refactor: address round 4 review comments

1. Remove isCommandOutput helper — inline instanceof check directly
   in handleYieldedValue. Reviewer: "Don't think we need this helper?"

2. Remove onPolling callback from DeviceFlowCallbacks in oauth.ts —
   reviewer: "We should also remove this from performDeviceFlow then?"
   The spinner in interactive-login.ts handles visual feedback now.

3. Convert 11 "yield new CommandOutput(..); return;" patterns to
   "return yield new CommandOutput(..)" one-liners across 9 files.

Note: outputConfig remains optional — 3 commands (auth/token,
cli/setup, init) legitimately don't define output configs.

Author: BYK

src/commands/api.ts

@@ -1210,7 +1210,6 @@ export const apiCommand = buildCommand({
       throw new OutputError(response.body);
     }
 
-    yield new CommandOutput(response.body);
-    return;
+    return yield new CommandOutput(response.body);
   },
 });

src/commands/auth/login.ts

@@ -182,8 +182,7 @@ export const loginCommand = buildCommand({
         // Non-fatal: user info is supplementary. Token remains stored and valid.
       }
 
-      yield new CommandOutput(result);
-      return;
+      return yield new CommandOutput(result);
     }
 
     // OAuth device flow

src/commands/auth/refresh.ts

@@ -105,7 +105,6 @@ Examples:
         : undefined,
     };
 
-    yield new CommandOutput(payload);
-    return;
+    return yield new CommandOutput(payload);
   },
 });

src/commands/auth/status.ts

@@ -190,7 +190,6 @@ export const statusCommand = buildCommand({
       verification: await verifyCredentials(),
     };
 
-    yield new CommandOutput(data);
-    return;
+    return yield new CommandOutput(data);
   },
 });

src/commands/auth/whoami.ts

@@ -65,7 +65,6 @@ export const whoamiCommand = buildCommand({
       // Cache update failure is non-essential — user identity was already fetched.
     }
 
-    yield new CommandOutput(user);
-    return;
+    return yield new CommandOutput(user);
   },
 });

src/commands/cli/fix.ts

@@ -735,7 +735,6 @@ export const fixCommand = buildCommand({
       throw new OutputError(result);
     }
 
-    yield new CommandOutput(result);
-    return;
+    return yield new CommandOutput(result);
   },
 });

src/commands/cli/upgrade.ts

@@ -494,8 +494,7 @@ export const upgradeCommand = buildCommand({
       flags,
     });
     if (resolved.kind === "done") {
-      yield new CommandOutput(resolved.result);
-      return;
+      return yield new CommandOutput(resolved.result);
     }
 
     const { target } = resolved;

src/commands/issue/plan.ts

@@ -225,8 +225,7 @@ export const planCommand = buildCommand({
       if (!flags.force) {
         const existingSolution = extractSolution(state);
         if (existingSolution) {
-          yield new CommandOutput(buildPlanData(state));
-          return;
+          return yield new CommandOutput(buildPlanData(state));
         }
       }
 
@@ -261,8 +260,7 @@ export const planCommand = buildCommand({
         throw new Error("Plan creation was cancelled.");
       }
 
-      yield new CommandOutput(buildPlanData(finalState));
-      return;
+      return yield new CommandOutput(buildPlanData(finalState));
     } catch (error) {
       // Handle API errors with friendly messages
       if (error instanceof ApiError) {

src/commands/project/create.ts

@@ -405,8 +405,7 @@ export const createCommand = buildCommand({
         expectedSlug,
         dryRun: true,
       };
-      yield new CommandOutput(result);
-      return;
+      return yield new CommandOutput(result);
     }
 
     // Create the project
@@ -433,7 +432,6 @@ export const createCommand = buildCommand({
       expectedSlug,
     };
 
-    yield new CommandOutput(result);
-    return;
+    return yield new CommandOutput(result);
   },
 });

src/lib/command.ts

@@ -307,13 +307,9 @@ export function buildCommand<
 
   const mergedParams = { ...existingParams, flags: mergedFlags };
 
-  function isCommandOutput(v: unknown): v is CommandOutput<unknown> {
-    return v instanceof CommandOutput;
-  }
-
   /**
-   * If the yielded value is a branded {@link CommandOutput}, render it via
-   * the output config. Void/undefined/Error/non-branded values are ignored.
+   * If the yielded value is a {@link CommandOutput}, render it via
+   * the output config. Void/undefined/Error/other values are ignored.
    */
   function handleYieldedValue(
     stdout: Writer,
@@ -322,13 +318,7 @@ export function buildCommand<
     // biome-ignore lint/suspicious/noExplicitAny: Renderer type mirrors erased OutputConfig<T>
     renderer?: HumanRenderer<any>
   ): void {
-    if (
-      !(outputConfig && renderer) ||
-      value === null ||
-      value === undefined ||
-      value instanceof Error ||
-      !isCommandOutput(value)
-    ) {
+    if (!(outputConfig && renderer && value instanceof CommandOutput)) {
       return;
     }