feat: pre-flight validation before rebase operations

src/cli.rs

@@ -242,7 +242,15 @@ Examples:
     },
 
     /// Fetch trunk, refresh it locally, and rebase stale branches onto their latest parent tips
-    Restack,
+    #[command(after_help = "\
+Examples:
+  ez restack
+  ez restack --force")]
+    Restack {
+        /// Force restack even if merge commits are detected in feature branches
+        #[arg(long)]
+        force: bool,
+    },
 
     /// Move up one branch in the stack
     Up,
@@ -353,11 +361,16 @@ Examples:
     #[command(after_help = "\
 Examples:
   ez move --onto main
-  ez move --onto feat/base")]
+  ez move --onto feat/base
+  ez move --force --onto main")]
     Move {
         /// New parent branch
         #[arg(long)]
         onto: String,
+
+        /// Force move even if merge commits or stale metadata are detected
+        #[arg(long)]
+        force: bool,
     },
 
     /// Merge the bottom PR of the current stack via GitHub

src/cmd/mod.rs

@@ -15,6 +15,7 @@ pub mod move_branch;
 pub mod mutation_guard;
 pub mod navigate;
 pub mod parent;
+pub mod preflight;
 pub mod pr_edit;
 pub mod pr_link;
 pub mod pr_view;

src/cmd/move_branch.rs

@@ -1,13 +1,14 @@
 use anyhow::{Result, bail};
 
+use crate::cmd::preflight;
 use crate::cmd::rebase_conflict;
 use crate::error::EzError;
 use crate::git;
 use crate::github;
 use crate::stack::StackState;
 use crate::ui;
 
-pub fn run(onto: &str) -> Result<()> {
+pub fn run(onto: &str, force: bool) -> Result<()> {
     let mut state = StackState::load()?;
     if let Some(root) = git::current_linked_worktree_root()? {
         ui::linked_worktree_warning(&root);
@@ -44,6 +45,16 @@ pub fn run(onto: &str) -> Result<()> {
         )));
     }
 
+    // Pre-flight: detect merge commits, stale metadata, and redundancy.
+    if let Some(check) = preflight::check_single(&state, &current) {
+        if preflight::report_and_check(&[check], force) {
+            bail!(EzError::UserMessage(
+                "move aborted — resolve the issues above or use `ez move --force --onto ...`"
+                    .to_string()
+            ));
+        }
+    }
+
     let meta = state.get_branch(&current)?;
     let old_parent = meta.parent.clone();
     let old_parent_head = meta.parent_head.clone();