huskies: merge 1176 bug base_branch fallback hardcodes master instead of auto-detecting

server/src/agents/merge/squash/mod.rs

@@ -17,6 +17,14 @@ use crate::config::ProjectConfig;
 /// causing `git cherry-pick merge-queue/…` to fail with "bad revision".
 static MERGE_LOCK: Mutex<()> = Mutex::new(());
 
+/// Resolve the base branch for `project_root` from config, or auto-detect it.
+fn resolve_base_branch(project_root: &Path) -> String {
+    let configured = crate::config::ProjectConfig::load(project_root)
+        .ok()
+        .and_then(|c| c.base_branch);
+    crate::worktree::resolve_base_branch(project_root, configured.as_deref())
+}
+
 pub(crate) fn run_squash_merge(
     project_root: &Path,
     branch: &str,
@@ -31,10 +39,7 @@ pub(crate) fn run_squash_merge(
     // A zero-commit branch produces an empty squash and a silent "nothing to
     // commit" failure.  Catch it early with a grep-able error before any merge
     // work starts.
-    let base_branch = crate::config::ProjectConfig::load(project_root)
-        .ok()
-        .and_then(|c| c.base_branch.clone())
-        .unwrap_or_else(|| "master".to_string());
+    let base_branch = resolve_base_branch(project_root);
 
     let ahead_out = Command::new("git")
         .args(["rev-list", "--count", &format!("{base_branch}..{branch}")])
@@ -316,11 +321,6 @@ pub(crate) fn run_squash_merge(
         .map(|o| String::from_utf8_lossy(&o.stdout).trim().to_string())
         .unwrap_or_default();
 
-    let base_branch = crate::config::ProjectConfig::load(project_root)
-        .ok()
-        .and_then(|c| c.base_branch.clone())
-        .unwrap_or_else(|| "master".to_string());
-
     if current_branch != base_branch {
         all_output.push_str(&format!(
             "=== VERIFICATION FAILED: expected branch '{base_branch}' but HEAD is on \

server/src/agents/merge/squash/tests_basic.rs

@@ -178,6 +178,79 @@ async fn squash_merge_clean_merge_succeeds() {
     );
 }
 
+#[tokio::test]
+async fn squash_merge_succeeds_on_main_based_repo_with_base_branch_unset() {
+    use std::fs;
+    use tempfile::tempdir;
+
+    let tmp = tempdir().unwrap();
+    let repo = tmp.path();
+
+    // Repo whose default branch is `main` — no `master` branch exists at all,
+    // and no `.huskies/project.toml` sets `base_branch`. run_squash_merge must
+    // auto-detect `main` instead of assuming `master` (bug 1176).
+    Command::new("git")
+        .args(["init", "-b", "main"])
+        .current_dir(repo)
+        .output()
+        .unwrap();
+    Command::new("git")
+        .args(["config", "user.email", "test@test.com"])
+        .current_dir(repo)
+        .output()
+        .unwrap();
+    Command::new("git")
+        .args(["config", "user.name", "Test"])
+        .current_dir(repo)
+        .output()
+        .unwrap();
+    Command::new("git")
+        .args(["commit", "--allow-empty", "-m", "init"])
+        .current_dir(repo)
+        .output()
+        .unwrap();
+
+    Command::new("git")
+        .args(["checkout", "-b", "feature/story-main_test"])
+        .current_dir(repo)
+        .output()
+        .unwrap();
+    fs::write(repo.join("new_file.txt"), "new content").unwrap();
+    Command::new("git")
+        .args(["add", "."])
+        .current_dir(repo)
+        .output()
+        .unwrap();
+    Command::new("git")
+        .args(["commit", "-m", "add new file"])
+        .current_dir(repo)
+        .output()
+        .unwrap();
+
+    Command::new("git")
+        .args(["checkout", "main"])
+        .current_dir(repo)
+        .output()
+        .unwrap();
+
+    let result = run_squash_merge(repo, "feature/story-main_test", "main_test").unwrap();
+
+    assert!(
+        matches!(
+            result,
+            super::MergeResult::Success {
+                conflicts_resolved: false,
+                ..
+            }
+        ),
+        "clean merge should succeed on a main-based repo; got: {result:?}"
+    );
+    assert!(
+        repo.join("new_file.txt").exists(),
+        "merged file should exist on main"
+    );
+}
+
 #[tokio::test]
 async fn squash_merge_nonexistent_branch_fails() {
     use tempfile::tempdir;

server/src/agents/pool/start/spawn.rs

@@ -189,10 +189,10 @@ pub(super) async fn run_agent_spawn(
     let wt_info = {
         let wt_path = crate::worktree::worktree_path(&project_root_clone, &sid);
         let branch = format!("feature/story-{sid}");
-        let base_branch = config_clone
-            .base_branch
-            .clone()
-            .unwrap_or_else(|| crate::worktree::detect_base_branch(&project_root_clone));
+        let base_branch = crate::worktree::resolve_base_branch(
+            &project_root_clone,
+            config_clone.base_branch.as_deref(),
+        );
         let deadline =
             tokio::time::Instant::now() + std::time::Duration::from_secs(worktree_wait_secs);
         loop {
@@ -260,6 +260,7 @@ pub(super) async fn run_agent_spawn(
     }
 
     let (command, mut args, mut prompt) = match config_clone.render_agent_args(
+        &project_root_clone,
         &wt_path_str,
         &sid,
         Some(&aname),