[Bug]: Per-message nudge triggers every turn after restart — lastPerMessageNudgeTokens not persisted when nudge fires without anchor changes #60

// ~line 6338
state.nudges.lastPerMessageNudgeTokens = currentTokens;
state.nudges.lastPerMessageNudgeTurn = state.currentTurn ?? 0;
However, saveSessionState() is only called when anchorsChanged is true:
// ~line 6380
if (anchorsChanged) {
    saveSessionState(state, logger).catch(() => {});
}
When a nudge triggers via the growth check (growthSinceLastNudge >= nudgeGrowthTokens) without any anchor changes (no compress/decompress operations), anchorsChanged remains false, and the updated lastPerMessageNudgeTokens is never persisted to disk.
On the next OpenCode restart:
1. loadSessionState() reads the stale lastPerMessageNudgeTokens from disk (e.g. 73018, set hours/turns ago)
2. currentTokens is now much higher (e.g. 142K)
3. growth = 142K - 73K = 69K >= nudgeGrowthTokens (30000) → nudge triggers
4. In-memory update again not persisted (anchorsChanged = false)
5. Infinite loop: nudge fires every turn for the entire session lifetime
Reproduction
1. Start a long session (1267+ turns, ~142K tokens)
2. Let a nudge fire naturally (growth exceeds nudgeGrowthTokens)
3. Ensure no compress/decompress happens around the same time
4. Restart OpenCode (close and reopen the TUI)
5. Send any message → nudge fires immediately
6. Send another message → nudge fires again
7. Repeat indefinitely
Expected behavior
After a nudge fires, lastPerMessageNudgeTokens should be persisted to disk so that on restart, the growth baseline is correct and the nudge only fires when actual new growth exceeds the threshold.
Environment
- OpenCode version: 1.17.13
- opencode-acp plugin version: 0.19
- OS: win10
Proposed fix
Change the save condition to also persist when a nudge has fired:
if (anchorsChanged || decision.shouldNudge) {
    saveSessionState(state, logger).catch(() => {});
}
(Older versions use shouldNudge instead of decision.shouldNudge — same fix applies.)
Session state evidence
{
  "nudges": {
    "lastPerMessageNudgeTokens": 73018,
    "lastPerMessageNudgeTurn": 1267
  },
  "lastUpdated": "2026-07-06T10:04:24"
}

### Expected Behavior

nudge state能被正确更新。if (anchorsChanged）改为if (anchorsChanged || decision.shouldNudge)后使用，不在每轮收到nudge触发。

### Debug Context Logs

```json
无log，llm上下文有