feat(step-context-update): update context window usage at end of each step

1 files changed, 7 insertions, 1 deletions

diff --git a/src/core/metrics/format.test.ts b/src/core/metrics/format.test.ts
index c7c4fbb..97170d0 100644
--- a/src/core/metrics/format.test.ts
+++ b/src/core/metrics/format.test.ts
@@ -351,8 +351,14 @@ describe("computeContextUsage", () => {
     expect(u.percent).toBeCloseTo(3.4102, 4);
   });
 
-  it("treats unknown contextSize as current 0", () => {
+  it("treats unknown contextSize as current null (never 0)", () => {
     const u = computeContextUsage(undefined, 1_000_000);
+    expect(u.current).toBeNull();
+    expect(u.percent).toBeNull();
+  });
+
+  it("an explicit 0 context size is a real reported value (current 0)", () => {
+    const u = computeContextUsage(0, 1_000_000);
     expect(u.current).toBe(0);
     expect(u.percent).toBe(0);
   });