fix: resolve errand worktree path for sendMessage instead of using agent-workdirs

Errand agents are spawned in the errand's git worktree (managed by
SimpleGitWorktreeManager), not in agent-workdirs/<alias>/.
sendUserMessage was deriving the cwd from worktreeId which pointed to
the non-existent agent-workdirs path. Now the errand.sendMessage
procedure resolves the actual worktree path and passes it through.

apps/server/agent/manager.ts

@@ -667,7 +667,7 @@ export class MultiProviderAgentManager implements AgentManager {
    * Does not use the conversations table — the message is injected directly
    * as the next resume prompt for the agent's Claude Code session.
    */
-  async sendUserMessage(agentId: string, message: string): Promise<void> {
+  async sendUserMessage(agentId: string, message: string, cwd?: string): Promise<void> {
     const agent = await this.repository.findById(agentId);
     if (!agent) throw new Error(`Agent not found: ${agentId}`);
 
@@ -682,7 +682,7 @@ export class MultiProviderAgentManager implements AgentManager {
     const provider = getProvider(agent.provider);
     if (!provider) throw new Error(`Unknown provider: ${agent.provider}`);
 
-    const agentCwd = this.processManager.getAgentWorkdir(agent.worktreeId);
+    const agentCwd = cwd ?? this.processManager.getAgentWorkdir(agent.worktreeId);
 
     // Clear previous signal.json
     const signalPath = join(agentCwd, '.cw/output/signal.json');

apps/server/agent/mock-manager.ts

@@ -534,7 +534,7 @@ export class MockAgentManager implements AgentManager {
    * Deliver a user message to a running errand agent.
    * Mock implementation: no-op (simulates message delivery without actual process interaction).
    */
-  async sendUserMessage(agentId: string, _message: string): Promise<void> {
+  async sendUserMessage(agentId: string, _message: string, _cwd?: string): Promise<void> {
     const record = this.agents.get(agentId);
     if (!record) {
       throw new Error(`Agent '${agentId}' not found`);

apps/server/agent/types.ts

@@ -272,5 +272,5 @@ export interface AgentManager {
    * @param agentId - The errand agent to message
    * @param message - The user's message text
    */
-  sendUserMessage(agentId: string, message: string): Promise<void>;
+  sendUserMessage(agentId: string, message: string, cwd?: string): Promise<void>;
 }

apps/server/trpc/routers/errand.ts

@@ -397,7 +397,23 @@ export function errandProcedures(publicProcedure: ProcedureBuilder) {
             });
           }
 
-          await agentManager.sendUserMessage(errand.agentId, input.message);
+          // Resolve errand worktree path — errand agents don't use agent-workdirs/
+          let worktreePath: string | undefined;
+          if (errand.projectId) {
+            const project = await requireProjectRepository(ctx).findById(errand.projectId);
+            if (project) {
+              try {
+                const clonePath = await resolveClonePath(project, ctx);
+                const wm = new SimpleGitWorktreeManager(clonePath);
+                const wt = await wm.get(errand.id);
+                if (wt) worktreePath = wt.path;
+              } catch {
+                // Fall through — sendUserMessage will use default path
+              }
+            }
+          }
+
+          await agentManager.sendUserMessage(errand.agentId, input.message, worktreePath);
           return { success: true };
         }),