fix(desktop): keep running session visible after New Session

[teknium1]

Summary

A running session no longer disappears from the Desktop sidebar when you start a New Session.

Root cause: the sidebar only renders rows from the loaded session list, which is repopulated by listSessions(limit, min_messages=1) to hide empty "Untitled" draft clutter. A running untitled session mid-turn has zero persisted messages, so that query drops it — even though it is still alive in state.db with running tui_gateway workers and still tracked in $workingSessionIds. "New session" clears the active view, the next refresh replaces the list, and the working session's row vanishes (the working marker had no row left to attach to).

Changes

• store/session.ts: new $workingSessionMeta atom + noteWorkingSessionMeta(); pure mergeWorkingSessions() that prepends a synthetic SessionInfo row for any working id absent from the loaded list (keyed by stored session id, drawn from cwd/model/started-at); meta is pruned when a session stops working
• use-session-state-cache.ts: record cwd/model when a session goes busy
• chat/sidebar/index.tsx: merge synthetic rows into the list before sort/index, so grouping, selection, and the working dot all work unchanged
• store/session.test.ts: coverage for the merge selector + meta lifecycle

The synthetic row is marked working and shown at top. Once the turn produces a message and the next refresh returns the real row, it replaces the synthetic one (same id). No backend change, no min_messages relaxation (empty-draft suppression preserved), pure Desktop UI state — no prompt-cache or message-flow invariants touched.

Validation

	Before	After
New Session while untitled agent running	running session drops out of sidebar	synthetic working row stays visible, keyed by stored id
Empty abandoned drafts	hidden	still hidden (unchanged)
Working session that is in the list	rendered	rendered (merge is a no-op)

• tsc -b — clean
• eslint on changed files — 0 errors
• vitest run src/store/session.test.ts — 8/8 passing

Infographic

Infographic

[teknium1]

Closing as redundant — this exact bug is already fixed on main by @OutThisLife in #37908 (commit 55a76ec, "fix(desktop): keep in-flight new chats from vanishing on refresh"). That fix uses the same approach keyed by working session id, but at the refresh layer: mergeWorkingSessions(previous, incoming, workingIds) preserves the real prior SessionInfo for any still-working session the server's listSessions(min_messages=1) omitted, which is cleaner than synthesizing a stub row. Thanks Brooklyn.