refactor(providers): one record per provider, one place for the key-and-URL decision (#988)

Every fact about a provider lives in one record in lib/providers.ts (SDK kind,
credential kind, env var prefix, default URL, picker group, four-language
notes, and a short model list for the six providers that cannot list models).
The thirteen tables keyed by provider name are gone. resolveEndpoint decides
whose key a call uses and where it goes; usesServerCredentials reads its
answer instead of mirroring getAIModel's branches; serverCredentialError holds
the server credential check once. The UI, the connection test and the routes
read the record's credential and sdk fields instead of comparing provider
names (44 such checks before, 6 after, in the admin panel's fixed-variable
branches).

Intended behavior changes: providers that can list their models have no
hand-written list; the settings dialog fetches the live list in the background
once credentials are entered for a provider without models and offers it
behind "Browse models". Azure has no placeholder default URL (old entries that
hold it still count as unset); the base URL field of Azure and of the new
"custom" OpenAI-compatible preset (CUSTOM_API_KEY, CUSTOM_BASE_URL) is
labelled required. The connection test answers 400 for an unknown provider
name; prototype names are refused everywhere. Provider lists in error messages
and the admin "add provider" dropdown follow the picker's order.

Also fixed, from before the refactor: the redirect guard drops x-access-code
on cross-origin redirects, and edgeOneEndpoint accepts the Origin header only
when it matches Host or X-Forwarded-Host.

Verification: a behavior snapshot of getAIModel's SDK factory calls and the
quota functions over 25 providers, 22 client override shapes and 9 server
environments (5843 rows), recorded on the old code and unchanged apart from
the intended changes; 752 unit tests, 65 provider e2e tests, tsc, biome,
next build. Reviewed by five models from one brief; their findings and the
resulting fixes are recorded in docs/plans/2026-10-provider-refactor.md.

tests/e2e/settings-providers.spec.ts

@@ -51,26 +51,45 @@ test("a first provider: pick it, fill in the key, test, use it", async ({
         tested.push(route.request().postDataJSON().modelId)
         await route.fulfill({ json: { valid: true, responseTime: 1400 } })
     })
+    const listedWith: string[] = []
+    await page.route("**/api/provider-models", async (route) => {
+        listedWith.push(route.request().postDataJSON().apiKey)
+        await route.fulfill({
+            json: {
+                models: [{ id: "deepseek-v4-pro" }, { id: "deepseek-chat" }],
+            },
+        })
+    })
     await openApp(page)
     await openSettings(page)
     const dialog = settingsDialog(page)
     await expect(dialog.getByText("Use your own API key")).toBeVisible()
 
     await dialog.getByTestId("pick-provider-deepseek").click()
-    // The first suggested model is added, and the key field has the cursor
+    // No model yet (DeepSeek lists its own), and the key field has the cursor
     await expect(
         dialog.getByRole("heading", { name: "DeepSeek", exact: true }),
     ).toBeVisible()
-    await expect(dialog.locator('input[title="deepseek-v4-pro"]')).toBeVisible()
     await expect(dialog.locator("#api-key")).toBeFocused()
     await expect(dialog.getByTestId("step-1-todo")).toBeVisible()
-    await expect(dialog.getByTestId("step-2-done")).toBeVisible()
+    await expect(dialog.getByTestId("step-2-todo")).toBeVisible()
     const testButton = dialog.getByTestId("test-models")
     await expect(testButton).toBeDisabled()
     await expect(dialog.getByText("Fill in the API key first.")).toBeVisible()
 
+    // The key is in: the list is fetched once by itself, without taking the
+    // focus; it is behind "Browse models"
     await dialog.locator("#api-key").fill("sk-1234")
     await expect(dialog.getByTestId("step-1-done")).toBeVisible()
+    const browse = dialog.getByRole("button", { name: "Browse models" })
+    await expect(browse).toBeVisible()
+    await expect(dialog.locator("#api-key")).toBeFocused()
+    expect(listedWith).toEqual(["sk-1234"])
+    await browse.click()
+    await page.getByRole("option", { name: "deepseek-v4-pro" }).click()
+    expect(listedWith).toEqual(["sk-1234"])
+    await expect(dialog.locator('input[title="deepseek-v4-pro"]')).toBeVisible()
+    await expect(dialog.getByTestId("step-2-done")).toBeVisible()
     await expect(testButton).toHaveText("Test deepseek-v4-pro")
     await testButton.click()
     // The visible panel, not the screen reader's copy
@@ -114,7 +133,7 @@ test("the provider picker searches, marks added ones, and Enter picks", async ({
         dialog.getByTestId("pick-provider-anthropic"),
     ).not.toContainText("Added")
     await expect(dialog.locator('[data-testid^="pick-provider-"]')).toHaveCount(
-        24,
+        25,
     )
 
     await search.fill("zzz")
@@ -552,6 +571,8 @@ test("a local server's base URL is shown from the start", async ({ page }) => {
 test("Azure needs its resource URL before it counts as connected", async ({
     page,
 }) => {
+    // An entry saved while Azure still had a placeholder default URL: the
+    // placeholder names no resource, so the entry is not set up yet
     await openApp(page, {
         config: {
             version: 1,
@@ -575,9 +596,7 @@ test("Azure needs its resource URL before it counts as connected", async ({
     await expect(dialog.getByTestId("step-1-todo")).toBeVisible()
     await expect(dialog.getByTestId("test-models")).toBeDisabled()
     await expect(
-        dialog.getByText(
-            "Fill in the API key and your Azure resource's base URL first.",
-        ),
+        dialog.getByText("Fill in the API key and the base URL first."),
     ).toBeVisible()
     await dialog
         .locator("#base-url")
@@ -585,6 +604,34 @@ test("Azure needs its resource URL before it counts as connected", async ({
     await expect(dialog.getByTestId("test-models")).toBeEnabled()
 })
 
+test("the OpenAI-compatible preset takes any URL and shows where requests go", async ({
+    page,
+}) => {
+    await openApp(page)
+    await openSettings(page)
+    const dialog = settingsDialog(page)
+    // Not among the popular ones: it is in the full picker
+    await dialog.getByRole("button", { name: /^See all \d+ providers/ }).click()
+    await dialog.getByTestId("pick-provider-custom").click()
+    await expect(
+        dialog.getByRole("heading", { name: "OpenAI-compatible", exact: true }),
+    ).toBeVisible()
+    // No URL yet: a key alone does not count as connected
+    await dialog.locator("#api-key").fill("any")
+    await expect(dialog.getByTestId("step-1-todo")).toBeVisible()
+    await expect(
+        dialog.getByText("Fill in the API key and the base URL first."),
+    ).toBeVisible()
+    // Its options start open; the URL field shows the chat endpoint
+    await dialog.locator("#base-url").fill("http://127.0.0.1:1234/v1")
+    await expect(
+        dialog.getByText(
+            "Requests go to http://127.0.0.1:1234/v1/chat/completions",
+        ),
+    ).toBeVisible()
+    await expect(dialog.getByTestId("step-1-done")).toBeVisible()
+})
+
 test("a model id typed for one provider does not follow to the next", async ({
     page,
 }) => {
@@ -650,10 +697,11 @@ test("a model list that loads leaves a refused test's mark", async ({
 })
 
 test("an empty model list says so and opens nothing", async ({ page }) => {
+    let models: { id: string }[] = []
     await page.route("**/api/provider-models", (route) =>
-        route.fulfill({ json: { models: [] } }),
+        route.fulfill({ json: { models } }),
     )
-    // OpenAI has suggested models: they come back once the key changes
+    // OpenAI lists its own models: nothing to browse until a list arrives
     await openApp(page, {
         config: {
             version: 1,
@@ -665,16 +713,24 @@ test("an empty model list says so and opens nothing", async ({ page }) => {
     await openSettings(page)
     const dialog = settingsDialog(page)
     await dialog.getByTestId("provider-row-o1").click()
+    // A key the provider already had fetches nothing by itself
+    await page.waitForTimeout(800)
+    await expect(
+        dialog.getByRole("button", { name: "Browse models" }),
+    ).toHaveCount(0)
     await dialog.getByRole("button", { name: /^Get all models from/ }).click()
     await expect(
         dialog.getByText("The provider returned no models."),
     ).toBeVisible()
+    // The picker did not open by itself
+    await expect(page.getByRole("listbox")).toHaveCount(0)
+    // A new key fetches the list again by itself; the list waits behind
+    // "Browse models" and the cursor stays in the key field
+    models = [{ id: "fresh-model" }]
     await dialog.locator("#api-key").fill("k-new")
     await expect(
         dialog.getByRole("button", { name: "Browse models" }),
     ).toBeVisible()
-    await page.waitForTimeout(300)
-    // The picker did not open by itself
     await expect(page.getByRole("listbox")).toHaveCount(0)
     await expect(dialog.locator("#api-key")).toBeFocused()
 })