Merge remote-tracking branch 'origin/main' into dominant

CLAUDE.md

@@ -87,6 +87,11 @@ or is upgraded under them — the build stamp on `/api/info`, the status
 indicator's states, the blocking overlay, grace and poll timings. Read it
 before changing reconnect behaviour on either client.
 
+`docs/COMMAND-BAR.md` is the contract for the `ctrl-k` command bar in both
+clients — how it opens, the sigils, the key model, the match-and-rank algorithm
+the two matchers must agree on, and the fixture table they are tested against.
+Read it before changing either bar or either matcher.
+
 `nix run .#dev` (or `just dev`) brings up the whole local stack under
 process-compose: a debug daemon on 127.0.0.1:7071, then Vite on :5173 once the
 daemon answers `/api/info`. The SPA proxies `/api/*` back to the daemon, so only

crates/maestro-tui/src/app.rs

@@ -87,10 +87,13 @@ pub struct App {
     /// that can move `Focus::Pane` (attach, tab switch, sidebar toggle,
     /// mouse) is covered without each one remembering to report it.
     focused_session: Option<Uuid>,
-    /// A sidebar highlight waiting out its debounce before it becomes a
+    /// A sidebar highlight waiting for the pane's minimum gap before it
-    /// preview (`docs/PREVIEW.md`). Walking the list with `j` held down must
+    /// becomes a preview (`docs/PREVIEW.md`). Walking the list with `j` held
-    /// not open an attach per row it passes over.
+    /// down must not open an attach per row it passes over.
     pending_preview: Option<(Uuid, std::time::Instant)>,
+    /// When the pane last swapped what it previews. `None` until the first
+    /// one, which is why a highlight landing on a still sidebar shows at once.
+    last_preview_at: Option<std::time::Instant>,
     /// Sessions attached only because they were previewed, oldest first. Kept
     /// connected past the preview so stepping back onto a row is instant, and
     /// bounded so a long walk doesn't leave a socket per session behind.
@@ -125,10 +128,11 @@ struct FrameKey {
 /// else changed.
 const CLOCK_REFRESH: Duration = Duration::from_secs(1);
 
-/// How long a highlight has to stand still before the pane previews it
+/// Shortest gap between two pane swaps (`docs/PREVIEW.md`). The first
-/// (`docs/PREVIEW.md`). Long enough that a fast walk down the list doesn't
+/// highlight to land shows at once; this only bounds how often the pane may
-/// attach to every row it crosses, short enough to read as immediate.
+/// follow after that, so a fast walk down the list attaches to the row it
-const PREVIEW_DELAY: Duration = Duration::from_millis(120);
+/// started on and the row it stopped on rather than every row between.
+const PREVIEW_GAP: Duration = Duration::from_millis(120);
 
 /// How many preview-only attaches to keep connected behind the current one.
 const PREVIEW_BUDGET: usize = 3;
@@ -213,6 +217,7 @@ impl App {
             clicks: ClickTracker::default(),
             focused_session: None,
             pending_preview: None,
+            last_preview_at: None,
             preview_lru: Vec::new(),
             last_frame: None,
             last_drawn_at: std::time::Instant::now(),
@@ -526,9 +531,10 @@ impl App {
     }
 
     /// Recompute what the pane should be previewing. A session highlighted in
-    /// the sidebar is previewed after [`PREVIEW_DELAY`]; anything else — a
+    /// the sidebar is previewed as soon as [`PREVIEW_GAP`] has passed since the
-    /// group row, the pane holding the keyboard, or the highlight already
+    /// last swap — immediately, for a highlight landing on a still list.
-    /// sitting on the attached session — clears the preview at once.
+    /// Anything else — a group row, the pane holding the keyboard, or the
+    /// highlight already sitting on the attached session — clears at once.
     fn refresh_preview(&mut self) {
         let wanted = match (self.state.focus, &self.state.sidebar_highlight) {
             (Focus::Sidebar, Some(SidebarItem::Session(sid))) => Some(*sid),
@@ -537,7 +543,12 @@ impl App {
         match wanted {
             Some(sid) if self.state.active_session() != Some(sid) => {
                 if self.state.preview != Some(sid) {
-                    self.pending_preview = Some((sid, std::time::Instant::now() + PREVIEW_DELAY));
+                    let now = std::time::Instant::now();
+                    let due = match self.last_preview_at {
+                        Some(last) if now < last + PREVIEW_GAP => last + PREVIEW_GAP,
+                        _ => now,
+                    };
+                    self.pending_preview = Some((sid, due));
                 }
             }
             _ => {
@@ -547,8 +558,8 @@ impl App {
         }
     }
 
-    /// The debounce elapsed: show the highlighted session, attaching it if
+    /// The pane is free to follow: show the highlighted session, attaching it
-    /// nothing already is.
+    /// if nothing already is.
     fn poll_due_preview_at(&mut self, now: std::time::Instant) -> Vec<Effect> {
         let Some((sid, due)) = self.pending_preview else {
             return Vec::new();
@@ -560,6 +571,7 @@ impl App {
         if self.state.preview == Some(sid) {
             return Vec::new();
         }
+        self.last_preview_at = Some(now);
         self.state.preview = Some(sid);
         // Set outside the input path, so nothing else marks the frame stale.
         self.epoch = self.epoch.wrapping_add(1);
@@ -1671,24 +1683,22 @@ mod tests {
         }
     }
 
-    fn after_debounce() -> std::time::Instant {
+    fn after_gap() -> std::time::Instant {
-        std::time::Instant::now() + PREVIEW_DELAY + Duration::from_millis(1)
+        std::time::Instant::now() + PREVIEW_GAP + Duration::from_millis(1)
     }
 
     /// docs/PREVIEW.md: the highlight shows a session in the pane without the
     /// tab taking it on.
     #[test]
-    fn highlighting_a_session_previews_it_once_the_debounce_elapses() {
+    fn highlighting_a_session_previews_it_without_waiting() {
         let a = Uuid::from_u128(1);
         let mut app = app_with_sessions(&[a]);
         app.dispatch(Action::SidebarNext);
 
-        // Nothing yet: the highlight has to stand still first.
+        // The list was still, so the pane follows on the next poll — no gap to
-        assert_eq!(app.poll_due_preview_at(std::time::Instant::now()), vec![]);
+        // wait out first (docs/PREVIEW.md).
-        assert_eq!(app.state.preview, None);
-
         assert_eq!(
-            app.poll_due_preview_at(after_debounce()),
+            app.poll_due_preview_at(std::time::Instant::now()),
             vec![Effect::Attach(a)]
         );
         assert_eq!(app.state.preview, Some(a));
@@ -1697,6 +1707,28 @@ mod tests {
         assert_eq!(app.state.active_tab().session(), None);
     }
 
+    /// The gap only bounds the *second* swap, so a burst costs two mounts.
+    #[test]
+    fn a_second_move_inside_the_gap_waits_for_it() {
+        let a = Uuid::from_u128(1);
+        let b = Uuid::from_u128(2);
+        let mut app = app_with_sessions(&[a, b]);
+
+        app.dispatch(Action::SidebarNext);
+        let now = std::time::Instant::now();
+        assert_eq!(app.poll_due_preview_at(now), vec![Effect::Attach(a)]);
+
+        app.dispatch(Action::SidebarNext);
+        assert_eq!(app.poll_due_preview_at(now), vec![]);
+        assert_eq!(app.state.preview, Some(a));
+
+        assert_eq!(
+            app.poll_due_preview_at(after_gap()),
+            vec![Effect::Attach(b)]
+        );
+        assert_eq!(app.state.preview, Some(b));
+    }
+
     /// A fast walk down the list attaches to where it stopped, not to every
     /// row it crossed.
     #[test]
@@ -1707,7 +1739,7 @@ mod tests {
         app.dispatch(Action::SidebarNext);
         app.dispatch(Action::SidebarNext);
 
-        let effects = app.poll_due_preview_at(after_debounce());
+        let effects = app.poll_due_preview_at(after_gap());
         assert_eq!(effects, vec![Effect::Attach(b)]);
         assert_eq!(app.state.preview, Some(b));
     }
@@ -1723,7 +1755,7 @@ mod tests {
 
         app.state.sidebar_highlight = Some(SidebarItem::Session(b));
         app.refresh_preview();
-        app.poll_due_preview_at(after_debounce());
+        app.poll_due_preview_at(after_gap());
         assert_eq!(app.state.preview, Some(b));
 
         app.state.sidebar_highlight = Some(SidebarItem::Session(a));
@@ -1743,7 +1775,7 @@ mod tests {
         app.state.focus = Focus::Sidebar;
         app.state.sidebar_highlight = Some(SidebarItem::Session(b));
         app.refresh_preview();
-        app.poll_due_preview_at(after_debounce());
+        app.poll_due_preview_at(after_gap());
 
         app.dispatch(Action::FocusPane(crate::action::Direction::Right));
         assert_eq!(app.state.preview, None);
@@ -1756,7 +1788,7 @@ mod tests {
         let a = Uuid::from_u128(1);
         let mut app = app_with_sessions(&[a]);
         app.dispatch(Action::SidebarNext);
-        app.poll_due_preview_at(after_debounce());
+        app.poll_due_preview_at(after_gap());
         // Stand in for the attach the effect would have opened.
         app.emulators.insert(a, fake_handle());
 
@@ -1775,10 +1807,13 @@ mod tests {
             .map(Uuid::from_u128)
             .collect();
         let mut app = app_with_sessions(&ids);
+        // Each row is previewed in its own gap window, so all of them land.
+        let mut clock = std::time::Instant::now();
         for id in &ids {
             app.state.sidebar_highlight = Some(SidebarItem::Session(*id));
             app.refresh_preview();
-            app.poll_due_preview_at(after_debounce());
+            clock += PREVIEW_GAP + Duration::from_millis(1);
+            app.poll_due_preview_at(clock);
             app.emulators.insert(*id, fake_handle());
         }
 

docs/COMMAND-BAR.md

@@ -0,0 +1,479 @@
+# COMMAND-BAR.md — the command bar contract
+
+One rule for the `ctrl-k` command bar in both clients, so the web bar and the
+TUI bar open the same way, rank the same results in the same order, and act on
+the same keys. Read this before changing either. Both clients implement exactly
+what is written here; if the behaviour needs to change, change it here first.
+
+The bar is one surface with three jobs: **go to a session**, **run a command**,
+**spawn into a directory**. It is not a new place to configure anything and it
+does not own any action — it chooses one and hands off to the flow that already
+implements it.
+
+## Opening
+
+`ctrl-k` opens the bar from anywhere:
+
+| Client | From | Notes |
+| --- | --- | --- |
+| TUI | Normal mode | Sidebar has the keyboard. |
+| TUI | Insert mode | The pane has the keyboard; the bar still opens. |
+| Web | Sidebar focused | Ordinary global binding. |
+| Web | Terminal focused | Intercepted before xterm sees it. |
+
+It is a **keymap entry like any other**, not a hard-wired key. In the TUI it is
+bound in both `DEFAULT_NORMAL` and `DEFAULT_INSERT` and is rebindable through
+`[tui.keymap.*]`; because the help overlay builds its lines from the live
+keymap, it appears there without a second list to maintain. In the web it is an
+entry in the command registry, so the `?` overlay lists it for the same reason.
+
+An attached xterm swallows every keystroke it is given, so the web binding is
+handled in the **capture phase**, ahead of the terminal — the same way the
+restart overlay swallows the app's shortcuts (`docs/RESTART.md`).
+
+### Escape hatch — sending a literal Ctrl-K
+
+Binding `ctrl-k` takes readline's kill-to-end-of-line away from every pane. The
+leader gives it back: **leader then `ctrl-k`** — `ctrl-a ctrl-k` by default —
+sends the literal `0x0B` byte to the focused pane and does not open the bar.
+
+The TUI already has a leader (`ctrl-a`, `[tui].leader`), and this chord goes
+through the existing chord resolution, so rebinding the leader rebinds the
+escape hatch with it — exactly as the leader's Insert-mode escape already
+works. **The web gains a leader for this**, defaulting to `ctrl-a` and
+mirroring the TUI's. `ctrl-a` is select-all in a browser; the web
+`preventDefault`s it, since selecting all of a terminal pane does nothing
+useful.
+
+Only Ctrl-K gets an escape hatch. No other control character is intercepted, so
+none of them needs one.
+
+### Focus round-trip
+
+Closing the bar returns the keyboard to whatever held it when the bar opened,
+the terminal included. A round trip through the bar never silently moves focus,
+and never counts as a focus change for the daemon: opening the bar does not
+report the pane unfocused, and closing it does not report a new focus. The bar
+is a view over the app, not a place in it.
+
+Opening the bar while a session is previewed (`docs/PREVIEW.md`) discards the
+preview first, like any other real change; the bar is not previewed into.
+
+## Structure
+
+The bar is a query line over a result list. By default the list is **flat and
+mixed** — sessions and commands ranked together — and rendered under **kind
+headers**: a header row naming the kind, then that kind's results.
+
+Grouping is a rendering of the ranking, never a reordering of it:
+
+- Results are ranked as one list by the algorithm below.
+- A kind's group holds its matches in that rank order.
+- **Groups are ordered by their best-scoring member.** The first row under the
+  first header is therefore the globally best result, and the highlight starts
+  on it.
+
+Two sigils, typed as the **first character** of the query, narrow the list to
+one kind:
+
+| Sigil | Kind | Candidates | Enter |
+| --- | --- | --- | --- |
+| `>` | commands | Every entry in the client's command registry — the web registry from the `?` overlay, the TUI's live `(chord, Action)` keymap for the current mode. | Runs the command. |
+| `~` | directories | Recent dirs (`GET /api/recent-dirs`) and the project list the spawn form already uses, with `GET /api/dirs` filling in as a path is typed. | Spawns a session there with every default resolved. |
+
+While a sigil is in force there is one kind, so the kind header is dropped. A
+command row shows its **key chord** beside its label, so the bar teaches the
+keymap instead of replacing it. A `~` spawn takes the same fast-forward path as
+`N` / `FastForwardSpawn`: an unresolvable default opens the pre-filled spawn
+form rather than failing silently.
+
+**Backspacing past a sigil returns to the mixed list.** The sigil is one
+character of the query like any other — deleting it is not a special key, it is
+the query becoming empty again.
+
+The sigil is only a sigil in first position. `>` or `~` typed anywhere else is
+a literal query character (a directory query is where a `~` is most likely to
+be typed twice, and the second one must reach the matcher).
+
+## Empty query
+
+With no sigil and an empty query the bar lists **sessions only, most recently
+focused first**, so `ctrl-k enter` is "back to where I just was". Commands and
+directories need a sigil or a query to appear; an empty bar is a session
+switcher.
+
+**Recency comes from the daemon**, not from client state — the same order in
+every client, on every device, including one that just loaded the page. The
+daemon stamps a last-focused time per session and ships it on the session like
+any other field (#145). Both of the ways focus moves stamp the same field: a
+client opening `/api/attach/:id`, and a client reporting focus explicitly at
+`POST /api/sessions/:id/focus` when it refocuses a pane that is already open.
+
+**A session that has never been focused sorts after every session that has**,
+and among those, most recently created first. Dead sessions sort after live
+ones regardless of recency: a session you cannot attach to is not where you
+just were.
+
+Under `>` an empty query lists every command in registry order. Under `~` it
+lists recent dirs, most recent first, then the project list.
+
+## Keys
+
+| Key | Action |
+| --- | --- |
+| `enter` | Open the highlighted result — attach the session, run the command, spawn into the directory. |
+| `tab` | Drill into the highlighted **session**'s action page. No effect on any other kind. |
+| `esc` | At the top level, close the bar. On an action page, return to the result list. |
+| `backspace` | Ordinary editing; at an empty query on an action page, return to the result list. |
+| `up` / `down` | Move the highlight. |
+| `ctrl-p` / `ctrl-n` | Move the highlight. |
+
+The highlight does not wrap: it stops at the first and last row. Kind headers
+are never landed on — they are labels, not rows.
+
+Enter on a session goes through the **same open path** the sidebar's click and
+the hash router already share, so a bar attach can never leave the layout in a
+state a click could not produce.
+
+### Drill-in — the session action page
+
+`tab` on a highlighted session opens that session's action page inside the same
+overlay: **kill**, **rename**, **spawn similar**. The page is still fuzzy
+searchable — the query line keeps working, now over those actions.
+
+- The overlay names the session being acted on, so the target is never
+  ambiguous.
+- Escape, or backspace at an empty query, returns to the result list **with the
+  previous query intact**. Drilling in and backing out is free.
+- Each action raises the flow it already has: kill goes through the existing
+  confirm-and-blockers dialog (`docs/WORKTREES.md`), rename through the
+  existing prompt pre-filled with the session's own name
+  (`docs/SIDEBAR.md`), spawn similar through the spawn form seeded from the
+  session's directory and command. The bar picks the action; it never
+  reimplements one.
+
+No actions beyond those three, and no action across more than one session.
+
+## Touch entry
+
+On the web, **tapping or focusing the sidebar's search field opens the bar**
+with an empty query. There is no `ctrl-k` on a phone and the product is
+mobile-first, so the field the operator already reaches for is the entry point.
+
+This **replaces** the sidebar's inline substring filter — one search affordance
+in the header, not two beside each other. The tree's "No matches" empty state
+belonged to that filter and goes with it; the bar's own no-results state takes
+over (see the fixture `F4`).
+
+At phone width the bar follows the bottom-sheet treatment the spawn modal
+already uses below 600px. Visuals otherwise come from `DESIGN.md`'s existing
+overlay tokens — the bar is the same family of surface as the spawn modal and
+the help overlay, not a new one.
+
+## What a candidate is
+
+The matcher is a pure function: `(query, candidates) → ranked subset with
+matched ranges`. It knows nothing about sessions, panes or the network. A
+candidate is a **kind** plus a set of **named text fields**, each with a fixed
+weight.
+
+| Kind | Field | Weight | Text |
+| --- | --- | --- | --- |
+| session | `name` | `0` | The name as the sidebar shows it: `metadata.name` if set, else the command line (`docs/SIDEBAR.md`'s fallback). |
+| session | `directory` | `-24` | The directory the sidebar groups it under, abbreviated: `~/dev/api`, not `/home/me/dev/api`. |
+| session | `command` | `-32` | The full command line, arguments included. |
+| session | `tool` | `-40` | The tool id the card's icon stands for (`claude`, `codex`, `opencode`, …), absent when the program is not one we have a mark for. |
+| command | `label` | `0` | The plain-language label — the web registry's label, the TUI's `Action::help_label`. |
+| directory | `path` | `0` | The path as displayed, abbreviated the same way. |
+
+A command's **key chord is displayed, not matched**. It is there to teach the
+keymap; matching it would make `>` results depend on a user's rebinds, and the
+two clients do not share a keymap.
+
+A candidate **matches** if at least one of its fields matches. Its score is the
+**best** `field score + field weight` across its fields, and the matched ranges
+it returns are those of that winning field — so a session found through its
+directory highlights inside the directory, not inside its name.
+
+## Match and rank
+
+Two independent implementations (#146 in TypeScript, #147 in Rust) must produce
+the same order for the same input. Everything below is exact.
+
+### Normalization
+
+- **Query**: lowercase, then remove every whitespace character. The result is
+  the *normalized query*. If it is empty, see "Empty query" below.
+- **Field text**: matched against its lowercased form. Bonuses are computed
+  against the **original** text, because case is a signal (`camelCase`) that
+  lowercasing destroys.
+- **Compact form** of a string: lowercase with whitespace removed. Used only
+  for the exact and prefix tests.
+
+Lowercasing is per-character simple lowercase (`char::to_lowercase` /
+`String.prototype.toLowerCase`). Positions are **character** positions —
+Unicode scalar values in Rust, UTF-16 code units in TypeScript, which agree for
+every character these fields realistically hold; ranges are returned in the
+host language's own unit, since they exist to slice that language's string.
+
+### What a match is
+
+Case-insensitive **subsequence**: every character of the normalized query
+appears in the lowercased field text, in order, not necessarily adjacent. A
+field with no such embedding does not match.
+
+### Word boundaries
+
+A matched character at position `p` earns exactly one character bonus, taking
+the first rule that applies:
+
+| Rule | Bonus |
+| --- | --- |
+| `p == 0` — first character of the field | `+18` |
+| The character before it is a **separator**: `/` `\` `-` `_` `.` `:` or a space | `+16` |
+| It is uppercase and the character before it is lowercase (a camelCase hump) | `+12` |
+| It is a digit and the character before it is not | `+12` |
+| Otherwise | `0` |
+
+That is one rule for both shapes the doc has to cover. In a **path**, `/` is a
+separator, so the first character of every segment is a word start: `foo` in
+`~/dev/foobar` starts a segment and outscores `foo` in `~/src/myfoo`, which
+starts nothing. In a **session name**, `-`, `_`, `.` and spaces do the same
+work, so `ws` reaches `web-search` more cheaply than `websearch`.
+
+### Score
+
+Let the query characters be matched at positions `p₀ < p₁ < … < pₘ₋₁`, and let
+`p₋₁ = -1`. For each matched character `i`, with `gap = pᵢ - pᵢ₋₁ - 1`:
+
+```
+contribution(i) = 16                      // every matched character
+                + bonus(pᵢ)               // the table above
+                + (gap == 0 ? +8          // adjacent to the previous match
+                            : -min(gap, 12))
+```
+
+`gap` for `i = 0` is the number of characters skipped before the first match, so
+a match that starts late is penalised exactly like an internal gap, and the cap
+is the same one.
+
+The **field score** is the sum of the contributions, plus at most one whole-field
+adjustment:
+
+- compact field text **equals** the normalized query → `+64`
+- else compact field text **starts with** the normalized query → `+32`
+
+Length is deliberately not in the score — it is a tie-break, so a long field
+never loses to a short one that matched worse.
+
+### Which embedding
+
+A query can sit in a field many ways. The one that counts is the
+**highest-scoring** embedding; among embeddings that score the same, the
+**leftmost** — compare position vectors element by element, smaller wins.
+
+Greedy leftmost-first matching is not sufficient and must not be used: in
+`maestro-tui`, `mtu` greedily takes `m₀ a₁ …` and never reaches `tui`. Both
+implementations use the obvious dynamic program over
+`(query index, text position)`, carrying the best score and its position
+vector, since the gap term depends only on the previous matched position.
+
+The whole-field adjustment is constant for a `(query, field)` pair, so adding it
+after the dynamic program cannot change which embedding wins.
+
+### Ordering
+
+Sort by score, highest first. Equal scores break in this order:
+
+1. **Kind** — `session`, then `command`, then `directory`.
+2. **Length of the matched field text**, shorter first.
+3. **The matched field text**, ascending, compared by code point, case
+   sensitive.
+4. **Input order.** The sort is stable, so candidates the caller ordered
+   deliberately — sessions most recently focused first, commands in registry
+   order — keep that order when nothing else separates them.
+
+Kind leads because that is the ruling the ambiguous cases need: a session named
+`kill` and the `kill` command that score alike put the session first, because
+the operator who typed a session's name meant the session.
+
+### Empty query
+
+A normalized query that is empty **matches every candidate**, each with score
+`0` and no ranges, in input order. The bar's own rules decide what is in the
+candidate list at that point (sessions only at the top level); the matcher does
+not filter by kind.
+
+## Fixtures
+
+These are the contract. Both matchers are tested against exactly these cases;
+the prose above is the explanation of why they come out this way.
+
+Candidates are written as `kind(fields)`; unlisted fields are absent.
+`session(name, dir, command, tool)`. Scores are shown for diagnosis — **the
+order is what is being asserted**, and an implementation that ranks correctly
+with different absolute numbers has still failed, because the numbers are how
+the next fixture stays predictable.
+
+### F1 — empty query keeps input order
+
+```
+query:      ""
+candidates: session("kill", "~/dev/api", "bash")
+            session("killer-app", "~/dev/killer-app", "claude --resume", "claude")
+            command("Kill selected session")
+expected:   session("kill")           score 0
+            session("killer-app")     score 0
+            command("Kill selected session")  score 0
+```
+
+Every candidate matches, in the order given. No ranges.
+
+### F2 — a session named `kill` against the `kill` command
+
+```
+query:      "kill"
+candidates: (as F1)
+expected:   session("kill")                   178   name
+            session("killer-app")             146   name
+            command("Kill selected session")  146   label
+```
+
+`kill` wins on the exact bonus. The other two **tie at 146** — both are a
+contiguous prefix match — and the kind tie-break puts the session first.
+
+### F3 — a fragment matching mid-segment inside a path
+
+```
+query:      "foo"
+candidates: directory("~/dev/foobar")
+            directory("~/src/myfoo")
+            directory("~/foo")
+expected:   directory("~/foo")         78   ranges [2,3,4]
+            directory("~/dev/foobar")  74   ranges [6,7,8]
+            directory("~/src/myfoo")   56   ranges [8,9,10]
+```
+
+The first two start a path segment; the third is mid-segment and loses by the
+whole boundary bonus. `~/foo` beats `~/dev/foobar` only because less was
+skipped before the match.
+
+### F4 — a query matching nothing
+
+```
+query:      "zzz"
+candidates: session("kill", "~/dev/api", "bash")
+            command("Kill selected session")
+expected:   (empty)
+```
+
+The matcher returns an empty list, never a list of zero-scored candidates. The
+bar renders its no-results state.
+
+### F5 — a non-contiguous subsequence
+
+```
+query:      "mtu"
+candidates: session("maestro-tui")
+            session("maestro-daemon")
+            session("mtui-scratch")
+expected:   session("mtui-scratch")  122   ranges [0,1,2]
+            session("maestro-tui")    91   ranges [0,8,9]
+```
+
+`maestro-daemon` has no `u` after its `t` and does not match. `maestro-tui`
+does, across a gap — which greedy matching would miss entirely.
+
+### F6 — a name beats a directory
+
+```
+query:      "api"
+candidates: session("api", "~/dev/web", "bash")
+            session("worker", "~/dev/api", "bash")
+expected:   session("api")     154   name
+            session("worker")   50   directory
+```
+
+The second session is found through its directory, and highlights there.
+
+### F7 — case-insensitive, tie broken by length
+
+```
+query:      "api"
+candidates: session("API-Gateway")
+            session("apiary")
+expected:   session("apiary")       122   name
+            session("API-Gateway")  122   name
+```
+
+Both are prefix matches and score identically. Same kind, so length decides:
+6 characters before 11. Input order does not save `API-Gateway`.
+
+### F8 — the tool field
+
+```
+query:      "claude"
+candidates: session("nameless", "~/dev/x", "claude --resume", "claude")
+            session("clay", "~/dev/y", "bash")
+expected:   session("nameless")  186   tool
+```
+
+`clay` has no `claude` subsequence anywhere and drops out. `nameless` matches
+its `tool` exactly (`+64`, weight `-40`, giving 186) which beats the prefix
+match on its `command` field (`+32`, weight `-32`, giving 162).
+
+### F9 — a word boundary inside a session name
+
+```
+query:      "ws"
+candidates: session("websearch")
+            session("web-search")
+expected:   session("web-search")  71   ranges [0,4]
+            session("websearch")   56   ranges [0,3]
+```
+
+The `s` after `-` earns the boundary bonus; the `s` inside `websearch` earns
+nothing.
+
+### F10 — command labels
+
+```
+query:      "se"
+candidates: command("Kill selected session")
+            command("Create a session")
+            command("Show help")
+expected:   command("Show help")             53   ranges [0,6]
+            command("Kill selected session") 51   ranges [5,6]
+            command("Create a session")      47   ranges [9,10]
+```
+
+`Show help` starts at position 0; the other two start at a word boundary but
+later, and pay for the skipped characters.
+
+### F11 — a query against session directories
+
+```
+query:      "dev"
+candidates: session("api", "~/dev/api", "bash")
+            session("notes", "~/documents/dev-notes", "nvim")
+            session("scratch", "~/srv/devops", "bash")
+expected:   session("api")      54   directory, ranges [2,3,4]
+            session("scratch")  50   directory, ranges [6,7,8]
+            session("notes")    44   directory, ranges [12,13,14]
+```
+
+All three start a path segment. They separate purely on how much was skipped
+first, and `notes` hits the `-12` gap cap.
+
+### F12 — exact beats prefix
+
+```
+query:      "quit"
+candidates: command("Quit Maestro")
+            command("Quit")
+expected:   command("Quit")           178   label
+            command("Quit Maestro")   146   label
+```
+
+The 32-point difference between the exact and prefix adjustments is the whole
+gap; nothing else about the two matches differs.

docs/PREVIEW.md

@@ -77,15 +77,19 @@ Nothing moves a second time on commit.
 
 ## Timing
 
-A preview follows the highlight closely enough to be usable as a way to look
+**A preview is never delayed.** Landing on a row — by pointer or by `j`/`k` —
-around, and lags a pointer enough not to flash rows crossed on the way
+shows it on the next frame, and so does leaving every row. There is no
-somewhere else.
+settling period in front of the first preview, because that period would sit
+in front of the one preview the operator actually meant.
 
-| Trigger | Delay |
+What is bounded is how *often* the pane may swap: at most once per 120 ms.
-|---|---|
+A burst inside one window — `j` held down, or the pointer sweeping the length
-| Keyboard step (`j`/`k`, arrows) | 60 ms |
+of the sidebar — shows the row it started on, then the row it ended on, and
-| Pointer hover (web, mouse only — never touch) | 150 ms |
+none of the rows in between. So a walk costs a couple of pane mounts rather
-| Clearing (highlight left every session) | same delay as the trigger that set it |
+than one per row, without the operator ever waiting on one.
+
+The highlight itself is not bounded by any of this: the row lights up on the
+same frame as the input, whatever the pane behind it is doing.
 
 Touch has no hover, and a tap already opens a session, so touch never previews.
 

web/src/catalog.ts

@@ -164,6 +164,10 @@ function renderNode(node: TreeNode, depth: number): HTMLElement {
     return wrap;
   }
 
+  // The row outlives the snapshot it was built from: a refresh that changes
+  // nothing structural patches it in place rather than replacing it, so the
+  // handlers below have to read the current session, not the one captured here.
+  let cur = node.session;
   const s = node.session;
   const now = Date.now();
   const row = document.createElement("a");
@@ -197,33 +201,74 @@ function renderNode(node: TreeNode, depth: number): HTMLElement {
   similarBtn.addEventListener("click", (ev) => {
     ev.preventDefault();
     ev.stopPropagation();
-    document.dispatchEvent(new CustomEvent(SPAWN_SIMILAR_EVENT, { detail: s }));
+    document.dispatchEvent(new CustomEvent(SPAWN_SIMILAR_EVENT, { detail: cur }));
   });
   const killBtn = row.querySelector(".leaf-kill") as HTMLButtonElement;
   killBtn.addEventListener("click", (ev) => {
     ev.preventDefault();
     ev.stopPropagation();
-    void requestKill(s, name);
+    void requestKill(cur, sessionName(cur));
   });
   row.addEventListener("click", () => {
-    document.dispatchEvent(new CustomEvent(SESSION_SELECT_EVENT, { detail: s.id }));
+    document.dispatchEvent(new CustomEvent(SESSION_SELECT_EVENT, { detail: cur.id }));
   });
   row.addEventListener("contextmenu", (ev) => {
     ev.preventDefault();
     ev.stopPropagation();
     openContextMenu(ev.clientX, ev.clientY, [
-      { label: "Rename…", onSelect: () => beginRename(row, s) },
+      { label: "Rename…", onSelect: () => beginRename(row, cur) },
       {
         label: "Spawn similar",
         onSelect: () =>
-          document.dispatchEvent(new CustomEvent(SPAWN_SIMILAR_EVENT, { detail: s })),
+          document.dispatchEvent(new CustomEvent(SPAWN_SIMILAR_EVENT, { detail: cur })),
+      },
+      {
+        label: "Kill session",
+        danger: true,
+        onSelect: () => void requestKill(cur, sessionName(cur)),
       },
-      { label: "Kill session", danger: true, onSelect: () => void requestKill(s, name) },
     ]);
   });
+  leafPatches.set(row, (next) => {
+    cur = next;
+    const nextSlug = activityColorSlug(next.activity ?? "Idle");
+    const nextWord = STATE_WORDS[nextSlug] ?? STATE_WORDS.idle;
+    row.setAttribute(
+      "aria-label",
+      `${sessionName(next)}, ${next.status === "Running" ? "running" : "exited"}, ${nextWord}`,
+    );
+    const rail = row.querySelector(".activity-rail");
+    if (rail) rail.outerHTML = activityRailMarkup(nextSlug, nextWord);
+    const meta = row.querySelector(".card-line2");
+    if (meta) meta.outerHTML = metaLine(next, Date.now());
+  });
   return row;
 }
 
+/** Refresh a standing card from a newer snapshot of its session, keeping the
+ *  element (and so the pointer's `:hover`) exactly where it is. Registered by
+ *  `renderNode`; only the bits `treeSignature` leaves out are rewritten. */
+const leafPatches = new WeakMap<HTMLElement, (s: Session) => void>();
+
+/**
+ * Everything about the tree that a patch cannot fix up.
+ *
+ * The daemon re-sends a session on every activity, foreground or cwd shift —
+ * a couple of times a minute per live session — and rebuilding the sidebar for
+ * each one drops `:hover` from the row under the pointer. Refreshes whose
+ * signature is unchanged are patched into the standing rows instead; anything
+ * that moves, renames, appears or dies changes the signature and rebuilds.
+ */
+function treeSignature(node: TreeNode): string {
+  if (node.kind === "folder") {
+    const head = `F:${node.name}:${node.path}:${collapsed.has(node.path)}`;
+    if (node.name && collapsed.has(node.path)) return head;
+    return `${head}(${node.children.map(treeSignature).join(",")})`;
+  }
+  const s = node.session;
+  return `L:${s.id}:${sessionName(s)}:${s.status}:${isProvisionalName(s)}`;
+}
+
 /**
  * Kill on the first click (#81): the daemon is the one that decides whether a
  * session may go, and it refuses over a worktree holding unsaved work. Only
@@ -371,7 +416,7 @@ export interface SidebarOptions {
    *  shell shows it in the content pane without opening it (docs/PREVIEW.md).
    *  `source` is there so a mouse sweep can be debounced differently from a
    *  keyboard step. */
-  onPreview?: (sessionId: string | null, source: "key" | "hover") => void;
+  onPreview?: (sessionId: string | null) => void;
 }
 
 export function renderSidebar(store: CatalogStore, opts: SidebarOptions = {}): SidebarHandle {
@@ -555,7 +600,7 @@ export function renderSidebar(store: CatalogStore, opts: SidebarOptions = {}): S
     navKey = next.dataset.navKey ?? null;
     applyNav();
     next.scrollIntoView({ block: "nearest" });
-    opts.onPreview?.(sessionOf(navKey), "key");
+    opts.onPreview?.(sessionOf(navKey));
   };
 
   /** Enter: open the highlighted session, or expand the highlighted folder. */
@@ -586,7 +631,7 @@ export function renderSidebar(store: CatalogStore, opts: SidebarOptions = {}): S
   const setHovered = (id: string | null) => {
     if (hovered === id) return;
     hovered = id;
-    opts.onPreview?.(id, "hover");
+    opts.onPreview?.(id);
   };
   treeHost.addEventListener("pointerover", (e) => {
     if (e.pointerType === "touch") return;
@@ -603,7 +648,7 @@ export function renderSidebar(store: CatalogStore, opts: SidebarOptions = {}): S
   treeHost.tabIndex = -1;
   // The keyboard walk's preview belongs to the list having the keyboard: once
   // it doesn't, the content pane goes back to what the operator actually opened.
-  treeHost.addEventListener("blur", () => opts.onPreview?.(null, "key"));
+  treeHost.addEventListener("blur", () => opts.onPreview?.(null));
 
   /** The session behind the highlighted row, if the highlight is on a card. */
   const highlightedSession = (): { row: HTMLElement; session: Session } | undefined => {
@@ -643,12 +688,24 @@ export function renderSidebar(store: CatalogStore, opts: SidebarOptions = {}): S
     e.preventDefault();
   });
 
+  /** Signature of what is currently on screen — see `treeSignature`. */
+  let renderedSignature: string | null = null;
+
   const refresh = () => {
     // Rebuilding the tree now would blow away the field being typed into.
     if (renamingId !== null) return;
     const state = store.snapshot();
     const sessions = [...state.sessions.values()];
     const tree = buildTree(sessions, homeDir, filter);
+    const signature = sessions.length === 0 ? `EMPTY:${filter.trim()}` : treeSignature(tree);
+    if (signature === renderedSignature) {
+      for (const row of treeHost.querySelectorAll<HTMLElement>(".tree-leaf")) {
+        const s = row.dataset.sessionId ? state.sessions.get(row.dataset.sessionId) : undefined;
+        if (s) leafPatches.get(row)?.(s);
+      }
+      return;
+    }
+    renderedSignature = signature;
     treeHost.replaceChildren();
     if (sessions.length === 0) {
       treeHost.appendChild(
@@ -672,7 +729,13 @@ export function renderSidebar(store: CatalogStore, opts: SidebarOptions = {}): S
       /* absolute paths are a fine fallback */
     });
 
-  const rerenderHandler = () => refresh();
+  // Dispatched when something outside the store changed what the tree should
+  // look like — a folder collapsed, a rename ended — none of which the store
+  // snapshot can show, so the signature check has to be bypassed.
+  const rerenderHandler = () => {
+    renderedSignature = null;
+    refresh();
+  };
   document.addEventListener("catalog-rerender", rerenderHandler);
 
   // "Spawn similar" (#28) is dispatched here and handled in main.ts, where the

web/src/catalogPatch.test.ts

@@ -0,0 +1,105 @@
+// @vitest-environment happy-dom
+import { beforeAll, describe, expect, it } from "vitest";
+
+import { renderSidebar } from "./catalog.js";
+import type { CatalogListener, CatalogStore } from "./events.js";
+import type { Session } from "./types.js";
+
+beforeAll(() => {
+  Object.defineProperty(window, "localStorage", {
+    value: { getItem: () => null, setItem: () => {} },
+  });
+  window.fetch = () => Promise.reject(new Error("offline"));
+});
+
+const ID = "11111111-2222-3333-4444-555555555555";
+
+function session(overrides: Partial<Session> = {}): Session {
+  return {
+    id: ID,
+    cwd: "/home/naps/tea/maestro",
+    command: "claude",
+    env: {},
+    metadata: {},
+    status: "Running",
+    created_at: "2026-08-24T10:00:00Z",
+    ...overrides,
+  };
+}
+
+/** A store whose updates actually reach subscribers, unlike the one-shot
+ *  harness in catalog.test.ts. */
+function liveStore(initial: Session[]) {
+  const state = { sessions: new Map(initial.map((s) => [s.id, s])) };
+  const listeners = new Set<CatalogListener>();
+  const store = {
+    snapshot: () => state,
+    subscribe: (fn: CatalogListener) => {
+      listeners.add(fn);
+      fn(state);
+      return () => listeners.delete(fn);
+    },
+  } as unknown as CatalogStore;
+  const push = (sessions: Session[]) => {
+    state.sessions = new Map(sessions.map((s) => [s.id, s]));
+    for (const fn of listeners) fn(state);
+  };
+  return { store, push };
+}
+
+const rowOf = (el: HTMLElement) => el.querySelector<HTMLElement>(".tree-leaf")!;
+
+describe("sidebar refresh keeps rows in place (docs/SIDEBAR.md)", () => {
+  it("patches an activity change into the standing row instead of rebuilding it", () => {
+    const { store, push } = liveStore([session({ activity: "Idle" })]);
+    const { el } = renderSidebar(store, {});
+    const before = rowOf(el);
+
+    push([session({ activity: "AwaitingInput" })]);
+
+    // Same element: a rebuild under the pointer would drop `:hover` and restart
+    // the row's transitions, which is the flicker this avoids.
+    expect(rowOf(el)).toBe(before);
+    // …and the card still tells the truth about the session.
+    expect(before.querySelector(".activity-rail")?.getAttribute("data-activity")).toBe(
+      "awaiting-input",
+    );
+    expect(before.querySelector(".card-line2")?.getAttribute("data-activity")).toBe(
+      "awaiting-input",
+    );
+    expect(before.getAttribute("aria-label")).toContain("Awaiting input");
+  });
+
+  it("rebuilds when the row set changes", () => {
+    const { store, push } = liveStore([session()]);
+    const { el } = renderSidebar(store, {});
+    const before = rowOf(el);
+
+    push([session(), session({ id: "99999999-2222-3333-4444-555555555555", command: "bash" })]);
+
+    expect(el.querySelectorAll(".tree-leaf")).toHaveLength(2);
+    expect(rowOf(el)).not.toBe(before);
+  });
+
+  it("rebuilds when a session dies", () => {
+    const { store, push } = liveStore([session()]);
+    const { el } = renderSidebar(store, {});
+    const before = rowOf(el);
+
+    push([session({ status: "Dead" })]);
+
+    expect(rowOf(el)).not.toBe(before);
+    expect(rowOf(el).dataset.status).toBe("dead");
+  });
+
+  it("rebuilds when a session is renamed", () => {
+    const { store, push } = liveStore([session()]);
+    const { el } = renderSidebar(store, {});
+    const before = rowOf(el);
+
+    push([session({ metadata: { name: "harmony" } })]);
+
+    expect(rowOf(el)).not.toBe(before);
+    expect(rowOf(el).querySelector(".leaf-name")?.textContent).toBe("harmony");
+  });
+});

web/src/main.ts

@@ -29,6 +29,7 @@ import { mountHud, type Hud } from "./hud.js";
 import { emptyLayout, type Layout, openSessions } from "./layout.js";
 import { createMultiView, type MultiView } from "./multiview.js";
 import { loadLayout, saveLayout } from "./persistence.js";
+import { createPreviewSchedule } from "./previewSchedule.js";
 import {
   FOCUS_PANE_EVENT,
   FOCUS_SIDEBAR_EVENT,
@@ -105,20 +106,14 @@ shellEl.dataset.route = "catalog";
 // point `mv` is assigned.
 let mv: MultiView;
 
-// Preview timing (docs/PREVIEW.md): a keyboard step shows almost at once; a
+// Preview timing (docs/PREVIEW.md): the first move shows at once, and a burst
-// mouse sweep waits long enough that rows crossed on the way somewhere else
+// — j held down, or the pointer sweeping the whole list — is coalesced so it
-// never flash up. The same delay applies to clearing, so the gap between two
+// costs a couple of pane mounts instead of one per row walked.
-// rows doesn't blink the previous view back.
+const schedulePreview = createPreviewSchedule((sessionId) => {
-const PREVIEW_DELAY = { key: 60, hover: 150 } as const;
+  ensureMultiView();
-let previewTimer: number | undefined;
+  mv?.previewSession(sessionId);
-function schedulePreview(sessionId: string | null, source: "key" | "hover"): void {
+  updateShellRoute();
-  clearTimeout(previewTimer);
+});
-  previewTimer = window.setTimeout(() => {
-    ensureMultiView();
-    mv?.previewSession(sessionId);
-    updateShellRoute();
-  }, PREVIEW_DELAY[source]);
-}
 
 const sidebar = renderSidebar(store, {
   onLeafDrag: (id, e) => mv?.beginSessionDrag(id, e),
@@ -418,7 +413,7 @@ document.addEventListener(FOCUS_SIDEBAR_EVENT, () => {
  *  on `hashchange` alone — a split or drag can move focus without the hash
  *  changing, leaving a click back onto that session's row silently ignored. */
 function focusSession(sessionId: string): void {
-  clearTimeout(previewTimer);
+  schedulePreview.cancel();
   showMultiView();
   mv.openSession(sessionId);
   updateShellRoute();

web/src/previewSchedule.test.ts

@@ -0,0 +1,92 @@
+import { describe, expect, it } from "vitest";
+
+import { createPreviewSchedule, PREVIEW_MIN_GAP_MS } from "./previewSchedule.js";
+
+/** Hand-driven clock + timer queue, so the schedule is asserted without waiting. */
+function harness() {
+  let now = 1_000;
+  const timers = new Map<number, { at: number; fn: () => void }>();
+  let nextHandle = 1;
+  const emitted: (string | null)[] = [];
+
+  const schedule = createPreviewSchedule((id) => emitted.push(id), {
+    now: () => now,
+    setTimer: (fn, ms) => {
+      const h = nextHandle++;
+      timers.set(h, { at: now + ms, fn });
+      return h;
+    },
+    clearTimer: (h) => {
+      timers.delete(h);
+    },
+  });
+
+  /** Advance the clock, firing any timer that comes due. */
+  const advance = (ms: number) => {
+    now += ms;
+    for (const [h, t] of [...timers]) {
+      if (t.at <= now) {
+        timers.delete(h);
+        t.fn();
+      }
+    }
+  };
+
+  return { schedule, emitted, advance };
+}
+
+describe("preview schedule", () => {
+  it("shows the first preview immediately", () => {
+    const { schedule, emitted } = harness();
+    schedule("s1");
+    expect(emitted).toEqual(["s1"]);
+  });
+
+  it("coalesces a burst into one trailing preview", () => {
+    const { schedule, emitted, advance } = harness();
+    // A pointer sweep across the list, or j held down: every row in between
+    // is walked well inside one gap.
+    schedule("s1");
+    schedule("s2");
+    schedule("s3");
+    expect(emitted).toEqual(["s1"]);
+    advance(PREVIEW_MIN_GAP_MS);
+    expect(emitted).toEqual(["s1", "s3"]);
+  });
+
+  it("shows the next preview immediately once the gap has passed", () => {
+    const { schedule, emitted, advance } = harness();
+    schedule("s1");
+    advance(PREVIEW_MIN_GAP_MS);
+    schedule("s2");
+    expect(emitted).toEqual(["s1", "s2"]);
+  });
+
+  it("drops a superseded trailing preview rather than replaying it", () => {
+    const { schedule, emitted, advance } = harness();
+    schedule("s1");
+    schedule("s2");
+    schedule("s1"); // back where we started inside the same gap
+    advance(PREVIEW_MIN_GAP_MS);
+    // s1 is already on screen, so the trailing edge has nothing to do.
+    expect(emitted).toEqual(["s1"]);
+  });
+
+  it("clears through the same gap, so leaving and re-entering does not blink", () => {
+    const { schedule, emitted, advance } = harness();
+    schedule("s1");
+    schedule(null); // pointer crosses the gap between two rows
+    schedule("s2");
+    advance(PREVIEW_MIN_GAP_MS);
+    expect(emitted).toEqual(["s1", "s2"]);
+  });
+
+  it("cancel drops a pending trailing preview", () => {
+    const { schedule, emitted, advance } = harness();
+    schedule("s1");
+    schedule("s2");
+    schedule.cancel();
+    advance(PREVIEW_MIN_GAP_MS);
+    expect(emitted).toEqual(["s1"]);
+  });
+});

web/src/previewSchedule.ts

@@ -0,0 +1,87 @@
+/**
+ * When the content pane follows the sidebar highlight (docs/PREVIEW.md).
+ *
+ * The highlight itself is never scheduled — that is a class on a row and lands
+ * on the same frame as the input. This governs only the pane swap behind it,
+ * which mounts a terminal and, for a session the connection pool isn't already
+ * holding, opens an attach socket the daemon answers with a `tmux capture-pane`.
+ *
+ * A plain debounce would put that cost in front of every preview, including the
+ * one preview the operator actually meant. Instead the first move shows at once
+ * and the rest of a burst is coalesced: walking a list with `j` held down, or
+ * sweeping the pointer from the top of the sidebar to the bottom, costs one
+ * preview at the start and one at the row you stopped on, not one per row.
+ */
+
+/** Shortest gap between two pane swaps. Long enough that a fast walk mounts a
+ *  couple of terminals rather than one per row; short enough that a deliberate
+ *  second move never waits on it. */
+export const PREVIEW_MIN_GAP_MS = 120;
+
+export interface PreviewScheduleDeps {
+  now?: () => number;
+  setTimer?: (fn: () => void, ms: number) => number;
+  clearTimer?: (handle: number) => void;
+  /** Override the gap; tests and callers otherwise take {@link PREVIEW_MIN_GAP_MS}. */
+  minGapMs?: number;
+}
+
+export interface PreviewSchedule {
+  (sessionId: string | null): void;
+  /** Drop a pending trailing preview without showing it. */
+  cancel(): void;
+}
+
+/**
+ * Wrap `show` so it fires on the leading edge and at most once per gap.
+ *
+ * `show` is called with the session to preview, or `null` to put back whatever
+ * the operator actually opened.
+ */
+export function createPreviewSchedule(
+  show: (sessionId: string | null) => void,
+  deps: PreviewScheduleDeps = {},
+): PreviewSchedule {
+  const now = deps.now ?? (() => Date.now());
+  const setTimer = deps.setTimer ?? ((fn, ms) => window.setTimeout(fn, ms));
+  const clearTimer = deps.clearTimer ?? ((h) => window.clearTimeout(h));
+  const minGap = deps.minGapMs ?? PREVIEW_MIN_GAP_MS;
+
+  let lastShownAt = Number.NEGATIVE_INFINITY;
+  let shown: string | null | undefined;
+  let pendingTimer: number | undefined;
+  let pendingId: string | null = null;
+
+  const emit = (id: string | null) => {
+    // Nothing to do when the burst ended on the view already up: re-showing it
+    // would tear down and re-mount the pane for no visible change.
+    if (shown === id) return;
+    shown = id;
+    lastShownAt = now();
+    show(id);
+  };
+
+  const cancelPending = () => {
+    if (pendingTimer === undefined) return;
+    clearTimer(pendingTimer);
+    pendingTimer = undefined;
+  };
+
+  const schedule = ((sessionId: string | null) => {
+    pendingId = sessionId;
+    const waited = now() - lastShownAt;
+    if (waited >= minGap) {
+      cancelPending();
+      emit(sessionId);
+      return;
+    }
+    if (pendingTimer !== undefined) return; // already waiting; `pendingId` wins
+    pendingTimer = setTimer(() => {
+      pendingTimer = undefined;
+      emit(pendingId);
+    }, minGap - waited);
+  }) as PreviewSchedule;
+
+  schedule.cancel = cancelPending;
+  return schedule;
+}

web/src/sidebarNav.test.ts

@@ -169,33 +169,30 @@ describe("sidebar keyboard navigation", () => {
 
 describe("sidebar preview requests (docs/PREVIEW.md)", () => {
   it("asks for a preview on every keyboard step, and for none once the list blurs", () => {
-    const seen: [string | null, string][] = [];
+    const seen: (string | null)[] = [];
-    const { el } = twoFolders({ onPreview: (id, source) => seen.push([id, source]) });
+    const { el } = twoFolders({ onPreview: (id) => seen.push(id) });
 
     press(tree(el), "j");
     press(tree(el), "j");
-    expect(seen).toEqual([
+    expect(seen).toEqual([A, B]);
-      [A, "key"],
-      [B, "key"],
-    ]);
 
     tree(el).dispatchEvent(new FocusEvent("blur"));
-    expect(seen.at(-1)).toEqual([null, "key"]);
+    expect(seen.at(-1)).toBe(null);
   });
 
   it("asks for a preview of the hovered card, and clears it on the way out", () => {
-    const seen: [string | null, string][] = [];
+    const seen: (string | null)[] = [];
-    const { el } = twoFolders({ onPreview: (id, source) => seen.push([id, source]) });
+    const { el } = twoFolders({ onPreview: (id) => seen.push(id) });
     const card = el.querySelectorAll<HTMLElement>(".tree-leaf")[0];
 
     card.dispatchEvent(new PointerEvent("pointerover", { bubbles: true, pointerType: "mouse" }));
-    expect(seen).toEqual([[A, "hover"]]);
+    expect(seen).toEqual([A]);
     // Moving within the same card is not a new preview.
     card.dispatchEvent(new PointerEvent("pointerover", { bubbles: true, pointerType: "mouse" }));
     expect(seen).toHaveLength(1);
 
     tree(el).dispatchEvent(new PointerEvent("pointerleave", { pointerType: "mouse" }));
-    expect(seen.at(-1)).toEqual([null, "hover"]);
+    expect(seen.at(-1)).toBe(null);
   });
 
   it("ignores touch, where a tap already opens the session", () => {

web/src/styles.css

@@ -1091,7 +1091,6 @@ textarea {
   cursor: pointer;
   font-family: var(--font-mono);
   font-size: var(--fs-12);
-  transition: color var(--dur-fast) var(--ease-out);
 }
 
 .tree-folder-header:hover {
@@ -1103,9 +1102,9 @@ textarea {
   text-align: center;
   color: var(--faint);
   font-size: var(--fs-11);
-  transition:
+  /* The rotation is the collapse animation and stays; the hover colour is
-    transform var(--dur) var(--ease-out),
+     immediate, like the row's own hover. */
-    color var(--dur-fast) var(--ease-out);
+  transition: transform var(--dur) var(--ease-out);
 }
 
 .tree-folder-header[aria-expanded="false"] .chevron {
@@ -1142,9 +1141,11 @@ textarea {
   border-radius: var(--r-1);
   color: var(--ink);
   position: relative;
-  transition:
+  /* No transition on `background`: it is what hover paints, and easing it puts
-    background var(--dur-fast) var(--ease-out),
+     a visible delay between the pointer landing on a row and the row admitting
-    box-shadow var(--dur-fast) var(--ease-out);
+     it. The ring (`.is-highlighted`, `.is-active`) still eases — that one
+     follows a keyboard walk, not the pointer. */
+  transition: box-shadow var(--dur-fast) var(--ease-out);
 }
 
 /* "Alive" reads as a faint wash on the row itself — no per-row status icon. */