fix(model-picker): list each provider/model combo separately (#970)

* fix(model-picker): list each provider/model combo separately

Previously, /model grouped models by name and showed all providers
that offer the same model (e.g. 'claude-sonnet-4-5 — anthropic, google-antigravity').
This was confusing because:
1. Users couldn't tell which provider would be used when selecting by number
2. The display implied choice between providers but selection was automatic

Now each provider/model combination is listed separately so users
can explicitly select the exact provider they want.

- Remove model grouping in buildModelPickerItems
- Display format changed from 'model — providers' to 'provider/model'
- pickProviderForModel now returns the single provider directly
- Updated tests to reflect new behavior

* fix: simplify model picker entries (#970) (thanks @mcinteerj)

---------

Co-authored-by: Keith the Silly Goose <keith@42bolton.macnet.nz>
Co-authored-by: Peter Steinberger <steipete@gmail.com>

src/auto-reply/reply/directive-handling.model.ts

@@ -18,7 +18,6 @@ import {
 import {
   buildModelPickerItems,
   type ModelPickerCatalogEntry,
-  pickProviderForModel,
   resolveProviderEndpointLabel,
 } from "./directive-handling.model-picker.js";
 import type { InlineDirectives } from "./directive-handling.parse.js";
@@ -126,7 +125,7 @@ export async function maybeHandleModelDirectiveInfo(params: {
     const current = `${params.provider}/${params.model}`;
     const lines: string[] = [`Current: ${current}`, "Pick: /model <#> or /model <provider/model>"];
     for (const [idx, item] of items.entries()) {
-      lines.push(`${idx + 1}) ${item.model} — ${item.providers.join(", ")}`);
+      lines.push(`${idx + 1}) ${item.provider}/${item.model}`);
     }
     lines.push("", "More: /model status");
     return { text: lines.join("\n") };
@@ -236,22 +235,13 @@ export function resolveModelSelectionFromDirective(params: {
         errorText: `Invalid model selection "${raw}". Use /model to list.`,
       };
     }
-    const picked = pickProviderForModel({
-      item,
-      preferredProvider: params.provider,
-    });
-    if (!picked) {
-      return {
-        errorText: `Invalid model selection "${raw}". Use /model to list.`,
-      };
-    }
-    const key = `${picked.provider}/${picked.model}`;
+    const key = `${item.provider}/${item.model}`;
     const aliases = params.aliasIndex.byKey.get(key);
     const alias = aliases && aliases.length > 0 ? aliases[0] : undefined;
     modelSelection = {
-      provider: picked.provider,
-      model: picked.model,
-      isDefault: picked.provider === params.defaultProvider && picked.model === params.defaultModel,
+      provider: item.provider,
+      model: item.model,
+      isDefault: item.provider === params.defaultProvider && item.model === params.defaultModel,
       ...(alias ? { alias } : {}),
     };
   } else {