feat: surface repo root in runtime prompt

src/config/types.agent-defaults.ts

@@ -99,6 +99,8 @@ export type AgentDefaultsConfig = {
   models?: Record<string, AgentModelEntryConfig>;
   /** Agent working directory (preferred). Used as the default cwd for agent runs. */
   workspace?: string;
+  /** Optional repository root for system prompt runtime line (overrides auto-detect). */
+  repoRoot?: string;
   /** Skip bootstrap (BOOTSTRAP.md creation, etc.) for pre-configured deployments. */
   skipBootstrap?: boolean;
   /** Max chars for injected bootstrap files before truncation (default: 20000). */