Fix fuzzy match scoring within Unicode lowercase expansions (#45475)

## Why

Matches starting inside a lowercase expansion such as `İ` → `i̇` could receive an incorrect prefix bonus or gap penalty, causing strings that lowercase identically to rank differently.

## What changed

Track the first matched position in the lowercased text directly when calculating scores. Preserve original character indices for highlighting.

## Testing

Add a skill popup regression test and snapshot covering ranking and highlighting for matches beginning at the combining dot in expanded and already-lowercase names.

GitOrigin-RevId: 78a8b79f1defca9f76fde5df945b0b1ff4af25da

codex-rs/tui/src/bottom_pane/skill_popup.rs

@@ -331,6 +331,33 @@ mod tests {
         insta::assert_snapshot!("skill_popup_scrolled", render_popup(&popup, /*width*/ 72));
     }
 
+    #[test]
+    fn lowercase_expansion_preserves_match_ranking_and_highlighting() {
+        let mut popup = SkillPopup::new(vec![
+            named_mention_item("İx", &[]),
+            named_mention_item("i\u{0307}x", &[]),
+            named_mention_item("aİx", &[]),
+            named_mention_item("ai\u{0307}x", &[]),
+        ]);
+        popup.set_query("\u{0307}x");
+
+        // Each pair lowercases identically. The dot starts a contiguous match,
+        // but not a prefix, even when it came from the expansion of 'İ'.
+        assert_eq!(
+            popup.filtered(),
+            vec![
+                (3, Some(vec![2, 3]), 0),
+                (2, Some(vec![1, 2]), 0),
+                (1, Some(vec![1, 2]), 0),
+                (0, Some(vec![0, 1]), 0),
+            ]
+        );
+        insta::assert_snapshot!(
+            "skill_popup_lowercase_expansion",
+            render_popup(&popup, /*width*/ 48)
+        );
+    }
+
     #[test]
     fn display_name_match_sorting_beats_worse_secondary_search_term_matches() {
         let mut popup = SkillPopup::new(vec![

codex-rs/tui/src/bottom_pane/snapshots/codex_tui__bottom_pane__skill_popup__tests__skill_popup_lowercase_expansion.snap

@@ -0,0 +1,36 @@
+---
+source: tui/src/bottom_pane/skill_popup.rs
+expression: "render_popup(&popup, 48)"
+---
+Buffer {
+    area: Rect { x: 0, y: 0, width: 48, height: 6 },
+    content: [
+        "  ai̇x  [Skill]                                  ",
+        "  aİx  [Skill]                                  ",
+        "  i̇x   [Skill]                                  ",
+        "  İx   [Skill]                                  ",
+        "                                                ",
+        "  Press enter to insert or esc to close         ",
+    ],
+    styles: [
+        x: 0, y: 0, fg: Reset, bg: Reset, underline: Reset, modifier: NONE,
+        x: 2, y: 0, fg: Cyan, bg: Reset, underline: Reset, modifier: BOLD,
+        x: 14, y: 0, fg: Reset, bg: Reset, underline: Reset, modifier: NONE,
+        x: 3, y: 1, fg: Reset, bg: Reset, underline: Reset, modifier: BOLD,
+        x: 5, y: 1, fg: Reset, bg: Reset, underline: Reset, modifier: NONE,
+        x: 7, y: 1, fg: Reset, bg: Reset, underline: Reset, modifier: DIM,
+        x: 14, y: 1, fg: Reset, bg: Reset, underline: Reset, modifier: NONE,
+        x: 2, y: 2, fg: Reset, bg: Reset, underline: Reset, modifier: BOLD,
+        x: 4, y: 2, fg: Reset, bg: Reset, underline: Reset, modifier: NONE,
+        x: 7, y: 2, fg: Reset, bg: Reset, underline: Reset, modifier: DIM,
+        x: 14, y: 2, fg: Reset, bg: Reset, underline: Reset, modifier: NONE,
+        x: 2, y: 3, fg: Reset, bg: Reset, underline: Reset, modifier: BOLD,
+        x: 4, y: 3, fg: Reset, bg: Reset, underline: Reset, modifier: NONE,
+        x: 7, y: 3, fg: Reset, bg: Reset, underline: Reset, modifier: DIM,
+        x: 14, y: 3, fg: Reset, bg: Reset, underline: Reset, modifier: NONE,
+        x: 8, y: 5, fg: Reset, bg: Reset, underline: Reset, modifier: DIM,
+        x: 13, y: 5, fg: Reset, bg: Reset, underline: Reset, modifier: NONE,
+        x: 27, y: 5, fg: Reset, bg: Reset, underline: Reset, modifier: DIM,
+        x: 30, y: 5, fg: Reset, bg: Reset, underline: Reset, modifier: NONE,
+    ]
+}

codex-rs/utils/fuzzy-match/src/lib.rs

@@ -8,7 +8,7 @@
 /// lowercased haystack back to the original character index in `haystack`.
 /// This ensures the returned indices can be safely used with
 /// `str::chars().enumerate()` consumers for highlighting, even when
-/// lowercasing expands certain characters (e.g., ß → ss, İ → i̇).
+/// lowercasing expands certain characters (e.g., İ → i̇).
 pub fn fuzzy_match(haystack: &str, needle: &str) -> Option<(Vec<usize>, i32)> {
     if needle.is_empty() {
         return Some((Vec::new(), i32::MAX));
@@ -26,6 +26,7 @@ pub fn fuzzy_match(haystack: &str, needle: &str) -> Option<(Vec<usize>, i32)> {
     let lowered_needle: Vec<char> = needle.to_lowercase().chars().collect();
 
     let mut result_orig_indices: Vec<usize> = Vec::with_capacity(lowered_needle.len());
+    let mut first_lower_pos: Option<usize> = None;
     let mut last_lower_pos: Option<usize> = None;
     let mut cur = 0usize;
     for &nc in lowered_needle.iter() {
@@ -40,18 +41,12 @@ pub fn fuzzy_match(haystack: &str, needle: &str) -> Option<(Vec<usize>, i32)> {
         }
         let pos = found_at?;
         result_orig_indices.push(lowered_to_orig_char_idx[pos]);
+        first_lower_pos.get_or_insert(pos);
         last_lower_pos = Some(pos);
     }
 
-    let first_lower_pos = if result_orig_indices.is_empty() {
-        0usize
-    } else {
-        let target_orig = result_orig_indices[0];
-        lowered_to_orig_char_idx
-            .iter()
-            .position(|&oi| oi == target_orig)
-            .unwrap_or(0)
-    };
+    // Score using the actual lowered positions, even within a character expansion.
+    let first_lower_pos = first_lower_pos?;
     // last defaults to first for single-hit; score = extra span between first/last hit
     // minus needle len (≥0).
     // Strongly reward prefix matches by subtracting 100 when the first hit is at index 0.