fix(tui): prevent sidebar scrollbar flash (#40056)

packages/tui/test/feature-plugins/sidebar-context.test.tsx

@@ -0,0 +1,70 @@
+/** @jsxImportSource @opentui/solid */
+import { expect, test } from "bun:test"
+import { RGBA } from "@opentui/core"
+import { testRender } from "@opentui/solid"
+import type { Context } from "@opencode-ai/plugin/tui/context"
+import { SidebarContext } from "../../src/feature-plugins/sidebar/context"
+
+function context(options?: { cost?: number; tokens?: number }) {
+  const color = RGBA.fromInts(200, 200, 200)
+  return {
+    theme: { text: { default: color, subdued: color } },
+    data: {
+      session: {
+        get: () => ({ location: { directory: "/workspace" } }),
+        cost: () => options?.cost ?? 0,
+        message: {
+          list: () =>
+            options?.tokens
+              ? [
+                  {
+                    id: "message",
+                    type: "assistant",
+                    model: { providerID: "provider", id: "model" },
+                    tokens: {
+                      input: options.tokens,
+                      output: 0,
+                      reasoning: 0,
+                      cache: { read: 0, write: 0 },
+                    },
+                  },
+                ]
+              : [],
+        },
+      },
+      location: {
+        model: { list: () => [] },
+      },
+    },
+  } as unknown as Context
+}
+
+test("sidebar omits context before usage is available", async () => {
+  const app = await testRender(() => <SidebarContext context={context()} sessionID="session" />, {
+    width: 42,
+    height: 8,
+  })
+
+  try {
+    await app.renderOnce()
+    expect(app.captureCharFrame()).not.toContain("Context")
+    expect(app.captureCharFrame()).not.toContain("Not measured")
+  } finally {
+    app.renderer.destroy()
+  }
+})
+
+test("sidebar shows available context usage", async () => {
+  const app = await testRender(() => <SidebarContext context={context({ tokens: 1234 })} sessionID="session" />, {
+    width: 42,
+    height: 8,
+  })
+
+  try {
+    await app.renderOnce()
+    expect(app.captureCharFrame()).toContain("Context")
+    expect(app.captureCharFrame()).toContain("1,234 tokens")
+  } finally {
+    app.renderer.destroy()
+  }
+})