Add session position indicator in header and refactor sibling logic

packages/opencode/src/cli/cmd/tui/context/sync.tsx

@@ -331,6 +331,14 @@ export const { use: useSync, provider: SyncProvider } = createSimpleContext({
           if (match.found) return store.session[match.index]
           return undefined
         },
+        siblings(sessionID: string) {
+          const session = result.session.get(sessionID)
+          if (!session) return []
+          const parentID = session.parentID ?? session.id
+          return store.session
+            .filter((x) => x.parentID === parentID || x.id === parentID)
+            .toSorted((b, a) => a.id.localeCompare(b.id))
+        },
         status(sessionID: string) {
           const session = result.session.get(sessionID)
           if (!session) return "idle"

packages/opencode/src/cli/cmd/tui/routes/session/header.tsx

@@ -7,10 +7,19 @@ import type { Session } from "@opencode-ai/sdk/v2"
 import { useKeybind } from "../../context/keybind"
 import { useTerminalDimensions } from "@opentui/solid"
 
-const Title = (props: { session: Accessor<Session>; truncate?: boolean }) => {
+const Title = (props: {
+  session: Accessor<Session>
+  truncate?: boolean
+  position: Accessor<{ current: number; total: number } | null>
+}) => {
   const { theme } = useTheme()
   return (
     <text fg={theme.text} wrapMode={props.truncate ? "none" : undefined} flexShrink={props.truncate ? 1 : 0}>
+      <Show when={props.position()}>
+        <span style={{ fg: theme.textMuted }}>
+          [{props.position()!.current}/{props.position()!.total}]{" "}
+        </span>
+      </Show>
       <span style={{ bold: true }}>#</span> <span style={{ bold: true }}>{props.session().title}</span>
     </text>
   )
@@ -28,6 +37,25 @@ export function Header() {
   const dimensions = useTerminalDimensions()
   const tall = createMemo(() => dimensions().height > 40)
 
+  // Calculate session position among siblings (parent + children)
+  const sessionPosition = createMemo(() => {
+    const current = session()
+    if (!current) return null
+
+    const siblings = sync.session.siblings(current.id)
+
+    // Only show counter if there are multiple sessions (parent has children)
+    if (siblings.length <= 1) return null
+
+    const currentIndex = siblings.findIndex((x) => x.id === current.id)
+    if (currentIndex === -1) return null
+
+    return {
+      current: currentIndex + 1, // 1-indexed for users
+      total: siblings.length,
+    }
+  })
+
   return (
     <box flexShrink={0}>
       <box
@@ -78,6 +106,11 @@ export function Header() {
             <Match when={session()?.parentID}>
               <box flexDirection="row" gap={2}>
                 <text fg={theme.text}>
+                  <Show when={sessionPosition()}>
+                    <span style={{ fg: theme.textMuted }}>
+                      [{sessionPosition()!.current}/{sessionPosition()!.total}]{" "}
+                    </span>
+                  </Show>
                   <b>Subagent session</b>
                 </text>
                 <text fg={theme.text}>
@@ -99,7 +132,7 @@ export function Header() {
             </Match>
             <Match when={true}>
               <box flexDirection="row" justifyContent="space-between" gap={1}>
-                <Title session={session} truncate={!tall()} />
+                <Title session={session} truncate={!tall()} position={sessionPosition} />
                 <Show when={showShare()}>
                   <text fg={theme.textMuted} wrapMode="none" flexShrink={0}>
                     /share{" "}

packages/opencode/src/cli/cmd/tui/routes/session/index.tsx

@@ -282,12 +282,11 @@ export function Session() {
   const local = useLocal()
 
   function moveChild(direction: number) {
-    const parentID = session()?.parentID ?? session()?.id
-    let children = sync.data.session
-      .filter((x) => x.parentID === parentID || x.id === parentID)
-      .toSorted((a, b) => (a.id < b.id ? -1 : a.id > b.id ? 1 : 0))
+    const currentSession = session()
+    if (!currentSession) return
+    const children = sync.session.siblings(currentSession.id)
     if (children.length === 1) return
-    let next = children.findIndex((x) => x.id === session()?.id) + direction
+    let next = children.findIndex((x) => x.id === currentSession.id) + direction
     if (next >= children.length) next = 0
     if (next < 0) next = children.length - 1
     if (children[next]) {