fix: require a model, default to empty value during onboarding

and add a WORKSPACE_PATH constant to make tracking that path easier

src/config/types.ts

@@ -1,4 +1,5 @@
 import { z } from 'zod';
+import { WORKSPACE_PATH } from './constants.ts'
 
 // ---------------------------------------------------------------------------
 // Mattermost
@@ -41,7 +42,7 @@ export type ChannelsConfig = z.infer<typeof ChannelsConfigSchema>;
 
 export const AgentConfigSchema = z.object({
   model: z.string().default('anthropic/claude-sonnet-4-5'),
-  workspacePath: z.string().default('~/.config/nanobot'),
+  workspacePath: z.string().default(WORKSPACE_PATH),
   maxTokens: z.number().int().default(4096),
   contextWindowTokens: z.number().int().default(65536),
   temperature: z.number().default(0.7),
@@ -113,14 +114,7 @@ export type HeartbeatConfig = z.infer<typeof HeartbeatConfigSchema>;
 
 export const ConfigSchema = z.object({
   providers: ProvidersConfigSchema.default(() => ({})),
-  agent: AgentConfigSchema.default(() => ({
-    model: 'anthropic/claude-sonnet-4-5',
-    workspacePath: '~/.config/nanobot',
-    maxTokens: 4096,
-    contextWindowTokens: 65536,
-    temperature: 0.7,
-    maxToolIterations: 40,
-  })),
+  agent: AgentConfigSchema,
   heartbeat: HeartbeatConfigSchema.default(() => ({ enabled: false, intervalMinutes: 30 })),
   channels: ChannelsConfigSchema.default(() => ({ sendProgress: true, sendToolHints: true })),
   tools: ToolsConfigSchema.default(() => ({