feat: relative working directory support and subagent tab cwd propagation

- Resolve relative cwd paths (e.g. ./subtask) against parent's working directory at runtime
- check-dir endpoint resolves relative paths and returns the resolved absolute path
- AgentBuilder shows resolved path below input for relative paths, updated helper text
- tab-created event now includes workingDirectory so subagent tabs display their cwd in sidebar
- Add workingDirectory to tab-created AgentEvent type definition
- spawnChildAgent stores resolved absolute path instead of raw relative path

1 files changed, 1 insertions, 0 deletions

diff --git a/packages/core/src/types/index.ts b/packages/core/src/types/index.ts
index ff47f49..c301822 100644
--- a/packages/core/src/types/index.ts
+++ b/packages/core/src/types/index.ts
@@ -47,6 +47,7 @@ export type AgentEvent =
 			keyId: string | null;
 			modelId: string | null;
 			parentTabId: string | null;
+			workingDirectory: string | null;
 	  }
 	| { type: "message-queued"; tabId: string; messageId: string; message: string }
 	| { type: "message-consumed"; tabId: string; messageIds: string[] }