feat(session): persist model tier overrides per session

Store per-session config in SQLite and route /model and /reset through command fast-paths so channel sessions keep independent model selection across reconnects and restarts.

src/context/compaction.ts

@@ -4,6 +4,7 @@ import type { MemoryStore } from '../memory/store.js';
 import { COMPACTION_SYSTEM_PROMPT, MEMORY_EXTRACTION_PROMPT } from '../backends/native/prompts.js';
 import { estimateMessageTokens } from './tokens.js';
 import { getMessageText } from '../models/media.js';
+import { selectImportantMessages } from './weighting.js';
 
 export interface CompactionConfig {
   /** Percentage of context window that triggers compaction (default: 80). */
@@ -12,6 +13,8 @@ export interface CompactionConfig {
   keepTurns: number;
   /** Maximum tokens for the compaction summary response. */
   summaryMaxTokens: number;
+  /** Preserve messages at or above this importance score from compaction. */
+  importanceThreshold: number;
 }
 
 export interface CompactionResult {
@@ -29,6 +32,7 @@ export const DEFAULT_COMPACTION_CONFIG: CompactionConfig = {
   thresholdPct: 80,
   keepTurns: 4,
   summaryMaxTokens: 1024,
+  importanceThreshold: 1,
 };
 
 export async function compactHistory(opts: {
@@ -56,10 +60,34 @@ export async function compactHistory(opts: {
   // Ensure toKeep starts with a user message to avoid assistant→assistant
   // after the compaction summary (which has role 'assistant').
   while (toKeep.length > 0 && toKeep[0].role === 'assistant') {
-    toCompact.push(toKeep.shift()!);
+    const shifted = toKeep.shift();
+    if (!shifted) {
+      break;
+    }
+    toCompact.push(shifted);
   }
 
-  const formattedConversation = toCompact.map((msg) => `${msg.role}: ${getMessageText(msg)}`).join('\n\n');
+  const preservedImportant = selectImportantMessages(toCompact, {
+    threshold: config.importanceThreshold,
+    maxMessages: Math.max(1, config.keepTurns),
+  });
+
+  const preservedSet = new Set(preservedImportant.map(item => item.index));
+  const toSummarize = toCompact.filter((_, index) => !preservedSet.has(index));
+
+  const formattedConversation = toSummarize.map((msg) => `${msg.role}: ${getMessageText(msg)}`).join('\n\n');
+
+  const preservedMessages = preservedImportant.map(item => item.message);
+
+  if (formattedConversation.trim().length === 0) {
+    const compactedMessages = [...preservedMessages, ...toKeep];
+    return {
+      messages: compactedMessages,
+      compactedCount: messages.length - compactedMessages.length,
+      tokensBefore: estimateMessageTokens(messages),
+      tokensAfter: estimateMessageTokens(compactedMessages),
+    };
+  }
 
   const tier = orchestrator.getDelegationTier('compaction');
 
@@ -99,9 +127,9 @@ export async function compactHistory(opts: {
   }
 
   return {
-    messages: [summaryMessage, ...toKeep],
-    compactedCount: toCompact.length,
+    messages: [...preservedMessages, summaryMessage, ...toKeep],
+    compactedCount: toSummarize.length,
     tokensBefore: estimateMessageTokens(messages),
-    tokensAfter: estimateMessageTokens([summaryMessage, ...toKeep]),
+    tokensAfter: estimateMessageTokens([...preservedMessages, summaryMessage, ...toKeep]),
   };
 }