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, 2 insertions, 38 deletions

diff --git a/modules/system-utils.el b/modules/system-utils.el
index e266cd15..008a5396 100644
--- a/modules/system-utils.el
+++ b/modules/system-utils.el
@@ -24,6 +24,7 @@
 ;;; Code:
 
 (require 'system-lib)
+(require 'external-open)
 
 (declare-function dired-get-file-for-visit "dired" ())
 (declare-function dired-file-name-at-point "dired" ())
@@ -57,13 +58,6 @@
 ;;; ------------------------------- Open File With ------------------------------
 ;; TASK: Favor this method over cj/open-this-file-with and add to custom buffer funcs
 
-(defun cj/--open-with-is-launcher-p (command)
-  "Return non-nil if COMMAND is a desktop launcher.
-Launchers (xdg-open, open, start) need to be called with `call-process'
-and a zero BUFFER argument so they fully detach from Emacs.  Other
-commands get `start-process-shell-command' so their output is visible."
-  (and (member command '("xdg-open" "open" "start")) t))
-
 (defun cj/open-file-with-command (command)
   "Open the current file with COMMAND.
 Works in both Dired buffers and regular file buffers.  Prompts for a
@@ -74,7 +68,7 @@ detached from Emacs."
 				   (read-file-name "File to open: "))))
 	(unless (and file (file-exists-p file))
 	  (error "No valid file found or selected"))
-	(if (cj/--open-with-is-launcher-p command)
+	(if (cj/external-open-launcher-p command)
 		(progn
 		  (call-process command nil 0 nil file)
 		  (message "Opening %s with %s..."
@@ -90,36 +84,6 @@ detached from Emacs."
 		(message "Running %s on %s..."
 				 (file-name-nondirectory file) command)))))
 
-(defun cj/identify-external-open-command ()
-  "Return the OS-default \"open\" command for this host.
-Signals an error if the host is unsupported."
-  (cond
-   ((env-linux-p)   "xdg-open")
-   ((env-macos-p)   "open")
-   ((env-windows-p) "start")
-   (t (error "External-open: unsupported host environment"))))
-
-(defun cj/xdg-open (&optional filename)
-  "Open FILENAME (or the file at point) with the OS default handler.
-Logs output and exit code to buffer *external-open.log*."
-  (interactive)
-  (let* ((file  (expand-file-name
-				 (or (cj/file-from-context filename)
-					 (user-error "No file associated with this buffer"))))
-		 (cmd   (cj/identify-external-open-command))
-		 (logbuf (get-buffer-create "*external-open.log*")))
-	(with-current-buffer logbuf
-	  (goto-char (point-max))
-	  (insert (format-time-string "[%Y-%m-%d %H:%M:%S] "))
-	  (insert (format "Opening: %s\n" file)))
-	(cond
-	 ((env-windows-p)
-	  (w32-shell-execute "open" file))
-	 (t
-	  (call-process cmd nil 0 nil file)
-	  (with-current-buffer logbuf
-		(insert "  → Launched asynchronously\n"))))
-	nil))
 
 ;;; ------------------------------ Server Shutdown ------------------------------