Extract CliError into src/errors.ts

CliError used to live in cli.ts and was imported by configFile.ts purely
to grab a one-line class — the dependency arrow said 'config-file loader
depends on the CLI parser' when really it just needed a shared error
type.

Moving CliError to its own errors.ts module flattens the graph:

  errors.ts  (no internal deps)
    |
    +-- cli.ts
    +-- configFile.ts
    +-- config.ts  (will use it in the next commit)

cli.ts re-exports CliError for any consumer that prefers to keep
importing it from there; the canonical home is now errors.ts.

src/cli.ts

@@ -27,14 +27,7 @@ import { fileURLToPath } from "node:url";
 import { parseArgs } from "node:util";
 
 import { DEFAULT_CONFIG, defaultConfigPath } from "./config.ts";
-
-/**
- * Thrown when CLI input is invalid (unknown option, missing value, bad
- * number, malformed config file). Distinct from runtime errors so the
- * entry point can exit with code 2 (user error) instead of code 1
- * (runtime failure).
- */
-export class CliError extends Error {}
+import { CliError } from "./errors.ts";
 
 /**
  * Result of `parseCliArgs`. Numeric fields are `undefined` when the user

src/config.ts

@@ -21,6 +21,8 @@
 
 import { join } from "node:path";
 
+import { CliError } from "./errors.ts";
+
 // Single source of truth for default values. The same file ships in the
 // install tree and is copied to $XDG_CONFIG_HOME/move/config.json on a
 // fresh install (only if no config exists there yet). Values use the CLI
@@ -141,7 +143,17 @@ export function defaultConfigPath(): string {
     if (xdg && xdg.length > 0) {
         return join(xdg, "move", "config.json");
     }
-    const home = process.env.HOME ?? "";
+    const home = process.env.HOME;
+    if (!home || home.length === 0) {
+        // Neither var is set; we don't have a sensible fallback. Throwing
+        // CliError lets the entry-point's normal handler surface this as
+        // 'move: cannot resolve default config path: ...' + exit 2 instead
+        // of silently producing '/.config/move/config.json' and bewildering
+        // the user with a downstream 'file not found' message.
+        throw new CliError(
+            "cannot resolve default config path: neither $XDG_CONFIG_HOME nor $HOME is set",
+        );
+    }
     return join(home, ".config", "move", "config.json");
 }
 

src/configFile.ts

@@ -27,8 +27,8 @@
 
 import { existsSync, readFileSync, statSync } from "node:fs";
 
-import { CliError } from "./cli.ts";
 import { defaultConfigPath, type ConfigOverrides } from "./config.ts";
+import { CliError } from "./errors.ts";
 
 const ALLOWED_KEYS: ReadonlySet<string> = new Set<string>([
     "moveInterval",

src/errors.ts

@@ -0,0 +1,16 @@
+/**
+ * errors.ts
+ * ---------
+ * Cross-cutting error types used by parsers, loaders, and config resolution.
+ * Kept in its own module so feature modules can import error types without
+ * pulling in unrelated implementation code (e.g., the JSON loader doesn't
+ * need to depend on the CLI parser just to throw a typed error).
+ */
+
+/**
+ * Thrown when user-supplied input is invalid: unknown CLI option, missing
+ * value, non-positive number, malformed config file, unresolvable default
+ * path, etc. Distinct from runtime errors so the top-level entry can exit
+ * with code 2 (user error) instead of code 1 (runtime failure).
+ */
+export class CliError extends Error {}

src/move.ts

@@ -49,7 +49,13 @@ try {
 }
 
 if (cliArgs.help) {
-    printHelp();
+    // printHelp() resolves defaultConfigPath(), which can throw CliError
+    // when neither $XDG_CONFIG_HOME nor $HOME is set.
+    try {
+        printHelp();
+    } catch (err: unknown) {
+        failUser(err);
+    }
     process.exit(0);
 }
 if (cliArgs.version) {