feat(ai-conversations): autosave on a periodic timer

The existing autosave only fired after gptel-send returned, so a
conversation paused mid-thought wasn't on disk if Emacs crashed. I
added a buffer-local repeating timer that calls
cj/gptel--save-buffer-to-file every cj/gptel-autosave-interval seconds
(default 60) for as long as cj/gptel--autosave-active-p holds.
Toggle-off and kill-buffer-hook cancel it cleanly.

Tests cover start/stop idempotency, the active-p predicate, the
kill-buffer cleanup hook, and the toggle integration.

2 files changed, 155 insertions, 10 deletions

diff --git a/modules/ai-conversations.el b/modules/ai-conversations.el
index 03ea6ec9..fc234a82 100644
--- a/modules/ai-conversations.el
+++ b/modules/ai-conversations.el
@@ -51,11 +51,53 @@ If displaying on the top or bottom, treat this value as a height fraction."
 (defvar-local cj/gptel-autosave-filepath nil
   "File path used for auto-saving the conversation buffer.")
 
+(defvar-local cj/gptel-autosave--timer nil
+  "Repeating timer used to auto-save the current GPTel buffer.")
+
+(defcustom cj/gptel-autosave-interval 60
+  "Seconds between periodic GPTel conversation autosaves."
+  :type 'number
+  :group 'cj/ai-conversations)
+
 (defvar cj/gptel-autosave-mode-line-format
   '(:eval (when (bound-and-true-p cj/gptel-autosave-enabled) " [AS]"))
   "Mode-line construct that surfaces autosave state in GPTel buffers.")
 (put 'cj/gptel-autosave-mode-line-format 'risky-local-variable t)
 
+(defun cj/gptel--autosave-active-p ()
+  "Return non-nil when the current buffer has an autosave target."
+  (and (bound-and-true-p gptel-mode)
+       cj/gptel-autosave-enabled
+       (stringp cj/gptel-autosave-filepath)
+       (> (length cj/gptel-autosave-filepath) 0)))
+
+(defun cj/gptel--autosave-stop-timer ()
+  "Cancel the current buffer's periodic autosave timer, if any."
+  (when cj/gptel-autosave--timer
+    (cancel-timer cj/gptel-autosave--timer)
+    (setq-local cj/gptel-autosave--timer nil)))
+
+(defun cj/gptel--autosave-timer-callback (buffer)
+  "Auto-save BUFFER from a periodic timer when autosave is still active."
+  (when (buffer-live-p buffer)
+    (with-current-buffer buffer
+      (if (cj/gptel--autosave-active-p)
+          (condition-case err
+              (cj/gptel--save-buffer-to-file (current-buffer) cj/gptel-autosave-filepath)
+            (error (message "cj/gptel periodic autosave failed: %s"
+                            (error-message-string err))))
+        (cj/gptel--autosave-stop-timer)))))
+
+(defun cj/gptel--autosave-start-timer ()
+  "Start the current buffer's periodic autosave timer when autosave is active."
+  (when (and (cj/gptel--autosave-active-p)
+             (not cj/gptel-autosave--timer))
+    (setq-local cj/gptel-autosave--timer
+                (run-with-timer cj/gptel-autosave-interval
+                                cj/gptel-autosave-interval
+                                #'cj/gptel--autosave-timer-callback
+                                (current-buffer)))))
+
 (defun cj/gptel-autosave-toggle ()
   "Toggle autosave on/off in the current GPTel buffer.
 Flips `cj/gptel-autosave-enabled' and forces a mode-line redisplay so
@@ -68,11 +110,13 @@ so a path exists to autosave to."
   (if cj/gptel-autosave-enabled
       (progn
         (setq-local cj/gptel-autosave-enabled nil)
+        (cj/gptel--autosave-stop-timer)
         (message "Autosave disabled"))
     (cond
      ((and (stringp cj/gptel-autosave-filepath)
            (> (length cj/gptel-autosave-filepath) 0))
       (setq-local cj/gptel-autosave-enabled t)
+      (cj/gptel--autosave-start-timer)
       (message "Autosave enabled (saving to %s)"
                (file-name-nondirectory cj/gptel-autosave-filepath)))
      ((y-or-n-p "No save target yet.  Save conversation first? ")
@@ -110,8 +154,13 @@ construct."
                 (append mode-line-format
                         (list 'cj/gptel-autosave-mode-line-format)))))
 
+(defun cj/gptel--install-autosave-buffer-hooks ()
+  "Install buffer-local cleanup hooks for GPTel autosave."
+  (add-hook 'kill-buffer-hook #'cj/gptel--autosave-stop-timer nil t))
+
 (with-eval-after-load 'gptel
-  (add-hook 'gptel-mode-hook #'cj/gptel--install-autosave-mode-line))
+  (add-hook 'gptel-mode-hook #'cj/gptel--install-autosave-mode-line)
+  (add-hook 'gptel-mode-hook #'cj/gptel--install-autosave-buffer-hooks))
 
 (defun cj/gptel--slugify-topic (s)
   "Return a filesystem-friendly slug for topic string S."
@@ -226,7 +275,8 @@ Enable autosave for subsequent AI responses to the same file."
 	  (cj/gptel--save-buffer-to-file buf filepath)
 	  (with-current-buffer buf
 		(setq-local cj/gptel-autosave-filepath filepath)
-		(setq-local cj/gptel-autosave-enabled t))
+		(setq-local cj/gptel-autosave-enabled t)
+		(cj/gptel--autosave-start-timer))
 	  (message "Conversation saved to: %s" filepath))))
 
 (defun cj/gptel-delete-conversation ()
@@ -261,7 +311,8 @@ Enable autosave for subsequent AI responses to the same file."
 (defun cj/gptel-load-conversation ()
   "Load a saved GPTel conversation into the AI-Assistant buffer.
 
-Prompt to save the current conversation first when appropriate, then enable autosave."
+Prompt to save the current conversation first when appropriate, then
+enable autosave."
   (interactive)
   (let ((ai-buffer (get-buffer-create "*AI-Assistant*")))
 	(when (and (with-current-buffer ai-buffer (> (buffer-size) 0))
@@ -289,7 +340,8 @@ Prompt to save the current conversation first when appropriate, then enable auto
 		(goto-char (point-max))
 		(set-buffer-modified-p t)
 		(setq-local cj/gptel-autosave-filepath filepath)
-		(setq-local cj/gptel-autosave-enabled t))
+		(setq-local cj/gptel-autosave-enabled t)
+		(cj/gptel--autosave-start-timer))
 	  (let ((buf (get-buffer "*AI-Assistant*")))
 		(unless (get-buffer-window buf)
 		  (display-buffer-in-side-window
diff --git a/tests/test-ai-conversations.el b/tests/test-ai-conversations.el
index 26b2423b..2d5aefd1 100644
--- a/tests/test-ai-conversations.el
+++ b/tests/test-ai-conversations.el
@@ -328,21 +328,107 @@
        ;; Must not signal even though the write will fail
        (cj/gptel--autosave-after-send)))))
 
+;; ------------------------------------------------------ autosave timer
+
+(ert-deftest test-ai-conversations-autosave-start-timer-normal ()
+  "Normal: starting autosave creates a repeating timer for the current buffer."
+  (with-temp-buffer
+    (setq-local gptel-mode t)
+    (setq-local cj/gptel-autosave-enabled t)
+    (setq-local cj/gptel-autosave-filepath "/tmp/foo.gptel")
+    (let ((calls nil))
+      (cl-letf (((symbol-function 'run-with-timer)
+                 (lambda (secs repeat function &rest args)
+                   (push (list secs repeat function args) calls)
+                   :fake-timer)))
+        (let ((cj/gptel-autosave-interval 17))
+          (cj/gptel--autosave-start-timer)))
+      (should (eq cj/gptel-autosave--timer :fake-timer))
+      (should (equal (caar calls) 17))
+      (should (equal (cadar calls) 17))
+      (should (eq (nth 2 (car calls)) #'cj/gptel--autosave-timer-callback))
+      (should (eq (car (nth 3 (car calls))) (current-buffer))))))
+
+(ert-deftest test-ai-conversations-autosave-start-timer-idempotent ()
+  "Boundary: starting autosave twice does not create a second timer."
+  (with-temp-buffer
+    (setq-local gptel-mode t)
+    (setq-local cj/gptel-autosave-enabled t)
+    (setq-local cj/gptel-autosave-filepath "/tmp/foo.gptel")
+    (setq-local cj/gptel-autosave--timer :existing-timer)
+    (let ((created 0))
+      (cl-letf (((symbol-function 'run-with-timer)
+                 (lambda (&rest _)
+                   (setq created (1+ created))
+                   :new-timer)))
+        (cj/gptel--autosave-start-timer))
+      (should (= created 0))
+      (should (eq cj/gptel-autosave--timer :existing-timer)))))
+
+(ert-deftest test-ai-conversations-autosave-stop-timer-cancels ()
+  "Normal: stopping autosave cancels the current buffer's timer."
+  (with-temp-buffer
+    (setq-local cj/gptel-autosave--timer :fake-timer)
+    (let ((cancelled nil))
+      (cl-letf (((symbol-function 'cancel-timer)
+                 (lambda (timer) (setq cancelled timer))))
+        (cj/gptel--autosave-stop-timer))
+      (should (eq cancelled :fake-timer))
+      (should-not cj/gptel-autosave--timer))))
+
+(ert-deftest test-ai-conversations-autosave-timer-callback-saves-active-buffer ()
+  "Normal: timer callback saves the live buffer when autosave is active."
+  (test-ai-conversations--with-temp-dir
+   (lambda (dir)
+     (let ((file (expand-file-name "timer.gptel" dir))
+           (buf (generate-new-buffer " *gptel timer test*")))
+       (unwind-protect
+           (with-current-buffer buf
+             (setq-local gptel-mode t)
+             (setq-local cj/gptel-autosave-enabled t)
+             (setq-local cj/gptel-autosave-filepath file)
+             (insert "timer body")
+             (cj/gptel--autosave-timer-callback buf)
+             (should (file-exists-p file)))
+         (when (buffer-live-p buf)
+           (kill-buffer buf)))))))
+
+(ert-deftest test-ai-conversations-autosave-timer-callback-stops-inactive-buffer ()
+  "Boundary: timer callback cancels itself when autosave is no longer active."
+  (let ((buf (generate-new-buffer " *gptel timer inactive*")))
+    (unwind-protect
+        (with-current-buffer buf
+          (setq-local gptel-mode t)
+          (setq-local cj/gptel-autosave-enabled nil)
+          (setq-local cj/gptel-autosave-filepath "/tmp/foo.gptel")
+          (setq-local cj/gptel-autosave--timer :fake-timer)
+          (let ((cancelled nil))
+            (cl-letf (((symbol-function 'cancel-timer)
+                       (lambda (timer) (setq cancelled timer))))
+              (cj/gptel--autosave-timer-callback buf))
+            (should (eq cancelled :fake-timer))
+            (should-not cj/gptel-autosave--timer)))
+      (when (buffer-live-p buf)
+        (kill-buffer buf)))))
+
 ;; ------------------------------------------------------ save-conversation
 
 (ert-deftest test-ai-conversations-save-conversation-interactive-new-topic ()
-  "Save-conversation writes file under the topic-slugged name."
+  "Save-conversation writes file, enables autosave, and starts a timer."
   (test-ai-conversations--with-temp-dir
    (lambda (dir)
      (let ((ai-buffer (generate-new-buffer "*AI-Assistant*")))
        (unwind-protect
            (progn
              (with-current-buffer ai-buffer
+               (setq-local gptel-mode t)
                (insert "session content"))
              (cl-letf (((symbol-function 'completing-read)
                         (lambda (&rest _) "Test Topic"))
                        ((symbol-function 'y-or-n-p)
-                        (lambda (&rest _) nil)))
+                        (lambda (&rest _) nil))
+                       ((symbol-function 'run-with-timer)
+                        (lambda (&rest _) :save-timer)))
                (cj/gptel-save-conversation)
                (let ((files (directory-files dir nil "test-topic_.*\\.gptel$")))
                  (should files)
@@ -350,7 +436,8 @@
                ;; Autosave state is set in the AI buffer
                (with-current-buffer ai-buffer
                  (should cj/gptel-autosave-enabled)
-                 (should (stringp cj/gptel-autosave-filepath)))))
+                 (should (stringp cj/gptel-autosave-filepath))
+                 (should (eq cj/gptel-autosave--timer :save-timer)))))
          (kill-buffer ai-buffer))))))
 
 (ert-deftest test-ai-conversations-save-conversation-error-no-buffer ()
@@ -417,13 +504,19 @@
     (should cj/gptel-autosave-enabled)))
 
 (ert-deftest test-ai-conversations-autosave-toggle-disables ()
-  "Toggle turns autosave off when already on."
+  "Toggle turns autosave off and cancels the periodic timer when already on."
   (with-temp-buffer
     (setq-local gptel-mode t)
     (setq-local cj/gptel-autosave-enabled t)
     (setq-local cj/gptel-autosave-filepath "/tmp/foo.gptel")
-    (cj/gptel-autosave-toggle)
-    (should-not cj/gptel-autosave-enabled)))
+    (setq-local cj/gptel-autosave--timer :fake-timer)
+    (let ((cancelled nil))
+      (cl-letf (((symbol-function 'cancel-timer)
+                 (lambda (timer) (setq cancelled timer))))
+        (cj/gptel-autosave-toggle))
+      (should-not cj/gptel-autosave-enabled)
+      (should (eq cancelled :fake-timer))
+      (should-not cj/gptel-autosave--timer))))
 
 (ert-deftest test-ai-conversations-autosave-toggle-prompts-when-no-filepath ()
   "Toggle prompts to save first when no filepath is configured."