feat(metrics): consume contextSize — current context-usage readout

Backend context-size handoff: re-pin [email protected] / [email protected]
(+ re-mirror .dispatch reference snapshots). Thread the optional contextSize
through core/metrics (done fold + durable + selectCurrentContextSize: latest
turn's defined value, undefined=>unknown never 0, durable-wins-over-live).
Chat store exposes currentContextSize; ContextSizeBadge renders
"N tokens in context" / "context size unknown" above the composer.
GLOSSARY: add context size / context window. 533 tests green.

1 files changed, 15 insertions, 0 deletions

diff --git a/src/core/metrics/format.test.ts b/src/core/metrics/format.test.ts
index 3eec93d..7c143d7 100644
--- a/src/core/metrics/format.test.ts
+++ b/src/core/metrics/format.test.ts
@@ -4,6 +4,7 @@ import {
 	computeCachePct,
 	computeExpectedCachePct,
 	computeTps,
+	formatContextSize,
 	viewCacheRate,
 	viewExpectedCache,
 	viewStepMetrics,
@@ -308,3 +309,17 @@ describe("viewExpectedCache", () => {
 		expect(v?.isHit).toBe(true);
 	});
 });
+
+describe("formatContextSize", () => {
+	it("formats a defined count with thousands separators", () => {
+		expect(formatContextSize(34102)).toBe("34,102 tokens in context");
+	});
+
+	it("renders a placeholder for undefined (never 0)", () => {
+		expect(formatContextSize(undefined)).toBe("context size unknown");
+	});
+
+	it("renders an explicit 0 as zero tokens (a real reported value)", () => {
+		expect(formatContextSize(0)).toBe("0 tokens in context");
+	});
+});