fix: centralize model prefix handling to prevent provider errors

Moves prefix stripping from individual providers to AgentService/IdeationService
and adds validation to ensure providers receive bare model IDs. This prevents
bugs like the Codex CLI receiving "codex-gpt-5.1-codex-max" instead of the
expected "gpt-5.1-codex-max".

- Add validateBareModelId() helper with fail-fast validation
- Add originalModel field to ExecuteOptions for logging
- Update all providers to validate model has no prefix
- Centralize prefix stripping in service layer
- Remove redundant prefix stripping from individual providers

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

libs/types/src/index.ts

@@ -185,6 +185,7 @@ export {
   addProviderPrefix,
   getBareModelId,
   normalizeModelString,
+  validateBareModelId,
 } from './provider-utils.js';
 
 // Pipeline types

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.`
+      );
+    }
+  }
+}

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;