Fix: Use trunkBranch parameter in SSHRuntime instead of HEAD

Previously, SSHRuntime ignored the trunkBranch parameter and always
created new branches from HEAD. This caused new branches to be created
from whatever HEAD was pointing to, rather than the specified trunk.

Changes:
- Use trunkBranch parameter instead of _trunkBranch (unused variable)
- Pass trunkBranch to 'git checkout -b' instead of hardcoded 'HEAD'
- Update comment to reflect correct behavior

This brings SSHRuntime in line with LocalRuntime, which correctly
uses the trunkBranch parameter when creating new branches via
'git worktree add -b'.

Fixes the integration test:
'creates new branch from specified trunk branch, not from default branch'

Author: ammar-agent

src/runtime/SSHRuntime.ts

@@ -586,13 +586,7 @@ export class SSHRuntime implements Runtime {
   }
 
   async initWorkspace(params: WorkspaceInitParams): Promise<WorkspaceInitResult> {
-    const {
-      projectPath,
-      branchName,
-      trunkBranch: _trunkBranch,
-      workspacePath,
-      initLogger,
-    } = params;
+    const { projectPath, branchName, trunkBranch, workspacePath, initLogger } = params;
 
     try {
       // 1. Sync project to remote (opportunistic rsync with scp fallback)
@@ -611,11 +605,9 @@ export class SSHRuntime implements Runtime {
       initLogger.logStep("Files synced successfully");
 
       // 2. Checkout branch remotely
-      // Note: After git clone, HEAD is already checked out to the default branch from the bundle
-      // We create new branches from HEAD instead of the trunkBranch name to avoid issues
-      // where the local repo's trunk name doesn't match the cloned repo's default branch
+      // If branch exists, check it out; otherwise create it from the specified trunk branch
       initLogger.logStep(`Checking out branch: ${branchName}`);
-      const checkoutCmd = `(git checkout ${JSON.stringify(branchName)} 2>/dev/null || git checkout -b ${JSON.stringify(branchName)} HEAD)`;
+      const checkoutCmd = `(git checkout ${JSON.stringify(branchName)} 2>/dev/null || git checkout -b ${JSON.stringify(branchName)} ${JSON.stringify(trunkBranch)})`;
 
       const checkoutStream = await this.exec(checkoutCmd, {
         cwd: workspacePath, // Use the full workspace path for git operations