refactor(external-open): extract external-open-lib for shared helpers

Same shared-helpers split-pattern that ai-vterm/vterm-config use
through cj-window-toggle-lib and that calendar-sync uses through
cj-org-text-lib.  Pull the two pure dispatch helpers out of the
external-open feature module into a sibling library so consumers
that only need the dispatch don't have to require the whole feature.

New `modules/external-open-lib.el' carries:
- `cj/external-open-command'
- `cj/external-open-launcher-p'

`modules/external-open.el' stays as the feature module: the
`default-open-extensions' defcustom, the `find-file' advice
(`cj/find-file-auto'), and the interactive commands (`cj/xdg-open',
`cj/open-this-file-with').  It now requires external-open-lib for
the dispatch helpers.

Migrate consumers:
- system-utils.el used to require `external-open' for
  `cj/external-open-launcher-p' alone -- now requires
  `external-open-lib' directly.
- dirvish-config.el calls `cj/external-open-command' from
  `cj/dirvish-open-file-manager-here' -- add an explicit
  `(require \='external-open-lib)'.

Test files renamed to match the system-lib naming pattern
(test-<library>-<feature>.el):
- test-external-open-command.el -> test-external-open-lib-command.el
- test-external-open-launcher-p.el -> test-external-open-lib-launcher-p.el

No behavior change.

2 files changed, 10 insertions, 10 deletions

diff --git a/tests/test-external-open-command.el b/tests/test-external-open-lib-command.el
index b408b305..7f54442c 100644
--- a/tests/test-external-open-command.el
+++ b/tests/test-external-open-lib-command.el
@@ -1,7 +1,7 @@
-;;; test-external-open-command.el --- Tests for cj/external-open-command -*- lexical-binding: t; -*-
+;;; test-external-open-lib-command.el --- Tests for cj/external-open-command -*- lexical-binding: t; -*-
 
 ;;; Commentary:
-;; Unit tests for `cj/external-open-command' in external-open.el.  The
+;; Unit tests for `cj/external-open-command' in external-open-lib.el.  The
 ;; function dispatches on host-environment predicates to return the
 ;; appropriate "open" command: xdg-open on Linux, open on macOS,
 ;; start on Windows.  Returns nil for unsupported hosts (callers that
@@ -16,7 +16,7 @@
 (setq package-user-dir (expand-file-name "elpa" user-emacs-directory))
 (package-initialize)
 (add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
-(require 'external-open)
+(require 'external-open-lib)
 
 (defmacro test-eoc--with-host (linux macos windows &rest body)
   "Run BODY with env-*-p predicates stubbed to LINUX, MACOS, WINDOWS."
@@ -61,5 +61,5 @@ user-error with a clear message."
   (test-eoc--with-host nil nil nil
     (should-not (cj/external-open-command))))
 
-(provide 'test-external-open-command)
-;;; test-external-open-command.el ends here
+(provide 'test-external-open-lib-command)
+;;; test-external-open-lib-command.el ends here
diff --git a/tests/test-external-open-launcher-p.el b/tests/test-external-open-lib-launcher-p.el
index 4aca3a55..928293b4 100644
--- a/tests/test-external-open-launcher-p.el
+++ b/tests/test-external-open-lib-launcher-p.el
@@ -1,7 +1,7 @@
-;;; test-external-open-launcher-p.el --- Tests for cj/external-open-launcher-p -*- lexical-binding: t; -*-
+;;; test-external-open-lib-launcher-p.el --- Tests for cj/external-open-launcher-p -*- lexical-binding: t; -*-
 
 ;;; Commentary:
-;; Unit tests for `cj/external-open-launcher-p' in external-open.el.
+;; Unit tests for `cj/external-open-launcher-p' in external-open-lib.el.
 ;; The predicate returns t for desktop launcher commands (xdg-open,
 ;; open, start) that need `call-process' with a zero buffer argument
 ;; to fully detach from Emacs.  Anything else returns nil.
@@ -14,7 +14,7 @@
 (setq package-user-dir (expand-file-name "elpa" user-emacs-directory))
 (package-initialize)
 (add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
-(require 'external-open)
+(require 'external-open-lib)
 
 ;;; Normal cases
 
@@ -51,5 +51,5 @@
   "Error: nil input is handled gracefully (not in the launcher list)."
   (should-not (cj/external-open-launcher-p nil)))
 
-(provide 'test-external-open-launcher-p)
-;;; test-external-open-launcher-p.el ends here
+(provide 'test-external-open-lib-launcher-p)
+;;; test-external-open-lib-launcher-p.el ends here