fix(desktop): preserve turn-elapsed timer across session switches

[yingliang-zhang]

Problem

The desktop status bar's turn-elapsed timer (running-timer) resets to 0:00 every time the user switches away from a busy session and switches back.

Root Cause

1. Gateway never reports turn_started_at: Neither session.resume responses nor session.info events include the turn start timestamp, so the desktop has no way to restore the clock after a session switch.

2. Cold-resume path loses the timer: use-session-actions/index.ts creates a new ClientSessionState with turnStartedAt: null (the default). When the subsequent session.info event arrives with running: true, gateway-event.ts falls back to state.turnStartedAt ?? Date.now() → Date.now() → timer resets to zero.

The warm-cache path correctly preserves turnStartedAt via syncSessionStateToView, but if session.usage RPC fails (e.g. pooled backend idle-reaped), the cache is purged and the cold path takes over — resetting the timer.

Fix

Gateway side (tui_gateway/server.py):

• _session_info(): extract turn_started_at from inflight_turn.started_at and include it in the info dict
• _live_session_payload(): include turn_started_at in the resume response payload

Desktop side (3 files):

• types/hermes.ts: add turn_started_at?: number | null to SessionResumeResponse
• lib/chat-messages.ts: add turn_started_at?: number | null to GatewayEventPayload
• use-session-actions/index.ts: cold-resume path uses resumed.turn_started_at (converted to ms) to restore the timer instead of defaulting to null
• gateway-event.ts: session.info busy-transition handler prefers gateway-reported turn_started_at over Date.now() fallback

Verification

• npx tsc --noEmit — PASS (0 errors)
• py_compile tui_gateway/server.py — PASS
• vitest run src/app/session/hooks/ — 117/121 pass; 4 failures are pre-existing on origin/main (confirmed by stashing changes and re-running)
• No personal info / internal paths in diff
• git log --oneline origin/main..HEAD shows only this commit

Changes

File	Change
tui_gateway/server.py	+16 lines: report turn_started_at in _session_info() and _live_session_payload()
apps/desktop/src/types/hermes.ts	+2: turn_started_at field on SessionResumeResponse
apps/desktop/src/lib/chat-messages.ts	+1: turn_started_at field on GatewayEventPayload
apps/desktop/src/app/session/hooks/use-session-actions/index.ts	+11: use resumed.turn_started_at in cold-resume path
apps/desktop/src/app/session/hooks/use-message-stream/gateway-event.ts	+8: prefer gateway turn_started_at in session.info handler

Total: +36/-2 across 5 files. No new config knobs — the field is purely additive.

[tonydwb]

Code Review Summary

Verdict: Comment

Overview

• 5 files changed, +36/-2 lines
• Preserves turn-elapsed timer across desktop session switches
• Fixes a UX issue where the timer would reset

Looks Good

• Well-scoped fix targeting the session switch path
• Proper state preservation in the desktop state manager
• No security concerns

---

Reviewed by Hermes Agent

[teknium1]

Thanks for tracing the cold-resume path; the implementation targets a real current-main gap.

Problems

• The new gateway-to-desktop timestamp contract has no regression test. Current protocol coverage for session.resume begins at tests/tui_gateway/test_protocol.py:296, and the existing cache coverage starts from an already-populated local turnStartedAt at apps/desktop/src/app/session/hooks/use-session-state-cache.test.tsx:83; neither covers a cold running-session resume.

Suggested changes

• Add a tui_gateway protocol test for an inflight_turn.started_at value through both session.resume and _session_info().
• Add desktop coverage that verifies turn_started_at converts to milliseconds on cold resume and is preferred over the Date.now() fallback in apps/desktop/src/app/session/hooks/use-message-stream/gateway-event.ts.

Automated hermes-sweeper review.

[yingliang-zhang]

Addressed in commit 97bb62b4a7cfd604cf43d03e7ecf737f9c945219: added a shared, JSON-round-tripped active-turn session.resume fixture/contract across gateway and Desktop. The Desktop now restores the elapsed timer only for running responses with a valid numeric turn_started_at; invalid or absent values clear stale state instead of synthesizing Date.now(). Focused gates: Python 84 passed; Desktop 28 passed; Node 22 typecheck passed.

[teknium1]

Salvaged and merged in #87237 — both your commits landed on main with authorship preserved (c1041d5 + fb27c1a → rebase-merged), including the gateway turn_started_at contract, the shared round-trip fixture you added after the sweeper review, and the cold-resume restore. One conflict was resolved in favor of main's newer live-turn transcript reconcile design (your !running gate predated it); on the heartbeat path your gateway timestamp now composes with the newly-added submit-time clock seed (#86923) as state.turnStartedAt ?? gatewayTurnStartedAt ?? Date.now(). Thanks for the careful root-cause work on both sides of the wire!