refactor: unify errand worktree paths to use agent-workdirs/<alias>/

Errands now create worktrees via ProcessManager.createWorktreesForProjects()
into agent-workdirs/<alias>/<project.name>/ instead of repos/<project>/.cw-worktrees/<errandId>.
This makes getAgentWorkdir + resolveAgentCwd work correctly for all agent types.

Key changes:
- Extract createWorktreesForProjects() from createProjectWorktrees() in ProcessManager
- Add resolveAgentCwd() to ProcessManager (probes for .cw/output in subdirs)
- Add projectId to SpawnAgentOptions for single-project agents (errands)
- Skip auto-cleanup for errand agents (worktrees persist for merge/abandon)
- Errand router uses agentManager.delete() for cleanup instead of SimpleGitWorktreeManager
- Remove cwd parameter from sendUserMessage (resolves via worktreeId)
- Add pruneProjectRepos() to CleanupManager for errand worktree refs

apps/server/agent/process-manager.ts

@@ -7,7 +7,7 @@
  */
 
 import { spawn } from 'node:child_process';
-import { openSync, closeSync, existsSync } from 'node:fs';
+import { openSync, closeSync, existsSync, readdirSync } from 'node:fs';
 import { mkdir, writeFile } from 'node:fs/promises';
 import { join } from 'node:path';
 import type { ProjectRepository } from '../db/repositories/project-repository.js';
@@ -46,6 +46,36 @@ export class ProcessManager {
     return join(this.workspaceRoot, 'agent-workdirs', alias);
   }
 
+  /**
+   * Resolve the actual working directory for an agent by probing
+   * for the subdirectory that contains .cw/output/.
+   */
+  resolveAgentCwd(alias: string): string {
+    const base = this.getAgentWorkdir(alias);
+
+    // Fast path: .cw/output exists at the base level
+    if (existsSync(join(base, '.cw', 'output'))) return base;
+
+    // Standalone agents use a workspace/ subdirectory
+    const workspaceSub = join(base, 'workspace');
+    if (existsSync(join(workspaceSub, '.cw'))) return workspaceSub;
+
+    // Initiative/errand agents may have written .cw/ inside a project
+    // subdirectory (e.g. agent-workdirs/<name>/<project-name>/.cw/).
+    try {
+      for (const entry of readdirSync(base, { withFileTypes: true })) {
+        if (entry.isDirectory() && entry.name !== '.cw') {
+          const sub = join(base, entry.name);
+          if (existsSync(join(sub, '.cw', 'output'))) return sub;
+        }
+      }
+    } catch {
+      // base dir may not exist
+    }
+
+    return base;
+  }
+
   /**
    * Create worktrees for all projects linked to an initiative.
    * Returns the base agent workdir path.
@@ -57,13 +87,11 @@ export class ProcessManager {
     branchName?: string,
   ): Promise<string> {
     const projects = await this.projectRepository.findProjectsByInitiativeId(initiativeId);
-    const agentWorkdir = this.getAgentWorkdir(alias);
 
     log.debug({
       alias,
       initiativeId,
       projectCount: projects.length,
-      agentWorkdir,
       baseBranch
     }, 'creating project worktrees');
 
@@ -74,6 +102,22 @@ export class ProcessManager {
       return this.createStandaloneWorktree(alias);
     }
 
+    return this.createWorktreesForProjects(alias, projects, baseBranch, branchName);
+  }
+
+  /**
+   * Create worktrees for a given list of projects under agent-workdirs/<alias>/.
+   * Used by both initiative-based and single-project (errand) agents.
+   * Returns the base agent workdir path.
+   */
+  async createWorktreesForProjects(
+    alias: string,
+    projects: Array<{ name: string; url: string; id: string; defaultBranch: string }>,
+    baseBranch?: string,
+    branchName?: string,
+  ): Promise<string> {
+    const agentWorkdir = this.getAgentWorkdir(alias);
+
     for (const project of projects) {
       const clonePath = await ensureProjectClone(project, this.workspaceRoot);
       const worktreeManager = new SimpleGitWorktreeManager(clonePath, undefined, agentWorkdir);