[Bug]: schedule_task gives unbound tasks baseRef "main", which breaks repos without a main branch #16577

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/server

Steps to reproduce

1. Use a project whose only default branch is master, with no main locally or on origin.
2. From an agent thread in that project, call the MCP tool schedule_task with bindToCurrentThread: false.
3. Open the task in Settings → Scheduled tasks, or read workspace_strategy_json in scheduled_tasks.

Expected behavior

An agent-created unbound task gets a workspace that resolves in its project, such as a worktree from the project's actual default branch. Failing that, the agent should be able to pass the workspace itself.

Actual behavior

Every unbound task created over MCP gets {"type":"worktree","baseRef":"main","startFromOrigin":true}, because scheduledTaskWorkspaceStrategy in apps/server/src/mcp/OrchestratorMcpService.ts returns that literal. Tracing a run through ThreadLaunchService:

1. It fetches origin.
2. remoteBranchExists finds no origin/main, so startRef falls back to the local main.
3. There is no local main, so createWorktree gets a ref that doesn't exist, and workspace preparation fails.

The creating agent can't see or fix this. schedule_task has no workspace parameter and the response doesn't show the strategy. update_scheduled_task has no workspace parameter either. Passing bindToCurrentThread to update_scheduled_task goes through the same function, so it overwrites a workspace the user had already fixed in the editor.

I corrected the task in the editor before its first run, so this failure comes from reading the code. I didn't watch a run fail.

Impact

Minor bug or occasional failure

Version or commit

0.0.46-nightly.20261006.2735, unchanged on main at 3d17862e.

Environment

Headless server on Linux arm64, desktop client on Windows, Claude Agent provider.

Workaround

Change the task's workspace in Settings → Scheduled tasks. The editor's branch picker lists real branches, and "Use the project checkout" works too. Afterwards, never pass bindToCurrentThread in an update_scheduled_task call.

Possible fix

Resolve the project's default branch instead of hardcoding "main". An optional workspaceStrategy on schedule_task and update_scheduled_task, like the one t3_thread_launch takes, would let agents choose root when their prompt manages its own worktrees. The comment on the update path explains that unbound tasks avoid the shared checkout on purpose, so a fresh worktree can stay the default.