refactor: introduce formatError centralizer + remove first batch of historical comments (TDD step 1 of first-principles plan)

tailscalectl/lib.js

@@ -33,8 +33,8 @@ function findActiveExitNode(peerMap) {
 
 var safeClipboardTools = ["dms", "wl-copy"]
 
-// Direct argv form — no sh -c, no escaping, no future injection surface (#49)
+    // Direct argv form — no sh -c, no escaping, no future injection surface.
-// clipmanctl intentionally dropped (niche optional history manager, not needed on DMS + Wayland)
+    // clipmanctl intentionally dropped (niche optional history manager, not needed on DMS + Wayland).
     var clipboardTools = {
     "dms":     { argv: ["dms", "cl", "copy"] },
     "wl-copy": { argv: ["wl-copy"] }
@@ -76,7 +76,7 @@ function getStrings() {
     }
 }
 
-// Light UI predicates extracted from QML (advances #43 — keeps view thin)
+    // Light UI predicates — keep the view thin.
     function shouldShowClearExitNode(currentExitNode) {
     return currentExitNode !== ""
 }
@@ -111,11 +111,22 @@ function errorMessage(cmd) {
         "disconnect": "Failed to disconnect from Tailscale",
         "set": "Failed to set exit node",
         "status": "Failed to read Tailscale status"
+    };
+    return messages[cmd] || "Tailscale command failed";
 }
-    return messages[cmd] || "Tailscale command failed"
+
+// Central error formatting for the widget. Used by both success and error paths.
+// detail is optional truncated stderr or extra context.
+function formatError(action, detail) {
+    var base = errorMessage(action);
+    if (detail && detail.length > 0) {
+        var truncated = detail.length > 120 ? detail.slice(0, 120) : detail;
+        return base + " — " + truncated;
+    }
+    return base;
 }
 
 // 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, shouldShowClearExitNode, isActiveExitNode }
+    module.exports = { parsePeers, makeExitNodeCommand, findActiveExitNode, errorMessage, formatError, 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, shouldShowClearExitNode, isActiveExitNode } = lib
+const { parsePeers, makeExitNodeCommand, findActiveExitNode, errorMessage, formatError, validateClipboardTool, buildCopyCommand, nextClipboardTool, allClipboardTools, buildToggleCommand, parseStatusResult, getStrings, shouldShowClearExitNode, isActiveExitNode } = lib
 
 /*
  * Test coverage note for #48:
@@ -240,3 +240,23 @@ test("parseStatusResult sets isConnected false for non-Running BackendState", ()
     const state = parseStatusResult(json)
     assert.strictEqual(state.isConnected, false)
 })
+
+// --- formatError (central error + detail formatting per first-principles plan) ---
+
+test("formatError returns base message without detail", () => {
+    assert.strictEqual(formatError("status"), "Failed to read Tailscale status")
+    assert.strictEqual(formatError("set"), "Failed to set exit node")
+})
+
+test("formatError appends and truncates detail", () => {
+    const longDetail = "x".repeat(200)
+    const msg = formatError("up", longDetail)
+    assert.ok(msg.includes("Failed to connect to Tailscale"))
+    assert.ok(msg.endsWith("x".repeat(120)))
+    assert.ok(msg.length < 200)
+})
+
+test("formatError handles empty or falsy detail gracefully", () => {
+    assert.strictEqual(formatError("down", ""), "Failed to disconnect from Tailscale")
+    assert.strictEqual(formatError("connect", null), "Failed to connect to Tailscale")
+})