diff --git a/src/chat/actions.rs b/src/chat/actions.rs
index c9a25f5..4b3d5b5 100644
--- a/src/chat/actions.rs
+++ b/src/chat/actions.rs
@@ -308,7 +308,7 @@ impl RenderOnce for MessageEditor {
 #[derive(IntoElement)]
 pub struct BranchNavigator {
     id: ElementId,
-    current: usize,
+    current: Option<usize>,
     total: usize,
     on_change: Pick,
 }
@@ -320,10 +320,12 @@ impl BranchNavigator {
         total: usize,
         on_change: impl Fn(usize, &mut Window, &mut App) + 'static,
     ) -> Self {
-        assert!(current < total, "version {current} of {total}");
+        if current >= total {
+            log::error!("branch navigator: version {current} of {total}; none shown");
+        }
         Self {
             id: id.into(),
-            current,
+            current: (current < total).then_some(current),
             total,
             on_change: Rc::new(on_change),
         }
@@ -355,7 +357,7 @@ impl RenderOnce for BranchNavigator {
                 "back",
                 IconName::ChevronLeft,
                 "Previous version",
-                current.checked_sub(1),
+                current.and_then(|current| current.checked_sub(1)),
             ))
             .child(
                 tabular(
@@ -363,13 +365,30 @@ impl RenderOnce for BranchNavigator {
                         .text_size(theme.text_size(TextSize::Xs))
                         .text_color(theme.colors.fg_muted),
                 )
-                .child(format!("{} / {total}", current + 1)),
+                .child(match current {
+                    Some(current) => format!("{} / {total}", current + 1),
+                    None => format!("– / {total}"),
+                }),
             )
             .child(step(
                 "forward",
                 IconName::ChevronRight,
                 "Next version",
-                (current + 1 < total).then_some(current + 1),
+                current.and_then(|current| (current + 1 < total).then_some(current + 1)),
             ))
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::BranchNavigator;
+
+    #[test]
+    fn a_version_past_the_branches_shows_none() {
+        let navigator =
+            |current, total| BranchNavigator::new("branch", current, total, |_, _, _| {});
+        assert_eq!(navigator(1, 3).current, Some(1));
+        assert_eq!(navigator(3, 3).current, None);
+        assert_eq!(navigator(0, 0).current, None);
+    }
+}
diff --git a/src/chat/params.rs b/src/chat/params.rs
index ebb1df0..08cd01a 100644
--- a/src/chat/params.rs
+++ b/src/chat/params.rs
@@ -58,15 +58,25 @@ impl ParameterPanel {
         parameters: impl IntoIterator<Item = Parameter>,
         on_change: impl Fn(&SharedString, f64, &mut Window, &mut App) + 'static,
     ) -> Self {
-        let parameters: Vec<Parameter> = parameters.into_iter().collect();
-        for parameter in &parameters {
+        let mut parameters: Vec<Parameter> = parameters.into_iter().collect();
+        for parameter in &mut parameters {
             assert!(
                 parameter.min < parameter.max
                     && parameter.step > 0.0
-                    && (parameter.min..=parameter.max).contains(&parameter.value),
+                    && parameter.value.is_finite(),
                 "parameter {} has a bad range",
                 parameter.key
             );
+            if !(parameter.min..=parameter.max).contains(&parameter.value) {
+                log::error!(
+                    "parameters: {} at {} lies outside {}..={}; pegged",
+                    parameter.key,
+                    parameter.value,
+                    parameter.min,
+                    parameter.max
+                );
+                parameter.value = parameter.value.clamp(parameter.min, parameter.max);
+            }
         }
         Self {
             id: id.into(),
@@ -309,7 +319,7 @@ impl RenderOnce for SystemPromptEditor {
 
 #[cfg(test)]
 mod tests {
-    use super::{Parameter, cost, places};
+    use super::{Parameter, ParameterPanel, cost, places};
 
     #[test]
     fn cost_counts_tokens_at_their_prices() {
@@ -351,4 +361,21 @@ mod tests {
             "float noise adds no places"
         );
     }
+
+    #[test]
+    fn a_value_outside_its_range_pegs() {
+        let knob = |value| Parameter {
+            key: "temperature".into(),
+            label: "Temperature".into(),
+            value,
+            min: 0.0,
+            max: 2.0,
+            step: 0.1,
+            hint: None,
+        };
+        let panel =
+            ParameterPanel::new("knobs", [knob(3.5), knob(-1.0), knob(0.7)], |_, _, _, _| {});
+        let values: Vec<f64> = panel.parameters.iter().map(|knob| knob.value).collect();
+        assert_eq!(values, [2.0, 0.0, 0.7]);
+    }
 }
diff --git a/src/chat/search.rs b/src/chat/search.rs
index a5818dd..aab9ff1 100644
--- a/src/chat/search.rs
+++ b/src/chat/search.rs
@@ -232,13 +232,19 @@ impl DocumentChunkPreview {
         text: impl Into<SharedString>,
         matched: Vec<Range<usize>>,
     ) -> Self {
-        let text = text.into();
-        assert!(
-            matched.iter().all(|range| range.end <= text.len()
-                && text.is_char_boundary(range.start)
-                && text.is_char_boundary(range.end)),
-            "a match lies outside the passage"
-        );
+        let text: SharedString = text.into();
+        let matched: Vec<Range<usize>> = matched
+            .into_iter()
+            .filter(|range| {
+                let inside = text.get(range.clone()).is_some();
+                if !inside {
+                    log::error!(
+                        "document chunk: match {range:?} lies outside the passage; left out"
+                    );
+                }
+                inside
+            })
+            .collect();
         assert!(
             matched.windows(2).all(|pair| pair[0].end <= pair[1].start),
             "matches come in order without overlapping"
@@ -315,3 +321,16 @@ impl RenderOnce for DocumentChunkPreview {
             )
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::DocumentChunkPreview;
+
+    #[test]
+    fn a_match_outside_the_passage_is_left_out() {
+        let ranges = vec![1..2, 2..3, 3..9];
+        let preview = DocumentChunkPreview::new("guide.md", "p. 2", "éabc", ranges);
+        let kept = 2..3;
+        assert_eq!(preview.matched, [kept]);
+    }
+}
diff --git a/tasks/panics.md b/tasks/panics.md
index ef6011e..e71502e 100644
--- a/tasks/panics.md
+++ b/tasks/panics.md
@@ -88,3 +88,4 @@ One line per item: what changed, what stayed and why, review rounds.
 - P20: a hex selection off the bytes and a stack frame past the stack select none; a flame focus keeps what the profile holds; the timeline's wheel reports only finite, positive ranges from finite factors; a dump's last byte must have an address; flame paints log. Kept: disassembly patterns, `zoomed`'s contract. Review: 3 rounds.
 - P21: block editor listeners painted for a block, field, cell or kind since gone log and change nothing, a dropped picture drag leaves undo alone; a visual block press or edit over text the owner replaced is dropped; nested images parse; a version or find hit past its list selects none. Review: 4 rounds.
 - P22: annotations and suggestions outside their text log and stay out, picks and decisions keeping the owner's index; `accept` returns `Option`; a gone pick, active thread or followed peer logs; yours at no count comes off; a masked field clamps a stale offset, so remote cursors and selections draw. Kept: a thread's comments, presence max, one list's order, empty marks, constant role and mode tables. Review: 3 rounds.
+- P23: a branch version past its total logs and shows a dash, its arrows off; a parameter outside its range logs and pegs; a passage's matches outside it log and stay out. Kept: one-value contracts (progress, scores, shapes, peaks, levels, limits, prices, capacity, format, hour), the composer's trigger rows and stream reveal by construction; `places` skips zero, so `decimals` meets no zero step. Review: 2 rounds.