fix: carry observed overflow token counts into compaction (#40357)

Merged via squash.

Prepared head SHA: b99eed4329bda45083cdedc2386c2c4041c034be
Co-authored-by: rabsef-bicrym <52549148+rabsef-bicrym@users.noreply.github.com>
Co-authored-by: jalehman <550978+jalehman@users.noreply.github.com>
Reviewed-by: @jalehman

test/setup.ts

@@ -10,12 +10,6 @@ vi.mock("@mariozechner/pi-ai", async (importOriginal) => {
   };
 });
 
-vi.mock("@mariozechner/pi-ai/oauth", () => ({
-  getOAuthApiKey: () => undefined,
-  getOAuthProviders: () => [],
-  loginOpenAICodex: vi.fn(),
-}));
-
 // Ensure Vitest environment is properly set
 process.env.VITEST = "true";
 // Config validation walks plugin manifests; keep an aggressive cache in tests to avoid