feat(ai-rewrite): add directive-picker wrappers around gptel-rewrite

`gptel-rewrite` is the killer feature for the keep-gptel decision,
and it now lives behind two commands instead of the bare call:

- `cj/gptel-rewrite-with-directive` (`C-; a r`, replacing the
  former bare `gptel-rewrite` binding): completing-read on a
  directive name from `cj/gptel-rewrite-directives`, then rewrite
  the active region.
- `cj/gptel-rewrite-redo-with-different-directive` (`C-; a R`):
  replay the prior region with a different directive.  The region
  is preserved via markers stored buffer-local on the first call so
  it survives accept/reject of the prior rewrite.

I picked the hook injection approach over an `:after`-advice +
state-capture pattern.  `gptel-rewrite-directives-hook` is an
abnormal hook gptel-rewrite already consults for a per-call
system message.  Wrapping the call in a one-shot `let`-binding on
that hook gives the directive exactly the lifetime of the rewrite
and leaves nothing to clean up.  Mutating `gptel-directives`
globally would mean either restoring it afterward or living with
the change -- both worse than the hook.

Directives ship inline as a `defcustom` alist with the six names
called out in the task -- `terse`, `fix-grammar`,
`refactor-readability`, `add-docstring`, `explain-as-comment`,
`shorten`.  Customization is a `customize-variable` or `setq`
away.

9 tests cover the defcustom shape (default names present, bodies
non-empty strings), the wrapper (normal path, no-region error,
unknown-directive error, last-state recording), and the redo
(replays the prior region, errors when no previous, excludes the
current directive from the re-pick prompt).  `gptel-rewrite`
stubbed in tests so no rewrite UI fires.

1 files changed, 6 insertions, 2 deletions

diff --git a/modules/ai-config.el b/modules/ai-config.el
index 6eff1ba6..c7a14cae 100644
--- a/modules/ai-config.el
+++ b/modules/ai-config.el
@@ -35,6 +35,8 @@
 (autoload 'cj/gptel-delete-conversation "ai-conversations" "Delete a saved AI conversation." t)
 (autoload 'cj/gptel-autosave-toggle "ai-conversations" "Toggle autosave in the current GPTel buffer." t)
 (autoload 'cj/gptel-quick-ask "ai-quick-ask" "One-shot quick-ask in a transient buffer." t)
+(autoload 'cj/gptel-rewrite-with-directive "ai-rewrite" "Pick a directive and run gptel-rewrite on the region." t)
+(autoload 'cj/gptel-rewrite-redo-with-different-directive "ai-rewrite" "Re-run the previous rewrite with a different directive." t)
 
 ;;; ------------------------- AI Config Helper Functions ------------------------
 
@@ -510,7 +512,8 @@ Works for any buffer, whether it's visiting a file or not."
   "m" #'cj/gptel-change-model        ;; change the LLM model
   "p" #'gptel-system-prompt          ;; change prompt
   "q" #'cj/gptel-quick-ask           ;; one-shot quick ask
-  "r" #'gptel-rewrite                ;; rewrite a region of code/text
+  "r" #'cj/gptel-rewrite-with-directive ;; rewrite region with a chosen directive
+  "R" #'cj/gptel-rewrite-redo-with-different-directive ;; redo last rewrite, new directive
   "c" #'cj/gptel-context-clear       ;; clear all context
   "s" #'cj/gptel-save-conversation   ;; save conversation
   "t" #'cj/toggle-gptel              ;; toggles the ai-assistant window
@@ -530,7 +533,8 @@ Works for any buffer, whether it's visiting a file or not."
     "C-; a m" "change model"
     "C-; a p" "change prompt"
     "C-; a q" "quick ask"
-    "C-; a r" "rewrite region"
+    "C-; a r" "rewrite region (directive)"
+    "C-; a R" "redo rewrite, new directive"
     "C-; a c" "clear context"
     "C-; a s" "save conversation"
     "C-; a t" "toggle window"