fix: skip standalone worktree when errand provides cwd

When spawn() receives an explicit cwd (errands), the manager was still
creating a standalone worktree at agent-workdirs/<alias>/ and injecting
its path into the workspace layout prompt. The agent then edited files
in the wrong directory — on a different branch than the errand's.

Now when cwd is provided, we skip worktree creation entirely and use
the caller's cwd for workspace layout, .cw/output/, and all paths.

apps/server/agent/manager.ts

@@ -233,9 +233,13 @@ export class MultiProviderAgentManager implements AgentManager {
       log.debug('no accounts available, spawning without account');
     }
 
-    // 2. Create isolated worktrees
+    // 2. Create isolated worktrees (skip when caller provides explicit cwd, e.g. errands)
     let agentCwd: string;
-    if (initiativeId) {
+    if (cwd) {
+      // Caller manages the worktree (errands). Use their cwd directly.
+      agentCwd = cwd;
+      log.info({ alias, agentCwd }, 'using caller-provided cwd, skipping worktree creation');
+    } else if (initiativeId) {
       log.debug({ alias, initiativeId, baseBranch, branchName }, 'creating initiative-based worktrees');
       agentCwd = await this.processManager.createProjectWorktrees(alias, initiativeId, baseBranch, branchName);
 
@@ -318,15 +322,13 @@ export class MultiProviderAgentManager implements AgentManager {
 
     // 4. Build spawn command
     const { command, args, env: providerEnv } = this.processManager.buildSpawnCommand(provider, prompt);
-    const finalCwd = cwd ?? agentCwd;
 
     log.info({
       agentId,
       alias,
       command,
       args: args.join(' '),
-      finalCwd,
+      agentCwd,
-      customCwdProvided: !!cwd,
       providerEnv: Object.keys(providerEnv)
     }, 'spawn command built');
 
@@ -342,7 +344,7 @@ export class MultiProviderAgentManager implements AgentManager {
 
     // 6. Spawn detached subprocess
     const { pid, outputFilePath, tailer } = await this.processManager.spawnDetached(
-      agentId, alias, command, args, cwd ?? agentCwd, processEnv, providerName, prompt,
+      agentId, alias, command, args, agentCwd, processEnv, providerName, prompt,
       (event) => this.outputHandler.handleStreamEvent(agentId, event, this.activeAgents.get(agentId)),
       this.createLogChunkCallback(agentId, alias, 1),
     );
@@ -351,7 +353,7 @@ export class MultiProviderAgentManager implements AgentManager {
 
     // Register agent and start polling BEFORE non-critical I/O so that a
     // diagnostic-write failure can never orphan a running process.
-    const activeEntry: ActiveAgent = { agentId, pid, tailer, outputFilePath, agentCwd: finalCwd };
+    const activeEntry: ActiveAgent = { agentId, pid, tailer, outputFilePath, agentCwd };
     this.activeAgents.set(agentId, activeEntry);
 
     // Emit spawned event
@@ -376,19 +378,19 @@ export class MultiProviderAgentManager implements AgentManager {
     // Write spawn diagnostic file (non-fatal — .cw/ may not exist yet for
     // agents spawned without inputContext, e.g. conflict-resolution agents)
     try {
-      const diagnosticDir = join(finalCwd, '.cw');
+      const diagnosticDir = join(agentCwd, '.cw');
       await mkdir(diagnosticDir, { recursive: true });
       const diagnostic = {
         timestamp: new Date().toISOString(),
         agentId,
         alias,
-        intendedCwd: finalCwd,
+        intendedCwd: agentCwd,
         worktreeId: agent.worktreeId,
         provider: providerName,
         command,
         args,
         env: processEnv,
-        cwdExistsAtSpawn: existsSync(finalCwd),
+        cwdExistsAtSpawn: existsSync(agentCwd),
         initiativeId: initiativeId || null,
         customCwdProvided: !!cwd,
         accountId: accountId || null,