diff --git a/crates/engine/src/cmd/solver/reports.rs b/crates/engine/src/cmd/solver/reports.rs
index 19500cab0..c2a5c6d84 100644
--- a/crates/engine/src/cmd/solver/reports.rs
+++ b/crates/engine/src/cmd/solver/reports.rs
@@ -52,14 +52,19 @@ pub(super) fn abs_ref(c: CellRef) -> String {
     format!("${}${}", gridcraft_core::col_to_letters(c.col), u64::from(c.row) + 1)
 }
 
+/// How many cells to the left and above a cell its name is searched for.
+const NAME_REACH: u32 = 1_000;
+
 /// A cell's name in the reports: the nearest text to its left and the nearest text above it.
 pub(super) fn cell_name(sh: &Sheet, c: CellRef) -> String {
     let text = |c: CellRef| match sh.value(c) {
         Value::Text(t) if !t.trim().is_empty() => Some(t.to_string()),
         _ => None,
     };
-    let left = (0..c.col).rev().find_map(|col| text(CellRef::new(c.row, col)));
-    let top = (0..c.row).rev().find_map(|row| text(CellRef::new(row, c.col)));
+    // Labels are next to their cells: looking further than this on a sparse sheet only costs time
+    // (a thousand cells near the last row would each probe a million empty coordinates).
+    let left = (c.col.saturating_sub(NAME_REACH)..c.col).rev().find_map(|col| text(CellRef::new(c.row, col)));
+    let top = (c.row.saturating_sub(NAME_REACH)..c.row).rev().find_map(|row| text(CellRef::new(row, c.col)));
     [left, top].into_iter().flatten().collect::<Vec<_>>().join(" ")
 }
 
@@ -438,3 +443,17 @@ pub(super) fn report(s: &mut Session, p: &Json) -> Result<Json> {
     }
     Ok(out)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn a_name_is_searched_only_a_bounded_distance() {
+        let mut sh = Sheet::new("S".to_string());
+        sh.set_cell(CellRef::new(0, 0), gridcraft_model::Cell::value(Value::text("Far")));
+        sh.set_cell(CellRef::new(5, 4), gridcraft_model::Cell::value(Value::text("Near")));
+        assert_eq!(cell_name(&sh, CellRef::new(5, 5)), "Near");
+        assert_eq!(cell_name(&sh, CellRef::new(0, NAME_REACH + 1)), "");
+    }
+}
diff --git a/crates/engine/src/cmd/whatif/scenarios.rs b/crates/engine/src/cmd/whatif/scenarios.rs
index 75bf147a0..cd779b2fb 100644
--- a/crates/engine/src/cmd/whatif/scenarios.rs
+++ b/crates/engine/src/cmd/whatif/scenarios.rs
@@ -189,6 +189,9 @@ pub(super) fn scenario_delete(s: &mut Session, p: &Json) -> Result<Json> {
     Ok(json!({"deleted": removed.name}))
 }
 
+/// Most changing-cell-by-scenario cells one Scenario Summary writes.
+const MAX_SUMMARY_CELLS: usize = 1_000_000;
+
 pub(super) fn scenario_summary(s: &mut Session, p: &Json) -> Result<Json> {
     const CMD: &str = "data.scenarioSummary";
     let d = s.doc()?;
@@ -211,17 +214,23 @@ pub(super) fn scenario_summary(s: &mut Session, p: &Json) -> Result<Json> {
     // Changing cells of every scenario, first-seen order; per scenario its values.
     let mut changing: Vec<CellRef> = Vec::new();
     let mut per: Vec<HashMap<CellRef, Value>> = Vec::new();
+    let mut seen: std::collections::HashSet<CellRef> = Default::default();
     for sc in &scenarios {
         let (_, cells) = cell_list(&d.wb, &sc.changing, CMD, MAX_SCENARIO_CELLS)?;
         let mut m = HashMap::new();
         for (c, v) in cells.iter().zip(sc.values.iter()) {
-            if !changing.contains(c) {
+            if seen.insert(*c) {
                 changing.push(*c);
             }
             m.insert(*c, json_value(v, &d.wb));
         }
         per.push(m);
     }
+    // The summary has a cell for every changing cell in every scenario, filled from the current
+    // value where a scenario doesn't set it, so small disjoint scenarios multiply.
+    if changing.len().saturating_mul(per.len()) > MAX_SUMMARY_CELLS {
+        return Err(bad(CMD, "the scenarios together change too many cells for a summary"));
+    }
     let current: Vec<Value> = changing.iter().map(|c| sh.value(*c)).collect();
     let current_results: Vec<Value> = results.iter().map(|c| sh.value(*c)).collect();
     let mut trial = Trial::new(d);
diff --git a/crates/engine/src/cmd/whatif/tests.rs b/crates/engine/src/cmd/whatif/tests.rs
index c1476e401..1c7f8c6f5 100644
--- a/crates/engine/src/cmd/whatif/tests.rs
+++ b/crates/engine/src/cmd/whatif/tests.rs
@@ -297,3 +297,14 @@ fn consolidate_by_position_and_label() {
     assert!(s.execute("data.consolidate", json!({"sources": []})).is_err());
     assert!(s.execute("data.consolidate", json!({"sources": ["A1"], "function": "median"})).is_err());
 }
+
+#[test]
+fn scenario_summary_refuses_a_matrix_over_its_cell_limit() {
+    let mut s = s();
+    // 200 scenarios of 32 disjoint cells: 6,400 changing cells x 200 scenarios = 1.28 million cells.
+    for i in 0..200 {
+        let (a, b) = (i * 32 + 1, i * 32 + 32);
+        s.execute("data.scenarioAdd", json!({"name": format!("S{i}"), "changing": format!("A{a}:A{b}")})).unwrap();
+    }
+    assert!(s.execute("data.scenarioSummary", json!({})).is_err());
+}
diff --git a/crates/engine/src/lib.rs b/crates/engine/src/lib.rs
index 6f61b239e..8c79c9b44 100644
--- a/crates/engine/src/lib.rs
+++ b/crates/engine/src/lib.rs
@@ -237,6 +237,19 @@ const JOURNAL_MAX_ENTRIES: usize = 10_000;
 pub(crate) const JOURNAL_MAX_BYTES: usize = 64 * 1024 * 1024;
 const UNDO_BYTES_LIMIT: usize = 128 * 1024 * 1024;
 
+/// Comment and hyperlink text of a sheet: a changed sheet's snapshot keeps its own copy of these
+/// strings (an edit deep-copies them), so they count against the history budget with the cells.
+fn sheet_text_bytes(sheet: &gridcraft_model::Sheet) -> usize {
+    let comments = sheet.comments.values().fold(0usize, |sum, c| {
+        let replies = c.replies.iter().fold(0usize, |n, (a, t)| n.saturating_add(a.len()).saturating_add(t.len()));
+        let dates = c.dates.iter().fold(0usize, |n, d| n.saturating_add(d.len()));
+        sum.saturating_add(std::mem::size_of::<gridcraft_model::Comment>() + c.author.len() + c.text.len() + replies + dates)
+    });
+    sheet.hyperlinks.values().fold(comments, |sum, h| {
+        sum.saturating_add(std::mem::size_of::<gridcraft_model::Hyperlink>() + h.target.len() + h.tooltip.as_ref().map_or(0, String::len))
+    })
+}
+
 fn history_retained_bytes(older: &Workbook, newer: &Workbook) -> usize {
     let mut bytes = std::mem::size_of::<Workbook>();
     for (index, sheet) in older.sheets.iter().enumerate() {
@@ -248,6 +261,7 @@ fn history_retained_bytes(older: &Workbook, newer: &Workbook) -> usize {
         let empty = gridcraft_model::CellStore::new();
         let next = newer.sheets.get(index).map_or(&empty, |next| &next.cells);
         bytes = bytes.saturating_add(sheet.cells.retained_bytes_against(next));
+        bytes = bytes.saturating_add(sheet_text_bytes(sheet));
     }
     // Snapshots share the macro list until a change to it; a snapshot with its own list keeps it.
     if !older.macros.shares(&newer.macros) {
diff --git a/crates/engine/src/tests.rs b/crates/engine/src/tests.rs
index fe42b6977..794134538 100644
--- a/crates/engine/src/tests.rs
+++ b/crates/engine/src/tests.rs
@@ -5572,3 +5572,14 @@ fn clearing_links_and_notes_keeps_allow_edit_ranges() {
     let sh = s.doc().unwrap().wb.active().unwrap().clone();
     assert!(sh.hyperlinks.is_empty() && sh.comments.is_empty());
 }
+
+#[test]
+fn history_charges_a_changed_sheets_comment_text() {
+    let mut s = s();
+    s.execute("review.newNote", json!({"cell": "A1", "text": "n".repeat(30_000), "author": "Example"})).unwrap();
+    let older = (*s.doc().unwrap().wb).clone();
+    s.execute("cell.set", json!({"cell": "B2", "input": "x"})).unwrap();
+    let newer = (*s.doc().unwrap().wb).clone();
+    // The older snapshot owns the comment text now that the sheet changed under it.
+    assert!(crate::history_retained_bytes(&older, &newer) >= 30_000);
+}