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, 7 insertions, 2 deletions

diff --git a/packages/api/src/routes/agents.ts b/packages/api/src/routes/agents.ts
index d3ca23f..1627674 100644
--- a/packages/api/src/routes/agents.ts
+++ b/packages/api/src/routes/agents.ts
@@ -99,11 +99,16 @@ agentsRoutes.get("/check-dir", (c) => {
 	if (dirPath === "~" || dirPath.startsWith("~/")) {
 		dirPath = path.join(os.homedir(), dirPath.slice(1));
 	}
+	// Resolve relative paths against the project root
+	if (!path.isAbsolute(dirPath)) {
+		const projectDir = process.env.DISPATCH_WORKING_DIR || process.cwd();
+		dirPath = path.resolve(projectDir, dirPath);
+	}
 	try {
 		const stat = fs.statSync(dirPath);
-		return c.json({ exists: stat.isDirectory() });
+		return c.json({ exists: stat.isDirectory(), resolved: dirPath });
 	} catch {
-		return c.json({ exists: false });
+		return c.json({ exists: false, resolved: dirPath });
 	}
 });