feat: implement resolvePreferredProvider function to determine provider preference

Author: zortos293

apps/server/src/orchestration/Layers/ProviderCommandReactor.test.ts

@@ -30,7 +30,7 @@ import { GitCore, type GitCoreShape } from "../../git/Services/GitCore.ts";
 import { TextGeneration, type TextGenerationShape } from "../../git/Services/TextGeneration.ts";
 import { OrchestrationEngineLive } from "./OrchestrationEngine.ts";
 import { OrchestrationProjectionPipelineLive } from "./ProjectionPipeline.ts";
-import { ProviderCommandReactorLive } from "./ProviderCommandReactor.ts";
+import { ProviderCommandReactorLive, resolvePreferredProvider } from "./ProviderCommandReactor.ts";
 import { OrchestrationEngineService } from "../Services/OrchestrationEngine.ts";
 import { ProviderCommandReactor } from "../Services/ProviderCommandReactor.ts";
 import * as NodeServices from "@effect/platform-node/NodeServices";
@@ -544,6 +544,11 @@ describe("ProviderCommandReactor", () => {
     expect(thread?.session?.providerName).toBe("copilot");
   });
 
+  it("prefers the locked thread provider over the inferred request provider", () => {
+    expect(resolvePreferredProvider(undefined, "copilot")).toBe("copilot");
+    expect(resolvePreferredProvider("codex", "copilot")).toBe("codex");
+  });
+
   it("infers the provider from the selected model on a pristine thread", async () => {
     const harness = await createHarness();
     const now = new Date().toISOString();

apps/server/src/orchestration/Layers/ProviderCommandReactor.ts

@@ -146,6 +146,13 @@ function isBuiltInModelForProvider(provider: ProviderKind, model: string | undef
   );
 }
 
+export function resolvePreferredProvider(
+  currentProvider: ProviderKind | undefined,
+  threadProvider: ProviderKind,
+): ProviderKind {
+  return currentProvider ?? threadProvider;
+}
+
 const make = Effect.gen(function* () {
   const orchestrationEngine = yield* OrchestrationEngineService;
   const providerService = yield* ProviderService;
@@ -274,8 +281,10 @@ const make = Effect.gen(function* () {
         detail: `Model '${options.model}' does not belong to provider '${threadProvider}' for thread '${threadId}'.`,
       });
     }
-    const preferredProvider: ProviderKind =
-      currentProvider ?? requestedProvider ?? defaultThreadProvider;
+    const preferredProvider: ProviderKind = resolvePreferredProvider(
+      currentProvider,
+      threadProvider,
+    );
     const desiredModel = options?.model ?? thread.model;
     const effectiveCwd = resolveThreadWorkspaceCwd({
       thread,