perf(sessions): extend transcript eviction grace from 20s to 3min

packages/core/src/sessions/sessionEventResidency.test.ts

@@ -1,11 +1,14 @@
 import type { AgentSession, SessionStatus } from "@posthog/shared";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
-import { SessionService, type SessionServiceDeps } from "./sessionService";
+import {
+  SESSION_EVENT_EVICT_GRACE_MS as GRACE_MS,
+  SessionService,
+  type SessionServiceDeps,
+} from "./sessionService";
 import { sessionStore, sessionStoreSetters } from "./sessionStore";
 
 const RUN = "run-res";
 const TASK = "task-res";
-const GRACE_MS = 20_000;
 
 const LOG_LINE = JSON.stringify({
   type: "notification",

packages/core/src/sessions/sessionService.ts

@@ -126,9 +126,10 @@ const SESSION_EVENT_FLUSH_MS = 16;
  * A backgrounded session's transcript is freed this long after it stops being
  * viewed, and reloaded from disk on return. Only disconnected (idle, no live
  * subscription) sessions are eligible, so no streamed event can append to an
- * evicted transcript.
+ * evicted transcript. Generous on purpose: reloading means a full log read and
+ * re-parse, so flipping between tasks within a few minutes must stay free.
  */
-const SESSION_EVENT_EVICT_GRACE_MS = 20_000;
+export const SESSION_EVENT_EVICT_GRACE_MS = 180_000;
 /**
  * On open, paint the last this-many bytes of the log immediately so a big
  * transcript shows its latest turns in tens of ms, while the authoritative
@@ -7027,6 +7028,12 @@ export class SessionService {
     if (session && session.eventCount > 0) return;
     if (!task.latest_run?.id || !task.latest_run?.log_url) return;
 
+    // Logs-only hydration grows the store like a connect does; bound the
+    // resident-session budget the same way (connectToTask and the cloud
+    // reconcile branch already do).
+    this.sessionLastUsedAt.set(task.id, Date.now());
+    void this.evictIdleSessions(task.id);
+
     this.loadLogsOnly({
       taskId: task.id,
       taskRunId: task.latest_run.id,

packages/core/src/sessions/sessionServiceEviction.test.ts

@@ -212,6 +212,33 @@ describe("SessionService idle session eviction", () => {
     expect(removeSession).not.toHaveBeenCalledWith("run-cloud-active");
   });
 
+  it("bounds the budget when reconciling a logs-only task", async () => {
+    const seeds = seedIdleSessions();
+    const { service, removeSession } = createHarness(seeds);
+    const loadLogsOnly = vi
+      .spyOn(service, "loadLogsOnly")
+      .mockResolvedValue(undefined);
+
+    service.reconcileTaskConnection({
+      task: {
+        id: "logs-only",
+        title: "logs-only",
+        description: "logs-only",
+        latest_run: { id: "run-logs-only", log_url: "https://logs" },
+      } as Task,
+      session: undefined,
+      repoPath: null,
+      isCloud: false,
+      isOnline: true,
+    } as ReconcileTaskConnectionParams);
+
+    await vi.waitFor(() => {
+      expect(removeSession).toHaveBeenCalledTimes(1);
+    });
+    expect(removeSession).toHaveBeenCalledWith("run-idle-0");
+    expect(loadLogsOnly).toHaveBeenCalled();
+  });
+
   it("evicts cloud sessions once their runs are terminal", async () => {
     const seeds = Array.from({ length: MAX_CONNECTED_SESSIONS }, (_, i) =>
       makeSession(`cloud-${i}`, i + 1, {