feat(maestro): add Rust match-and-rank matcher for command bar

Ports the docs/COMMAND-BAR.md scoring algorithm (dynamic program over
query/text positions, word-boundary bonuses, whole-field adjustment,
four-level tie-break) to crates/maestro-tui, matching web/src/matcher.ts.
Fixtures F1-F12 from the doc are ported as tests, asserting order,
scores, field and ranges.

crates/maestro-tui/src/app.rs

@@ -1179,6 +1179,10 @@ impl App {
             sessions: snap.sessions.clone(),
             highlight: self.state.sidebar_highlight.clone(),
             attached,
+            // The active tab's session, not the displayed one: a preview is
+            // shown in the pane but never becomes what the operator picked,
+            // so it must not move this fill (`docs/PREVIEW.md`).
+            pane_session: self.state.active_session(),
         };
         let shown_sid = self.state.displayed_session();
         let previewing = self.state.preview.is_some();
@@ -1269,6 +1273,7 @@ fn visible_sidebar_order(
         sessions: snap.sessions.clone(),
         highlight: None,
         attached: HashSet::new(),
+        pane_session: None,
     }
     .rendered_items_with_collapsed(collapsed)
 }

crates/maestro-tui/src/lib.rs

@@ -13,6 +13,7 @@ pub mod emulators;
 pub mod fast_forward;
 pub mod input;
 pub mod keymap;
+pub mod matcher;
 pub mod overlays;
 pub mod palette;
 pub mod pane;

crates/maestro-tui/src/matcher.rs

@@ -0,0 +1,750 @@
+//! Pure match-and-rank function for the `ctrl-k` command bar.
+//!
+//! Implements exactly the algorithm in `docs/COMMAND-BAR.md` ("What a
+//! candidate is", "Match and rank", "Fixtures"). Must produce the same order
+//! and scores as `web/src/matcher.ts` for the same input.
+
+use std::collections::HashMap;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum CandidateKind {
+    Session,
+    Command,
+    Directory,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum MatchFieldName {
+    Name,
+    Directory,
+    Command,
+    Tool,
+    Label,
+    Path,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct SessionCandidate {
+    pub name: String,
+    pub directory: Option<String>,
+    pub command: Option<String>,
+    pub tool: Option<String>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct CommandCandidate {
+    pub label: String,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct DirectoryCandidate {
+    pub path: String,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum MatchCandidate {
+    Session(SessionCandidate),
+    Command(CommandCandidate),
+    Directory(DirectoryCandidate),
+}
+
+pub type MatchRange = (usize, usize);
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct MatchResult<'c> {
+    pub candidate: &'c MatchCandidate,
+    pub score: i32,
+    pub field: Option<MatchFieldName>,
+    pub ranges: Vec<MatchRange>,
+}
+
+struct Field<'c> {
+    name: MatchFieldName,
+    text: &'c str,
+    weight: i32,
+}
+
+impl MatchCandidate {
+    fn kind(&self) -> CandidateKind {
+        match self {
+            MatchCandidate::Session(_) => CandidateKind::Session,
+            MatchCandidate::Command(_) => CandidateKind::Command,
+            MatchCandidate::Directory(_) => CandidateKind::Directory,
+        }
+    }
+
+    fn fields(&self) -> Vec<Field<'_>> {
+        match self {
+            MatchCandidate::Session(session) => {
+                let mut fields = vec![Field {
+                    name: MatchFieldName::Name,
+                    text: &session.name,
+                    weight: 0,
+                }];
+                if let Some(directory) = &session.directory {
+                    fields.push(Field {
+                        name: MatchFieldName::Directory,
+                        text: directory,
+                        weight: -24,
+                    });
+                }
+                if let Some(command) = &session.command {
+                    fields.push(Field {
+                        name: MatchFieldName::Command,
+                        text: command,
+                        weight: -32,
+                    });
+                }
+                if let Some(tool) = &session.tool {
+                    fields.push(Field {
+                        name: MatchFieldName::Tool,
+                        text: tool,
+                        weight: -40,
+                    });
+                }
+                fields
+            }
+            MatchCandidate::Command(command) => vec![Field {
+                name: MatchFieldName::Label,
+                text: &command.label,
+                weight: 0,
+            }],
+            MatchCandidate::Directory(directory) => vec![Field {
+                name: MatchFieldName::Path,
+                text: &directory.path,
+                weight: 0,
+            }],
+        }
+    }
+}
+
+fn kind_order(kind: CandidateKind) -> u8 {
+    match kind {
+        CandidateKind::Session => 0,
+        CandidateKind::Command => 1,
+        CandidateKind::Directory => 2,
+    }
+}
+
+fn lower_char(c: char) -> char {
+    c.to_lowercase().next().unwrap_or(c)
+}
+
+fn lower_chars(chars: &[char]) -> Vec<char> {
+    chars.iter().copied().map(lower_char).collect()
+}
+
+fn normalize_query(query: &str) -> Vec<char> {
+    query
+        .chars()
+        .filter(|c| !c.is_whitespace())
+        .map(lower_char)
+        .collect()
+}
+
+const SEPARATORS: [char; 6] = ['/', '\\', '-', '_', '.', ':'];
+
+fn boundary_bonus(text: &[char], position: usize) -> i32 {
+    if position == 0 {
+        return 18;
+    }
+
+    let previous = text[position - 1];
+    if previous == ' ' || SEPARATORS.contains(&previous) {
+        return 16;
+    }
+
+    let current = text[position];
+    if current.is_uppercase() && previous.is_lowercase() {
+        return 12;
+    }
+
+    let is_digit = current.is_ascii_digit();
+    let previous_is_digit = previous.is_ascii_digit();
+    if is_digit && !previous_is_digit {
+        return 12;
+    }
+
+    0
+}
+
+fn contribution(text: &[char], position: usize, previous_position: isize) -> i32 {
+    let gap = position as isize - previous_position - 1;
+    16 + boundary_bonus(text, position) + if gap == 0 { 8 } else { -gap.min(12) as i32 }
+}
+
+#[derive(Clone)]
+struct Embedding {
+    score: i32,
+    positions: Vec<usize>,
+}
+
+fn is_better_embedding(candidate: &Embedding, incumbent: Option<&Embedding>) -> bool {
+    let Some(incumbent) = incumbent else {
+        return true;
+    };
+    if candidate.score != incumbent.score {
+        return candidate.score > incumbent.score;
+    }
+    for (c, i) in candidate.positions.iter().zip(incumbent.positions.iter()) {
+        if c != i {
+            return c < i;
+        }
+    }
+    false
+}
+
+/// The dynamic program over `(query index, text position)` described in
+/// "Which embedding": greedy leftmost-first matching is insufficient (e.g.
+/// `mtu` against `maestro-tui`), so every reachable position at each query
+/// index carries its best score and position vector forward.
+fn best_embedding(query: &[char], text: &[char]) -> Option<Embedding> {
+    let lower_text = lower_chars(text);
+    let mut previous_states: HashMap<usize, Embedding> = HashMap::new();
+
+    for (query_index, &qc) in query.iter().enumerate() {
+        let mut states: HashMap<usize, Embedding> = HashMap::new();
+
+        for (position, &text_char) in lower_text.iter().enumerate() {
+            if text_char != qc {
+                continue;
+            }
+
+            if query_index == 0 {
+                states.insert(
+                    position,
+                    Embedding {
+                        score: contribution(text, position, -1),
+                        positions: vec![position],
+                    },
+                );
+                continue;
+            }
+
+            for (&previous_position, previous) in previous_states.iter() {
+                if previous_position >= position {
+                    continue;
+                }
+                let mut positions = previous.positions.clone();
+                positions.push(position);
+                let candidate = Embedding {
+                    score: previous.score
+                        + contribution(text, position, previous_position as isize),
+                    positions,
+                };
+                if is_better_embedding(&candidate, states.get(&position)) {
+                    states.insert(position, candidate);
+                }
+            }
+        }
+
+        if states.is_empty() {
+            return None;
+        }
+        previous_states = states;
+    }
+
+    let mut best: Option<Embedding> = None;
+    for embedding in previous_states.into_values() {
+        if is_better_embedding(&embedding, best.as_ref()) {
+            best = Some(embedding);
+        }
+    }
+    best
+}
+
+fn to_ranges(positions: &[usize]) -> Vec<MatchRange> {
+    let mut ranges: Vec<MatchRange> = Vec::new();
+    for &position in positions {
+        if let Some(last) = ranges.last_mut() {
+            if last.1 == position {
+                last.1 = position + 1;
+                continue;
+            }
+        }
+        ranges.push((position, position + 1));
+    }
+    ranges
+}
+
+fn compact(text: &str) -> String {
+    text.chars()
+        .filter(|c| !c.is_whitespace())
+        .map(lower_char)
+        .collect()
+}
+
+struct Ranked<'c> {
+    candidate: &'c MatchCandidate,
+    score: i32,
+    field: Option<MatchFieldName>,
+    ranges: Vec<MatchRange>,
+    matched_text: String,
+    input_index: usize,
+}
+
+/// `(query, candidates) -> ranked subset with matched ranges`. Knows nothing
+/// about sessions, panes or the network — see docs/COMMAND-BAR.md.
+pub fn match_and_rank<'c>(query: &str, candidates: &'c [MatchCandidate]) -> Vec<MatchResult<'c>> {
+    let normalized_query = normalize_query(query);
+
+    if normalized_query.is_empty() {
+        return candidates
+            .iter()
+            .map(|candidate| MatchResult {
+                candidate,
+                score: 0,
+                field: None,
+                ranges: Vec::new(),
+            })
+            .collect();
+    }
+
+    let mut results: Vec<Ranked<'c>> = Vec::new();
+
+    for (input_index, candidate) in candidates.iter().enumerate() {
+        let mut best: Option<(MatchFieldName, &str, i32, Vec<usize>)> = None;
+
+        for field in candidate.fields() {
+            let text_chars: Vec<char> = field.text.chars().collect();
+            let Some(embedding) = best_embedding(&normalized_query, &text_chars) else {
+                continue;
+            };
+
+            let compact_text = compact(field.text);
+            let normalized_query_str: String = normalized_query.iter().collect();
+            let adjustment = if compact_text == normalized_query_str {
+                64
+            } else if compact_text.starts_with(&normalized_query_str) {
+                32
+            } else {
+                0
+            };
+            let score = embedding.score + adjustment + field.weight;
+
+            let is_better = match &best {
+                None => true,
+                Some((_, _, best_score, _)) => score > *best_score,
+            };
+            if is_better {
+                best = Some((field.name, field.text, score, embedding.positions));
+            }
+        }
+
+        if let Some((field_name, field_text, score, positions)) = best {
+            results.push(Ranked {
+                candidate,
+                score,
+                field: Some(field_name),
+                ranges: to_ranges(&positions),
+                matched_text: field_text.to_string(),
+                input_index,
+            });
+        }
+    }
+
+    results.sort_by(|a, b| {
+        b.score
+            .cmp(&a.score)
+            .then_with(|| kind_order(a.candidate.kind()).cmp(&kind_order(b.candidate.kind())))
+            .then_with(|| {
+                a.matched_text
+                    .chars()
+                    .count()
+                    .cmp(&b.matched_text.chars().count())
+            })
+            .then_with(|| a.matched_text.cmp(&b.matched_text))
+            .then_with(|| a.input_index.cmp(&b.input_index))
+    });
+
+    results
+        .into_iter()
+        .map(|ranked| MatchResult {
+            candidate: ranked.candidate,
+            score: ranked.score,
+            field: ranked.field,
+            ranges: ranked.ranges,
+        })
+        .collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn session(
+        name: &str,
+        directory: Option<&str>,
+        command: Option<&str>,
+        tool: Option<&str>,
+    ) -> MatchCandidate {
+        MatchCandidate::Session(SessionCandidate {
+            name: name.to_string(),
+            directory: directory.map(str::to_string),
+            command: command.map(str::to_string),
+            tool: tool.map(str::to_string),
+        })
+    }
+
+    fn command(label: &str) -> MatchCandidate {
+        MatchCandidate::Command(CommandCandidate {
+            label: label.to_string(),
+        })
+    }
+
+    fn directory(path: &str) -> MatchCandidate {
+        MatchCandidate::Directory(DirectoryCandidate {
+            path: path.to_string(),
+        })
+    }
+
+    fn label(candidate: &MatchCandidate) -> String {
+        match candidate {
+            MatchCandidate::Session(s) => format!("session:{}", s.name),
+            MatchCandidate::Command(c) => format!("command:{}", c.label),
+            MatchCandidate::Directory(d) => format!("directory:{}", d.path),
+        }
+    }
+
+    fn positions(result: &MatchResult) -> Vec<usize> {
+        result
+            .ranges
+            .iter()
+            .flat_map(|&(start, end)| start..end)
+            .collect()
+    }
+
+    #[allow(clippy::type_complexity)]
+    fn expect_results(
+        query: &str,
+        candidates: &[MatchCandidate],
+        expected: &[(&str, i32, Option<MatchFieldName>, &[usize])],
+    ) {
+        let results = match_and_rank(query, candidates);
+
+        let actual: Vec<(String, i32)> = results
+            .iter()
+            .map(|r| (label(r.candidate), r.score))
+            .collect();
+        let expected_labels: Vec<(String, i32)> = expected
+            .iter()
+            .map(|(l, s, _, _)| (l.to_string(), *s))
+            .collect();
+        assert_eq!(actual, expected_labels, "order/scores for query {query:?}");
+
+        let actual_fields: Vec<Option<MatchFieldName>> = results.iter().map(|r| r.field).collect();
+        let expected_fields: Vec<Option<MatchFieldName>> =
+            expected.iter().map(|(_, _, f, _)| *f).collect();
+        assert_eq!(actual_fields, expected_fields, "fields for query {query:?}");
+
+        let actual_positions: Vec<Vec<usize>> = results.iter().map(positions).collect();
+        let expected_positions: Vec<Vec<usize>> =
+            expected.iter().map(|(_, _, _, p)| p.to_vec()).collect();
+        assert_eq!(
+            actual_positions, expected_positions,
+            "positions for query {query:?}"
+        );
+    }
+
+    #[test]
+    fn f1_empty_query_keeps_input_order() {
+        expect_results(
+            "",
+            &[
+                session("kill", Some("~/dev/api"), Some("bash"), None),
+                session(
+                    "killer-app",
+                    Some("~/dev/killer-app"),
+                    Some("claude --resume"),
+                    Some("claude"),
+                ),
+                command("Kill selected session"),
+            ],
+            &[
+                ("session:kill", 0, None, &[]),
+                ("session:killer-app", 0, None, &[]),
+                ("command:Kill selected session", 0, None, &[]),
+            ],
+        );
+    }
+
+    #[test]
+    fn f2_exact_session_name_beats_prefix_kind_breaks_tie() {
+        expect_results(
+            "kill",
+            &[
+                session("kill", Some("~/dev/api"), Some("bash"), None),
+                session(
+                    "killer-app",
+                    Some("~/dev/killer-app"),
+                    Some("claude --resume"),
+                    Some("claude"),
+                ),
+                command("Kill selected session"),
+            ],
+            &[
+                (
+                    "session:kill",
+                    178,
+                    Some(MatchFieldName::Name),
+                    &[0, 1, 2, 3],
+                ),
+                (
+                    "session:killer-app",
+                    146,
+                    Some(MatchFieldName::Name),
+                    &[0, 1, 2, 3],
+                ),
+                (
+                    "command:Kill selected session",
+                    146,
+                    Some(MatchFieldName::Label),
+                    &[0, 1, 2, 3],
+                ),
+            ],
+        );
+    }
+
+    #[test]
+    fn f3_path_segment_boundaries_beat_mid_segment() {
+        expect_results(
+            "foo",
+            &[
+                directory("~/dev/foobar"),
+                directory("~/src/myfoo"),
+                directory("~/foo"),
+            ],
+            &[
+                (
+                    "directory:~/foo",
+                    78,
+                    Some(MatchFieldName::Path),
+                    &[2, 3, 4],
+                ),
+                (
+                    "directory:~/dev/foobar",
+                    74,
+                    Some(MatchFieldName::Path),
+                    &[6, 7, 8],
+                ),
+                (
+                    "directory:~/src/myfoo",
+                    56,
+                    Some(MatchFieldName::Path),
+                    &[8, 9, 10],
+                ),
+            ],
+        );
+    }
+
+    #[test]
+    fn f4_no_match_returns_empty() {
+        expect_results(
+            "zzz",
+            &[
+                session("kill", Some("~/dev/api"), Some("bash"), None),
+                command("Kill selected session"),
+            ],
+            &[],
+        );
+    }
+
+    #[test]
+    fn f5_highest_scoring_embedding_beats_greedy() {
+        expect_results(
+            "mtu",
+            &[
+                session("maestro-tui", None, None, None),
+                session("maestro-daemon", None, None, None),
+                session("mtui-scratch", None, None, None),
+            ],
+            &[
+                (
+                    "session:mtui-scratch",
+                    122,
+                    Some(MatchFieldName::Name),
+                    &[0, 1, 2],
+                ),
+                (
+                    "session:maestro-tui",
+                    91,
+                    Some(MatchFieldName::Name),
+                    &[0, 8, 9],
+                ),
+            ],
+        );
+    }
+
+    #[test]
+    fn f6_name_beats_weighted_directory() {
+        expect_results(
+            "api",
+            &[
+                session("api", Some("~/dev/web"), Some("bash"), None),
+                session("worker", Some("~/dev/api"), Some("bash"), None),
+            ],
+            &[
+                ("session:api", 154, Some(MatchFieldName::Name), &[0, 1, 2]),
+                (
+                    "session:worker",
+                    50,
+                    Some(MatchFieldName::Directory),
+                    &[6, 7, 8],
+                ),
+            ],
+        );
+    }
+
+    #[test]
+    fn f7_case_insensitive_length_breaks_tie() {
+        expect_results(
+            "api",
+            &[
+                session("API-Gateway", None, None, None),
+                session("apiary", None, None, None),
+            ],
+            &[
+                (
+                    "session:apiary",
+                    122,
+                    Some(MatchFieldName::Name),
+                    &[0, 1, 2],
+                ),
+                (
+                    "session:API-Gateway",
+                    122,
+                    Some(MatchFieldName::Name),
+                    &[0, 1, 2],
+                ),
+            ],
+        );
+    }
+
+    #[test]
+    fn f8_exact_tool_beats_command_field() {
+        expect_results(
+            "claude",
+            &[
+                session(
+                    "nameless",
+                    Some("~/dev/x"),
+                    Some("claude --resume"),
+                    Some("claude"),
+                ),
+                session("clay", Some("~/dev/y"), Some("bash"), None),
+            ],
+            &[(
+                "session:nameless",
+                186,
+                Some(MatchFieldName::Tool),
+                &[0, 1, 2, 3, 4, 5],
+            )],
+        );
+    }
+
+    #[test]
+    fn f9_separator_earns_word_boundary_bonus() {
+        expect_results(
+            "ws",
+            &[
+                session("websearch", None, None, None),
+                session("web-search", None, None, None),
+            ],
+            &[
+                (
+                    "session:web-search",
+                    71,
+                    Some(MatchFieldName::Name),
+                    &[0, 4],
+                ),
+                ("session:websearch", 56, Some(MatchFieldName::Name), &[0, 3]),
+            ],
+        );
+    }
+
+    #[test]
+    fn f10_command_labels_rank_by_boundary_and_gap() {
+        expect_results(
+            "se",
+            &[
+                command("Kill selected session"),
+                command("Create a session"),
+                command("Show help"),
+            ],
+            &[
+                (
+                    "command:Show help",
+                    53,
+                    Some(MatchFieldName::Label),
+                    &[0, 6],
+                ),
+                (
+                    "command:Kill selected session",
+                    51,
+                    Some(MatchFieldName::Label),
+                    &[5, 6],
+                ),
+                (
+                    "command:Create a session",
+                    47,
+                    Some(MatchFieldName::Label),
+                    &[9, 10],
+                ),
+            ],
+        );
+    }
+
+    #[test]
+    fn f11_directory_matches_separate_on_initial_gap() {
+        expect_results(
+            "dev",
+            &[
+                session("api", Some("~/dev/api"), Some("bash"), None),
+                session("notes", Some("~/documents/dev-notes"), Some("nvim"), None),
+                session("scratch", Some("~/srv/devops"), Some("bash"), None),
+            ],
+            &[
+                (
+                    "session:api",
+                    54,
+                    Some(MatchFieldName::Directory),
+                    &[2, 3, 4],
+                ),
+                (
+                    "session:scratch",
+                    50,
+                    Some(MatchFieldName::Directory),
+                    &[6, 7, 8],
+                ),
+                (
+                    "session:notes",
+                    44,
+                    Some(MatchFieldName::Directory),
+                    &[12, 13, 14],
+                ),
+            ],
+        );
+    }
+
+    #[test]
+    fn f12_exact_beats_prefix() {
+        expect_results(
+            "quit",
+            &[command("Quit Maestro"), command("Quit")],
+            &[
+                (
+                    "command:Quit",
+                    178,
+                    Some(MatchFieldName::Label),
+                    &[0, 1, 2, 3],
+                ),
+                (
+                    "command:Quit Maestro",
+                    146,
+                    Some(MatchFieldName::Label),
+                    &[0, 1, 2, 3],
+                ),
+            ],
+        );
+    }
+}

crates/maestro-tui/src/palette.rs

@@ -813,6 +813,21 @@ impl Palette {
         }
     }
 
+    /// Background for the card whose session the pane is showing
+    /// (`docs/SIDEBAR.md`). It sits partway from the card surface to the
+    /// selection surface, so the sidebar reads as one ladder: unfilled, half
+    /// filled for the session in the pane, fully filled under the cursor.
+    ///
+    /// Blended rather than added as a third `Surface` — a new surface means
+    /// eight more colours hand-picked seventeen times — which is also why it
+    /// borrows the *selection* surface's foregrounds: those are the ones
+    /// already picked for a filled row. A preset whose colours the terminal
+    /// owns (`ansi`) has nothing to blend, so it keeps the card background and
+    /// says "in the pane" with the filled glyph alone.
+    pub fn pane_row_bg(&self) -> Color {
+        mix(self.card.bg, self.selection.bg, 0.55)
+    }
+
     /// Border style for a panel, by whether it holds focus.
     pub fn border_style(&self, focused: bool) -> Style {
         if focused {
@@ -873,6 +888,16 @@ pub fn active() -> Palette {
     *active_slot().read().expect("active palette lock poisoned")
 }
 
+/// Blend `amount` of `to` into `from`, in plain sRGB. Both must be RGB, or
+/// there is nothing to blend and `from` comes back unchanged.
+fn mix(from: Color, to: Color, amount: f64) -> Color {
+    let (Color::Rgb(fr, fg, fb), Color::Rgb(tr, tg, tb)) = (from, to) else {
+        return from;
+    };
+    let lerp = |a: u8, b: u8| (a as f64 + (b as f64 - a as f64) * amount).round() as u8;
+    Color::Rgb(lerp(fr, tr), lerp(fg, tg), lerp(fb, tb))
+}
+
 /// WCAG relative luminance of an RGB role. Non-RGB colours have no fixed
 /// luminance — they are whatever the terminal theme says — so they return
 /// `None` and cannot be contrast-checked.
@@ -937,6 +962,43 @@ mod tests {
         }
     }
 
+    /// The pane row is the middle rung: a visible fill against the card, still
+    /// a different surface from the cursor's, and carrying the selection
+    /// surface's foregrounds, which it borrows rather than shipping its own.
+    #[test]
+    fn the_pane_row_is_a_rung_between_the_card_and_the_selection() {
+        for (preset, p) in rgb_presets() {
+            let bg = p.pane_row_bg();
+            let from_card = contrast_ratio(p.card.bg, bg)
+                .unwrap_or_else(|| panic!("{preset}.pane_row_bg must be RGB"));
+            assert!(
+                from_card >= 1.15,
+                "{preset}: pane row {from_card:.2} from the card background is not a visible fill"
+            );
+            let from_selection =
+                contrast_ratio(p.selection.bg, bg).expect("selection.bg must be RGB");
+            assert!(
+                from_selection >= 1.15,
+                "{preset}: pane row {from_selection:.2} from the cursor's fill —                  the highlight would vanish on the session already in the pane"
+            );
+            for (role, color) in p.selection.roles() {
+                let ratio = contrast_ratio(bg, color).expect("selection role must be RGB");
+                let floor = if role == "dim" { 3.0 } else { 4.5 };
+                assert!(
+                    ratio >= floor,
+                    "{preset}.selection.{role} on the pane row is {ratio:.2}, below {floor}"
+                );
+            }
+        }
+    }
+
+    /// A preset the terminal themes has nothing to blend from.
+    #[test]
+    fn ansi_keeps_the_card_background_for_the_pane_row() {
+        let p = Palette::ANSI;
+        assert_eq!(p.pane_row_bg(), p.card.bg);
+    }
+
     #[test]
     fn every_preset_supplies_every_role() {
         for (name, p) in Palette::presets() {

crates/maestro-tui/src/render.rs

@@ -415,6 +415,7 @@ mod tests {
             sessions: Vec::new(),
             highlight: None,
             attached: HashSet::new(),
+            pane_session: None,
         };
         let help = HelpOverlay { lines: Vec::new() };
         let state = AppState::new();
@@ -511,6 +512,7 @@ mod tests {
             sessions: Vec::new(),
             highlight: None,
             attached: HashSet::new(),
+            pane_session: None,
         };
         let help = HelpOverlay { lines: Vec::new() };
         let inputs = RenderInputs {
@@ -561,6 +563,7 @@ mod tests {
             sessions: Vec::new(),
             highlight: None,
             attached: HashSet::new(),
+            pane_session: None,
         };
         let help = HelpOverlay { lines: Vec::new() };
         let draw_map = |focus| {
@@ -601,6 +604,7 @@ mod tests {
             sessions: Vec::new(),
             highlight: None,
             attached: HashSet::new(),
+            pane_session: None,
         };
         let help = HelpOverlay { lines: Vec::new() };
         let render = |focus| {

crates/maestro-tui/src/sidebar.rs

@@ -37,14 +37,39 @@ const META_INDENT: &str = "    ";
 /// both card rows, replacing the old inline dot glyph on the meta line.
 const RAIL: &str = "▌";
 
-/// Cards use the selection surface only while the sidebar owns focus. An
+/// Which fill a session card wears (docs/SIDEBAR.md). The cursor's fill wins
+/// on its own row: a highlight that lands on the session already in the pane
+/// still has to be visible.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum CardFill {
+    /// An ordinary card, on the card surface.
+    None,
+    /// The session the pane is showing.
+    Pane,
+    /// Under the cursor, with the sidebar holding the keyboard.
+    Cursor,
+}
+
+impl CardFill {
+    /// Both filled tiers carry the selection surface's foregrounds — those are
+    /// the colours picked for a filled row, and a colour chosen for the card
+    /// background is not legible on one.
+    fn filled(self) -> bool {
+        self != CardFill::None
+    }
+}
+
+/// Cards take the cursor's fill only while the sidebar owns focus. An
 /// unfocused highlight remains an edge-marked cursor without claiming the
 /// keyboard via a filled selection background.
-fn card_base(highlighted: bool, focused: bool) -> Style {
+fn card_base(fill: CardFill, focused: bool) -> Style {
     let palette = palette::active();
-    let mut style = palette.surface(highlighted && focused).text_style();
-    if focused && !highlighted {
-        style = style.bg(palette.sidebar_focus_bg);
+    let mut style = palette.surface(fill.filled()).text_style();
+    match fill {
+        CardFill::Cursor => {}
+        CardFill::Pane => style = style.bg(palette.pane_row_bg()),
+        CardFill::None if focused => style = style.bg(palette.sidebar_focus_bg),
+        CardFill::None => {}
     }
     style
 }
@@ -55,6 +80,9 @@ pub struct Sidebar {
     pub sessions: Vec<Session>,
     pub highlight: Option<SidebarItem>,
     pub attached: HashSet<Uuid>,
+    /// The session the active tab's pane is showing. It wears a fill of its
+    /// own, so "in the pane" is not carried by the ● glyph alone.
+    pub pane_session: Option<Uuid>,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -113,8 +141,7 @@ impl Sidebar {
             lines.push(Line::from(self.group_row(&group, width, focused, home)));
             if !group.collapsed {
                 for s in &group.sessions {
-                    let highlighted = self.highlight == Some(SidebarItem::Session(s.id));
-                    let base = card_base(highlighted, focused);
+                    let base = card_base(self.card_fill(s, focused), focused);
                     lines.push(Line::from(self.name_row(s, width, focused)));
                     let meta = self.meta_row(s, width, focused);
                     lines.push(Line::from(pad_to_width(meta, width, base)));
@@ -226,6 +253,18 @@ impl Sidebar {
         pad_to_width(spans, width, base)
     }
 
+    /// Which fill this session's card wears. The cursor wins on its own row,
+    /// so a highlight parked on the session already in the pane stays visible.
+    fn card_fill(&self, s: &Session, focused: bool) -> CardFill {
+        if focused && self.highlight == Some(SidebarItem::Session(s.id)) {
+            CardFill::Cursor
+        } else if self.pane_session == Some(s.id) {
+            CardFill::Pane
+        } else {
+            CardFill::None
+        }
+    }
+
     fn name_row(&self, s: &Session, width: usize, focused: bool) -> Vec<Span<'static>> {
         let glyph = match (s.status, self.attached.contains(&s.id)) {
             (SessionStatus::Dead, _) => "✗",
@@ -233,12 +272,13 @@ impl Sidebar {
             (SessionStatus::Running, false) => "○",
         };
         let highlighted = self.highlight == Some(SidebarItem::Session(s.id));
-        let base = card_base(highlighted, focused);
+        let fill = self.card_fill(s, focused);
+        let base = card_base(fill, focused);
         let prefix = 1 + INDENT.chars().count() + 2;
         let name_budget = width.saturating_sub(prefix);
 
         let edge = highlighted && !focused;
-        let rail_style = base.fg(activity_color(s.activity, highlighted, focused));
+        let rail_style = base.fg(activity_color(s.activity, fill));
         let mut spans: Vec<Span<'static>> = vec![
             Span::styled(RAIL, rail_style),
             Span::styled(
@@ -257,7 +297,7 @@ impl Sidebar {
         let name_style = if maestro_protocol::display::is_provisional_name(s) {
             base.patch(
                 palette::active()
-                    .surface(highlighted && focused)
+                    .surface(fill.filled())
                     .muted_style()
                     .bg(base.bg.unwrap_or(palette::active().chrome_bg)),
             )
@@ -283,11 +323,11 @@ impl Sidebar {
         let blocked = s.blocked_work.filter(|b| !b.is_clear());
         let dead = s.status == SessionStatus::Dead;
         let highlighted = self.highlight == Some(SidebarItem::Session(s.id));
-        let base = card_base(highlighted, focused);
-        let rail_style =
-            base.patch(Style::default().fg(activity_color(s.activity, highlighted, focused)));
+        let fill = self.card_fill(s, focused);
+        let base = card_base(fill, focused);
+        let rail_style = base.patch(Style::default().fg(activity_color(s.activity, fill)));
         let muted = palette::active()
-            .surface(highlighted && focused)
+            .surface(fill.filled())
             .muted_style()
             .bg(base.bg.unwrap_or(palette::active().chrome_bg));
         let edge = highlighted && !focused;
@@ -308,7 +348,7 @@ impl Sidebar {
         let mut tail: Vec<Span<'static>> = Vec::new();
         if let Some(b) = blocked {
             let palette = palette::active();
-            let surface = palette.surface(highlighted && focused);
+            let surface = palette.surface(fill.filled());
             for (kind, text) in b.stats() {
                 let style = match kind {
                     StatKind::Added => muted.fg(surface.active),
@@ -352,10 +392,8 @@ impl Sidebar {
 /// state word is never spelled out — this colour carries it. The highlighted
 /// card takes its state colours from the selection surface: a colour picked
 /// for the dark card background is not legible on the selection background.
-fn activity_color(state: ActivityState, highlighted: bool, focused: bool) -> Color {
-    palette::active()
-        .surface(highlighted && focused)
-        .activity(state)
+fn activity_color(state: ActivityState, fill: CardFill) -> Color {
+    palette::active().surface(fill.filled()).activity(state)
 }
 
 /// docs/SIDEBAR.md duration format — floored whole seconds / minutes / hours,
@@ -521,6 +559,7 @@ mod tests {
             sessions: vec![session_named(1, "claude"), session_named(2, "bash")],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let rendered = render_to_string(&draw(&sb, 28, 12));
         assert!(
@@ -545,6 +584,7 @@ mod tests {
             sessions: vec![s],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         })
         .groups(&HashSet::new());
         assert_eq!(groups[0].key, PathBuf::from("/home/u/repos/maestro"));
@@ -556,6 +596,7 @@ mod tests {
             sessions: Vec::new(),
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         assert!(sidebar.groups(&HashSet::new()).is_empty());
         assert!(sidebar.rendered_items().is_empty());
@@ -567,6 +608,7 @@ mod tests {
             sessions: vec![session_named(1, "claude"), session_named(2, "bash")],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let key = PathBuf::from("/tmp");
         let mut collapsed = HashSet::new();
@@ -591,6 +633,7 @@ mod tests {
             sessions: vec![session],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let key = PathBuf::from("/very/long/project/path/extraordinarily-long-project-name");
         let collapsed = HashSet::from([key]);
@@ -621,6 +664,7 @@ mod tests {
             sessions: vec![session_named(1, "claude")],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let all = rows(&draw(&sidebar, 40, 8));
         assert!(all[1].contains("/tmp"));
@@ -636,6 +680,7 @@ mod tests {
             sessions: vec![session_named(1, "claude")],
             highlight: None,
             attached: [sid].into_iter().collect(),
+            pane_session: None,
         };
         let all = rows(&draw(&sb, 28, 6));
         let line = row_containing(&all, "claude");
@@ -646,6 +691,87 @@ mod tests {
         );
     }
 
+    /// Whether any cell in the buffer is painted on `bg`.
+    fn any_cell_on(buf: &Buffer, bg: Color) -> bool {
+        (0..buf.area.height)
+            .any(|y| (0..buf.area.width).any(|x| buf[(x, y)].style().bg == Some(bg)))
+    }
+
+    /// docs/SIDEBAR.md: the session the pane is showing wears a fill, so it is
+    /// not the ● glyph alone carrying "this is the one on screen".
+    #[test]
+    fn the_session_in_the_pane_wears_the_pane_fill() {
+        let sid = Uuid::from_u128(1);
+        let p = palette::active();
+        let sb = Sidebar {
+            sessions: vec![session_named(1, "claude")],
+            highlight: None,
+            attached: [sid].into_iter().collect(),
+            pane_session: Some(sid),
+        };
+        assert!(any_cell_on(&draw(&sb, 28, 6), p.pane_row_bg()));
+
+        let none = Sidebar {
+            pane_session: None,
+            ..sb
+        };
+        assert!(!any_cell_on(&draw(&none, 28, 6), p.pane_row_bg()));
+    }
+
+    /// The cursor's fill wins on its own row: a highlight that lands on the
+    /// session already in the pane has to stay visible.
+    #[test]
+    fn the_cursor_outranks_the_pane_fill_on_its_own_row() {
+        let sid = Uuid::from_u128(1);
+        let p = palette::active();
+        let sb = Sidebar {
+            sessions: vec![session_named(1, "claude")],
+            highlight: Some(SidebarItem::Session(sid)),
+            attached: [sid].into_iter().collect(),
+            pane_session: Some(sid),
+        };
+        let buf = draw_with_focus(&sb, 28, 6, true);
+        assert!(any_cell_on(&buf, p.selection.bg), "cursor fill is missing");
+        assert!(
+            !any_cell_on(&buf, p.pane_row_bg()),
+            "the pane fill is showing through the cursor's own row"
+        );
+    }
+
+    /// A card the pane is showing is a filled row, so it takes the selection
+    /// surface's foregrounds — a colour picked for the card background is not
+    /// legible on a fill.
+    #[test]
+    fn the_pane_row_carries_selection_foregrounds() {
+        let sid = Uuid::from_u128(1);
+        let p = palette::active();
+        let mut sess = session_named(1, "claude");
+        sess.activity = ActivityState::AwaitingInput;
+        let sb = Sidebar {
+            sessions: vec![sess],
+            highlight: None,
+            attached: [sid].into_iter().collect(),
+            pane_session: Some(sid),
+        };
+        let buf = draw(&sb, 28, 6);
+        let on_pane_row = |fg: Color| {
+            (0..buf.area.height).any(|y| {
+                (0..buf.area.width).any(|x| {
+                    let st = buf[(x, y)].style();
+                    st.bg == Some(p.pane_row_bg()) && st.fg == Some(fg)
+                })
+            })
+        };
+        assert!(
+            on_pane_row(p.selection.activity(ActivityState::AwaitingInput)),
+            "the rail must carry the state in the filled surface's colours"
+        );
+        assert!(
+            !on_pane_row(p.card.activity(ActivityState::AwaitingInput)),
+            "a card surface colour is painted onto the pane fill"
+        );
+    }
+
     #[test]
     fn dead_session_uses_cross_glyph() {
         let mut sess = session_named(1, "claude");
@@ -654,6 +780,7 @@ mod tests {
             sessions: vec![sess],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let buf = draw(&sb, 28, 6);
         let all = rows(&buf);
@@ -682,6 +809,7 @@ mod tests {
             sessions: vec![blocked, clear, unprobed],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let all = rows(&draw(&sb, 44, 10));
 
@@ -728,6 +856,7 @@ mod tests {
             sessions: vec![generated, settled],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let buf = draw(&sb, 44, 8);
         let palette = palette::active();
@@ -760,6 +889,7 @@ mod tests {
             sessions: vec![s],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let buf = draw(&sb, 44, 8);
         let palette = palette::active();
@@ -786,6 +916,7 @@ mod tests {
             sessions: vec![s],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let all = rows(&draw(&sb, 28, 8));
         assert_eq!(content(&all[0]), "sessions");
@@ -817,6 +948,7 @@ mod tests {
             sessions: vec![s],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let all = rows(&draw(&sb, 28, 8));
         let idx = all.iter().position(|l| l.contains("claude")).unwrap();
@@ -856,6 +988,7 @@ mod tests {
                 sessions: vec![s],
                 highlight: None,
                 attached: Default::default(),
+                pane_session: None,
             };
             let buf = draw(&sb, 28, 8);
             let found = (0..buf.area.height)
@@ -884,6 +1017,7 @@ mod tests {
                 sessions: vec![s],
                 highlight: Some(SidebarItem::Session(Uuid::from_u128(1))),
                 attached: Default::default(),
+                pane_session: None,
             };
             let buf = draw(&sb, 28, 8);
             let on_selection = |fg: Color| {
@@ -923,6 +1057,7 @@ mod tests {
             sessions: vec![s],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let all = rows(&draw(&sb, 28, 8));
         let idx = all.iter().position(|l| l.contains("claude")).unwrap();
@@ -942,6 +1077,7 @@ mod tests {
             sessions: vec![s],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let all = rows(&draw(&sb, 60, 6));
         let meta = content(&all[3]);
@@ -970,6 +1106,7 @@ mod tests {
             sessions: vec![s],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let all = rows(&draw(&sb, 28, 8));
         let idx = all.iter().position(|l| l.contains("claude")).unwrap();
@@ -999,6 +1136,7 @@ mod tests {
             sessions: vec![s],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let all = rows(&draw(&sb, 40, 8));
         let idx = all.iter().position(|l| l.contains("claude")).unwrap();
@@ -1026,6 +1164,7 @@ mod tests {
             sessions: vec![s],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let all = rows(&draw(&sb, 40, 8));
         let idx = all.iter().position(|l| l.contains("claude")).unwrap();
@@ -1054,6 +1193,7 @@ mod tests {
             sessions: vec![s],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let all = rows(&draw(&sb, 42, 8));
         let idx = all.iter().position(|l| l.contains("claude")).unwrap();
@@ -1087,6 +1227,7 @@ mod tests {
             sessions: vec![legacy],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let rendered = render_to_string(&draw(&sb, 40, 8));
         assert!(
@@ -1130,6 +1271,7 @@ mod tests {
             sessions: vec![s],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let rendered = render_to_string(&draw(&sb, 28, 6));
         assert!(
@@ -1145,6 +1287,7 @@ mod tests {
             sessions: vec![s],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let all = rows(&draw(&sb, 40, 6));
         assert!(
@@ -1166,6 +1309,7 @@ mod tests {
             sessions: vec![s],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let all = rows(&draw(&sb, 9, 6));
         assert!(
@@ -1192,6 +1336,7 @@ mod tests {
             sessions: vec![s],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let all = rows(&draw(&sb, 29, 6));
         assert!(all[3].contains("~1"), "{:?}", all[3]);
@@ -1216,6 +1361,7 @@ mod tests {
             sessions: vec![s],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let all = rows(&draw(&sb, 40, 6));
         assert!(all[3].contains("~1"), "{:?}", all[3]);
@@ -1237,6 +1383,7 @@ mod tests {
             sessions: vec![highlighted],
             highlight: Some(SidebarItem::Session(Uuid::from_u128(1))),
             attached: Default::default(),
+            pane_session: None,
         };
         let buf = draw(&sb, 28, 8);
         for y in 0..buf.area.height {
@@ -1262,6 +1409,7 @@ mod tests {
             sessions: vec![one, two],
             highlight: Some(SidebarItem::Session(Uuid::from_u128(1))),
             attached: Default::default(),
+            pane_session: None,
         };
         let buf = draw(&sb, 28, 8);
         let all = rows(&buf);
@@ -1297,6 +1445,7 @@ mod tests {
             sessions: vec![session_named(1, "claude")],
             highlight: Some(SidebarItem::Session(Uuid::from_u128(1))),
             attached: Default::default(),
+            pane_session: None,
         };
         let buf = draw_with_focus(&sb, 28, 8, false);
         let y = (0..buf.area.height)
@@ -1316,6 +1465,7 @@ mod tests {
                 sessions: vec![session_named(1, "claude")],
                 highlight: None,
                 attached: Default::default(),
+                pane_session: None,
             },
             28,
             8,
@@ -1336,6 +1486,7 @@ mod tests {
             sessions: vec![s],
             highlight: None,
             attached: Default::default(),
+            pane_session: None,
         };
         let buf = draw(&sb, 28, 8);
         let y = buf.content.iter().position(|c| c.symbol() == "c").unwrap() as u16 / buf.area.width;
@@ -1354,6 +1505,7 @@ mod tests {
             sessions: vec![session_named(1, "claude")],
             highlight: Some(SidebarItem::Session(Uuid::from_u128(1))),
             attached: Default::default(),
+            pane_session: None,
         };
         let all = rows(&draw(&sb, 28, 8));
         let line = content(row_containing(&all, "claude"));
@@ -1371,6 +1523,7 @@ mod tests {
             sessions: vec![one, two],
             highlight: Some(SidebarItem::Session(Uuid::from_u128(1))),
             attached: Default::default(),
+            pane_session: None,
         };
         let all = rows(&draw(&sb, 28, 8));
         let line = row_containing(&all, "bash");
@@ -1390,6 +1543,7 @@ mod tests {
             sessions: vec![s],
             highlight: Some(SidebarItem::Session(Uuid::from_u128(1))),
             attached: Default::default(),
+            pane_session: None,
         };
         let all = rows(&draw(&sb, 28, 8));
         let line = row_containing(&all, "an-unreasonably");

docs/PREVIEW.md

@@ -49,9 +49,9 @@ Web client (`--preview` and friends in `web/src/styles.css`):
 | The sidebar row being previewed | Filled with the preview hue, over whatever open/focused state the row already had. |
 | A hovered sidebar row, and the keyboard cursor on a session | A lighter wash of the same hue, because both are what previews a row. |
 
-Rows say it with fill, not with an edge: the only ring left in the session list
-is `.is-active`'s, which means "open in a pane". The dashed edges belong to the
-pane — the canvas ring and the throwaway tab.
+Rows say it with fill, not with an edge — see the tier ladder in
+`docs/SIDEBAR.md`, which previewing sits at the bottom of. The dashed edges
+belong to the pane: the canvas ring and the throwaway tab.
 
 The hue is a palette token, not a fixed colour: a palette whose accent already
 sits on it moves it (`--preview-h`), so "previewing" and "picked" never collide.

docs/SIDEBAR.md

@@ -177,6 +177,38 @@ surface; a colour chosen for the card background is never painted onto the
 selection background. Contrast is a property of the palette (values are RGB)
 and is asserted in the palette's tests, not left to the terminal theme.
 
+## Which row is filled
+
+Both clients say every one of these with a **background fill**, never an edge.
+A row is usually several of them at once, so they form a ladder: the tier
+furthest down wins the paint.
+
+| Tier | Web | TUI |
+|---|---|---|
+| Alive | 6% accent wash | — (the rail carries it) |
+| Under the pointer or the keyboard walk | preview hue, light | selection surface, while the sidebar holds the keyboard |
+| Open in some pane, not the focused one | 6% accent wash (`.is-open`) | — (the `●` glyph carries it) |
+| Showing in the pane | `--accent-fill` | `pane_row_bg()` — partway from the card surface to the selection surface |
+| Previewing (`docs/PREVIEW.md`) | `--preview-tint` | — (no preview colour role yet) |
+
+The web ladder is written as one ordered run of equal-specificity rules in
+`styles.css`, every qualifier inside `:where()`, so the order they appear in
+*is* the precedence. Add a tier where it belongs in that run, never by piling
+on another class to out-weigh the rule above it.
+
+The TUI's two filled tiers both carry the **selection** surface's foregrounds,
+since those are the colours picked for a filled row. `pane_row_bg()` is
+blended from the two surfaces rather than shipped as a third one — a third
+surface would mean eight more colours hand-picked seventeen times — and the
+palette tests assert it stays a visible step from both. The cursor's fill wins
+on its own row, so a highlight parked on the session already in the pane is
+still visible.
+
+The one edge left in either list is the TUI's `▏` marker, which stands in for
+the cursor's fill while the pane holds the keyboard, and the web's ring on a
+highlighted **folder** row — a folder previews nothing, so it has no fill to
+step up to.
+
 The duration text inherits its state's colour; the exited and command
 fragments use the surface's `muted` role, as do the diff stat's `~`, `?` and
 `↑` fragments. Only `+` and `-` step outside the surface's muted role, and they

web/src/styles.css

@@ -101,9 +101,11 @@
     oklch(0.99 0.005 var(--preview-h)),
     oklch(0.19 0.045 var(--preview-h))
   );
-  /* Opaque, not a wash: the previewed row reads as a fill, and a fill has to
-     land on the same colour whatever tier the row was already painted. */
+  /* Opaque, not a wash: session rows read as fills, and a fill has to land on
+     the same colour whatever tier the row was already painted. `--accent-fill`
+     is the same recipe on the accent, so the two tiers differ by hue alone. */
   --preview-tint: color-mix(in oklab, var(--preview) 30%, var(--surface-2));
+  --accent-fill: color-mix(in oklab, var(--accent) 30%, var(--surface-2));
   --preview-ring: light-dark(
     oklch(0.55 0.16 var(--preview-h) / 0.5),
     oklch(0.78 0.14 var(--preview-h) / 0.6)
@@ -1148,38 +1150,35 @@ textarea {
   transition: box-shadow var(--dur-fast) var(--ease-out);
 }
 
-/* "Alive" reads as a faint wash on the row itself — no per-row status icon. */
-.tree-leaf[data-status="running"] {
+/* Session-row tiers (docs/SIDEBAR.md). A row is usually several of these at
+   once, so every qualifier below sits in `:where()`: each rule is worth the
+   same specificity and the ladder is decided purely by the order they appear
+   in, latest wins. Add a tier where it belongs in that order, not by piling on
+   another class to out-weigh the rule above it. Each tier paints a background
+   and nothing else — the list says all of this with fill, never an edge. */
+
+/* 1. Alive. A faint wash on the row itself — no per-row status icon. */
+.tree-leaf:where([data-status="running"]) {
   background: color-mix(in oklab, var(--accent) 6%, transparent);
 }
 
-/* Hovering a row is what previews it (docs/PREVIEW.md), so hover reads in the
-   preview hue — never the accent, which belongs to the row actually open. */
-.tree-leaf:hover {
+/* 2. Under the pointer, or under the keyboard walk. Both are what previews a
+   row (docs/PREVIEW.md), so both read in the preview hue — never the accent,
+   which belongs to the row actually open. */
+.tree-leaf:where(:hover, .is-highlighted) {
   background: color-mix(in oklab, var(--preview) 12%, var(--surface-2));
 }
 
-.tree-leaf[data-status="running"]:hover {
+.tree-leaf:where([data-status="running"]):where(:hover, .is-highlighted) {
   background: color-mix(in oklab, var(--preview) 18%, var(--surface-2));
 }
 
-.tree-leaf:focus-visible {
+.tree-leaf:where(:focus-visible) {
   outline: none;
   background: color-mix(in oklab, var(--accent) 16%, var(--surface-2));
 }
 
-/* Where the keyboard walk (j/k) is standing. On a session row the cursor is
-   also what previews it, so it reads exactly like a hover — the preview hue,
-   deepening to the full fill once the preview lands. A folder row previews
-   nothing, so it keeps the plain cursor ring. */
-.tree-leaf.is-highlighted {
-  background: color-mix(in oklab, var(--preview) 12%, var(--surface-2));
-}
-
-.tree-leaf.is-highlighted[data-status="running"] {
-  background: color-mix(in oklab, var(--preview) 18%, var(--surface-2));
-}
-
+/* A folder row previews nothing, so its cursor stays a ring. */
 .tree-folder-header.is-highlighted {
   box-shadow: inset 0 0 0 2px var(--accent-ring);
 }
@@ -1188,25 +1187,24 @@ textarea {
   outline: none;
 }
 
-/* The session currently mounted in the content pane. */
-.tree-leaf.is-active,
-.tree-leaf.is-active[data-status="running"] {
-  background: var(--accent-tint);
-  box-shadow: inset 0 0 0 1px var(--accent-ring);
+/* 3. Open in some pane, but not the focused one (issue #33). */
+.tree-leaf:where(.is-open) {
+  background: color-mix(in oklab, var(--accent) 6%, transparent);
+}
+
+/* 4. The session currently mounted in the content pane. */
+.tree-leaf:where(.is-active) {
+  background: var(--accent-fill);
 }
 
 .tree-leaf.is-active .leaf-name {
   color: var(--ink);
 }
 
-/* The row the content pane is previewing right now — after `.is-active` so a
-   preview of an already-open session still reads as provisional. */
-.tree-leaf.is-previewing,
-.tree-leaf.is-previewing[data-status="running"],
-.tree-leaf.is-previewing.is-active,
-.tree-leaf.is-previewing.is-highlighted {
+/* 5. The row the content pane is previewing right now. Last, so previewing a
+   session that is already open still reads as provisional. */
+.tree-leaf:where(.is-previewing) {
   background: var(--preview-tint);
-  box-shadow: none;
 }
 
 /* Exited sessions recede: dimmed name + an "exited" badge carry status, so it's
@@ -3300,13 +3298,6 @@ input.leaf-rename:focus {
   border-radius: var(--r-1);
 }
 
-/* sidebar two-tier highlight (issue #33).
-   .is-active = focused pane (loud, from existing rule); .is-open = open
-   elsewhere (quiet). */
-.tree-leaf.is-open {
-  background: color-mix(in oklab, var(--accent) 6%, transparent);
-}
-
 /* =========================================================================
    multi-view mobile (#35): below 860px only the focused pane is shown — no tab
    bar, no pane switcher; the sidebar drawer (☰) is the navigation.