fix(llm): let an interrogation use the credential its route already stored

A configuration surface never holds a stored secret — it edits a redacted
descriptor — so once a key is saved, the draft it sends carries the route and
the endpoint and no credential at all. The interrogation went out
unauthenticated and the endpoint's 401 came back as "check the API key",
pointing at the one thing that was fine.

A named route now supplies its own credential, resolved exactly as a request
to it would be. A key typed into the form still wins: it is the one under
test, and may be the replacement for the stored one that is failing.

Resolution is a callback the probe invokes past the catalog short-circuit and
the protocol check, so a route answered from the installed registry costs no
credential lookup — and cannot fail over a credential the question never
needed.

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

@@ -8,8 +8,11 @@ import { getBuiltinModels } from '@earendil-works/pi-ai/providers/all'
 import { discoverModels } from '../src/discovery.ts'
 
 const servers: Server[] = []
+/** Credential variables a test set, cleared so the next one starts unset. */
+const touchedEnv: string[] = []
 
 afterEach(async () => {
+  for (const name of touchedEnv.splice(0)) Reflect.deleteProperty(process.env, name)
   await Promise.all(servers.splice(0).map(server => new Promise(resolve => server.close(resolve))))
 })
 
@@ -140,6 +143,50 @@ describe('draft-provider model discovery', () => {
     expect(server.headers[0]?.authorization).toBeUndefined()
   })
 
+  it('authenticates a configured route the draft cannot supply a key for', async () => {
+    // What the Models page actually sends after a key is saved: the form holds
+    // the redacted descriptor, so the draft names the route and the endpoint
+    // and no credential at all. Interrogating unauthenticated would answer 401
+    // and read as a wrong key.
+    const server = await listingServer({ body: JSON.stringify({ data: [{ id: 'm' }] }) })
+    const ctx = new Context()
+    await ctx.plugin(LlmService)
+    process.env['ACME_GATEWAY_KEY'] = 'stored-key'
+    touchedEnv.push('ACME_GATEWAY_KEY')
+    await ctx.plugin(LlmPiAi, {
+      providers: {
+        'acme-gateway': {
+          apiKeyEnv: 'ACME_GATEWAY_KEY',
+          api: 'openai-completions',
+          baseURL: server.url,
+          models: [{ id: 'acme-large' }],
+        },
+      },
+    })
+
+    await ctx.llm.discoverModels('llm-pi-ai', { provider: 'acme-gateway', baseURL: server.url })
+    // A key typed into the form is the one being tested — possibly the
+    // replacement for the stored one — so it wins.
+    await ctx.llm.discoverModels('llm-pi-ai', { provider: 'acme-gateway', baseURL: server.url, apiKey: 'typed' })
+    // A route no profile declares yet is the create case: nothing is stored.
+    await ctx.llm.discoverModels('llm-pi-ai', { provider: 'not-declared-yet', baseURL: server.url })
+
+    expect(server.headers.map(headers => headers.authorization))
+      .toEqual(['Bearer stored-key', 'Bearer typed', undefined])
+  })
+
+  it('leaves a catalog route\'s credential unresolved, having never reached the network', async () => {
+    // The catalog answers before any endpoint is asked, so a route whose
+    // profile names a credential that is not set must still answer rather than
+    // failing over a key the interrogation never needed.
+    const ctx = new Context()
+    await ctx.plugin(LlmService)
+    Reflect.deleteProperty(process.env, 'ABSENT_FOR_DISCOVERY')
+    await ctx.plugin(LlmPiAi, { providers: { deepseek: { apiKeyEnv: 'ABSENT_FOR_DISCOVERY' } } })
+
+    await expect(ctx.llm.discoverModels('llm-pi-ai', { provider: 'deepseek' })).resolves.not.toHaveLength(0)
+  })
+
   it('drops unusable rows rather than failing the whole listing', async () => {
     const server = await listingServer({
       body: JSON.stringify({