src/ai/llm_client.rs

@@ -315,11 +315,23 @@ impl ChatHistoryStore {
     /// `preferred_leaf` when it lives in that child's subtree (so the
     /// caller's current view maps onto its own option and can be filtered
     /// out client-side), otherwise the most recent (max-id) descendant leaf.
+    ///
+    /// Snippets preview the first visible message that *differs* between
+    /// the branches, not blindly the first child: Rewind & Regenerate
+    /// resends the identical question, so the first child is often shared
+    /// across siblings and would make every option read the same.
     pub fn branch_options_at(&self, fork_node_id: u64, preferred_leaf: u64) -> Vec<BranchLeafInfo> {
-        self.children_of(fork_node_id)
+        struct Candidate {
+            rep: u64,
+            message_count: usize,
+            /// User/assistant contents after the divergence, tool
+            /// scaffolding (tool results, empty dispatch turns) skipped.
+            visible: Vec<String>,
+        }
+        let candidates: Vec<Candidate> = self
+            .children_of(fork_node_id)
             .iter()
-            .enumerate()
-            .map(|(i, child)| {
+            .map(|child| {
                 let leaves = self.descendant_leaves(child.id);
                 let rep = if leaves.contains(&preferred_leaf) {
                     preferred_leaf
@@ -328,21 +340,56 @@ impl ChatHistoryStore {
                 };
                 let path = self.path_to_leaf(rep).unwrap_or_default();
                 let message_count = path.len();
-                // Snippet: first visible message *after* the divergence point —
-                // skip tool scaffolding (tool results, empty dispatch turns).
-                let snippet = path
+                let visible: Vec<String> = path
                     .iter()
                     .skip_while(|n| n.id != child.id)
-                    .find(|n| {
+                    .filter(|n| {
                         (n.message.role == "user" || n.message.role == "assistant")
                             && !n.message.content.trim().is_empty()
                     })
-                    .map(|n| n.message.content.chars().take(100).collect::<String>())
+                    .map(|n| n.message.content.clone())
+                    .collect();
+                Candidate {
+                    rep,
+                    message_count,
+                    visible,
+                }
+            })
+            .collect();
+
+        // Walk forward past positions where every branch has the same
+        // content; stop at the first divergence (or when any branch runs
+        // out — a length difference is itself distinguishing).
+        let mut snippet_idx = 0usize;
+        loop {
+            let contents: Vec<Option<&String>> = candidates
+                .iter()
+                .map(|c| c.visible.get(snippet_idx))
+                .collect();
+            let all_present_and_equal =
+                contents.iter().all(|c| c.is_some()) && contents.windows(2).all(|w| w[0] == w[1]);
+            if !all_present_and_equal {
+                break;
+            }
+            snippet_idx += 1;
+        }
+
+        candidates
+            .into_iter()
+            .enumerate()
+            .map(|(i, c)| {
+                // A branch exhausted before the divergence index falls back
+                // to its own last message so it still shows *something*.
+                let snippet = c
+                    .visible
+                    .get(snippet_idx)
+                    .or_else(|| c.visible.last())
+                    .map(|s| s.chars().take(100).collect::<String>())
                     .unwrap_or_default();
                 BranchLeafInfo {
-                    id: rep,
+                    id: c.rep,
                     snippet,
-                    message_count,
+                    message_count: c.message_count,
                     position: Some(i + 1),
                 }
             })
@@ -629,6 +676,41 @@ mod tests {
         assert_eq!(opts[1].id, c2);
     }
 
+    #[test]
+    fn branch_options_snippet_skips_shared_resent_question() {
+        // Rewind & Regenerate resends the identical question, so both
+        // branches' first child matches — the preview must advance to the
+        // first *differing* message (the assistant replies) or every
+        // option would read the same.
+        let mut store = ChatHistoryStore::empty();
+        let root = store.append_node(None, mk_msg("assistant", "prior reply"));
+        let q1 = store.append_node(Some(root), mk_msg("user", "same question"));
+        let _a1 = store.append_node(Some(q1), mk_msg("assistant", "first answer"));
+        let q2 = store.append_node(Some(root), mk_msg("user", "same question"));
+        let a2 = store.append_node(Some(q2), mk_msg("assistant", "second answer"));
+
+        let opts = store.branch_options_at(root, a2);
+        assert_eq!(opts.len(), 2);
+        assert_eq!(opts[0].snippet, "first answer");
+        assert_eq!(opts[1].snippet, "second answer");
+    }
+
+    #[test]
+    fn branch_options_snippet_falls_back_when_branch_exhausted() {
+        // One branch is just the shared question (no reply yet); the other
+        // continues past it. The shorter branch falls back to its own last
+        // message rather than showing an empty preview.
+        let mut store = ChatHistoryStore::empty();
+        let root = store.append_node(None, mk_msg("assistant", "prior reply"));
+        let _q1 = store.append_node(Some(root), mk_msg("user", "same question"));
+        let q2 = store.append_node(Some(root), mk_msg("user", "same question"));
+        let a2 = store.append_node(Some(q2), mk_msg("assistant", "second answer"));
+
+        let opts = store.branch_options_at(root, a2);
+        assert_eq!(opts[0].snippet, "same question");
+        assert_eq!(opts[1].snippet, "second answer");
+    }
+
     #[test]
     fn branch_options_snippet_skips_tool_scaffolding() {
         let mut store = ChatHistoryStore::empty();