refactor(external-open): consolidate OS-open dispatch in external-open.el

Phase 4 of utility-consolidation. Three previously-overlapping helpers (system-utils' `cj/identify-external-open-command' and `cj/--open-with-is-launcher-p', plus the dirvish-only `cj/--file-manager-program-for' shipped earlier today) all answered "which OS-open program should I run?".  Pull the answer into one place: external-open.el.

Move and rename:

- `cj/--open-with-is-launcher-p' (system-utils) -> `cj/external-open-launcher-p' (external-open). Public name now matches its module.
- `cj/identify-external-open-command' (system-utils) -> `cj/external-open-command' (external-open). Returns nil for unsupported hosts instead of signaling -- callers that need a command must handle nil explicitly. The wrapper `cj/xdg-open' (also moved into external-open) converts nil to a `user-error' with a clear message, preserving the user-facing failure shape.
- Delete dirvish's `cj/--file-manager-program-for' helper. `cj/dirvish-open-file-manager-here' now calls `cj/external-open-command' directly. The shell-command fallback for nil-program preserves the previous escape hatch.

Break the system-utils <-> external-open recursive require by moving `cj/xdg-open' (the only system-utils function that external-open used) into external-open along with the dispatch.

Tests reorganized to match the move. Two new test files (`test-external-open-command.el', `test-external-open-launcher-p.el') replace the two system-utils-named test files. The dirvish file-manager-program test goes away with the helper. 11 tests covering Normal/Boundary/Error for the dispatch (plus the new "unsupported host returns nil" contract).

Add `(require \='external-open)' to system-utils.el and `(require \='system-lib)' to external-open.el (for `cj/file-from-context' which xdg-open uses).

1 files changed, 0 insertions, 54 deletions

diff --git a/tests/test-dirvish-config-file-manager-program.el b/tests/test-dirvish-config-file-manager-program.el
deleted file mode 100644
index bfd4cad9..00000000
--- a/tests/test-dirvish-config-file-manager-program.el
+++ /dev/null
@@ -1,54 +0,0 @@
-;;; test-dirvish-config-file-manager-program.el --- Tests for the file-manager dispatch -*- lexical-binding: t; -*-
-
-;;; Commentary:
-;; `cj/--file-manager-program-for' is the pure dispatch behind
-;; `cj/dirvish-open-file-manager-here'.  Given whether xdg-open is
-;; present and the running `system-type', it returns the program name
-;; the wrapper should call -- or nil to signal the wrapper should fall
-;; back to a shell-command.  Keeping `executable-find' and `system-type'
-;; outside lets the helper be tested without faking the live machine.
-
-;;; Code:
-
-(require 'ert)
-(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))
-(add-to-list 'load-path (expand-file-name "elpa/dirvish-2.3.0/extensions"
-                                          user-emacs-directory))
-(require 'user-constants)
-(require 'keybindings)
-(require 'dirvish-config)
-
-(ert-deftest test-cj--file-manager-program-for-xdg-open-on-linux ()
-  "Normal: xdg-open present on Linux returns xdg-open."
-  (should (equal (cj/--file-manager-program-for t 'gnu/linux)
-                 "xdg-open")))
-
-(ert-deftest test-cj--file-manager-program-for-xdg-open-wins-on-macos ()
-  "Boundary: xdg-open present even on macOS returns xdg-open (Linux-isms ported)."
-  (should (equal (cj/--file-manager-program-for t 'darwin)
-                 "xdg-open")))
-
-(ert-deftest test-cj--file-manager-program-for-darwin-no-xdg ()
-  "Normal: macOS without xdg-open returns open."
-  (should (equal (cj/--file-manager-program-for nil 'darwin)
-                 "open")))
-
-(ert-deftest test-cj--file-manager-program-for-windows-no-xdg ()
-  "Normal: Windows without xdg-open returns explorer."
-  (should (equal (cj/--file-manager-program-for nil 'windows-nt)
-                 "explorer")))
-
-(ert-deftest test-cj--file-manager-program-for-linux-without-xdg-falls-back ()
-  "Boundary: Linux without xdg-open returns nil so the wrapper shells out."
-  (should-not (cj/--file-manager-program-for nil 'gnu/linux)))
-
-(ert-deftest test-cj--file-manager-program-for-unknown-system-falls-back ()
-  "Boundary: an unknown `system-type' with no xdg-open returns nil."
-  (should-not (cj/--file-manager-program-for nil 'haiku)))
-
-(provide 'test-dirvish-config-file-manager-program)
-;;; test-dirvish-config-file-manager-program.el ends here