fix(preprocess): keep first occurrence of repeated headers/footers

Document titles, column headers, and newsletter mastheads that repeat
on every page were being fully stripped by strip_repeated_lines. Now
the first page's occurrence is preserved so the content appears once.

Fixes missing titles like "VOICE OF SOUTH MARION" in tax certificate
PDFs and column headers in IRS forms.

src/markdown/preprocess.rs

@@ -423,9 +423,13 @@ pub(crate) fn strip_repeated_lines(lines: Vec<TextLine>, page_count: u32) -> Vec
     //   (a) its individual text matches a candidate, OR
     //   (b) its Y-band's coalesced text matches a band candidate, OR
     //   (c) any sibling in its Y-band was removed (propagation).
+    //
+    // The first occurrence (lowest page number) of each repeated header/footer
+    // is kept so that document titles, column headers, etc. appear once.
     let mut removal_set: HashSet<usize> = HashSet::new();
 
-    // (a) Lines matching individual candidates at edge positions
+    // Track which page first shows each candidate (to preserve first occurrence)
+    let mut first_page_individual: HashMap<String, u32> = HashMap::new();
     for (idx, line) in lines.iter().enumerate() {
         if !is_y_at_edge(line.y, line.page, &page_sorted_ys, EDGE_LINE_COUNT) {
             continue;
@@ -433,11 +437,18 @@ pub(crate) fn strip_repeated_lines(lines: Vec<TextLine>, page_count: u32) -> Vec
         let text = line.text();
         let normalized = normalize_for_comparison(&text);
         if candidates.contains(&normalized) {
-            removal_set.insert(idx);
+            let first = first_page_individual.entry(normalized).or_insert(line.page);
+            if line.page > *first {
+                removal_set.insert(idx);
+            } else if line.page == *first {
+                // Keep this occurrence (first page)
+            }
         }
     }
 
-    // (b) Lines in Y-bands whose coalesced text matches a band candidate
+    // Track first page for band candidates
+    let mut first_page_band: HashMap<String, u32> = HashMap::new();
+    // First pass: find first page for each band candidate
     for (&(page, _), indices) in &y_bands {
         if indices.len() < 2 {
             continue;
@@ -455,8 +466,35 @@ pub(crate) fn strip_repeated_lines(lines: Vec<TextLine>, page_count: u32) -> Vec
             .join(" ");
         let normalized = normalize_for_comparison(&coalesced);
         if band_candidates.contains(&normalized) {
-            for &idx in &sorted_indices {
-                removal_set.insert(idx);
+            let first = first_page_band.entry(normalized).or_insert(page);
+            if page < *first {
+                *first = page;
+            }
+        }
+    }
+    // Second pass: mark for removal (skip first page)
+    for (&(page, _), indices) in &y_bands {
+        if indices.len() < 2 {
+            continue;
+        }
+        let band_y = lines[indices[0]].y;
+        if !is_y_at_edge(band_y, page, &page_sorted_ys, EDGE_LINE_COUNT) {
+            continue;
+        }
+        let mut sorted_indices = indices.clone();
+        sorted_indices.sort();
+        let coalesced: String = sorted_indices
+            .iter()
+            .map(|&i| lines[i].text())
+            .collect::<Vec<_>>()
+            .join(" ");
+        let normalized = normalize_for_comparison(&coalesced);
+        if band_candidates.contains(&normalized) {
+            let first = first_page_band.get(&normalized).copied().unwrap_or(0);
+            if page > first {
+                for &idx in &sorted_indices {
+                    removal_set.insert(idx);
+                }
             }
         }
     }
@@ -598,4 +636,51 @@ mod tests {
         let result = merge_heading_lines(lines, 12.0, &heading_tiers, None);
         assert_eq!(result.len(), 2, "should merge font-based heading lines");
     }
+
+    #[test]
+    fn test_strip_repeated_keeps_first_occurrence() {
+        // Simulate a repeated page header on 10 pages.
+        // Each page has a running header at y=750 and many unique body lines.
+        let mut lines = Vec::new();
+        for page in 1..=10u32 {
+            // Header at top
+            lines.push(make_line(
+                "VOICE OF SOUTH MARION May fifteen twenty twenty five",
+                10.0,
+                page,
+                750.0,
+                None,
+            ));
+            // Body content — unique text per line per page (no digits to strip)
+            for j in 0..20u32 {
+                lines.push(make_line(
+                    &format!(
+                        "parcel r-{:04}-{:03} owner smith address oak street",
+                        page * 100 + j,
+                        page
+                    ),
+                    10.0,
+                    page,
+                    600.0 - j as f32 * 15.0,
+                    None,
+                ));
+            }
+        }
+
+        let result = strip_repeated_lines(lines, 10);
+
+        // The header should appear exactly once (page 1)
+        let header_count = result
+            .iter()
+            .filter(|l| l.text().contains("VOICE OF SOUTH MARION"))
+            .count();
+        assert_eq!(header_count, 1, "repeated header should be kept once");
+
+        // First occurrence should be on page 1
+        let first_header = result
+            .iter()
+            .find(|l| l.text().contains("VOICE OF SOUTH MARION"))
+            .unwrap();
+        assert_eq!(first_header.page, 1, "first occurrence should be on page 1");
+    }
 }