bug(tui): session.child.first and child cycle order break after session-ID encoding wraps (2026-08-14)

Description

session.child.first (Ctrl+X+Down, "Go to first child session") is supposed to land on the newest child, but after the session-ID encoding wraps around, it lands on an old subagent instead. The subagent footer then shows a position like (50 of 112) that has no relation to the navigation order.

Root cause: children() in packages/tui/src/routes/session/index.tsx (line 207) sorts siblings by session ID string:

const children = createMemo(() => {
  const parentID = session()?.parentID ?? session()?.id
  return 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))
})

and session IDs (packages/schema/src/identifier.ts) are descending-encoded timestamps:

const current = BigInt(timestamp) * 0x1000n + BigInt(counter)
const value = descending ? ~current : current
// 6-byte hex prefix

So the lexicographically smallest ID is the newest-created session — within one encoding cycle. The 48-bit value wraps when timestamp_ms * 0x1000 + counter crosses a multiple of 2^48, which happened globally at 2026-08-14 11:19:55 UTC (26 * 2^36 ms since epoch; next wrap ~2028-10). After the wrap, every new session ID sorts after all pre-wrap IDs, so:

• moveFirstChild() (index.tsx:442, children().find(x => !!x.parentID)) lands on the newest pre-wrap child, not the actual newest.
• moveChild() Left/Right cycling (index.tsx:448) is scrambled the same way.

The subagent footer counter uses yet a third order — subagent-footer.tsx:25-28 sorts siblings by time.created ascending (oldest = "1 of M") — so the displayed (N of M) never matches the navigation sequence. Session.children (backend) applies no ORDER BY, so ordering is purely a frontend concern.

Verified by reproducing the encoding against real session IDs: the smallest-ID child of an 829-child tree was created ~16 min before the wrap, while the actual newest child (created days later) ranks ~756th in ID order.

Steps to reproduce

1. Have a parent session whose subagents span the wrap boundary — in practice, any session created before 2026-08-14 11:19:55 UTC that keeps spawning subagents (e.g. a long-running session from July 2026).
2. Navigate into that parent, press Ctrl+X+Down (session.child.first), or cycle with Left/Right (session.child.next/previous).
3. Observe: it lands on a subagent that is not the newest; the footer shows e.g. (50 of 112) — its creation-time position among siblings (oldest = 1).

Suggested fix

Sort children by time instead of ID string in index.tsx children():

.toSorted((a, b) => b.time.updated - a.time.updated)

(or b.time.created - a.time.created to match the "newest created" semantics session.child.first already implies), and align the footer counter in subagent-footer.tsx to the same ordering so (N of M) reflects navigation order.

OpenCode version

1.18.18

Operating System

Windows 11

Terminal

Windows Terminal