feat(llm-pi-ai): dormant bare mount — routes live entirely in the settings plane

An empty or omitted providers dict is now the valid dormant posture: the
adapter mounts with zero routes and no catalog entries, registers routes
the moment the llm-pi-ai settings section supplies profiles, and drops
them when it empties. The TUI demo mounts the adapter bare, so adding an
openai/anthropic provider is purely a settings.yaml (or, next PR, web
form) operation with per-request apiKeyEnv credential resolution.

packages/llm/llm-pi-ai/tests/adapter.spec.ts

@@ -395,7 +395,9 @@ describe('provider profile lifecycle', () => {
   })
 
   it('validates empty, unknown, legacy-shaped, and explicitly blank profiles', () => {
-    expect(() => resolveProfiles({})).toThrow(/at least one/)
+    // Empty and omitted dicts are the dormant zero-route posture, not errors.
+    expect(resolveProfiles({}).size).toBe(0)
+    expect(resolveProfiles(undefined).size).toBe(0)
     expect(() => resolveProfiles({ '': {} })).toThrow(/non-empty/)
     expect(() => resolveProfiles({ 'not-real': {} })).toThrow(/unknown/)
     // The pre-release array shape and its per-profile provider field fail

packages/llm/llm-pi-ai/tests/dynamic-config.spec.ts

@@ -42,6 +42,30 @@ async function boot(dir: string, config: LlmPiAi.Config): Promise<Context> {
 }
 
 describe('request-level dynamic profiles', () => {
+  it('mounts bare and dormant, then registers routes the moment settings supply providers', async () => {
+    vi.stubEnv('PI_DYNAMIC_KEY', '')
+    const dir = await home()
+    await writeFile(join(dir, '.env'), 'PI_DYNAMIC_KEY=pk-from-settings\n')
+    const server = await mockServer([{ events: textEvents }])
+    // The exact product posture: `- id: llm-pi-ai` with no config at all.
+    const ctx = await boot(dir, {})
+
+    expect(ctx.llm.listProviders()).toEqual([])
+    await ctx.settings.update(NS, {
+      providers: { deepseek: { apiKeyEnv: 'PI_DYNAMIC_KEY', baseURL: server.url } },
+    })
+    expect(ctx.llm.listProviders().map(provider => provider.id)).toEqual(['deepseek'])
+    await expect(ctx.llm.listModels('deepseek')).resolves.not.toHaveLength(0)
+
+    const result = await assemble(ctx, { provider: 'deepseek', model: 'deepseek-v4-flash', messages: [] })
+    expect(result.message.content).toEqual([{ type: 'text', text: 'hello' }])
+    expect(server.headers[0]?.authorization).toBe('Bearer pk-from-settings')
+
+    // Emptying the user layer returns the adapter to its dormant state.
+    await ctx.settings.replace(NS, {})
+    expect(ctx.llm.listProviders()).toEqual([])
+  })
+
   it('adds a provider route from settings and drops it when the user layer resets', async () => {
     const dir = await home()
     const server = await mockServer([{ events: textEvents }])