diff --git a/apps/server/src/providers/claude-provider.ts b/apps/server/src/providers/claude-provider.ts
index 92b0fdf7..2eceb422 100644
--- a/apps/server/src/providers/claude-provider.ts
+++ b/apps/server/src/providers/claude-provider.ts
@@ -10,7 +10,7 @@ import { BaseProvider } from './base-provider.js';
 import { classifyError, getUserFriendlyErrorMessage, createLogger } from '@automaker/utils';
 
 const logger = createLogger('ClaudeProvider');
-import { getThinkingTokenBudget } from '@automaker/types';
+import { getThinkingTokenBudget, validateBareModelId } from '@automaker/types';
 import type {
   ExecuteOptions,
   ProviderMessage,
@@ -53,6 +53,10 @@ export class ClaudeProvider extends BaseProvider {
    * Execute a query using Claude Agent SDK
    */
   async *executeQuery(options: ExecuteOptions): AsyncGenerator<ProviderMessage> {
+    // Validate that model doesn't have a provider prefix
+    // AgentService should strip prefixes before passing to providers
+    validateBareModelId(options.model, 'ClaudeProvider');
+
     const {
       prompt,
       model,
diff --git a/apps/server/src/providers/codex-provider.ts b/apps/server/src/providers/codex-provider.ts
index 858ff206..54e13989 100644
--- a/apps/server/src/providers/codex-provider.ts
+++ b/apps/server/src/providers/codex-provider.ts
@@ -31,6 +31,7 @@ import type {
 import {
   CODEX_MODEL_MAP,
   supportsReasoningEffort,
+  validateBareModelId,
   type CodexApprovalPolicy,
   type CodexSandboxMode,
   type CodexAuthStatus,
@@ -663,6 +664,10 @@ export class CodexProvider extends BaseProvider {
   }
 
   async *executeQuery(options: ExecuteOptions): AsyncGenerator<ProviderMessage> {
+    // Validate that model doesn't have a provider prefix
+    // AgentService should strip prefixes before passing to providers
+    validateBareModelId(options.model, 'CodexProvider');
+
     try {
       const mcpServers = options.mcpServers ?? {};
       const hasMcpServers = Object.keys(mcpServers).length > 0;
@@ -760,6 +765,7 @@ export class CodexProvider extends BaseProvider {
         }
       }
 
+      // Model is already bare (no prefix) - validated by executeQuery
       const args = [
         CODEX_EXEC_SUBCOMMAND,
         CODEX_YOLO_FLAG,
diff --git a/apps/server/src/providers/cursor-provider.ts b/apps/server/src/providers/cursor-provider.ts
index aedae441..6cefc279 100644
--- a/apps/server/src/providers/cursor-provider.ts
+++ b/apps/server/src/providers/cursor-provider.ts
@@ -28,7 +28,7 @@ import type {
   ModelDefinition,
   ContentBlock,
 } from './types.js';
-import { stripProviderPrefix } from '@automaker/types';
+import { validateBareModelId } from '@automaker/types';
 import { validateApiKey } from '../lib/auth-utils.js';
 import { getEffectivePermissions } from '../services/cursor-config-service.js';
 import {
@@ -317,8 +317,8 @@ export class CursorProvider extends CliProvider {
   }
 
   buildCliArgs(options: ExecuteOptions): string[] {
-    // Extract model (strip 'cursor-' prefix if present)
-    const model = stripProviderPrefix(options.model || 'auto');
+    // Model is already bare (no prefix) - validated by executeQuery
+    const model = options.model || 'auto';
 
     // Build CLI arguments for cursor-agent
     // NOTE: Prompt is NOT included here - it's passed via stdin to avoid
@@ -649,6 +649,10 @@ export class CursorProvider extends CliProvider {
   async *executeQuery(options: ExecuteOptions): AsyncGenerator<ProviderMessage> {
     this.ensureCliDetected();
 
+    // Validate that model doesn't have a provider prefix
+    // AgentService should strip prefixes before passing to providers
+    validateBareModelId(options.model, 'CursorProvider');
+
     if (!this.cliPath) {
       throw this.createError(
         CursorErrorCode.NOT_INSTALLED,
diff --git a/apps/server/src/services/agent-service.ts b/apps/server/src/services/agent-service.ts
index 5e29d0db..abf4c0ab 100644
--- a/apps/server/src/services/agent-service.ts
+++ b/apps/server/src/services/agent-service.ts
@@ -7,6 +7,7 @@ import path from 'path';
 import * as secureFs from '../lib/secure-fs.js';
 import type { EventEmitter } from '../lib/events.js';
 import type { ExecuteOptions, ThinkingLevel, ReasoningEffort } from '@automaker/types';
+import { stripProviderPrefix } from '@automaker/types';
 import {
   readImageAsBase64,
   buildPromptWithImages,
@@ -290,13 +291,17 @@ export class AgentService {
       const maxTurns = sdkOptions.maxTurns;
       const allowedTools = sdkOptions.allowedTools as string[] | undefined;
 
-      // Get provider for this model
+      // Get provider for this model (with prefix)
       const provider = ProviderFactory.getProviderForModel(effectiveModel);
 
+      // Strip provider prefix - providers should receive bare model IDs
+      const bareModel = stripProviderPrefix(effectiveModel);
+
       // Build options for provider
       const options: ExecuteOptions = {
         prompt: '', // Will be set below based on images
-        model: effectiveModel,
+        model: bareModel, // Bare model ID (e.g., "gpt-5.1-codex-max", "composer-1")
+        originalModel: effectiveModel, // Original with prefix for logging (e.g., "codex-gpt-5.1-codex-max")
         cwd: effectiveWorkDir,
         systemPrompt: sdkOptions.systemPrompt,
         maxTurns: maxTurns,
diff --git a/apps/server/src/services/ideation-service.ts b/apps/server/src/services/ideation-service.ts
index 7973db05..81fc3de6 100644
--- a/apps/server/src/services/ideation-service.ts
+++ b/apps/server/src/services/ideation-service.ts
@@ -40,6 +40,7 @@ import type { SettingsService } from './settings-service.js';
 import type { FeatureLoader } from './feature-loader.js';
 import { createChatOptions, validateWorkingDirectory } from '../lib/sdk-options.js';
 import { resolveModelString } from '@automaker/model-resolver';
+import { stripProviderPrefix } from '@automaker/types';
 
 const logger = createLogger('IdeationService');
 
@@ -201,7 +202,7 @@ export class IdeationService {
         existingWorkContext
       );
 
-      // Resolve model alias to canonical identifier
+      // Resolve model alias to canonical identifier (with prefix)
       const modelId = resolveModelString(options?.model ?? 'sonnet');
 
       // Create SDK options
@@ -214,9 +215,13 @@ export class IdeationService {
 
       const provider = ProviderFactory.getProviderForModel(modelId);
 
+      // Strip provider prefix - providers need bare model IDs
+      const bareModel = stripProviderPrefix(modelId);
+
       const executeOptions: ExecuteOptions = {
         prompt: message,
-        model: modelId,
+        model: bareModel,
+        originalModel: modelId,
         cwd: projectPath,
         systemPrompt: sdkOptions.systemPrompt,
         maxTurns: 1, // Single turn for ideation
@@ -648,7 +653,7 @@ export class IdeationService {
         existingWorkContext
       );
 
-      // Resolve model alias to canonical identifier
+      // Resolve model alias to canonical identifier (with prefix)
       const modelId = resolveModelString('sonnet');
 
       // Create SDK options
@@ -661,9 +666,13 @@ export class IdeationService {
 
       const provider = ProviderFactory.getProviderForModel(modelId);
 
+      // Strip provider prefix - providers need bare model IDs
+      const bareModel = stripProviderPrefix(modelId);
+
       const executeOptions: ExecuteOptions = {
         prompt: prompt.prompt,
-        model: modelId,
+        model: bareModel,
+        originalModel: modelId,
         cwd: projectPath,
         systemPrompt: sdkOptions.systemPrompt,
         maxTurns: 1,
diff --git a/apps/server/tests/unit/providers/claude-provider.test.ts b/apps/server/tests/unit/providers/claude-provider.test.ts
index a02d3b5a..f107c4f4 100644
--- a/apps/server/tests/unit/providers/claude-provider.test.ts
+++ b/apps/server/tests/unit/providers/claude-provider.test.ts
@@ -37,6 +37,7 @@ describe('claude-provider.ts', () => {
 
       const generator = provider.executeQuery({
         prompt: 'Hello',
+        model: 'claude-opus-4-5-20251101',
         cwd: '/test',
       });
 
@@ -88,6 +89,7 @@ describe('claude-provider.ts', () => {
 
       const generator = provider.executeQuery({
         prompt: 'Test',
+        model: 'claude-opus-4-5-20251101',
         cwd: '/test',
       });
 
@@ -112,6 +114,7 @@ describe('claude-provider.ts', () => {
 
       const generator = provider.executeQuery({
         prompt: 'Test',
+        model: 'claude-opus-4-5-20251101',
         cwd: '/test',
         abortController,
       });
@@ -140,6 +143,7 @@ describe('claude-provider.ts', () => {
 
       const generator = provider.executeQuery({
         prompt: 'Current message',
+        model: 'claude-opus-4-5-20251101',
         cwd: '/test',
         conversationHistory,
         sdkSessionId: 'test-session-id',
@@ -170,6 +174,7 @@ describe('claude-provider.ts', () => {
 
       const generator = provider.executeQuery({
         prompt: arrayPrompt as any,
+        model: 'claude-opus-4-5-20251101',
         cwd: '/test',
       });
 
@@ -189,6 +194,7 @@ describe('claude-provider.ts', () => {
 
       const generator = provider.executeQuery({
         prompt: 'Test',
+        model: 'claude-opus-4-5-20251101',
         cwd: '/test',
       });
 
@@ -214,6 +220,7 @@ describe('claude-provider.ts', () => {
 
       const generator = provider.executeQuery({
         prompt: 'Test',
+        model: 'claude-opus-4-5-20251101',
         cwd: '/test',
       });
 
diff --git a/libs/types/src/index.ts b/libs/types/src/index.ts
index edc7dd0b..ec1a57d0 100644
--- a/libs/types/src/index.ts
+++ b/libs/types/src/index.ts
@@ -185,6 +185,7 @@ export {
   addProviderPrefix,
   getBareModelId,
   normalizeModelString,
+  validateBareModelId,
 } from './provider-utils.js';
 
 // Pipeline types
diff --git a/libs/types/src/provider-utils.ts b/libs/types/src/provider-utils.ts
index 143420c6..1842d12c 100644
--- a/libs/types/src/provider-utils.ts
+++ b/libs/types/src/provider-utils.ts
@@ -196,3 +196,37 @@ export function normalizeModelString(model: string | undefined | null): string {
 
   return model;
 }
+
+/**
+ * Validate that a model ID does not contain a provider prefix
+ *
+ * Providers should receive bare model IDs (e.g., "gpt-5.1-codex-max", "composer-1")
+ * without provider prefixes (e.g., NOT "codex-gpt-5.1-codex-max", NOT "cursor-composer-1").
+ *
+ * This validation ensures the ProviderFactory properly stripped prefixes before
+ * passing models to providers.
+ *
+ * @param model - Model ID to validate
+ * @param providerName - Name of the provider for error messages
+ * @throws Error if model contains a provider prefix
+ *
+ * @example
+ * validateBareModelId("gpt-5.1-codex-max", "CodexProvider");  // ✅ OK
+ * validateBareModelId("codex-gpt-5.1-codex-max", "CodexProvider");  // ❌ Throws error
+ */
+export function validateBareModelId(model: string, providerName: string): void {
+  if (!model || typeof model !== 'string') {
+    throw new Error(`[${providerName}] Invalid model ID: expected string, got ${typeof model}`);
+  }
+
+  for (const [provider, prefix] of Object.entries(PROVIDER_PREFIXES)) {
+    if (model.startsWith(prefix)) {
+      throw new Error(
+        `[${providerName}] Model ID should not contain provider prefix '${prefix}'. ` +
+          `Got: '${model}'. ` +
+          `This is likely a bug in ProviderFactory - it should strip the '${provider}' prefix ` +
+          `before passing the model to the provider.`
+      );
+    }
+  }
+}
diff --git a/libs/types/src/provider.ts b/libs/types/src/provider.ts
index 3c41259b..d9848a1b 100644
--- a/libs/types/src/provider.ts
+++ b/libs/types/src/provider.ts
@@ -81,7 +81,10 @@ export interface McpHttpServerConfig {
  */
 export interface ExecuteOptions {
   prompt: string | Array<{ type: string; text?: string; source?: object }>;
+  /** Bare model ID without provider prefix (e.g., "gpt-5.1-codex-max", "composer-1") */
   model: string;
+  /** Original model ID with provider prefix for logging (e.g., "codex-gpt-5.1-codex-max") */
+  originalModel?: string;
   cwd: string;
   systemPrompt?: string | SystemPromptPreset;
   maxTurns?: number;