fix(mcp): remove dead mutableConfig, fix misleading comment, and add installer tests

- Remove unused `mutableConfig` object in config.ts (dead code)
- Update comment to accurately describe type-cast assignment approach
  (not Object.defineProperty) and document `as const` runtime behavior
- Use MINIMUM_QSV_VERSION constant instead of hardcoded ">= 17.0.0"
  to prevent version string from going stale
- Log errors in sendToolListChanged catch handler instead of swallowing
- Export detectPackageManager and getManualInstructions for testability
- Add installer.test.ts with unit tests for both functions

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jqnatividad

.claude/skills/src/config.ts

@@ -906,16 +906,6 @@ export const config = {
   })(),
 } as const;
 
-/**
- * Mutable configuration fields that can change after initialization.
- * These are separated from the frozen `config` object because they need
- * to be updated when qsv is installed or the binary path changes at runtime.
- */
-const mutableConfig = {
-  qsvBinPath: config.qsvBinPath,
-  qsvValidation: config.qsvValidation,
-};
-
 /**
  * Re-run qsv binary detection and validation.
  * Called after a successful installation to refresh the config state.
@@ -926,11 +916,10 @@ export function revalidateQsvBinary(): {
   validation: QsvValidationResult;
 } {
   const result = initializeQsvBinaryPath();
-  mutableConfig.qsvBinPath = result.path;
-  mutableConfig.qsvValidation = result.validation;
 
-  // Update the config object's mutable fields via Object.defineProperty
-  // since the rest of config is frozen via `as const`
+  // Update config via type-cast assignment. This works because `as const`
+  // only produces a deeply-readonly TypeScript type — it does NOT call
+  // Object.freeze() at runtime, so the object remains mutable in JS.
   (config as { qsvBinPath: string }).qsvBinPath = result.path;
   (config as { qsvValidation: QsvValidationResult }).qsvValidation = result.validation;
 

.claude/skills/src/installer.ts

@@ -27,7 +27,7 @@ type PackageManager = "homebrew" | "scoop" | "none";
 /**
  * Detect available package manager for the current platform.
  */
-function detectPackageManager(): PackageManager {
+export function detectPackageManager(): PackageManager {
   const command = process.platform === "win32" ? "where" : "which";
 
   if (process.platform === "darwin" || process.platform === "linux") {
@@ -143,7 +143,7 @@ async function installViaScoop(): Promise<InstallResult> {
 /**
  * Return manual installation instructions when no supported package manager is available.
  */
-function getManualInstructions(platform: NodeJS.Platform): InstallResult {
+export function getManualInstructions(platform: NodeJS.Platform): InstallResult {
   const baseUrl = "https://github.com/dathere/qsv/releases/latest";
 
   let instructions: string;

.claude/skills/src/mcp-server.ts

@@ -694,7 +694,7 @@ class QsvMcpServer {
           });
           // Send tools/list_changed notification so the client re-fetches the full tool list
           if (setupResult.revalidated) {
-            this.server.sendToolListChanged().catch(() => {});
+            this.server.sendToolListChanged().catch((err: unknown) => console.error("[Server] Failed to send tools/list_changed:", err));
           }
           return setupResult.response;
         }

.claude/skills/src/mcp-tools.ts

@@ -26,7 +26,7 @@ import type { SkillExecutor } from "./executor.js";
 import type { Server } from "@modelcontextprotocol/sdk/server/index.js";
 import { executeDescribegptWithSampling, runQsvCapture } from "./mcp-sampling.js";
 import type { SkillLoader } from "./loader.js";
-import { config, getDetectionDiagnostics } from "./config.js";
+import { config, getDetectionDiagnostics, MINIMUM_QSV_VERSION } from "./config.js";
 import { formatBytes, findSimilarFiles, errorResult, successResult, isReservedCachePath, reservedCachePathError, getErrorMessage, isNodeError, describegptFallbackResult } from "./utils.js";
 import {
   detectDuckDb,
@@ -4123,7 +4123,7 @@ export async function handleSetupCall(
       `qsv was installed via ${result.method}, but validation failed:\n` +
       `${revalidation.validation.error}\n\n` +
       `The installed version may not meet the minimum requirements. ` +
-      `Please install qsv ${config.qsvValidation.version ? ">= 17.0.0" : ""} with Polars support ` +
+      `Please install qsv >= ${MINIMUM_QSV_VERSION} with Polars support ` +
       `from https://github.com/dathere/qsv#installation`,
     ),
   };

.claude/skills/tests/installer.test.ts

@@ -0,0 +1,64 @@
+/**
+ * Unit tests for the installer module
+ */
+
+import { test } from "node:test";
+import assert from "node:assert";
+import { detectPackageManager, getManualInstructions } from "../src/installer.js";
+
+test("detectPackageManager returns a valid package manager type", () => {
+  const result = detectPackageManager();
+  assert.ok(
+    result === "homebrew" || result === "scoop" || result === "none",
+    `Expected homebrew, scoop, or none but got: ${result}`,
+  );
+});
+
+test("detectPackageManager returns homebrew or none on non-Windows", () => {
+  if (process.platform !== "win32") {
+    const result = detectPackageManager();
+    assert.notStrictEqual(result, "scoop", "scoop should not be detected on non-Windows");
+  }
+});
+
+test("getManualInstructions returns instructions for macOS", () => {
+  const result = getManualInstructions("darwin");
+  assert.strictEqual(result.success, false);
+  assert.strictEqual(result.method, "manual");
+  assert.ok(result.instructions, "should have instructions");
+  assert.ok(result.instructions!.includes("macOS"), "should mention macOS");
+  assert.ok(result.instructions!.includes("Homebrew"), "should mention Homebrew");
+  assert.ok(
+    result.instructions!.includes("github.com/dathere/qsv/releases"),
+    "should include releases URL",
+  );
+});
+
+test("getManualInstructions returns instructions for Windows", () => {
+  const result = getManualInstructions("win32");
+  assert.strictEqual(result.success, false);
+  assert.strictEqual(result.method, "manual");
+  assert.ok(result.instructions, "should have instructions");
+  assert.ok(result.instructions!.includes("Windows"), "should mention Windows");
+  assert.ok(result.instructions!.includes("Scoop"), "should mention Scoop");
+});
+
+test("getManualInstructions returns instructions for Linux", () => {
+  const result = getManualInstructions("linux");
+  assert.strictEqual(result.success, false);
+  assert.strictEqual(result.method, "manual");
+  assert.ok(result.instructions, "should have instructions");
+  assert.ok(result.instructions!.includes("Linux"), "should mention Linux");
+  assert.ok(
+    result.instructions!.includes("cargo install"),
+    "should include build from source option",
+  );
+});
+
+test("getManualInstructions handles unknown platforms as Linux", () => {
+  const result = getManualInstructions("freebsd" as NodeJS.Platform);
+  assert.strictEqual(result.success, false);
+  assert.strictEqual(result.method, "manual");
+  assert.ok(result.instructions, "should have instructions for unknown platform");
+  assert.ok(result.instructions!.includes("Linux"), "should fall back to Linux instructions");
+});