On every startup, the cleanup service throws repeated env_cleanup_error log entries for any repository where the default branch is not main and origin/HEAD is not set (e.g. repos using master). The error message itself tells users to set worktree.baseBranch in .archon/config.yaml — but this config value is silently ignored, making the suggestion ineffective.

Log output:
{"level":40,"module":"git","repoPath":"/home/user/myrepo","msg":"default_branch_detection_failed"}
{"level":50,"module":"cleanup","err":{"message":"Cannot detect default branch for /home/user/myrepo: 
neither origin/HEAD nor origin/main exist. Set worktree.baseBranch in .archon/config.yaml to specify 
the branch explicitly."},"msg":"env_cleanup_error"}

This repeats three times per startup (once per tracked environment) and never resolves regardless of what is written in .archon/config.yaml.

To reproduce

Have a git repository with master as the default branch and no origin/HEAD set
Create .archon/config.yaml in the repo root with:

yaml
worktree:
  baseBranch: master

Start Archon (bun run dev)
Observe repeated env_cleanup_error entries in the logs — the config has no effect

You can verify origin/HEAD is not set with:

bash
git symbolic-ref refs/remotes/origin/HEAD
# fatal: ref refs/remotes/origin/HEAD is not a symbolic ref

Expected behaviour
When worktree.baseBranch is set in .archon/config.yaml, Archon should use that value as the base branch and skip the git auto-detection entirely. No errors should appear on startup.

Root cause
loadRepoConfig in packages/core/src/config/config-loader.ts already correctly reads and merges worktree.baseBranch from .archon/config.yaml (lines 454–455). The type is defined, the parsing works, the merge works.
The problem is in packages/core/src/services/cleanup-service.ts around line 310, where getDefaultBranch(mainRepoPath) is called directly without first consulting the repo config:
typescript// Current (broken):

const mainRepoPath = toRepoPath(env.codebase_default_cwd);
const mainBranch = await getDefaultBranch(mainRepoPath);

loadRepoConfig is not imported in cleanup-service.ts at all. The pattern for doing this correctly already exists in packages/git/src/repo.ts line 100:
typescript
const branchToSync = baseBranch ?? (await getDefaultBranch(workspacePath));
Suggested fix
Two small changes to packages/core/src/services/cleanup-service.ts:

1. Add imports alongside the existing imports at the top of the file:

typescriptimport { loadRepoConfig } from '../config/config-loader';
import { toBranchName } from '@archon/git';

2. Replace the getDefaultBranch call (~line 309):
   typescript// After (fixed):

const mainRepoPath = toRepoPath(env.codebase_default_cwd);
const repoConfig = await loadRepoConfig(env.codebase_default_cwd);
const mainBranch = repoConfig?.worktree?.baseBranch
  ? toBranchName(repoConfig.worktree.baseBranch.trim())
  : await getDefaultBranch(mainRepoPath);

No other files need to change.

How to test
Before the fix — confirm the bug:

Set up a repo with master as default branch, no origin/HEAD
Add .archon/config.yaml with worktree.baseBranch: master
Start Archon and observe env_cleanup_error still appears

After the fix — confirm it works:

Same setup as above
Start Archon — logs should show server_ready and cleanup_completed with errors: 0, no env_cleanup_error

A unit test should be added to the cleanup service test suite verifying that when loadRepoConfig returns a config with worktree.baseBranch set, getDefaultBranch is never called and no error is thrown.

## Impact

- Affected workflows/commands:
- Reproduction rate: Always / Intermittent / Once
- Workaround available? If so, describe:
- Data loss risk? (`Yes/No`)

## Scope

- Package(s) likely involved: `core|workflows|isolation|git|adapters|server|web|cli|paths`
- Module (if known): e.g. `workflows:executor`, `adapters:slack`