fix(server): Claude on Bedrock runs the model picked in the composer

apps/server/src/claudeModelOptions.ts

@@ -12,14 +12,19 @@ import {
   normalizeClaudeCatalogEffort,
   resolveClaudeCatalogApiModelId,
   resolveClaudeCatalogEffort,
+  resolveClaudeModelSlug,
   type ClaudeModelCatalog,
 } from "./provider/ClaudeModelCatalog.ts";
 
+const CLAUDE_CODE_MODEL_ALIASES = new Set(["opus", "sonnet", "haiku", "fable"]);
+
 export interface CompiledClaudeModelSelection {
   readonly apiModelId: string;
   readonly effort: string | undefined;
   readonly promptEffort: string | undefined;
   readonly settings: Readonly<Record<string, boolean>>;
+  /** The alias of a custom model named like one, which Claude Code would otherwise expand. */
+  readonly pinnedAlias: string | undefined;
   readonly queryIdentity: string;
 }
 
@@ -51,11 +56,23 @@ export function compileClaudeModelSelection(
   };
   const apiModelId = resolveClaudeCatalogApiModelId(catalog, selection);
   const promptEffort = resolvePromptInjectedEffort(capabilities, rawEffort) ?? undefined;
+  // An alias the catalog routes a built-in model to is Claude Code's own and is not pinned.
+  const pinnedAlias =
+    CLAUDE_CODE_MODEL_ALIASES.has(apiModelId) &&
+    resolveClaudeModelSlug(catalog, selection.model) === apiModelId
+      ? apiModelId
+      : undefined;
   return {
     apiModelId,
     effort,
     promptEffort,
     settings,
-    queryIdentity: JSON.stringify({ apiModelId, effort: effort ?? null, settings }),
+    pinnedAlias,
+    queryIdentity: JSON.stringify({
+      apiModelId,
+      effort: effort ?? null,
+      settings,
+      pinnedAlias: pinnedAlias ?? null,
+    }),
   };
 }