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.test.ts

@@ -31,6 +31,7 @@ describe('compactHistory', () => {
     thresholdPct: 80,
     keepTurns: 2,  // keeps last 4 messages
     summaryMaxTokens: 1024,
+    importanceThreshold: 1,
   };
 
   it('returns no-op when messages count is at or below keepTurns threshold', async () => {
@@ -100,6 +101,7 @@ describe('compactHistory', () => {
     expect(DEFAULT_COMPACTION_CONFIG.thresholdPct).toBe(80);
     expect(DEFAULT_COMPACTION_CONFIG.keepTurns).toBe(4);
     expect(DEFAULT_COMPACTION_CONFIG.summaryMaxTokens).toBe(1024);
+    expect(DEFAULT_COMPACTION_CONFIG.importanceThreshold).toBe(1);
   });
 
   it('shifts leading assistant messages from toKeep into toCompact to ensure user-first', async () => {
@@ -120,4 +122,28 @@ describe('compactHistory', () => {
     expect(result.messages[1].role).toBe('user');
     expect(result.messages[1].content).toBe('Message 6');
   });
+
+  it('preserves high-importance older turns instead of compacting them', async () => {
+    const messages: Message[] = [
+      { role: 'user', content: 'hello' },
+      { role: 'assistant', content: 'hi' },
+      { role: 'user', content: 'I prefer concise responses and markdown tables.' },
+      { role: 'assistant', content: 'noted' },
+      { role: 'user', content: 'Message 4' },
+      { role: 'assistant', content: 'Message 5' },
+      { role: 'user', content: 'Message 6' },
+      { role: 'assistant', content: 'Message 7' },
+    ];
+
+    const orchestrator = makeMockOrchestrator();
+    const result = await compactHistory({
+      messages,
+      orchestrator,
+      config: { ...config, importanceThreshold: 0.45 },
+    });
+
+    expect(result.messages.some(msg => typeof msg.content === 'string' && msg.content.includes('I prefer concise responses'))).toBe(true);
+    expect(result.messages.some(msg => typeof msg.content === 'string' && msg.content.includes('[Summary of earlier conversation]'))).toBe(true);
+    expect(result.messages.length).toBeGreaterThan(5);
+  });
 });

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]),
   };
 }