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+;;; external-open-lib.el --- Pure helpers for OS open-with dispatch -*- lexical-binding: t; -*-
+
+;; Author: Craig Jennings <c@cjennings.net>
+
+;;; Commentary:
+
+;; Pure helpers for resolving the OS-default "open" command and
+;; recognizing desktop launchers.  No side effects, no state.  The
+;; feature module (`external-open.el') uses these helpers; consumers
+;; that only need the dispatch (system-utils' "open with command",
+;; dirvish's "open file manager here") require this library directly
+;; instead of the feature module.
+;;
+;; Pulled out of `external-open.el' as part of utility-consolidation
+;; Phase 4.  See `docs/design/utility-consolidation.org'.
+
+;;; Code:
+
+(require 'host-environment)
+
+(defun cj/external-open-command ()
+  "Return the OS-default \"open\" command for this host, or nil if unsupported.
+Returns one of \"xdg-open\" (Linux), \"open\" (macOS), \"start\" (Windows).
+Callers that require a command should error on nil with a contextual
+message so the user sees what feature is unavailable."
+  (cond
+   ((env-linux-p)   "xdg-open")
+   ((env-macos-p)   "open")
+   ((env-windows-p) "start")
+   (t nil)))
+
+(defun cj/external-open-launcher-p (command)
+  "Return non-nil when 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 (stringp command)
+       (member command '("xdg-open" "open" "start"))
+       t))
+
+(provide 'external-open-lib)
+;;; external-open-lib.el ends here