Fix compaction replay dropping history on missing firstKeptEntryId

packages/dmoss-agent/src/core/session/session-manager.ts

@@ -579,7 +579,14 @@ function buildSessionContext(state: SessionState): Message[] {
     const compactionIdx = path.findIndex(
       (entry) => entry.type === "compaction" && entry.id === compaction.id,
     );
-    let foundFirstKept = false;
+    // If firstKeptEntryId is missing from the path (corruption/race — the codec
+    // only warns on load), the kept tail would otherwise be silently dropped on
+    // replay, losing recent history the compaction summary does NOT cover. Fall
+    // back to keeping every pre-compaction entry instead of dropping them.
+    const firstKeptExists = path
+      .slice(0, compactionIdx < 0 ? 0 : compactionIdx)
+      .some((entry) => entry.id === compaction.firstKeptEntryId);
+    let foundFirstKept = !firstKeptExists;
     for (let i = 0; i < compactionIdx; i++) {
       const entry = path[i];
       if (entry.id === compaction.firstKeptEntryId) {

packages/dmoss-agent/test/session-compaction-replay.spec.mjs

@@ -0,0 +1,44 @@
+#!/usr/bin/env node
+/**
+ * Compaction replay must not silently drop kept history when
+ * compaction.firstKeptEntryId is missing from the path (corruption/race — the
+ * JSONL codec only warns on load). Before the fix, buildSessionContext never
+ * flipped foundFirstKept, so every pre-compaction entry was dropped, losing
+ * recent history the summary does NOT cover. Red before / green after.
+ *
+ * Run:
+ *   npm run build -w @rdk-moss/agent
+ *   node packages/dmoss-agent/test/session-compaction-replay.spec.mjs
+ */
+import assert from 'node:assert/strict';
+import fs from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
+import { SessionManager } from '../dist/core/session/session-manager.js';
+
+const tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'dmoss-compaction-replay-'));
+try {
+  const sm = new SessionManager(tmpDir);
+  const key = 's1';
+
+  await sm.append(key, { role: 'user', content: 'PRECOMP-1' });
+  await sm.append(key, { role: 'assistant', content: 'PRECOMP-2' });
+  await sm.append(key, { role: 'user', content: 'PRECOMP-3' });
+  // Compaction whose firstKeptEntryId does NOT exist in the path.
+  await sm.appendCompaction(key, 'THE-COMPACTION-SUMMARY', 'nonexistent-kept-id', 100);
+  await sm.append(key, { role: 'assistant', content: 'POSTCOMP-1' });
+
+  const ctx = await sm.load(key);
+  const text = JSON.stringify(ctx);
+
+  assert.match(text, /THE-COMPACTION-SUMMARY/, 'compaction summary must be replayed');
+  assert.match(text, /POSTCOMP-1/, 'post-compaction message must be present');
+  // The core bug: pre-compaction kept messages must NOT vanish when
+  // firstKeptEntryId is missing.
+  assert.match(text, /PRECOMP-1/, 'pre-compaction history must not be lost when firstKeptEntryId is missing');
+  assert.match(text, /PRECOMP-3/, 'all pre-compaction messages preserved');
+
+  console.log('  [PASS] compaction replay preserves history when firstKeptEntryId is missing');
+} finally {
+  fs.rmSync(tmpDir, { recursive: true, force: true });
+}