Prefer Copilot env before default engine override

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

Author: Copilot

README.md

@@ -296,7 +296,7 @@ configureAgent(codexEngine());
 configureAgent(geminiEngine());
 ```
 
-If you do not call `configureAgent(...)`, Rig now auto-selects a default engine from environment variables: `ANTHROPIC_API_KEY` → `anthropicEngine()`, `OPENAI_API_KEY` → `codexEngine()`, `GEMINI_API_KEY`/`GOOGLE_API_KEY` → `geminiEngine()`, otherwise `copilotEngine()`. Set `RIG_ENGINE` to `copilot`, `anthropic`, `codex`, or `gemini` to force one explicitly.
+If you do not call `configureAgent(...)`, Rig now auto-selects a default engine from environment variables: `COPILOT_SDK_URI` → `copilotEngine()`, then `RIG_ENGINE` (`copilot` | `anthropic` | `codex` | `gemini`) if set, then `ANTHROPIC_API_KEY` → `anthropicEngine()`, `OPENAI_API_KEY` → `codexEngine()`, `GEMINI_API_KEY`/`GOOGLE_API_KEY` → `geminiEngine()`, otherwise `copilotEngine()`.
 
 `piEngine()` uses the maintained `@earendil-works/pi-agent-core` package and requires the provider for model lookup. `anthropicEngine()` uses `@anthropic-ai/sdk`. Both adapters preserve conversation state across repair turns and map Rig tools to their SDK tool runners.
 

skills/rig/references/runtime.md

@@ -86,11 +86,12 @@ configureAgent(geminiEngine());
 ```
 
 - If you do not call `configureAgent(...)`, Rig auto-selects an engine from env vars:
+  - `COPILOT_SDK_URI` → `copilotEngine()`
+  - `RIG_ENGINE` (`copilot` | `anthropic` | `codex` | `gemini`) to force a specific default when Copilot URI is not set.
   - `ANTHROPIC_API_KEY` → `anthropicEngine()`
   - `OPENAI_API_KEY` → `codexEngine()`
   - `GEMINI_API_KEY` or `GOOGLE_API_KEY` → `geminiEngine()`
   - otherwise → `copilotEngine()`
-  - set `RIG_ENGINE` (`copilot` | `anthropic` | `codex` | `gemini`) to force a specific default.
 - `copilotEngine()` uses the Copilot SDK HTTP transport by default; launcher `--server` selects stdio.
 - `piEngine({ provider })` uses `@earendil-works/pi-agent-core` and requires a provider for model lookup.
 - `anthropicEngine()` uses `@anthropic-ai/sdk` and reads `ANTHROPIC_API_KEY`.

skills/rig/rig.ts

@@ -457,13 +457,13 @@ function resolveDefaultEngineKind(options: DefaultEngineOptions = {}): DefaultEn
   if (options.startServer) {
     return "copilot";
   }
+  if (hasNonEmptyEnv("COPILOT_SDK_URI")) {
+    return "copilot";
+  }
   const configuredEngine = process.env["RIG_ENGINE"]?.trim().toLowerCase();
   if (configuredEngine === "copilot" || configuredEngine === "anthropic" || configuredEngine === "codex" || configuredEngine === "gemini") {
     return configuredEngine;
   }
-  if (hasNonEmptyEnv("COPILOT_SDK_URI")) {
-    return "copilot";
-  }
   if (hasNonEmptyEnv("ANTHROPIC_API_KEY")) {
     return "anthropic";
   }

src/launcher-default-engine.test.ts

@@ -75,8 +75,11 @@ beforeEach(() => {
   mocks.codexRun.mockClear();
   mocks.codexStartThread.mockClear();
   delete process.env["COPILOT_SDK_URI"];
+  delete process.env["RIG_ENGINE"];
   delete process.env["ANTHROPIC_API_KEY"];
   delete process.env["OPENAI_API_KEY"];
+  delete process.env["GEMINI_API_KEY"];
+  delete process.env["GOOGLE_API_KEY"];
 });
 
 it("uses the launcher cwd when mounting the default copilot engine", async () => {
@@ -126,6 +129,33 @@ it("uses COPILOT_SDK_URI when mounting the default copilot engine", async () =>
   }
 });
 
+it("prefers COPILOT_SDK_URI over RIG_ENGINE when mounting the default engine", async () => {
+  const sendAndWait = vi.fn().mockResolvedValue(JSON.stringify("copilot-preferred"));
+  mocks.createSession.mockResolvedValue({ sendAndWait });
+  process.env["COPILOT_SDK_URI"] = "http://127.0.0.1:4242";
+  process.env["RIG_ENGINE"] = "anthropic";
+  process.env["ANTHROPIC_API_KEY"] = "test-key";
+  mocks.forUri.mockImplementation(((url: string) => ({ kind: "uri", url })) as any);
+
+  const fixturePath = resolve(dirname(fileURLToPath(import.meta.url)), "./launcher.fixture.ts");
+
+  try {
+    await launchRigProgram(fixturePath);
+
+    const call = agent({
+      name: "launcher-default-engine-copilot-preferred-test",
+      input: s.object({}),
+    });
+    const result = await call({});
+    expect(result).toBe("copilot-preferred");
+    expect(mocks.forUri).toHaveBeenCalledWith("http://127.0.0.1:4242");
+    expect(mocks.copilotClientCtor).toHaveBeenCalled();
+    expect(mocks.anthropicConstructor).not.toHaveBeenCalled();
+  } finally {
+    mocks.forUri.mockImplementation(mocks.defaultForUri);
+  }
+});
+
 it("automatically mounts anthropicEngine when ANTHROPIC_API_KEY is set", async () => {
   process.env["ANTHROPIC_API_KEY"] = "test-key";
   const fixturePath = resolve(dirname(fileURLToPath(import.meta.url)), "./launcher.fixture.ts");