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.

1 files changed, 0 insertions, 65 deletions

diff --git a/tests/test-external-open-command.el b/tests/test-external-open-command.el
deleted file mode 100644
index b408b305..00000000
--- a/tests/test-external-open-command.el
+++ /dev/null
@@ -1,65 +0,0 @@
-;;; test-external-open-command.el --- Tests for cj/external-open-command -*- lexical-binding: t; -*-
-
-;;; Commentary:
-;; Unit tests for `cj/external-open-command' in external-open.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
-;; require a command should error on nil with a contextual message).
-
-;;; Code:
-
-(require 'ert)
-(require 'cl-lib)
-(require 'package)
-
-(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)
-
-(defmacro test-eoc--with-host (linux macos windows &rest body)
-  "Run BODY with env-*-p predicates stubbed to LINUX, MACOS, WINDOWS."
-  (declare (indent 3))
-  `(cl-letf (((symbol-function 'env-linux-p)   (lambda () ,linux))
-             ((symbol-function 'env-macos-p)   (lambda () ,macos))
-             ((symbol-function 'env-windows-p) (lambda () ,windows)))
-     ,@body))
-
-;;; Normal cases
-
-(ert-deftest test-eoc-linux-returns-xdg-open ()
-  "Normal: Linux host returns \"xdg-open\"."
-  (test-eoc--with-host t nil nil
-    (should (string= "xdg-open" (cj/external-open-command)))))
-
-(ert-deftest test-eoc-macos-returns-open ()
-  "Normal: macOS host returns \"open\"."
-  (test-eoc--with-host nil t nil
-    (should (string= "open" (cj/external-open-command)))))
-
-(ert-deftest test-eoc-windows-returns-start ()
-  "Normal: Windows host returns \"start\"."
-  (test-eoc--with-host nil nil t
-    (should (string= "start" (cj/external-open-command)))))
-
-;;; Boundary cases
-
-(ert-deftest test-eoc-dispatch-order-linux-wins ()
-  "Boundary: Linux check runs first; wins when predicates disagree.
-Documents the dispatch order.  A real host only returns t from one
-of these anyway -- but if something goes wrong, Linux takes priority."
-  (test-eoc--with-host t t t
-    (should (string= "xdg-open" (cj/external-open-command)))))
-
-(ert-deftest test-eoc-unsupported-host-returns-nil ()
-  "Boundary: when no platform predicate returns non-nil, returns nil.
-Callers requiring a command must handle the nil case explicitly --
-this is a behavior change from the prior `cj/identify-external-open-command'
-which signaled an error.  The wrapper `cj/xdg-open' converts nil to a
-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