fix(426): verify cherry-pick landed on master before marking story done

After the cherry-pick step in run_squash_merge, verify:
1. project_root is on the base branch (not a merge-queue branch)
2. HEAD commit has actual code changes (not an empty/story-only diff)

If either check fails, return success=false so the story stays in merge
stage for retry instead of being phantom-advanced to done.

Also rename move_story_to_archived → move_story_to_done.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/src/agents/lifecycle.rs

@@ -102,7 +102,7 @@ pub fn feature_branch_has_unmerged_changes(project_root: &Path, story_id: &str)
 /// * If the story is in `4_merge/`, it is moved to `5_done/` and committed.
 /// * If the story is already in `5_done/` or `6_archived/`, this is a no-op (idempotent).
 /// * If the story is not found in `2_current/`, `4_merge/`, `5_done/`, or `6_archived/`, an error is returned.
-pub fn move_story_to_archived(project_root: &Path, story_id: &str) -> Result<(), String> {
+pub fn move_story_to_done(project_root: &Path, story_id: &str) -> Result<(), String> {
     let sk = project_root.join(".storkit").join("work");
     let current_path = sk.join("2_current").join(format!("{story_id}.md"));
     let merge_path = sk.join("4_merge").join(format!("{story_id}.md"));
@@ -584,10 +584,10 @@ mod tests {
         assert!(result.unwrap_err().contains("not found in work/2_current/"));
     }
 
-    // ── move_story_to_archived tests ──────────────────────────────────────────
+    // ── move_story_to_done tests ──────────────────────────────────────────
 
     #[test]
-    fn move_story_to_archived_finds_in_merge_dir() {
+    fn move_story_to_done_finds_in_merge_dir() {
         use std::fs;
         let tmp = tempfile::tempdir().unwrap();
         let root = tmp.path();
@@ -595,16 +595,16 @@ mod tests {
         fs::create_dir_all(&merge_dir).unwrap();
         fs::write(merge_dir.join("22_story_test.md"), "test").unwrap();
 
-        move_story_to_archived(root, "22_story_test").unwrap();
+        move_story_to_done(root, "22_story_test").unwrap();
 
         assert!(!merge_dir.join("22_story_test.md").exists());
         assert!(root.join(".storkit/work/5_done/22_story_test.md").exists());
     }
 
     #[test]
-    fn move_story_to_archived_error_when_not_in_current_or_merge() {
+    fn move_story_to_done_error_when_not_in_current_or_merge() {
         let tmp = tempfile::tempdir().unwrap();
-        let result = move_story_to_archived(tmp.path(), "99_nonexistent");
+        let result = move_story_to_done(tmp.path(), "99_nonexistent");
         assert!(result.unwrap_err().contains("4_merge"));
     }
 

server/src/agents/merge.rs

@@ -383,6 +383,71 @@ pub(crate) fn run_squash_merge(
         });
     }
 
+    // ── Verify code landed on the correct branch ──────────────────
+    // Guard against the cherry-pick silently landing on the wrong branch
+    // (e.g. a merge-queue branch from a concurrent merge).  If the current
+    // branch is not the base branch, or the HEAD commit has no code diff,
+    // treat the merge as failed so the story stays in the merge stage.
+    let current_branch = Command::new("git")
+        .args(["rev-parse", "--abbrev-ref", "HEAD"])
+        .current_dir(project_root)
+        .output()
+        .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 \
+             '{current_branch}'. Cherry-pick landed on wrong branch. ===\n"
+        ));
+        cleanup_merge_workspace(project_root, &merge_wt_path, &merge_branch);
+        return Ok(SquashMergeResult {
+            success: false,
+            had_conflicts,
+            conflicts_resolved,
+            conflict_details: Some(format!(
+                "Cherry-pick landed on '{current_branch}' instead of '{base_branch}'"
+            )),
+            output: all_output,
+            gates_passed: true,
+        });
+    }
+
+    // Verify HEAD commit has actual code changes (not an empty cherry-pick).
+    // Exclude .storkit/ so that story-file-only commits don't pass this check.
+    let diff_stat = Command::new("git")
+        .args(["diff", "--stat", "HEAD~1..HEAD", "--", ".", ":(exclude).storkit"])
+        .current_dir(project_root)
+        .output()
+        .map(|o| String::from_utf8_lossy(&o.stdout).trim().to_string())
+        .unwrap_or_default();
+
+    if diff_stat.is_empty() {
+        all_output.push_str(
+            "=== VERIFICATION FAILED: cherry-pick produced no code changes on master. ===\n",
+        );
+        cleanup_merge_workspace(project_root, &merge_wt_path, &merge_branch);
+        return Ok(SquashMergeResult {
+            success: false,
+            had_conflicts,
+            conflicts_resolved,
+            conflict_details: Some(
+                "Cherry-pick commit contains no code changes (empty diff)".to_string(),
+            ),
+            output: all_output,
+            gates_passed: true,
+        });
+    }
+
+    all_output.push_str(&format!(
+        "=== Verified: cherry-pick landed on '{base_branch}' with code changes ===\n"
+    ));
+
     // ── Clean up ──────────────────────────────────────────────────
     cleanup_merge_workspace(project_root, &merge_wt_path, &merge_branch);
     all_output.push_str("=== Merge-queue cleanup complete ===\n");

server/src/agents/mod.rs

@@ -10,7 +10,7 @@ use crate::config::AgentConfig;
 use serde::{Deserialize, Serialize};
 
 pub use lifecycle::{
-    close_bug_to_archive, feature_branch_has_unmerged_changes, move_story_to_archived,
+    close_bug_to_archive, feature_branch_has_unmerged_changes, move_story_to_done,
     move_story_to_merge, move_story_to_qa, move_story_to_stage, reject_story_from_qa,
 };
 pub use pool::AgentPool;

server/src/agents/pool/lifecycle.rs

@@ -1729,7 +1729,7 @@ stage = "coder"
 
     #[tokio::test]
     async fn archiving_story_removes_agent_entries_from_pool() {
-        use crate::agents::lifecycle::move_story_to_archived;
+        use crate::agents::lifecycle::move_story_to_done;
         use std::fs;
 
         let tmp = tempfile::tempdir().unwrap();
@@ -1746,7 +1746,7 @@ stage = "coder"
 
         assert_eq!(pool.list_agents().unwrap().len(), 3);
 
-        move_story_to_archived(root, "60_story_cleanup").unwrap();
+        move_story_to_done(root, "60_story_cleanup").unwrap();
         pool.remove_agents_for_story("60_story_cleanup");
 
         let remaining = pool.list_agents().unwrap();

server/src/agents/pool/pipeline/advance.rs

@@ -308,7 +308,7 @@ impl AgentPool {
                             "[pipeline] Post-merge tests passed for '{story_id}'. Moving to done."
                         );
                         if let Err(e) =
-                            crate::agents::lifecycle::move_story_to_archived(&project_root, story_id)
+                            crate::agents::lifecycle::move_story_to_done(&project_root, story_id)
                         {
                             slog_error!("[pipeline] Failed to move '{story_id}' to done: {e}");
                         }

server/src/agents/pool/pipeline/merge.rs

@@ -104,7 +104,7 @@ impl AgentPool {
         }
 
         let story_archived =
-            crate::agents::lifecycle::move_story_to_archived(project_root, story_id).is_ok();
+            crate::agents::lifecycle::move_story_to_done(project_root, story_id).is_ok();
         if story_archived {
             self.remove_agents_for_story(story_id);
         }