feat(core): Expand filtering into pipeline supporting multiple text search modes.

Modes include: exact match, smart-case, and regular expressions.

crates/pikl-core/src/query/navigation.rs

@@ -113,6 +113,34 @@ impl Viewport {
         }
     }
 
+    /// Move cursor up by `n` half-pages (half viewport height
+    /// each). Clamps to the top.
+    pub fn half_page_up(&mut self, n: usize) {
+        if self.height == 0 {
+            return;
+        }
+        let half = (self.height / 2).max(1);
+        let distance = half.saturating_mul(n);
+        self.cursor = self.cursor.saturating_sub(distance);
+        if self.cursor < self.scroll_offset {
+            self.scroll_offset = self.cursor;
+        }
+    }
+
+    /// Move cursor down by `n` half-pages (half viewport height
+    /// each). Clamps to the last item.
+    pub fn half_page_down(&mut self, n: usize) {
+        if self.height == 0 || self.filtered_count == 0 {
+            return;
+        }
+        let half = (self.height / 2).max(1);
+        let distance = half.saturating_mul(n);
+        self.cursor = (self.cursor + distance).min(self.filtered_count - 1);
+        if self.cursor >= self.scroll_offset + self.height {
+            self.scroll_offset = self.cursor - self.height + 1;
+        }
+    }
+
     /// Move cursor down by `n` pages (viewport height each).
     /// Clamps to the last item.
     pub fn page_down(&mut self, n: usize) {
@@ -353,4 +381,106 @@ mod tests {
         v.set_height(3);
         assert!(v.cursor() < v.scroll_offset() + 3);
     }
+
+    // -- half_page unit tests --
+
+    #[test]
+    fn half_page_down_basic() {
+        let mut v = viewport(10, 30);
+        v.half_page_down(1);
+        assert_eq!(v.cursor(), 5);
+        assert_eq!(v.scroll_offset(), 0);
+    }
+
+    #[test]
+    fn half_page_down_scrolls() {
+        let mut v = viewport(10, 30);
+        // Move cursor near viewport edge, then half page down
+        v.half_page_down(1); // cursor 5
+        v.half_page_down(1); // cursor 10, should scroll
+        assert_eq!(v.cursor(), 10);
+        assert_eq!(v.scroll_offset(), 1);
+    }
+
+    #[test]
+    fn half_page_down_clamps() {
+        let mut v = viewport(10, 12);
+        v.half_page_down(1); // cursor 5
+        v.half_page_down(1); // cursor 10
+        v.half_page_down(1); // clamps to 11
+        assert_eq!(v.cursor(), 11);
+    }
+
+    #[test]
+    fn half_page_down_n_multiplier() {
+        let mut v = viewport(10, 30);
+        v.half_page_down(3); // (10/2)*3 = 15
+        assert_eq!(v.cursor(), 15);
+    }
+
+    #[test]
+    fn half_page_up_basic() {
+        let mut v = viewport(10, 30);
+        v.half_page_down(2); // cursor 10
+        v.half_page_up(1); // cursor 5
+        assert_eq!(v.cursor(), 5);
+    }
+
+    #[test]
+    fn half_page_up_clamps_at_top() {
+        let mut v = viewport(10, 30);
+        v.half_page_down(1); // cursor 5
+        v.half_page_up(1); // cursor 0
+        assert_eq!(v.cursor(), 0);
+        v.half_page_up(1); // still 0
+        assert_eq!(v.cursor(), 0);
+    }
+
+    #[test]
+    fn half_page_up_scrolls() {
+        let mut v = viewport(10, 30);
+        // Scroll down far enough that offset > 0
+        v.half_page_down(3); // cursor 15, offset 6
+        assert!(v.scroll_offset() > 0);
+        // Now half page up should track cursor back
+        v.half_page_up(1); // cursor 10
+        v.half_page_up(1); // cursor 5
+        assert_eq!(v.cursor(), 5);
+        // Offset should have followed cursor if it went above
+        assert!(v.scroll_offset() <= v.cursor());
+    }
+
+    #[test]
+    fn half_page_height_one() {
+        let mut v = viewport(1, 10);
+        // max(1/2, 1) = 1, moves 1 item
+        v.half_page_down(1);
+        assert_eq!(v.cursor(), 1);
+    }
+
+    #[test]
+    fn half_page_height_two() {
+        let mut v = viewport(2, 10);
+        // 2/2 = 1, moves 1 item
+        v.half_page_down(1);
+        assert_eq!(v.cursor(), 1);
+    }
+
+    #[test]
+    fn half_page_zero_height() {
+        let mut v = viewport(0, 10);
+        v.half_page_down(1);
+        assert_eq!(v.cursor(), 0);
+        v.half_page_up(1);
+        assert_eq!(v.cursor(), 0);
+    }
+
+    #[test]
+    fn half_page_empty_list() {
+        let mut v = viewport(10, 0);
+        v.half_page_down(1);
+        assert_eq!(v.cursor(), 0);
+        v.half_page_up(1);
+        assert_eq!(v.cursor(), 0);
+    }
 }