diff --git a/crates/maestro-tui/src/palette.rs b/crates/maestro-tui/src/palette.rs
index b21bdde..59a51b7 100644
--- a/crates/maestro-tui/src/palette.rs
+++ b/crates/maestro-tui/src/palette.rs
@@ -13,8 +13,8 @@
 //!
 //! Each surface carries its own activity colours. A state colour picked for
 //! the dark card background is not legible on the selection background, so
-//! the selected card uses the selection surface's own state colours; the dot
-//! keeps carrying the state either way (docs/SIDEBAR.md).
+//! the selected card uses the selection surface's own state colours; the
+//! rail keeps carrying the state either way (docs/SIDEBAR.md).
 //!
 //! [`Palette::DARK`] — graphite, no accent hue — is the default.
 //! [`Palette::LIGHT`] is its light peer and [`Palette::ANSI`] uses
diff --git a/crates/maestro-tui/src/sidebar.rs b/crates/maestro-tui/src/sidebar.rs
index 01518a0..a773a99 100644
--- a/crates/maestro-tui/src/sidebar.rs
+++ b/crates/maestro-tui/src/sidebar.rs
@@ -1,7 +1,7 @@
 //! Sidebar widget — session cards per `docs/SIDEBAR.md`.
 //!
-//! Line 1: status glyph (● attached / ○ live / ✗ dead) + name.
-//! Line 2: activity dot + duration in the state's colour, plus the
+//! Line 1: activity rail + status glyph (● attached / ○ live / ✗ dead) + name.
+//! Line 2: activity rail + duration in the state's colour, plus the
 //! adaptive detail, blocked-work, exited, and command fragments.
 
 use std::collections::{BTreeMap, HashSet};
@@ -33,6 +33,9 @@ const META_LINE_AFTER_SECS: i64 = 30;
 const PLAUSIBLE_SINCE_YEAR: i32 = 2010;
 const INDENT: &str = "  ";
 const META_INDENT: &str = "    ";
+/// docs/SIDEBAR.md: a one-column activity rail leads the indent gutter on
+/// 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
 /// unfocused highlight remains an edge-marked cursor without claiming the
@@ -203,7 +206,9 @@ impl Sidebar {
         );
         let chevron = Span::styled(chevron, base);
         let count = Span::styled(count, surface.muted_style().bg(row_bg));
-        let label_budget = width.saturating_sub(prefix.width() + chevron.width() + count.width());
+        // "1 +" is the blank leading column matching the session rows' rail.
+        let label_budget =
+            width.saturating_sub(1 + prefix.width() + chevron.width() + count.width());
         let mut label = Vec::new();
         if let Some(stem) = name.stem {
             label.push(Span::styled(
@@ -213,7 +218,9 @@ impl Sidebar {
         }
         label.push(Span::styled(name.last, base));
 
-        let mut spans = vec![prefix, chevron];
+        // A blank leading column, matching the width the activity rail adds
+        // to session rows, so folder labels keep aligning under names.
+        let mut spans = vec![Span::styled(" ", base), prefix, chevron];
         spans.extend(fit_to_width(label, label_budget));
         spans.push(count);
         pad_to_width(spans, width, base)
@@ -227,11 +234,13 @@ impl Sidebar {
         };
         let highlighted = self.highlight == Some(SidebarItem::Session(s.id));
         let base = card_base(highlighted, focused);
-        let prefix = INDENT.chars().count() + 2;
+        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 mut spans: Vec<Span<'static>> = vec![
+            Span::styled(RAIL, rail_style),
             Span::styled(
                 if edge { "▏ " } else { INDENT },
                 if edge {
@@ -250,7 +259,8 @@ impl Sidebar {
         pad_to_width(spans, width, base)
     }
 
-    /// The adaptive second line: `<dot> [<duration>] [<detail>] [<blocked work> | exited] <command>`.
+    /// The adaptive second line: `[<duration>] [<detail>] [<blocked work> | exited] <command>`,
+    /// led by the activity rail (docs/SIDEBAR.md).
     fn meta_row(&self, s: &Session, width: usize, focused: bool) -> Vec<Span<'static>> {
         let now = Utc::now();
         let held = held_for(s, now);
@@ -261,7 +271,7 @@ impl Sidebar {
         let dead = s.status == SessionStatus::Dead;
         let highlighted = self.highlight == Some(SidebarItem::Session(s.id));
         let base = card_base(highlighted, focused);
-        let dot_style =
+        let rail_style =
             base.patch(Style::default().fg(activity_color(s.activity, highlighted, focused)));
         let muted = palette::active()
             .surface(highlighted && focused)
@@ -269,6 +279,7 @@ impl Sidebar {
             .bg(base.bg.unwrap_or(palette::active().chrome_bg));
         let edge = highlighted && !focused;
         let mut spans = vec![
+            Span::styled(RAIL, rail_style),
             Span::styled(
                 if edge { "  ▏ " } else { META_INDENT },
                 if edge {
@@ -277,11 +288,9 @@ impl Sidebar {
                     base
                 },
             ),
-            Span::styled("●", dot_style),
         ];
         if let Some(d) = held.filter(|_| held_secs >= META_LINE_AFTER_SECS) {
-            spans.push(Span::styled(" ", base));
-            spans.push(Span::styled(format_state_duration(d), dot_style));
+            spans.push(Span::styled(format_state_duration(d), rail_style));
         }
         let mut tail: Vec<Span<'static>> = Vec::new();
         if let Some(b) = blocked {
@@ -689,7 +698,7 @@ mod tests {
 
     /// The additions and deletions are the only coloured fragments: they are
     /// what a reader scans for, and colouring the rest would make the line
-    /// compete with the activity dot.
+    /// compete with the activity rail.
     #[test]
     fn the_diff_colours_only_its_additions_and_deletions() {
         let mut s = session_named(1, "claude");
@@ -735,8 +744,8 @@ mod tests {
         assert_eq!(content(&all[0]), "sessions");
         assert!(row_containing(&all, "claude").contains('○'));
         assert!(
-            all[3].contains('●'),
-            "line 2 must carry the dot: {:?}",
+            all[3].contains(RAIL),
+            "line 2 must carry the rail: {:?}",
             all[3]
         );
         assert!(
@@ -752,7 +761,7 @@ mod tests {
     }
 
     /// Rule 1 of docs/SIDEBAR.md: held in state longer than 30s earns the
-    /// meta line, with the floored duration next to the dot.
+    /// meta line, with the floored duration next to the rail.
     #[test]
     fn long_held_session_gets_a_meta_line_with_duration() {
         let mut s = session_named(1, "claude");
@@ -765,7 +774,7 @@ mod tests {
         let all = rows(&draw(&sb, 28, 8));
         let idx = all.iter().position(|l| l.contains("claude")).unwrap();
         let meta = &all[idx + 1];
-        assert!(meta.contains('●'), "meta line carries the dot: {meta:?}");
+        assert!(meta.contains(RAIL), "meta line carries the rail: {meta:?}");
         assert!(meta.contains("1m"), "expected 1m in: {meta:?}");
     }
 
@@ -782,10 +791,10 @@ mod tests {
         assert_eq!(fmt(7200), "2h");
     }
 
-    /// The dot and duration carry the activity state's colour; the state word
-    /// is never spelled out (docs/SIDEBAR.md colour table).
+    /// The rail and duration carry the activity state's colour; the state
+    /// word is never spelled out (docs/SIDEBAR.md colour table).
     #[test]
-    fn meta_line_dot_uses_the_contract_colour_per_state() {
+    fn meta_line_rail_uses_the_contract_colour_per_state() {
         for state in [
             ActivityState::Active,
             ActivityState::Idle,
@@ -808,7 +817,7 @@ mod tests {
         }
     }
 
-    /// The selected card keeps carrying its state on the dot, but in the
+    /// The selected card keeps carrying its state on the rail, but in the
     /// selection surface's own colours. A state colour picked for the dark
     /// card background painted onto the selection background is the contrast
     /// bug this palette fixes — this test fails if it comes back.
@@ -845,7 +854,7 @@ mod tests {
             );
             assert!(
                 on_selection(p.selection.activity(state)),
-                "{state:?}: the dot must still carry the state on the selected card"
+                "{state:?}: the rail must still carry the state on the selected card"
             );
             let ratio = palette::contrast_ratio(p.selection.bg, p.selection.activity(state))
                 .expect("palette roles are RGB");
@@ -945,7 +954,7 @@ mod tests {
         let all = rows(&draw(&sb, 40, 8));
         let idx = all.iter().position(|l| l.contains("claude")).unwrap();
         let meta = &all[idx + 1];
-        assert!(meta.contains('●'), "meta line carries the dot: {meta:?}");
+        assert!(meta.contains(RAIL), "meta line carries the rail: {meta:?}");
         assert!(
             meta.contains("1m"),
             "duration precedes the detail: {meta:?}"
@@ -1018,7 +1027,7 @@ mod tests {
 
     /// docs/SIDEBAR.md: a payload predating #102 carries an epoch
     /// `activity_since` and so contributes no duration — a card must not claim
-    /// the session has been idle since 1970. The dot still renders when some
+    /// the session has been idle since 1970. The rail still renders when some
     /// other trigger puts line 2 on screen.
     #[test]
     fn epoch_activity_since_renders_no_duration() {
@@ -1035,10 +1044,10 @@ mod tests {
             rendered.contains("exited"),
             "dead session must still show line 2:\n{rendered}"
         );
-        for line in rendered.lines().filter(|l| l.contains('●')) {
+        for line in rendered.lines().filter(|l| l.contains(RAIL)) {
             assert!(
                 !line
-                    .split('●')
+                    .split(RAIL)
                     .nth(1)
                     .unwrap_or("")
                     .trim_start()
@@ -1101,7 +1110,7 @@ mod tests {
     }
 
     #[test]
-    fn narrow_meta_line_keeps_dot_and_truncates_command() {
+    fn narrow_meta_line_keeps_rail_and_truncates_command() {
         let s = session_named(1, "name");
         let sb = Sidebar {
             sessions: vec![s],
@@ -1110,8 +1119,8 @@ mod tests {
         };
         let all = rows(&draw(&sb, 9, 6));
         assert!(
-            all[3].contains('●'),
-            "dot must survive narrow cards: {:?}",
+            all[3].contains(RAIL),
+            "rail must survive narrow cards: {:?}",
             all[3]
         );
         assert!(
diff --git a/docs/SIDEBAR.md b/docs/SIDEBAR.md
index 499147f..b3ee4ad 100644
--- a/docs/SIDEBAR.md
+++ b/docs/SIDEBAR.md
@@ -37,23 +37,45 @@ itself is not.
 Line 2 reads left to right:
 
 ```
-<dot> [<duration>] [<detail>] [<diff stat> | exited] <command>
+[<duration>] [<detail>] [<diff stat> | exited] <command>
 ```
 
-Its minimum content is therefore the dot and the command.
+Its minimum content is therefore just the command.
 
-`<dot>` is a single filled glyph (`●` on both clients) carrying the activity
-state's colour, and `<duration>` follows in the same colour when shown. There
-is no state word and no second badge: the dot exists so the state is still
-legible when a row is dimmed or the terminal renders the duration in the
-default fg. The dot is an unconditional part of line 2; the bracketed
-fragments appear only when their trigger holds.
+The activity state does not render as an inline glyph on line 2 — a **rail**
+carries it instead: a coloured bar in the gutter to the left of the card, the
+space nesting already reserves for indentation. The rail paints for every
+card, `Idle` included, and is independent of whatever line 2 has to say; a
+card with nothing else to report still shows its rail next to the bare
+command. `<duration>` follows in the rail's colour when shown. There is no
+state word and no second badge: the rail exists so the state is still legible
+when a row is dimmed or the terminal renders the duration in the default fg.
+
+In the **web client** the rail is a 5px bar positioned inside the row's own
+indent gutter — it shifts outward with nesting depth exactly as the gutter
+does — spanning the full card height. It carries motion, reserved for states
+that need attention (DESIGN.md's "living signals" rule): a slow breathing
+opacity while `Active`, a hard blink while `AwaitingInput`, a fast flash while
+`Error`. `Idle` is solid and still, on purpose. `prefers-reduced-motion`
+leaves every state as a solid bar.
+
+In the **TUI** the rail is a one-column-wide block glyph (`▌`) in the state's
+palette role, leading the existing indent gutter (`INDENT`/`META_INDENT`) on
+both the name row and the meta row, so the two lines read as one continuous
+bar. Folder headers gain a matching blank leading column so labels still
+align under session names. The TUI has no render cadence to animate against,
+so its rail is always static — colour is the whole signal there, as it
+always was.
+
+Either client's rail carries the accessibility duty the old inline dot did:
+it is the element whose `title`/`aria-label` names the state, so status still
+never relies on colour alone.
 
 `<duration>` renders only once the session has been held in its current
 activity state longer than **30 seconds** (`activity_since` from #102) — under
-that threshold the duration is absent and the dot renders alone. A payload
-that predates #102 (no usable `activity_since`) likewise contributes no
-duration — the dot still renders. This rule now governs only the duration
+that threshold the duration is absent and the rail carries the state alone. A
+payload that predates #102 (no usable `activity_since`) likewise contributes
+no duration — the rail still renders. This rule now governs only the duration
 fragment; it no longer decides whether line 2 exists.
 
 `<detail>` is an agent-reported string (#105) — e.g. why a session is in
diff --git a/web/src/catalog.test.ts b/web/src/catalog.test.ts
index fd0e4ab..bb9f461 100644
--- a/web/src/catalog.test.ts
+++ b/web/src/catalog.test.ts
@@ -224,9 +224,10 @@ describe("session cards (#107)", () => {
       activity_since: ago(5_000),
     });
     const el = renderSidebar(storeWith([s])).el;
-    const line2 = rowFor(el, s.id)?.querySelector<HTMLElement>(".card-line2");
+    const row = rowFor(el, s.id);
+    const line2 = row?.querySelector<HTMLElement>(".card-line2");
     expect(line2).not.toBeNull();
-    expect(line2?.querySelector(".activity-dot")).not.toBeNull();
+    expect(row?.querySelector(".activity-rail")).not.toBeNull();
     expect(line2?.querySelector(".activity-duration")).toBeNull();
     expect(line2?.querySelector(".leaf-cmd")).not.toBeNull();
   });
@@ -238,9 +239,10 @@ describe("session cards (#107)", () => {
       activity_since: ago(4 * 60_000 + 30_000),
     });
     const el = renderSidebar(storeWith([s])).el;
-    const line2 = rowFor(el, s.id)?.querySelector<HTMLElement>(".card-line2");
+    const row = rowFor(el, s.id);
+    const line2 = row?.querySelector<HTMLElement>(".card-line2");
     expect(line2?.dataset.activity).toBe("active");
-    expect(line2?.querySelector(".activity-dot")).not.toBeNull();
+    expect(row?.querySelector(".activity-rail")).not.toBeNull();
     expect(line2?.querySelector(".activity-duration")?.textContent).toBe("4m");
   });
 
@@ -355,9 +357,9 @@ describe("session cards (#107)", () => {
     });
     const el = renderSidebar(storeWith([s])).el;
     const row = rowFor(el, s.id) as HTMLElement;
-    const dot = row.querySelector<HTMLElement>(".activity-dot");
-    expect(dot?.getAttribute("title")).toContain("Awaiting input");
-    expect(dot?.getAttribute("aria-label")).toContain("Awaiting input");
+    const rail = row.querySelector<HTMLElement>(".activity-rail");
+    expect(rail?.getAttribute("title")).toContain("Awaiting input");
+    expect(rail?.getAttribute("aria-label")).toContain("Awaiting input");
     expect(row.textContent).not.toMatch(/awaiting.?input/i);
   });
 
diff --git a/web/src/catalog.ts b/web/src/catalog.ts
index d2314f6..0a0a77c 100644
--- a/web/src/catalog.ts
+++ b/web/src/catalog.ts
@@ -58,8 +58,9 @@ const collapsed = new Set<string>();
  * would otherwise replace the field the user is typing into. */
 let renamingId: string | null = null;
 
-// docs/SIDEBAR.md: the state word is never rendered — the dot's colour carries
-// it. It survives only in tooltips/aria labels so meaning is not colour-only.
+// docs/SIDEBAR.md: the state word is never rendered — the rail's colour
+// carries it. It survives only in tooltips/aria labels so meaning is not
+// colour-only.
 const STATE_WORDS: Record<string, string> = {
   active: "Active",
   idle: "Idle",
@@ -67,17 +68,24 @@ const STATE_WORDS: Record<string, string> = {
   error: "Error",
 };
 
+/** docs/SIDEBAR.md: the activity rail sits inside the row's own indent
+ * gutter, so it shifts outward with nesting depth exactly as that gutter
+ * does. `depth * 16 + 8` is the same expression `renderNode` uses for the
+ * row's own padding — the rail sits just inside it. */
+function activityRailMarkup(slug: string, stateWord: string, depth: number): string {
+  const left = depth * 16 + 2;
+  return `<span class="activity-rail" data-activity="${slug}" style="left:${left}px" role="img" title="${escapeHtml(stateWord)}" aria-label="${escapeHtml(stateWord)}"></span>`;
+}
+
 function metaLine(s: Session, now: number): string {
   const dead = s.status === "Dead";
   const blockers = sessionBlockers(s);
   const slug = activityColorSlug(s.activity ?? "Idle");
-  const stateWord = STATE_WORDS[slug] ?? STATE_WORDS.idle;
   const held = activityHeldMs(s.activity_since, now);
   const duration =
     held !== null && held >= META_LINE_MIN_HOLD_MS ? activityDurationLabel(held) : null;
 
   const fragments = [
-    `<span class="activity-dot" role="img" title="${escapeHtml(stateWord)}" aria-label="${escapeHtml(stateWord)}"></span>`,
     duration ? `<span class="activity-duration">${duration}</span>` : "",
     s.activity_detail
       ? `<span class="activity-detail">${escapeHtml(s.activity_detail)}</span>`
@@ -156,14 +164,15 @@ function renderNode(node: TreeNode, depth: number): HTMLElement {
   const running = s.status === "Running";
   row.dataset.status = running ? "running" : "dead";
   const name = sessionName(s);
-  const stateWord =
-    STATE_WORDS[activityColorSlug(s.activity ?? "Idle")] ?? STATE_WORDS.idle;
+  const slug = activityColorSlug(s.activity ?? "Idle");
+  const stateWord = STATE_WORDS[slug] ?? STATE_WORDS.idle;
   row.setAttribute(
     "aria-label",
     `${name}, ${running ? "running" : "exited"}, ${stateWord}`,
   );
   // docs/SIDEBAR.md: line 1 reserves action width, and line 2 is unconditional.
   row.innerHTML = `
+    ${activityRailMarkup(slug, stateWord, depth)}
     <span class="card-line1">
       <span class="leaf-name">${escapeHtml(name)}</span>
       <span class="leaf-actions">
diff --git a/web/src/kit.ts b/web/src/kit.ts
index f1a721e..1883aab 100644
--- a/web/src/kit.ts
+++ b/web/src/kit.ts
@@ -66,12 +66,15 @@ function leafRow(opts: {
   (row as HTMLAnchorElement).href = "#/kit";
   row.dataset.status = opts.status;
   if (opts.active) row.classList.add("is-active");
-  row.style.paddingLeft = `${(opts.indent ?? 0) * 16 + 8}px`;
+  const depth = opts.indent ?? 0;
+  row.style.paddingLeft = `${depth * 16 + 8}px`;
   const flags = [
     opts.status === "dead" ? `<span class="card-flag">exited</span>` : "",
     opts.cmd !== opts.name ? `<span class="card-flag leaf-cmd">${opts.cmd}</span>` : "",
   ].join("");
+  const activity = opts.activity ?? "idle";
   row.innerHTML = `
+    <span class="activity-rail" data-activity="${activity}" style="left:${depth * 16 + 2}px" title="${activity}"></span>
     <span class="card-line1">
       <span class="leaf-name">${opts.name}</span>
       <span class="leaf-actions">
@@ -79,7 +82,7 @@ function leafRow(opts: {
         <button class="leaf-act leaf-kill" type="button" title="Kill session">✕</button>
       </span>
     </span>
-    ${opts.activity ? `<span class="card-line2" data-activity="${opts.activity}"><span class="activity-dot" title="${opts.activity}"></span><span class="activity-duration">${opts.duration ?? ""}</span>${flags}</span>` : ""}
+    ${opts.activity ? `<span class="card-line2" data-activity="${opts.activity}"><span class="activity-duration">${opts.duration ?? ""}</span>${flags}</span>` : ""}
   `;
   return row;
 }
@@ -201,11 +204,15 @@ export function renderKit(): HTMLElement {
     const activeLine = h(
       "span",
       "card-line2",
-      `<span class="activity-dot"></span><span class="activity-duration">4m</span>`,
+      `<span class="activity-duration">4m</span>`,
     );
     activeLine.setAttribute("data-activity", "active");
+    const rail = h("span", "activity-rail");
+    rail.dataset.activity = "active";
+    rail.style.cssText = "position:static;display:inline-block;height:14px;";
     body.append(
       specimen("folder-count", h("span", "folder-count", "4")),
+      specimen("activity-rail · active", rail),
       specimen("card-line2 · active", activeLine),
       specimen("attach-state · open", h("span", "attach-state", "live")),
     );
@@ -225,7 +232,7 @@ export function renderKit(): HTMLElement {
   {
     const { el, body } = section(
       "Session rows — nested by host, then directory",
-      "docs/SIDEBAR.md cards: line 1 is name + top-right actions (the name truncates before it can reach them); line 2 only when there's something to say — dot + duration in the state's colour, then blocked-work / exited fragments.",
+      "docs/SIDEBAR.md cards: line 1 is name + top-right actions (the name truncates before it can reach them); the activity rail sits in the indent gutter to the left; line 2 carries duration in the state's colour, then blocked-work / exited fragments, whenever there's something to say.",
     );
     const list = h("div", "kit-tree");
     list.append(
diff --git a/web/src/styles.css b/web/src/styles.css
index de547f7..83fa9b8 100644
--- a/web/src/styles.css
+++ b/web/src/styles.css
@@ -1393,12 +1393,34 @@ input.leaf-rename:focus {
   color: var(--danger);
 }
 
-.activity-dot {
-  width: 7px;
-  height: 7px;
-  border-radius: 50%;
+/* docs/SIDEBAR.md: the activity rail replaces the old inline dot. It sits
+   inside the row's own indent gutter (`.tree-leaf` is already positioned),
+   at a `left` set inline per nesting depth — see `activityRailMarkup` in
+   catalog.ts. Idle stays solid and still on purpose: motion is reserved for
+   states that need attention (DESIGN.md's "living signals" rule). */
+.activity-rail {
+  position: absolute;
+  top: 4px;
+  bottom: 4px;
+  width: 5px;
+  border-radius: 2px;
   background: currentColor;
-  flex: 0 0 auto;
+}
+
+.activity-rail[data-activity="active"] {
+  color: var(--live);
+  animation: pulse 2.4s var(--ease-out) infinite;
+}
+.activity-rail[data-activity="idle"] {
+  color: var(--border-strong);
+}
+.activity-rail[data-activity="awaiting-input"] {
+  color: var(--warn);
+  animation: blink 1.2s steps(1) infinite;
+}
+.activity-rail[data-activity="error"] {
+  color: var(--danger);
+  animation: rail-flash 1.4s ease-out infinite;
 }
 
 .activity-duration {
@@ -2593,6 +2615,25 @@ input.leaf-rename:focus {
   }
 }
 
+@keyframes rail-flash {
+  0%,
+  100% {
+    opacity: 1;
+  }
+  15% {
+    opacity: 0.25;
+  }
+  30% {
+    opacity: 1;
+  }
+  45% {
+    opacity: 0.25;
+  }
+  60% {
+    opacity: 1;
+  }
+}
+
 /* ---------- responsive ---------- */
 
 @media (max-width: 520px) {
@@ -2642,7 +2683,8 @@ input.leaf-rename:focus {
   }
   .brand-dot,
   [data-status="running"] .leaf-status::before,
-  .tally-live::before {
+  .tally-live::before,
+  .activity-rail {
     animation: none;
   }
 }