refactor(ai-config): extract gptel model-apply step, drop dead branch

cj/gptel-change-model applied the selection inline (scope dispatch + message) and re-checked (stringp model) on a value already interned to a symbol. Extract cj/--gptel-apply-model-selection (scope backend model backend-name), which sets the vars globally or buffer-locally and returns the message; the dead stringp branch is gone. Adds direct coverage of both scopes.

2 files changed, 61 insertions, 8 deletions

diff --git a/modules/ai-config.el b/modules/ai-config.el
index 20bf6ec88..97af1296d 100644
--- a/modules/ai-config.el
+++ b/modules/ai-config.el
@@ -233,6 +233,20 @@ Returns a string like \"Anthropic - Claude: claude-opus-4-7\"."
             (or backend-name "AI")
             (cj/gptel--model-to-string current-model))))
 
+(defun cj/--gptel-apply-model-selection (scope backend model backend-name)
+  "Set gptel BACKEND and MODEL, globally or buffer-locally per SCOPE.
+SCOPE is \"global\" or \"buffer\"; any non-\"global\" value is buffer-local.
+MODEL is a symbol.  BACKEND-NAME is the display name for the confirmation.
+Returns the confirmation message string."
+  (if (string= scope "global")
+      (progn
+        (setq gptel-backend backend)
+        (setq gptel-model model)
+        (format "Changed to %s model: %s (global)" backend-name model))
+    (setq-local gptel-backend backend)
+    (setq-local gptel-model model)
+    (format "Changed to %s model: %s (buffer-local)" backend-name model)))
+
 ;; Backend/model switching commands
 (defun cj/gptel-change-model ()
   "Change the GPTel backend and select a model from that backend.
@@ -257,14 +271,8 @@ necessary. Prompt for whether to apply the selection globally or buffer-locally.
            (backend (nth 1 model-info))
            (model (intern (nth 2 model-info)))
            (backend-name (nth 3 model-info)))
-      (if (string= scope "global")
-          (progn
-            (setq gptel-backend backend)
-            (setq gptel-model model)
-            (message "Changed to %s model: %s (global)" backend-name model))
-        (setq-local gptel-backend backend)
-        (setq-local gptel-model (if (stringp model) (intern model) model))
-        (message "Changed to %s model: %s (buffer-local)" backend-name model)))))
+      (message "%s" (cj/--gptel-apply-model-selection
+                     scope backend model backend-name)))))
 
 (defun cj/gptel-switch-backend ()
   "Switch the GPTel backend and then choose one of its models."
diff --git a/tests/test-ai-config--apply-model-selection.el b/tests/test-ai-config--apply-model-selection.el
new file mode 100644
index 000000000..4ccd6d7a0
--- /dev/null
+++ b/tests/test-ai-config--apply-model-selection.el
@@ -0,0 +1,45 @@
+;;; test-ai-config--apply-model-selection.el --- Tests for cj/--gptel-apply-model-selection -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; cj/--gptel-apply-model-selection is the apply step extracted from the
+;; interactive cj/gptel-change-model: it sets gptel-backend/gptel-model globally
+;; or buffer-locally and returns the confirmation message.  The extraction also
+;; dropped a dead `(if (stringp model) ...)' branch (model is always a symbol by
+;; that point).
+
+;;; Code:
+
+(require 'ert)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'ai-config)
+
+(defvar gptel-backend)
+(defvar gptel-model)
+
+(ert-deftest test-ai-config-apply-model-global-sets-globals ()
+  "Normal: global scope assigns the global vars and reports (global)."
+  (let ((gptel-backend nil) (gptel-model nil))
+    (let ((msg (cj/--gptel-apply-model-selection "global" 'mybackend 'mymodel "MyAI")))
+      (should (eq gptel-backend 'mybackend))
+      (should (eq gptel-model 'mymodel))
+      (should (string-match-p "MyAI" msg))
+      (should (string-match-p "mymodel" msg))
+      (should (string-match-p "global" msg)))))
+
+(ert-deftest test-ai-config-apply-model-buffer-sets-buffer-locals ()
+  "Normal: buffer scope makes the vars buffer-local and reports (buffer-local)."
+  (let ((gptel-backend 'orig) (gptel-model 'origm))
+    (with-temp-buffer
+      (let ((msg (cj/--gptel-apply-model-selection "buffer" 'be 'mo "Name")))
+        (should (local-variable-p 'gptel-backend))
+        (should (local-variable-p 'gptel-model))
+        (should (eq gptel-backend 'be))
+        (should (eq gptel-model 'mo))
+        (should (string-match-p "buffer-local" msg))))
+    ;; outside the temp buffer the globals are untouched
+    (should (eq gptel-backend 'orig))
+    (should (eq gptel-model 'origm))))
+
+(provide 'test-ai-config--apply-model-selection)
+;;; test-ai-config--apply-model-selection.el ends here