query navigation

```task
id: SHARD-WP-0002-T16
status: todo
priority: medium
state_hub_task_id: "b00ca669-59d6-454a-8d6e-f34694e35192"
```

New thread from the conceptual (Xanadu, ZigZag) + modern-tool (Roam, Notion, Obsidian/
Dataview) dives and the synthesis (`260614-shard-spectrum-synthesis` §4). No existing
task owns the addressing/identity/navigation layer that transclusion, overlay,
equivalence, and dimensional views depend on. Refines T8 (transclusion/projection depth)
and T5 (union composition); consumes T11 capabilities.

- **Span addressing** — a portable sub-page address. Adopt **native span IDs** where the
  backend mints them (Roam `:block/uid`, Notion/CRDT UUID, Joplin/Trilium page-level id)
  or carries them in-file (Obsidian `^id`, **Logseq `id::` — block-level AND git-diffable,
  the sweet spot**); fall back to **content fingerprint** or path+range otherwise. Open:
  wrap native IDs in a shard-scoped address so they survive projection and don't collide
  across shards (Xanadu tumbler is the unreached ideal). (UC-51, UC-44.)
- **Content identity** — detect that two pages are the same / derived content by
  fingerprint or span-set overlap, **path-independently** — the equivalence mechanism
  UC-27 left open. Enables reverse transclusion (UC-45). (UC-46.)
- **Identity vs placement** — separate **page identity from placement** (Trilium **note vs
  branch**: a page cloned into many locations = a DAG). One entity, N placements (paths/
  shards); no single canonical path — the namespace-level form of the clone/reference
  primitive. (UC-66, UC-22.)
- **Transclusion as one reference-not-copy primitive** — unify Xanadu transclusion,
  ZigZag clone, Roam/Obsidian/Logseq embed, Notion synced block, **Trilium note cloning**
  over the addressable union (synthesis v2 §3). Compose-by-reference pages (UC-44) and
  reverse lookup (UC-45) are views over it.
- **Dimensional / query navigation** — model the union so each relationship (namespace,
  genealogy, version, shard, equivalence, links) is a navigable **dimension** (ZigZag),
  and a page can be **query-defined** (Dataview/Notion linked DB, UC-54). **Delegate**
  view computation to a shard's native query engine where present (Roam/Logseq Datalog,
  Notion/AppFlowy DB query, XWiki XWQL); **else build a derived index over the
  projection** (Logseq DataScript-over-files pattern, UC-63). (UC-47, UC-48, UC-52,
  UC-54, UC-63.)
- **Boundary:** this is a **derived lens over canonical files+journal**, never a new
  store (ZigZag dive §6); the many-to-many link graph stays a graph index, not a rank.

**Inputs:** `xanadu` §2–§5; `zigzag` §2–§6; `roam` §2–§4, §7; `notion` §2; `obsidian`
§2–§3; `logseq` §1–§3; `trilium` §2–§3; `shard-spectrum-synthesis` §3–§5 (v2).
**UCs:** UC-44, UC-45, UC-46, UC-47, UC-48, UC-51, UC-52, UC-54, UC-63, UC-66.

**Tradeoffs:** Native-ID adoption (cheap, backend-coupled) vs a portable address scheme
(harder, uniform); core navigation API vs internal organizing concept; query delegation
(fast, backend-dependent) vs orchestrator-computed (uniform, costly).

---

## Acceptance criteria

- `spec/FederationArchitecture.md` exists with all ten federation topic sections
  (T1–T10) and an explicit **decisions / deferred / open** table per topic.
- The **adapter contract** section of `spec/TechnicalSpecificationDocument.md` exists,
  populated by T11–T16, with the capability vocabulary (T11, the **thirteen spectra**)
  reconciled against the T10 federation-ops matrix.
- Each decision honors INTENT: mechanism over policy, union without erasure,
  overlay before mutation, no silent remote mutation, shard sovereignty,
  capability-aware adapters, Markdown-first / backend-neutral.
- UC-26–UC-67 are traceable to architecture / adapter-contract sections
  (UC-34–UC-43 to T11–T15; UC-44–UC-67 to T11–T16 per
  `research/260614-shard-spectrum-synthesis/findings.md` §4, v2).
- Conflicts or dependencies on `SHARD-WP-0001` outputs are listed (e.g.
  namespace model affects equivalent-page identity; page model T12 affects
  resolution/overlays).
- `SHARD-WP-0001` and `SHARD-WP-0002` can proceed in parallel where topics
  are independent; merge conflicts in spec are resolved before implementation
  workplan starts.

## Suggested task order

**Federation architecture (T1–T10):**
1. T1 positioning (frames everything)
2. T2 remix primitives + T3 equivalent identity (parallel)
3. T4 history model
4. T5 composition + T6 notification (parallel)
5. T7 lifecycle + T8 transclusion (parallel)
6. T9 policy catalog + T10 capability matrix (parallel, finalize doc)

**Adapter contract (T11–T16)** — can start in parallel with T1; T11 first as it
frames the rest, and pair it with T10 (shared capability vocabulary):
7. T11 contract & the thirteen capability spectra (frames T12–T16; sync with T10)
8. T12 page model + T13 history portability (parallel; T13 aligns with T4)
9. T14 binding + T15 syntax translation (parallel)
10. T16 addressing, identity & navigation (refines T8/T5; finalize adapter-contract spec)