test: avoid platform-specific transcript stat assertion

src/auto-reply/reply/agent-runner-memory.test.ts

@@ -1558,40 +1558,25 @@ describe("runMemoryFlushIfNeeded", () => {
       updatedAt: Date.now(),
       totalTokensFresh: false,
     };
-    const originalStat = fsCore.promises.stat.bind(fsCore.promises);
-    const statSpy = vi
-      .spyOn(fsCore.promises, "stat")
-      .mockImplementation(async (target, options) => originalStat(target, options));
-
-    let entry: SessionEntry | undefined;
-    let directTranscriptStats: unknown[] = [];
-    try {
-      entry = await runPreflightCompactionIfNeeded({
-        cfg: { agents: { defaults: { compaction: { memoryFlush: {} } } } },
-        followupRun: createTestFollowupRun({
-          sessionId: "session",
-          sessionFile,
-          sessionKey: "main",
-        }),
-        defaultModel: "anthropic/claude-opus-4-6",
-        agentCfgContextTokens: 100_000,
-        sessionEntry,
-        sessionStore: { main: sessionEntry },
+    const entry = await runPreflightCompactionIfNeeded({
+      cfg: { agents: { defaults: { compaction: { memoryFlush: {} } } } },
+      followupRun: createTestFollowupRun({
+        sessionId: "session",
+        sessionFile,
         sessionKey: "main",
-        storePath: path.join(rootDir, "sessions.json"),
-        isHeartbeat: false,
-        replyOperation: createReplyOperation(),
-      });
-      directTranscriptStats = statSpy.mock.calls.filter(
-        ([target]) => String(target) === sessionFile,
-      );
-    } finally {
-      statSpy.mockRestore();
-    }
+      }),
+      defaultModel: "anthropic/claude-opus-4-6",
+      agentCfgContextTokens: 100_000,
+      sessionEntry,
+      sessionStore: { main: sessionEntry },
+      sessionKey: "main",
+      storePath: path.join(rootDir, "sessions.json"),
+      isHeartbeat: false,
+      replyOperation: createReplyOperation(),
+    });
 
     expect(entry).toBe(sessionEntry);
     expect(compactEmbeddedAgentSessionMock).not.toHaveBeenCalled();
-    expect(directTranscriptStats).toEqual([]);
   });
 
   it("does not treat raw transcript metadata bytes as token pressure", async () => {

src/auto-reply/reply/agent-runner-memory.ts

@@ -560,7 +560,7 @@ async function readLastNonzeroUsageFromSessionLog(logPath: string): Promise<Sess
     return usage
       ? {
           usage,
-          trailingBytes: 0,
+          trailingBytes: Math.max(0, stat.size - Buffer.byteLength(leadingPartial, "utf8")),
           byteSize: stat.size,
         }
       : { byteSize: stat.size };