fix(voice): suppress "Welcome back" on quick reconnects (<60s)

[liususan091219]

Summary

When Gemini Live session drops and reconnects within 60 seconds (network blip, not a real away), silently resume instead of re-greeting the user. Eliminates the jarring "Welcome back" every few sentences that interrupts long voice sessions.

What changed

• src/task-bridge.ts — new getSecondsSinceLastTurn() helper reads the timestamp of the most recent conversation.log line (any turn or SESSION_END marker)
• src/voice-agent.ts — in MainAgent.greeting, when getRecentConversation() returns non-empty (we're in a reconnect), check the gap:
  • < 60s → tell Gemini to stay silent, no "Welcome back"
  • ≥ 60s or null → keep existing "Welcome back briefly" behavior

The existing REPLAYED-HISTORY injection is preserved in both branches — only the post-replay user-facing utterance differs. Clean exits (SESSION_END logged) still fall through to the normal fresh-greeting path.

Why this scope

bodhi has been fixed several times around reconnect state machines already; this PR doesn't touch bodhi. It's a thin application-layer UX improvement: the app already knows when the last turn happened (conversation.log), we just weren't reading that timestamp to distinguish "network blip reconnect" from "user came back later."

Test plan

• TypeScript compiles (npx tsc --noEmit clean)
• Voice agent restarted locally with this branch; Susan confirmed "好像welcome back没了" during a live test
• Manual verification of slow-reconnect path: disconnect >60s → "Welcome back" still fires

🤖 Generated with Claude Code

[sonichi]

Joint MacBook + Mini cold review — 1 issue confirmed.

Finding (Mini): getSecondsSinceLastTurn() reads any role, not just user/assistant turns.

Verified against src/task-bridge.ts:393 — logConversation('core-agent', '[task:...] ...') writes a line every time the result watcher delivers a task result. So the conversation log contains:

• user / assistant voice turns
• core-agent task-result lines (from the proactive loop or any background task)
• SESSION_END markers

getSecondsSinceLastTurn() reads the last line regardless of role, so a recent task-result write makes a long-away user look like a quick reconnect — and the "Welcome back" gets suppressed when it shouldn't.

Concrete failure mode: user is away 5 minutes, proactive loop ships a task result 30s before they reconnect → getSecondsSinceLastTurn() returns 30 → isQuickReconnect=true → silent reconnect even though the user expected a greeting.

Suggested fix: walk the log from the end backwards, skipping core-agent and SESSION_END lines, return the timestamp of the most recent user or assistant line. Optionally bound the search to lines after the most recent SESSION_END (mirrors how getRecentConversation() already trims).

This is a UX nit (greeting suppressed when it shouldn't be), not a correctness bug — but worth fixing before merge since it's a 5-line change. Comment review, not request-changes.

[liususan091219]

getSecondsSinceLastTurn() reads the last line regardless of role, so a recent task-result write makes a long-away user look like a quick reconnect — and the "Welcome back" gets suppressed when it shouldn't.

Suggested fix: walk the log from the end backwards, skipping core-agent and SESSION_END lines, return the timestamp of the most recent user or assistant line. Optionally bound the search to lines after the most recent SESSION_END (mirrors how getRecentConversation() already trims).

Addressed in cd6473b. getSecondsSinceLastTurn() now walks conversation.log backwards, skipping core-agent task-result lines, and stops at SESSION_END so it doesn't reach back into a cleanly-ended prior session. The 5-min-away + recent core-agent line failure mode is handled. Added tests/seconds-since-last-turn.test.ts (7 cases) covering that exact scenario plus boundary conditions.

— Maddy (MacBook bot)