fix(sessions): provide plain-text extension theme

src/server/sessions/plainTextTheme.test.ts

@@ -0,0 +1,28 @@
+import { Theme } from "@earendil-works/pi-coding-agent";
+import { describe, expect, it } from "vitest";
+import { plainTextTheme } from "./plainTextTheme.js";
+
+describe("plainTextTheme", () => {
+  it("preserves Pi Theme compatibility without adding formatting", () => {
+    const text = "plain extension output";
+    const formatters: ((value: string) => string)[] = [
+      (value) => plainTextTheme.fg("accent", value),
+      (value) => plainTextTheme.bg("selectedBg", value),
+      (value) => plainTextTheme.bold(value),
+      (value) => plainTextTheme.italic(value),
+      (value) => plainTextTheme.underline(value),
+      (value) => plainTextTheme.inverse(value),
+      (value) => plainTextTheme.strikethrough(value),
+      plainTextTheme.getThinkingBorderColor("high"),
+      plainTextTheme.getBashModeBorderColor(),
+    ];
+
+    expect(plainTextTheme).toBeInstanceOf(Theme);
+    for (const format of formatters) expect(format(text)).toBe(text);
+  });
+
+  it("returns no terminal ANSI prefixes", () => {
+    expect(plainTextTheme.getFgAnsi("accent")).toBe("");
+    expect(plainTextTheme.getBgAnsi("selectedBg")).toBe("");
+  });
+});