refactor(sessions): add explicit merge activity policies

src/config/sessions/store.ts

@@ -1,4 +1,3 @@
-import crypto from "node:crypto";
 import fs from "node:fs";
 import path from "node:path";
 import { acquireSessionWriteLock } from "../../agents/session-write-lock.js";
@@ -39,6 +38,7 @@ import {
 import { applySessionStoreMigrations } from "./store-migrations.js";
 import {
   mergeSessionEntry,
+  mergeSessionEntryPreserveActivity,
   normalizeSessionRuntimeModelFields,
   type SessionEntry,
 } from "./types.js";
@@ -738,14 +738,9 @@ export async function recordSessionMetaFromInbound(params: {
         return null;
       }
       const next = existing
-        ? normalizeSessionRuntimeModelFields({
-            ...existing,
-            ...patch,
-            // Inbound metadata updates must not refresh activity timestamps;
-            // idle reset evaluation relies on updatedAt from actual session turns.
-            sessionId: existing.sessionId ?? crypto.randomUUID(),
-            updatedAt: existing.updatedAt ?? Date.now(),
-          })
+        ? // Inbound metadata updates must not refresh activity timestamps;
+          // idle reset evaluation relies on updatedAt from actual session turns.
+          mergeSessionEntryPreserveActivity(existing, patch)
         : mergeSessionEntry(existing, patch);
       store[resolved.normalizedKey] = next;
       for (const legacyKey of resolved.legacyKeys) {

src/config/sessions/types.ts

@@ -225,12 +225,31 @@ export function setSessionRuntimeModel(
   return true;
 }
 
-export function mergeSessionEntry(
+export type SessionEntryMergePolicy = "touch-activity" | "preserve-activity";
+
+type MergeSessionEntryOptions = {
+  policy?: SessionEntryMergePolicy;
+  now?: number;
+};
+
+function resolveMergedUpdatedAt(
   existing: SessionEntry | undefined,
   patch: Partial<SessionEntry>,
+  options?: MergeSessionEntryOptions,
+): number {
+  if (options?.policy === "preserve-activity" && existing) {
+    return existing.updatedAt ?? patch.updatedAt ?? options.now ?? Date.now();
+  }
+  return Math.max(existing?.updatedAt ?? 0, patch.updatedAt ?? 0, options?.now ?? Date.now());
+}
+
+export function mergeSessionEntryWithPolicy(
+  existing: SessionEntry | undefined,
+  patch: Partial<SessionEntry>,
+  options?: MergeSessionEntryOptions,
 ): SessionEntry {
   const sessionId = patch.sessionId ?? existing?.sessionId ?? crypto.randomUUID();
-  const updatedAt = Math.max(existing?.updatedAt ?? 0, patch.updatedAt ?? 0, Date.now());
+  const updatedAt = resolveMergedUpdatedAt(existing, patch, options);
   if (!existing) {
     return normalizeSessionRuntimeModelFields({ ...patch, sessionId, updatedAt });
   }
@@ -248,6 +267,22 @@ export function mergeSessionEntry(
   return normalizeSessionRuntimeModelFields(next);
 }
 
+export function mergeSessionEntry(
+  existing: SessionEntry | undefined,
+  patch: Partial<SessionEntry>,
+): SessionEntry {
+  return mergeSessionEntryWithPolicy(existing, patch);
+}
+
+export function mergeSessionEntryPreserveActivity(
+  existing: SessionEntry | undefined,
+  patch: Partial<SessionEntry>,
+): SessionEntry {
+  return mergeSessionEntryWithPolicy(existing, patch, {
+    policy: "preserve-activity",
+  });
+}
+
 export function resolveFreshSessionTotalTokens(
   entry?: Pick<SessionEntry, "totalTokens" | "totalTokensFresh"> | null,
 ): number | undefined {