fix(config): stop lowercasing filesystem paths (#613)

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

tests/unit/config/path-casing.test.ts

@@ -0,0 +1,67 @@
+import { dump } from "js-yaml";
+import { beforeEach, describe, expect, test } from "vitest";
+
+import { loadConfig } from "~/server/config/load";
+
+import { clearFakeFiles, createFakeFile } from "../setup/overlay-fs";
+
+const CONFIG_PATH = "/etc/headplane/config.yaml";
+
+function writeConfig(overrides: {
+  server?: Record<string, unknown>;
+  headscale?: Record<string, unknown>;
+}) {
+  createFakeFile(
+    CONFIG_PATH,
+    dump({
+      server: {
+        host: "0.0.0.0",
+        port: 3000,
+        cookie_secret: "abcdefghijklmnopqrstuvwxyz123456",
+        cookie_secure: false,
+        ...overrides.server,
+      },
+      headscale: { url: "http://localhost:8080", ...overrides.headscale },
+    }),
+  );
+}
+
+// `string.lower` rewrites the value it validates rather than rejecting it, so
+// declaring a filesystem path with it silently points Headplane at a different
+// directory on a case-sensitive filesystem.
+describe("filesystem paths preserve their casing", () => {
+  beforeEach(() => {
+    clearFakeFiles();
+  });
+
+  test("loadConfig_withMixedCaseDataPath_preservesIt", async () => {
+    writeConfig({ server: { data_path: "/srv/Headplane" } });
+    const config = await loadConfig(CONFIG_PATH);
+
+    expect(config.server.data_path).toBe("/srv/Headplane");
+  });
+
+  test("loadConfig_withMixedCaseHeadscalePaths_preservesThem", async () => {
+    writeConfig({
+      headscale: {
+        config_path: "/opt/Headscale/config.yaml",
+        dns_records_path: "/opt/Headscale/records.json",
+        tls_cert_path: "/opt/Headscale/Cert.pem",
+      },
+    });
+    const config = await loadConfig(CONFIG_PATH);
+
+    expect(config.headscale.config_path).toBe("/opt/Headscale/config.yaml");
+    expect(config.headscale.dns_records_path).toBe("/opt/Headscale/records.json");
+    expect(config.headscale.tls_cert_path).toBe("/opt/Headscale/Cert.pem");
+  });
+
+  test("loadConfig_withMixedCaseCookieDomain_stillLowercasesIt", async () => {
+    // Not a path: DNS is case-insensitive, so normalising here is correct and
+    // should stay.
+    writeConfig({ server: { cookie_domain: "Headplane.Example.COM" } });
+    const config = await loadConfig(CONFIG_PATH);
+
+    expect(config.server.cookie_domain).toBe("headplane.example.com");
+  });
+});