The URL says which provider set runs, and the seam stops claiming otherwise

The seam arrived carrying a switching design that no longer holds. It presented
runtime hot-switching as what shaped it — selection in state, a key on <Refine>
to drop the previous backend's cache — and it read the backend from a build
global whose comment claimed build.ts defined it. Nothing ever did, and nothing
could have: this project serves from src/ in production too, so that define
block never reaches what runs.

What replaces it is a URL. The default provider set lives at the root, another
behind a path prefix naming it, and moving between them is a link. The reload is
the mechanism rather than a cost to avoid: it discards the cache and the session
with no code to undo them. So the switch helpers are gone and the file is
smaller than what it replaced.

The resolution is a pure function with its own tests, including the case that is
true today — an empty registry, where every URL is the default. The router does
NOT yet strip the prefix, deliberately: it is a shared primitive every screen
depends on, the suites that would prove a change to it are not run here, and no
URL carries a prefix while one backend is registered. That half lands with the
second backend, which is what makes it testable.

Three claims the move to this base falsified are corrected too. The inbox the
count comment points at is local here, not on another branch. The worked
provider implementation is not in this branch's ancestry. And the MeetingPoint
shape exists here, so its binding stops being optional — a backend that cannot
carry one of the four entities cannot serve the app, and nothing optional should
let a half-backend register quietly.

Also: both usage declarations are named usage_festipod.md, so the stem is now
ambiguous as a link. They are referred to by folder path, and both are listed
under publish so each provider can re-find its own if it moves.

.project/concepts/data-layer/_debt.md

@@ -1,15 +0,0 @@
-# Doc-debt — data-layer
-
-> Presence of a block = doc to update. Processed → delete the block; no blocks left → delete this file.
-> One block = one "big change": `why` + `files` + `verify` (leaves to review).
-
-## Block: the Refine seam's comments describe a switching design this base superseded
-
-- **why**: The Refine seam was carried over verbatim from `festipod-refine` and lands here as unreferenced scaffolding, on a base that has moved past two of its stated premises. `RefineProvider.tsx` presents **runtime hot-switching** as what shapes the file (selection held in React state, `key={backend.name}` remounting `<Refine>` so the previous backend's cache is discarded); the product decision since is **one app variant per provider set, selected by URL, with a full page reload** — there is no in-session switch left for the file to be shaped by. And both `RefineProvider.tsx` and `providers/index.ts` say the per-backend sign-in barrier is "the next piece" because `AuthGate` gates on the NextGraph session; on this base `AuthGate` renders no access screen of its own and delegates the whole access experience to the SDK. The prose was left untouched on transfer on purpose — it is settled with the wiring, not during the carry-over.
-- **files**: `src/shared/refine/RefineProvider.tsx`, `src/shared/refine/providers/index.ts`, `src/shared/refine/providers/types.ts`
-- **verify (what must be updated)**:
-  - `RefineProvider.tsx` header — "SWITCHING AT RUNTIME is what shapes this file", the `key`/remount rationale, and whether `switchTo` / `useBackendSelection` survive at all once the selection is a URL plus a reload.
-  - `RefineProvider.tsx` — the "What is NOT solved here is the sign-in: `AuthGate` still gates on the NextGraph session … That is the next piece" paragraph, against this base's `src/app/AuthGate.tsx`.
-  - `providers/index.ts` — same sign-in claim, plus the build-injected `__FESTIPOD_BACKEND__` global it reads: `build.ts` on this base defines no such thing, so `initialBackendName()` can only ever fall back to the first registered backend.
-  - Branch-relative phrasing that points nowhere from here: `types.ts` "the inbox on the sibling branch" (that inbox is local — `src/shared/data/registration.ts`) and `providers/index.ts` "the worked implementation is in this branch's history" (it is on `festipod-refine`, not in this branch's ancestry).
-  - Leaves: `data-layer/_overview.md` gained the seam's triggers but still describes no seam, and `brief_2026-10-03_structure-for-two-rights-models` states the contract is in code — both to revisit once the seam is actually wired.

.project/concepts/data-layer/_overview.md

@@ -16,8 +16,11 @@ How Festipod **persists its data** through NextGraph (P2P, local-first, end-to-e
 
 Each external interface this concept consumes lives in **its own folder**, holding the provider's engagement (pulled, version-pinned) and — once Festipod actually consumes it — our own declaration beside it.
 
-- `polyfill-surface/` — [[contract_polyfill-surface]], **the data contract, PULLED from the provider and version-pinned**: the `@ng-eventually/polyfill` surface the app codes against, what it guarantees and what it refuses to promise. The ONLY reference — never open the provider's own sources. Beside it, [[usage_festipod]] — what the app *actually* calls, the conditions it needs, and the frictions measured against the engagement. **Frictions are how a need reaches the provider**: put it there, then signal it out of band.
+- `polyfill-surface/` — [[contract_polyfill-surface]], **the data contract, PULLED from the provider and version-pinned**: the `@ng-eventually/polyfill` surface the app codes against, what it guarantees and what it refuses to promise. The ONLY reference — never open the provider's own sources. Beside it, `polyfill-surface/usage_festipod.md` — what the app *actually* calls, the conditions it needs, and the frictions measured against the engagement. **Frictions are how a need reaches the provider**: put it there, then signal it out of band.
 - `indexing-layer/` — [[contract_indexing-layer]], the `@ng-helpers/indexing` engagement, PULLED and pinned on `v1.0.0`: creating an index, depositing references into it, curating it, reading it back. **Nothing consumes it yet** — no declaration is authored beside it, deliberately, since an empty one would say nothing.
+- `activitypods-providers/` — [[contract_activitypods-providers]], a RECONSTRUCTION rather than a pull: that package publishes no engagement, so the leaf is **our own pinned observation** of it, to be re-verified at every version bump. Beside it, `activitypods-providers/usage_festipod.md`, our declaration toward it. Nothing is wired yet — the Refine seam that would use it (`src/shared/refine/`) carries no backend.
+
+Two declarations now share the name `usage_festipod.md`, so refer to either by its folder path rather than by wikilink — the stem alone no longer says which.
 
 ## Model & data
 - [[knowledge_nextgraph-stack]] — the SHEX shapes, the reactive ORM bindings, `build:orm`, injection through `ngSession`

.project/contracts.yaml

@@ -23,8 +23,11 @@
 # committed.
 
 publish:
-  # Key qualified by interface: a second declaration is coming for the NextGraph+polyfill
-  # backend, and publish keys must stay unique.
+  # Both declarations are named `usage_festipod.md`, so the keys are qualified by their
+  # interface — publish keys must stay unique, and the bare subject no longer says which.
+  # Listing a declaration here is what lets its provider re-find it with `list --from`
+  # after it moves; it sends nothing on its own.
+  polyfill-surface--festipod: concepts/data-layer/polyfill-surface/usage_festipod.md
   activitypods-providers--festipod: concepts/data-layer/activitypods-providers/usage_festipod.md
 
 consume: