notification catalogue: GET /api/notify/mapping

the piece that makes a new notification kind a server change rather than an
app store release. a push carries a code and integers; this is what the code
means, synced to the device instead of compiled into it.

deliberately the same shape as affordances rather than a second mechanism: a
`notifications/` directory of yaml in the plugin repository, copied to
capabilities/notifications/<publisher>/<appName>/ on install, removed on
uninstall. publish.ts mirrors affordances/publish.ts closely enough to diff.

the namespace is DERIVED from where the file lands, never from what it
declares — same rule as mountPrefix. a plugin writing `officer/core:test` as a
key gets `<publisher>/<plugin>:officer/core:test` and the real core entry is
untouched. that is the security property of the whole scheme and it is pinned
by test.

version is a content hash, not a counter. a counter needs somewhere to live
and is then wrong after a restore, a rollback, or two servers built from the
same install; a hash needs no storage and is right in all three. so the client
compares mv !== version, and both docs now say so — i had written "higher".

core entries ship in code rather than on disk, because capabilities/ is
installed rather than committed and `test` has to exist on a machine that has
installed nothing — it is what first light is proved with.

read from disk per request, not memoised: installing a plugin has to change
the answer without a restart, or it presents as "the new plugin's
notifications don't work", which is the hardest kind of bug to place.

verified live: 401 through the platform, plugin catalogue appearing and
disappearing with no restart, version returning to its prior value when the
plugin is removed. 10 catalogue tests, 100% coverage of catalogue.ts.

docs/push-notifications.md

@@ -130,18 +130,27 @@ An entry says how to render and where to go:
 | `route`  | the deep link, with `{id}` interpolated                        |
 | `thread` | grouping key, so like-notifications collapse rather than stack |
 
-**Plugins declare their own**, on the affordances pattern (`src/servers/affordances/publish.ts`): a
-directory in the plugin repository, copied to a platform-managed store on install, removed on uninstall,
-namespaced `<publisher>/<appName>/`. That mechanism already exists and is understood; a second one for
+**Plugins declare their own**, on the affordances pattern (`src/servers/notifications/publish.ts`, which
+deliberately mirrors `affordances/publish.ts`): a `notifications/` directory of YAML in the plugin
+repository, copied to `capabilities/notifications/<publisher>/<appName>/` on install and removed on
+uninstall.
+
+The namespace is **derived from where the file lands, never from what it declares** — the same rule as
+`mountPrefix`. A plugin therefore cannot claim `officer/core:` or another publisher's codes by writing
+them into its own catalogue; it would have to install itself somewhere it cannot. This is pinned by test. That mechanism already exists and is understood; a second one for
 notifications would drift from it. The platform aggregates every installed plugin's catalogue plus its own
 into the response above, and `version` increments whenever that aggregate changes.
 
 ### Staying in sync, and the fallback
 
 Every push carries `mv`, the mapping version it was rendered against. The app compares it to its cached
-version and **resyncs in the background when it is behind** — so the mapping normally catches up before an
+version and **resyncs in the background when they differ** — so the mapping normally catches up before an
 unknown code can arrive.
 
+`version` is a **content hash, not a counter**, so the test is `mv !== version` rather than `mv > version`.
+A counter would need somewhere to live and would then be wrong after a restore, a rollback, or two servers
+built from the same install; a hash needs no storage and is right in all three.
+
 When a push still outruns the sync, the fallback renders:
 
 > **Unknown notification**