fix(sessions): clear stale contextTokens on model switch (#38044)

Merged via squash.

Prepared head SHA: bac2df4b7f
Co-authored-by: yuweuii <82372187+yuweuii@users.noreply.github.com>
Co-authored-by: jalehman <550978+jalehman@users.noreply.github.com>
Reviewed-by: @jalehman

src/auto-reply/status.test.ts

@@ -4,6 +4,7 @@ import { afterEach, describe, expect, it, vi } from "vitest";
 import { normalizeTestText } from "../../test/helpers/normalize-text.js";
 import { withTempHome } from "../../test/helpers/temp-home.js";
 import type { OpenClawConfig } from "../config/config.js";
+import { applyModelOverrideToSessionEntry } from "../sessions/model-overrides.js";
 import { createSuccessfulImageMediaDecision } from "./media-understanding.test-fixtures.js";
 import {
   buildCommandsMessage,
@@ -172,6 +173,39 @@ describe("buildStatusMessage", () => {
     expect(normalizeTestText(text)).toContain("Context: 200k/1.0m");
   });
 
+  it("recomputes context window from the active model after switching away from a smaller session override", () => {
+    const sessionEntry = {
+      sessionId: "switch-back",
+      updatedAt: 0,
+      providerOverride: "local",
+      modelOverride: "small-model",
+      contextTokens: 4_096,
+      totalTokens: 1_024,
+    };
+
+    applyModelOverrideToSessionEntry({
+      entry: sessionEntry,
+      selection: {
+        provider: "local",
+        model: "large-model",
+        isDefault: true,
+      },
+    });
+
+    const text = buildStatusMessage({
+      agent: {
+        model: "local/large-model",
+        contextTokens: 65_536,
+      },
+      sessionEntry,
+      sessionKey: "agent:main:main",
+      sessionScope: "per-sender",
+      queue: { mode: "collect", depth: 0 },
+    });
+
+    expect(normalizeTestText(text)).toContain("Context: 1.0k/66k");
+  });
+
   it("uses per-agent sandbox config when config and session key are provided", () => {
     const text = buildStatusMessage({
       config: {