diff --git a/packages/cli/src/nonInteractiveCli.ts b/packages/cli/src/nonInteractiveCli.ts
index bae45e1e32..bf1f4e4d6d 100644
--- a/packages/cli/src/nonInteractiveCli.ts
+++ b/packages/cli/src/nonInteractiveCli.ts
@@ -15,7 +15,14 @@ import { isSlashCommand } from './ui/utils/commandUtils.js';
 import type { LoadedSettings } from './config/settings.js';
 import {
   convertSessionToClientHistory,
+  FatalError,
+  FatalAuthenticationError,
   FatalInputError,
+  FatalSandboxError,
+  FatalConfigError,
+  FatalTurnLimitedError,
+  FatalToolExecutionError,
+  FatalCancellationError,
   promptIdContext,
   OutputFormat,
   JsonFormatter,
@@ -341,20 +348,60 @@ export async function runNonInteractive({
       };
 
       const reconstructFatalError = (event: AgentEvent<'error'>): Error => {
-        const errToThrow = new Error(event.message);
         const errorMeta = event._meta;
+        const name =
+          typeof errorMeta?.['errorName'] === 'string'
+            ? errorMeta['errorName']
+            : undefined;
+
+        let errToThrow: Error;
+        switch (name) {
+          case 'FatalAuthenticationError':
+            errToThrow = new FatalAuthenticationError(event.message);
+            break;
+          case 'FatalInputError':
+            errToThrow = new FatalInputError(event.message);
+            break;
+          case 'FatalSandboxError':
+            errToThrow = new FatalSandboxError(event.message);
+            break;
+          case 'FatalConfigError':
+            errToThrow = new FatalConfigError(event.message);
+            break;
+          case 'FatalTurnLimitedError':
+            errToThrow = new FatalTurnLimitedError(event.message);
+            break;
+          case 'FatalToolExecutionError':
+            errToThrow = new FatalToolExecutionError(event.message);
+            break;
+          case 'FatalCancellationError':
+            errToThrow = new FatalCancellationError(event.message);
+            break;
+          case 'FatalError':
+            errToThrow = new FatalError(
+              event.message,
+              typeof errorMeta?.['exitCode'] === 'number'
+                ? errorMeta['exitCode']
+                : 1,
+            );
+            break;
+          default:
+            errToThrow = new Error(event.message);
+            if (name) {
+              Object.defineProperty(errToThrow, 'name', {
+                value: name,
+                enumerable: true,
+              });
+            }
+            break;
+        }
+
         if (errorMeta?.['exitCode'] !== undefined) {
           Object.defineProperty(errToThrow, 'exitCode', {
             value: errorMeta['exitCode'],
             enumerable: true,
           });
         }
-        if (errorMeta?.['errorName'] !== undefined) {
-          Object.defineProperty(errToThrow, 'name', {
-            value: errorMeta['errorName'],
-            enumerable: true,
-          });
-        }
         if (errorMeta?.['code'] !== undefined) {
           Object.defineProperty(errToThrow, 'code', {
             value: errorMeta['code'],
@@ -555,7 +602,18 @@ export async function runNonInteractive({
             streamEnded = true;
             break;
           }
+          case 'initialize':
+          case 'session_update':
+          case 'agent_start':
+          case 'tool_update':
+          case 'elicitation_request':
+          case 'elicitation_response':
+          case 'usage':
+          case 'custom':
+            // Explicitly ignore these non-interactive events
+            break;
           default:
+            event satisfies never;
             break;
         }
       }
diff --git a/packages/cli/src/utils/errors.ts b/packages/cli/src/utils/errors.ts
index 5e48abed99..774d9e994c 100644
--- a/packages/cli/src/utils/errors.ts
+++ b/packages/cli/src/utils/errors.ts
@@ -20,7 +20,6 @@ import {
   coreEvents,
   getErrorType,
   getErrorMessage,
-  getErrorType,
 } from '@google/gemini-cli-core';
 import { runSyncCleanup } from './cleanup.js';
 
diff --git a/packages/core/src/agent/legacy-agent-session.test.ts b/packages/core/src/agent/legacy-agent-session.test.ts
index 8cd92ca08d..38bea34910 100644
--- a/packages/core/src/agent/legacy-agent-session.test.ts
+++ b/packages/core/src/agent/legacy-agent-session.test.ts
@@ -200,40 +200,6 @@ describe('LegacyAgentSession', () => {
       await collectEvents(session, { streamId: streamId ?? undefined });
     });
 
-    it('accepts legacy message-array sends without displayContent', async () => {
-      const sendMock = deps.client.sendMessageStream as ReturnType<
-        typeof vi.fn
-      >;
-      sendMock.mockReturnValue(
-        makeStream([
-          {
-            type: GeminiEventType.Finished,
-            value: { reason: FinishReason.STOP, usageMetadata: undefined },
-          },
-        ]),
-      );
-
-      const session = new LegacyAgentSession(deps);
-      const { streamId } = await session.send({
-        message: [{ type: 'text', text: 'hi' }],
-      });
-
-      const userMessage = session.events.find(
-        (e): e is AgentEvent<'message'> =>
-          e.type === 'message' && e.role === 'user' && e.streamId === streamId,
-      );
-      expect(userMessage?.content).toEqual([{ type: 'text', text: 'hi' }]);
-      await vi.advanceTimersByTimeAsync(0);
-      expect(sendMock).toHaveBeenCalledWith(
-        [{ text: 'hi' }],
-        expect.any(AbortSignal),
-        'test-prompt',
-        undefined,
-        false,
-        undefined,
-      );
-    });
-
     it('returns streamId before emitting agent_start', async () => {
       const sendMock = deps.client.sendMessageStream as ReturnType<
         typeof vi.fn
diff --git a/packages/core/src/agent/legacy-agent-session.ts b/packages/core/src/agent/legacy-agent-session.ts
index fa1d652eb2..667c85f5ed 100644
--- a/packages/core/src/agent/legacy-agent-session.ts
+++ b/packages/core/src/agent/legacy-agent-session.ts
@@ -93,9 +93,6 @@ class LegacyAgentProtocol implements AgentProtocol {
         'LegacyAgentSession.send() only supports message sends for the moment.',
       );
     }
-    const normalizedMessage = Array.isArray(message)
-      ? { content: message, displayContent: undefined }
-      : message;
 
     if (this._activeStreamId) {
       // TODO: Interactive may eventually allow selected in-stream sends such as
@@ -108,16 +105,16 @@ class LegacyAgentProtocol implements AgentProtocol {
 
     this._beginNewStream();
     const streamId = this._translationState.streamId;
-    const parts = contentPartsToGeminiParts(normalizedMessage.content);
+    const parts = contentPartsToGeminiParts(message.content);
     const userMessage = this._makeUserMessageEvent(
-      normalizedMessage.content,
-      normalizedMessage.displayContent,
+      message.content,
+      message.displayContent,
       payload._meta,
     );
 
     this._emit([userMessage]);
 
-    this._scheduleRunLoop(parts, normalizedMessage.displayContent);
+    this._scheduleRunLoop(parts, message.displayContent);
 
     return { streamId };
   }
diff --git a/packages/core/src/agent/types.ts b/packages/core/src/agent/types.ts
index 512a8c9507..9bc3e81e0f 100644
--- a/packages/core/src/agent/types.ts
+++ b/packages/core/src/agent/types.ts
@@ -46,12 +46,10 @@ type RequireExactlyOne<T> = {
 }[keyof T];
 
 interface AgentSendPayloads {
-  message:
-    | ContentPart[]
-    | {
-        content: ContentPart[];
-        displayContent?: string;
-      };
+  message: {
+    content: ContentPart[];
+    displayContent?: string;
+  };
   elicitations: ElicitationResponse[];
   update: { title?: string; model?: string; config?: Record<string, unknown> };
   action: { type: string; data: unknown };