feat: add git worktree session support with improved UI

Implement comprehensive worktree session support allowing users to spawn sessions in temporary git worktrees. Includes backend worktree management, full-stack integration, and refined UI for session type selection.

Backend:
- Add worktree creation/removal utilities with branch management
- Track worktree metadata (basePath, branch, name, path) in session metadata
- Automatic cleanup of worktrees when sessions fail or exit
- Enhanced error handling with stderr tail logging

UI improvements:
- Redesign session type toggle with improved alignment and spacing
- Move worktree description inline with label for cleaner layout
- Add branch name input field that appears when worktree mode selected
- Auto-focus on worktree input when switching modes
- Reduce gap between radio options from gap-3 to gap-1.5
- Update descriptive text and placeholders for clarity

Integration:
- Thread worktree parameters through API client, RPC handlers, and daemon
- Add worktreeEnv utility to read worktree info from environment
- Update session spawning to support both simple and worktree modes

cli/src/api/apiMachine.ts

@@ -70,7 +70,7 @@ export class ApiMachineClient {
 
     setRPCHandlers({ spawnSession, stopSession, requestShutdown }: MachineRpcHandlers): void {
         this.rpcHandlerManager.registerHandler('spawn-happy-session', async (params: any) => {
-            const { directory, sessionId, machineId, approvedNewDirectoryCreation, agent, yolo, token } = params || {}
+            const { directory, sessionId, machineId, approvedNewDirectoryCreation, agent, yolo, token, sessionType, worktreeName } = params || {}
 
             if (!directory) {
                 throw new Error('Directory is required')
@@ -83,7 +83,9 @@ export class ApiMachineClient {
                 approvedNewDirectoryCreation,
                 agent,
                 yolo,
-                token
+                token,
+                sessionType,
+                worktreeName
             })
 
             switch (result.type) {

cli/src/api/rpc/RpcHandlerManager.ts

@@ -51,7 +51,10 @@ export class RpcHandlerManager {
             const result = await handler(params as any)
             return JSON.stringify(result)
         } catch (error) {
-            this.logger('[RPC] [ERROR] Error handling request', { error })
+            const details = error instanceof Error
+                ? { message: error.message, stack: error.stack }
+                : { error: String(error) }
+            this.logger('[RPC] [ERROR] Error handling request', details)
             return JSON.stringify({
                 error: error instanceof Error ? error.message : 'Unknown error'
             })
@@ -91,4 +94,3 @@ export class RpcHandlerManager {
 export function createRpcHandlerManager(config: RpcHandlerConfig): RpcHandlerManager {
     return new RpcHandlerManager(config)
 }
-

cli/src/api/types.ts

@@ -41,6 +41,13 @@ export type Metadata = {
     archivedBy?: string
     archiveReason?: string
     flavor?: string
+    worktree?: {
+        basePath: string
+        branch: string
+        name: string
+        worktreePath?: string
+        createdAt?: number
+    }
 }
 
 export const MetadataSchema = z.object({
@@ -69,7 +76,14 @@ export const MetadataSchema = z.object({
     lifecycleStateSince: z.number().optional(),
     archivedBy: z.string().optional(),
     archiveReason: z.string().optional(),
-    flavor: z.string().optional()
+    flavor: z.string().optional(),
+    worktree: z.object({
+        basePath: z.string(),
+        branch: z.string(),
+        name: z.string(),
+        worktreePath: z.string().optional(),
+        createdAt: z.number().optional()
+    }).optional()
 }).passthrough()
 
 export type AgentState = {