perf(header): cap session tabs at 20; tooltip data loads on hover only

Auto-add means the strip only grows, so past 20 tabs the oldest one
leaves the working set (the newly opened tab is always the survivor).
The branch/worktree/PR/project subscriptions that feed the hover
tooltip moved into the tooltip body component, which mounts only while
the tooltip is open — a resting tab now subscribes only to its status
dot's session status and unread count.

packages/ui/src/components/layout/SessionTabsStrip.tsx

@@ -97,6 +97,81 @@ const useTabProjectLabel = (directory: string | null): string | null =>
     return null;
   }, [directory]));
 
+/**
+ * Tooltip body for one tab. Lives in its own component so the branch,
+ * worktree, PR and project subscriptions exist only while the tooltip is
+ * open — the resting tab pays only for its status dot.
+ */
+const SessionTabTooltipBody: React.FC<{ tab: SessionTab; title: string }> = ({ tab, title }) => {
+  const { t } = useI18n();
+  const directory = normalizePath(resolveGlobalSessionDirectory(tab.session) ?? null);
+  const projectLabel = useTabProjectLabel(directory);
+  const worktreeMetadata = useSessionUIStore((state) => state.worktreeMetadata);
+  const allBranches = useGitAllBranches();
+  const branchLabel = React.useMemo(() => {
+    const meta = worktreeMetadata.get(tab.id);
+    if (meta?.branch?.trim()) return meta.branch.trim();
+    if (directory) return allBranches.get(directory)?.trim() || null;
+    return null;
+  }, [worktreeMetadata, allBranches, tab.id, directory]);
+  const prSummary = usePrVisualSummary(directory && branchLabel ? getGitHubPrStatusKey(directory, branchLabel) : null);
+  const prIconColor = prSummary ? `var(--pr-${prSummary.visualState})` : undefined;
+  const prStatusLabel = React.useMemo(() => {
+    if (!prSummary) return null;
+    switch (prSummary.visualState) {
+      case 'merged':
+        return t('sessions.sidebar.group.pr.status.merged');
+      case 'open':
+        return (prSummary.canMerge === true || prSummary.mergeableState === 'clean' || prSummary.checks?.state === 'success')
+          ? t('sessions.sidebar.group.pr.status.readyToMerge')
+          : t('sessions.sidebar.group.pr.status.open');
+      case 'blocked':
+        return prSummary.mergeableState === 'dirty'
+          ? t('sessions.sidebar.group.pr.status.mergeConflicts')
+          : t('sessions.sidebar.group.pr.status.mergeBlocked');
+      case 'draft':
+        return t('sessions.sidebar.group.pr.status.draft');
+      case 'closed':
+        return t('sessions.sidebar.group.pr.status.closed');
+      default:
+        return null;
+    }
+  }, [prSummary, t]);
+  const sessionTimestamp = tab.session.time?.updated || tab.session.time?.created || 0;
+  return (
+    <div className="flex min-w-44 flex-col gap-1.5 text-left text-xs">
+      <div className="flex items-center justify-between gap-3">
+        <span className="min-w-0 truncate font-medium text-foreground">{title}</span>
+        {sessionTimestamp ? (
+          <span className="flex-shrink-0 text-muted-foreground" title={formatSessionDateLabel(sessionTimestamp)}>
+            {formatSessionCompactDateLabel(sessionTimestamp)}
+          </span>
+        ) : null}
+      </div>
+      {projectLabel ? (
+        <div className="flex min-w-0 items-center gap-1.5 text-muted-foreground">
+          <Icon name="folder" className="h-3 w-3 flex-shrink-0" />
+          <span className="min-w-0 truncate">{projectLabel}</span>
+        </div>
+      ) : null}
+      {branchLabel ? (
+        <div className="flex min-w-0 items-center gap-1.5 text-muted-foreground">
+          <Icon name="git-branch" className="h-3 w-3 flex-shrink-0" style={prIconColor ? { color: prIconColor } : undefined} />
+          <span className="min-w-0 truncate">{branchLabel}</span>
+        </div>
+      ) : null}
+      {prSummary && prStatusLabel ? (
+        <div className="flex min-w-0 items-center gap-1.5">
+          <Icon name="git-pull-request" className="h-3 w-3 flex-shrink-0" style={prIconColor ? { color: prIconColor } : undefined} />
+          <span className="min-w-0 truncate" style={prIconColor ? { color: prIconColor } : undefined}>
+            #{prSummary.number} · {prStatusLabel}
+          </span>
+        </div>
+      ) : null}
+    </div>
+  );
+};
+
 /**
  * One tab, active or not. The tab drags to reorder; the menu and close
  * controls sit in a hover-revealed overlay at the tab's end (menu first,
@@ -139,41 +214,6 @@ const SessionTabItem: React.FC<{
     ? t('sessions.sidebar.session.status.active')
     : t('sessions.sidebar.session.status.unread');
 
-  const directory = normalizePath(resolveGlobalSessionDirectory(tab.session) ?? null);
-  const projectLabel = useTabProjectLabel(directory);
-  const worktreeMetadata = useSessionUIStore((state) => state.worktreeMetadata);
-  const allBranches = useGitAllBranches();
-  const branchLabel = React.useMemo(() => {
-    const meta = worktreeMetadata.get(tab.id);
-    if (meta?.branch?.trim()) return meta.branch.trim();
-    if (directory) return allBranches.get(directory)?.trim() || null;
-    return null;
-  }, [worktreeMetadata, allBranches, tab.id, directory]);
-  const prSummary = usePrVisualSummary(directory && branchLabel ? getGitHubPrStatusKey(directory, branchLabel) : null);
-  const prIconColor = prSummary ? `var(--pr-${prSummary.visualState})` : undefined;
-  const prStatusLabel = React.useMemo(() => {
-    if (!prSummary) return null;
-    switch (prSummary.visualState) {
-      case 'merged':
-        return t('sessions.sidebar.group.pr.status.merged');
-      case 'open':
-        return (prSummary.canMerge === true || prSummary.mergeableState === 'clean' || prSummary.checks?.state === 'success')
-          ? t('sessions.sidebar.group.pr.status.readyToMerge')
-          : t('sessions.sidebar.group.pr.status.open');
-      case 'blocked':
-        return prSummary.mergeableState === 'dirty'
-          ? t('sessions.sidebar.group.pr.status.mergeConflicts')
-          : t('sessions.sidebar.group.pr.status.mergeBlocked');
-      case 'draft':
-        return t('sessions.sidebar.group.pr.status.draft');
-      case 'closed':
-        return t('sessions.sidebar.group.pr.status.closed');
-      default:
-        return null;
-    }
-  }, [prSummary, t]);
-  const sessionTimestamp = tab.session.time?.updated || tab.session.time?.created || 0;
-
   const menuArgsFor = (components: SessionTabMenuComponents): SessionTabMenuArgs => ({
     session: tab.session,
     isActive,
@@ -309,36 +349,7 @@ const SessionTabItem: React.FC<{
           </TooltipTrigger>
           {!anyMenuOpen && !isDragging ? (
             <TooltipContent side="bottom" sideOffset={8} className="max-w-xs text-left">
-              <div className="flex min-w-44 flex-col gap-1.5 text-left text-xs">
-                <div className="flex items-center justify-between gap-3">
-                  <span className="min-w-0 truncate font-medium text-foreground">{title}</span>
-                  {sessionTimestamp ? (
-                    <span className="flex-shrink-0 text-muted-foreground" title={formatSessionDateLabel(sessionTimestamp)}>
-                      {formatSessionCompactDateLabel(sessionTimestamp)}
-                    </span>
-                  ) : null}
-                </div>
-                {projectLabel ? (
-                  <div className="flex min-w-0 items-center gap-1.5 text-muted-foreground">
-                    <Icon name="folder" className="h-3 w-3 flex-shrink-0" />
-                    <span className="min-w-0 truncate">{projectLabel}</span>
-                  </div>
-                ) : null}
-                {branchLabel ? (
-                  <div className="flex min-w-0 items-center gap-1.5 text-muted-foreground">
-                    <Icon name="git-branch" className="h-3 w-3 flex-shrink-0" style={prIconColor ? { color: prIconColor } : undefined} />
-                    <span className="min-w-0 truncate">{branchLabel}</span>
-                  </div>
-                ) : null}
-                {prSummary && prStatusLabel ? (
-                  <div className="flex min-w-0 items-center gap-1.5">
-                    <Icon name="git-pull-request" className="h-3 w-3 flex-shrink-0" style={prIconColor ? { color: prIconColor } : undefined} />
-                    <span className="min-w-0 truncate" style={prIconColor ? { color: prIconColor } : undefined}>
-                      #{prSummary.number} · {prStatusLabel}
-                    </span>
-                  </div>
-                ) : null}
-              </div>
+              <SessionTabTooltipBody tab={tab} title={title} />
             </TooltipContent>
           ) : null}
         </Tooltip>

packages/ui/src/lib/theme/themes/openchamber-dark.json

@@ -37,7 +37,7 @@
       "border": "#242323",
       "borderHover": "#504e4c",
       "borderFocus": "#da7c47",
-      "selection": "#b9a5992b",
+      "selection": "#c8c6c52b",
       "selectionForeground": "#c9c5ba",
       "focus": "#da7c47",
       "focusRing": "#da7c4755",

packages/ui/src/stores/useSessionTabsStore.test.ts

@@ -32,6 +32,15 @@ describe('useSessionTabsStore', () => {
     expect(useSessionTabsStore.getState().tabIds).toBe(before);
   });
 
+  test('caps the working set at 20, evicting the oldest tab', () => {
+    useSessionTabsStore.setState({ tabIds: Array.from({ length: 20 }, (_, i) => `s${i}`) });
+    useSessionTabsStore.getState().ensureTab('s-new');
+    const ids = useSessionTabsStore.getState().tabIds;
+    expect(ids).toHaveLength(20);
+    expect(ids[0]).toBe('s1');
+    expect(ids.at(-1)).toBe('s-new');
+  });
+
   test('removeTabs drops only confirmed-gone ids and no-ops otherwise', () => {
     useSessionTabsStore.setState({ tabIds: ['a', 'b'] });
     const before = useSessionTabsStore.getState().tabIds;

packages/ui/src/stores/useSessionTabsStore.ts

@@ -24,6 +24,8 @@ interface SessionTabsStore {
   removeTabs: (sessionIds: readonly string[]) => void;
 }
 
+const MAX_SESSION_TABS = 20;
+
 type PersistedSessionTabs = { tabIds: string[] };
 
 export const useSessionTabsStore = create<SessionTabsStore>()(
@@ -36,7 +38,11 @@ export const useSessionTabsStore = create<SessionTabsStore>()(
           if (!sessionId) return;
           const { tabIds } = get();
           if (tabIds.includes(sessionId)) return;
-          set({ tabIds: [...tabIds, sessionId] });
+          // Soft cap: with auto-add the strip only ever grows, so past the cap
+          // the oldest tab (never the one being opened, which lands last)
+          // leaves the working set.
+          const next = [...tabIds, sessionId];
+          set({ tabIds: next.length > MAX_SESSION_TABS ? next.slice(next.length - MAX_SESSION_TABS) : next });
         },
 
         closeTab: (sessionId) => {