fix: validate runtime name length before deploy

src/cli/operations/deploy/preflight.ts

@@ -55,6 +55,8 @@ export function formatError(err: unknown): string {
  * Also validates AWS credentials are configured before proceeding.
  * Returns the project context needed for subsequent steps.
  */
+const MAX_RUNTIME_NAME_LENGTH = 48;
+
 export async function validateProject(): Promise<PreflightContext> {
   // Find the agentcore config directory, walking up from cwd if needed
   const configRoot = requireConfigRoot();
@@ -68,12 +70,35 @@ export async function validateProject(): Promise<PreflightContext> {
   const projectSpec = await configIO.readProjectSpec();
   const awsTargets = await configIO.readAWSDeploymentTargets();
 
+  // Validate runtime names don't exceed AWS limits
+  validateRuntimeNames(projectSpec);
+
   // Validate AWS credentials before proceeding with build/synth
   await validateAwsCredentials();
 
   return { projectSpec, awsTargets, cdkProject };
 }
 
+/**
+ * Validates that combined runtime names (projectName_runtimeName) don't exceed AWS limits.
+ */
+function validateRuntimeNames(projectSpec: AgentCoreProjectSpec): void {
+  const projectName = projectSpec.name;
+  for (const agent of projectSpec.agents) {
+    const runtimeName = agent.runtime?.name;
+    if (runtimeName) {
+      const combinedName = `${projectName}_${runtimeName}`;
+      if (combinedName.length > MAX_RUNTIME_NAME_LENGTH) {
+        throw new Error(
+          `Runtime name too long: "${combinedName}" (${combinedName.length} chars). ` +
+            `AWS limits runtime names to ${MAX_RUNTIME_NAME_LENGTH} characters. ` +
+            `Shorten the project name or runtime.name in agentcore.json.`
+        );
+      }
+    }
+  }
+}
+
 /**
  * Builds the CDK project.
  */

src/schema/schemas/agent-env.ts

@@ -98,11 +98,11 @@ export type Instrumentation = z.infer<typeof InstrumentationSchema>;
  */
 const AgentRuntimeNameSchema = z
   .string()
-  .min(1)
-  .max(48)
+  .min(1, 'Runtime name is required')
+  .max(23, 'Runtime name must be 23 characters or less (AWS runtime name limit)')
   .regex(
-    /^[a-zA-Z][a-zA-Z0-9_]{0,47}$/,
-    'Must begin with a letter and contain only alphanumeric characters and underscores (max 48 chars)'
+    /^[a-zA-Z][a-zA-Z0-9_]{0,22}$/,
+    'Runtime name must start with a letter and contain only alphanumeric characters and underscores'
   );
 
 const CodeZipRuntimeSchema = z.object({

src/schema/schemas/agentcore-project.ts

@@ -11,18 +11,19 @@ import { z } from 'zod';
 /**
  * Project name validation (CloudFormation logical ID compatible).
  * Used in CloudFormation stack naming - must start with letter, alphanumeric only.
- * Max 36 chars to allow room for suffixes in generated resource names.
+ * Max 23 chars because runtime names are generated as {projectName}_{runtimeName}
+ * and AWS limits agentRuntimeName to 48 characters total.
  *
  * Also validates against reserved names that would conflict with Python packages
  * when creating virtual environments (e.g., 'openai', 'anthropic', 'langchain').
  */
 export const ProjectNameSchema = z
   .string()
-  .min(1)
-  .max(36)
+  .min(1, 'Project name is required')
+  .max(23, 'Project name must be 23 characters or less (AWS runtime name limit)')
   .regex(
-    /^[A-Za-z][A-Za-z0-9]{0,35}$/,
-    'Must start with a letter and contain only alphanumeric characters (max 36 chars)'
+    /^[A-Za-z][A-Za-z0-9]{0,22}$/,
+    'Project name must start with a letter and contain only alphanumeric characters'
   )
   .refine(name => !isReservedProjectName(name), {
     message: 'This name conflicts with a Python package dependency. Please choose a different name.',