refactor: extract shouldShowClearExitNode and isActiveExitNode to lib.js (TDD) — light progress on #43

- Two small pure UI predicates moved out of QML delegate
- QML now calls TailscaleLib.* (thinner glue)
- New tests + all existing tests pass
- No new state, no architecture change

Written by AI agent working for @jtmorris. Model: Grok build-0.1.

tailscalectl/TailscaleWidget.qml

@@ -202,7 +202,7 @@ PluginComponent {
                     }
 
                     MouseArea {
-                        visible: root.currentExitNode !== ""
+                        visible: TailscaleLib.shouldShowClearExitNode(root.currentExitNode)
                         cursorShape: Qt.PointingHandCursor
                         hoverEnabled: true
                         anchors.verticalCenter: parent.verticalCenter
@@ -292,7 +292,7 @@ PluginComponent {
                                     id: exitNodeButton
                                     text: "↗"
                                     font.pixelSize: Theme.fontSizeSmall
-                                    color: root.currentExitNode === modelData.hostname ? Theme.primary : Theme.surfaceVariantText
+                                    color: TailscaleLib.isActiveExitNode(root.currentExitNode, modelData.hostname) ? Theme.primary : Theme.surfaceVariantText
                                 }
                             }
                         }

tailscalectl/lib.js

@@ -76,6 +76,15 @@ function getStrings() {
     }
 }
 
+// Light UI predicates extracted from QML (advances #43 — keeps view thin)
+function shouldShowClearExitNode(currentExitNode) {
+    return currentExitNode !== ""
+}
+
+function isActiveExitNode(currentExitNode, hostname) {
+    return currentExitNode === hostname
+}
+
 function parseStatusResult(jsonText) {
     try {
         const data = JSON.parse(jsonText)
@@ -108,5 +117,5 @@ function errorMessage(cmd) {
 
 // CommonJS export for Node.js tests (ignored by QML)
 if (typeof module !== "undefined" && module.exports) {
-    module.exports = { parsePeers, makeExitNodeCommand, findActiveExitNode, errorMessage, validateClipboardTool, buildCopyCommand, nextClipboardTool, allClipboardTools, buildToggleCommand, parseStatusResult, getStrings }
+    module.exports = { parsePeers, makeExitNodeCommand, findActiveExitNode, errorMessage, validateClipboardTool, buildCopyCommand, nextClipboardTool, allClipboardTools, buildToggleCommand, parseStatusResult, getStrings, shouldShowClearExitNode, isActiveExitNode }
 }

test/lib.test.js

@@ -1,7 +1,7 @@
 import { test } from "node:test"
 import assert from "node:assert"
 import lib from "../tailscalectl/lib.js"
-const { parsePeers, makeExitNodeCommand, findActiveExitNode, errorMessage, validateClipboardTool, buildCopyCommand, nextClipboardTool, allClipboardTools, buildToggleCommand, parseStatusResult, getStrings } = lib
+const { parsePeers, makeExitNodeCommand, findActiveExitNode, errorMessage, validateClipboardTool, buildCopyCommand, nextClipboardTool, allClipboardTools, buildToggleCommand, parseStatusResult, getStrings, shouldShowClearExitNode, isActiveExitNode } = lib
 
 test("parsePeers extracts exitNode from ExitNodeOption", () => {
     const peerMap = {
@@ -157,6 +157,17 @@ test("getStrings.copied interpolates the text", () => {
     assert.ok(msg.includes("100.64.0.5"))
 })
 
+test("shouldShowClearExitNode returns true only when there is a current exit node", () => {
+    assert.strictEqual(shouldShowClearExitNode("router"), true)
+    assert.strictEqual(shouldShowClearExitNode(""), false)
+})
+
+test("isActiveExitNode correctly identifies the active exit node button", () => {
+    assert.strictEqual(isActiveExitNode("gluetun-sjc", "gluetun-sjc"), true)
+    assert.strictEqual(isActiveExitNode("gluetun-sjc", "gluetun-den"), false)
+    assert.strictEqual(isActiveExitNode("", "router"), false)
+})
+
 // --- buildToggleCommand ---
 
 test("buildToggleCommand returns down command when connected", () => {