fix(ai-config): force tab-width=8 in gptel org-mode prompt buffers

gptel's `gptel--with-buffer-copy-internal` copies the source buffer's `major-mode` symbol but doesn't run mode hooks. An inherited-org-mode prompt buffer keeps `tab-width` at this config's global default of 4 instead of the 8 that `org-mode-hook` would set. When gptel later parses the prompt buffer with `org-element`, Org's `tab-width=8` guard raises "Tab width in Org files must be 8, not 4."

I was hitting this on every second `gptel-magit-generate-message` from COMMIT_EDITMSG. `vc-config.el` sets `git-commit-major-mode 'org-mode'`, and the diffs contained list-shaped content that `org-element--list-struct` parsed.

The advice forces `tab-width=8` in the prompt buffer when its inherited mode is org-mode. It's a local workaround for an upstream gap. An upstream patch to run `(delay-mode-hooks (funcall major-mode))` in the buffer-copy is the real fix. I'll send it next.

1 files changed, 22 insertions, 0 deletions

diff --git a/modules/ai-config.el b/modules/ai-config.el
index 4a3d6a82..2783bc18 100644
--- a/modules/ai-config.el
+++ b/modules/ai-config.el
@@ -379,6 +379,28 @@ Works for any buffer, whether it's visiting a file or not."
   (advice-add 'gptel-send :before #'cj/gptel--refresh-org-prefix)
   (add-hook 'gptel-post-response-functions #'cj/gptel-insert-model-heading))
 
+;; Workaround: gptel's `gptel--with-buffer-copy-internal' copies the
+;; source buffer's `major-mode' symbol into the prompt buffer but does
+;; not run mode hooks, so `org-mode-hook' never fires there.  In this
+;; config the global `tab-width' default is 4, while `org-mode-hook'
+;; sets it to 8 — so an inherited-org-mode prompt buffer keeps
+;; `tab-width=4', and Org's `org-element--list-struct' guard raises
+;; "Tab width in Org files must be 8" when gptel later parses it.
+;;
+;; Triggered in practice by `gptel-magit-generate-message' run from
+;; COMMIT_EDITMSG with `git-commit-major-mode' set to `org-mode' (see
+;; modules/vc-config.el).  Force `tab-width=8' before `body-thunk'
+;; runs so the prompt buffer satisfies Org's invariant.
+(define-advice gptel--with-buffer-copy-internal
+    (:around (orig buf start end body-thunk) cj/fix-org-tab-width)
+  "Force `tab-width=8' in the gptel prompt buffer when its inherited
+`major-mode' is `org-mode'."
+  (funcall orig buf start end
+           (lambda ()
+             (when (eq major-mode 'org-mode)
+               (setq-local tab-width 8))
+             (funcall body-thunk))))
+
 ;;; ---------------------------- Toggle GPTel Window ----------------------------
 
 (defun cj/toggle-gptel ()