feat(settings): serve every registered namespace and key plugin cards on it

A plugin that registered a settings namespace could not reach the browser
configuration page: the api-proxy filtered every read and gated every
write through two hardcoded namespace lists, and the plugin configuration
section rendered an unordered list of cards carrying an opaque id rather
than the namespace they edit. Both gates lived in this repository, so a
user-authored plugin was configurable only by hand-editing settings.yaml.

The proxy now serves whatever ctx.settings.describe() returns and adds no
boundary of its own; a name no registration answers folds into the seam's
own settings-rejected, and the settings-not-exposed code retires. The
settings seam is untouched: which client may read a namespace, and which
page renders it, are facts about consumers.

settings.plugin.item becomes a keyed slot whose key is the namespace a
card edits, following tool.call.toolview. The section reads describe once
and dispatches the intersection of the slot ledger and the served set, so
a namespace another surface owns renders nothing without declaring
anything, and a card for an uncomposed plugin is never dispatched.

packages/client/ui-plugin-config/tests/stores.client.spec.ts

@@ -8,6 +8,7 @@ import { stubSettingsScope, type StubSettingsScope } from '@deepseek-ai/dsh-clie
 import { CardForm, numberField, textField } from '../src/client/card-store.ts'
 import { AgentLoopCardController, type AgentLoopSettings } from '../src/client/agent-loop-store.ts'
 import { BashCardController, type BashSettings } from '../src/client/bash-store.ts'
+import { PluginConfigSectionController } from '../src/client/section-store.ts'
 import { WebSearchCardController, type WebSearchSettings } from '../src/client/web-search-store.ts'
 
 /** Make the stub behave like a Host that accepts every write. */
@@ -538,3 +539,96 @@ describe('WebSearchCardController', () => {
     expect(credentials.set).not.toHaveBeenCalled()
   })
 })
+
+describe('PluginConfigSectionController', () => {
+  function settingsApi(namespaces: string[]) {
+    const describe = vi.fn(() => Promise.resolve({
+      rpcId: 's-1' as never,
+      result: {
+        ok: true as const,
+        value: {
+          writable: true,
+          hasDocument: true,
+          namespaces: namespaces.map(ns => ({
+            ns, schema: {}, value: {}, applies: 'live' as const, secrets: [], revision: 0,
+          })),
+        },
+      },
+    }))
+    return { api: { settings: { describe } } as never, describe }
+  }
+
+  /** Slot ledger stand-in: one stored entry per registered card key. */
+  function ledger(...keys: string[]) {
+    return keys.map(key => ({ component: null, options: { key } }))
+  }
+
+  it('dispatches the served namespaces a card claims, in card registration order', async () => {
+    const settings = settingsApi(['bash', 'ui-theme', 'agent-loop'])
+    const controller = new PluginConfigSectionController(settings.api, () => ledger('agent-loop', 'bash'))
+
+    await controller.load()
+
+    // ui-theme is served but claimed by no card here — another surface owns
+    // it. The order is the cards', not the Host's: plugin activation can
+    // reorder the description between boots.
+    expect(controller.inject().hooks.pluginConfigSection.getSnapshot().namespaces)
+      .toEqual(['agent-loop', 'bash'])
+  })
+
+  it('never dispatches a card whose namespace this deployment does not serve', async () => {
+    const settings = settingsApi(['bash'])
+    const controller = new PluginConfigSectionController(settings.api, () => ledger('bash', 'web-search-deepseek'))
+
+    await controller.load()
+
+    expect(controller.inject().hooks.pluginConfigSection.getSnapshot().namespaces).toEqual(['bash'])
+  })
+
+  it('takes a card registered after the read without asking the Host again', async () => {
+    const settings = settingsApi(['bash'])
+    let entries = ledger()
+    const controller = new PluginConfigSectionController(settings.api, () => entries)
+    await controller.load()
+    expect(controller.inject().hooks.pluginConfigSection.getSnapshot().namespaces).toEqual([])
+
+    entries = ledger('bash')
+    controller.refresh()
+
+    expect(controller.inject().hooks.pluginConfigSection.getSnapshot().namespaces).toEqual(['bash'])
+    expect(settings.describe).toHaveBeenCalledOnce()
+  })
+
+  it('keeps the namespaces it knew when a read fails', async () => {
+    const settings = settingsApi(['bash'])
+    const controller = new PluginConfigSectionController(settings.api, () => ledger('bash'))
+    await controller.load()
+    settings.describe.mockRejectedValueOnce(new Error('offline') as never)
+
+    await controller.load()
+
+    expect(controller.inject().hooks.pluginConfigSection.getSnapshot().namespaces).toEqual(['bash'])
+  })
+
+  it('publishes nothing once disposed, and never claims it was answered', async () => {
+    const settings = settingsApi(['bash'])
+    const controller = new PluginConfigSectionController(settings.api, () => ledger('bash'))
+
+    controller.dispose()
+    await controller.load()
+
+    expect(controller.inject().hooks.pluginConfigSection.getSnapshot())
+      .toEqual({ loaded: false, namespaces: [] })
+    expect(settings.describe).not.toHaveBeenCalled()
+  })
+
+  it('reports the Host answered even when it serves nothing this section shows', async () => {
+    const settings = settingsApi(['ui-theme'])
+    const controller = new PluginConfigSectionController(settings.api, () => ledger('bash'))
+
+    await controller.load()
+
+    expect(controller.inject().hooks.pluginConfigSection.getSnapshot())
+      .toEqual({ loaded: true, namespaces: [] })
+  })
+})