Add slash command runner API (#212)

* Add command runner API

* Require a pi session for command running

pi-coding-agent-run-command is a public boundary, so a missing chat buffer should be a caller-visible error rather than a quiet no-op.  Keep the helper deliberately scoped to the current pi buffer session, document that scope, and cover the exact command text it sends.

---------

Co-authored-by: Daniel Nouri <daniel.nouri@gmail.com>

Author: bobrowadam

pi-coding-agent-menu.el

@@ -1058,18 +1058,44 @@ MESSAGES is a vector of plists from get_fork_messages."
 
 ;;;; Custom Commands
 
+(defun pi-coding-agent--command-chat-buffer-or-error ()
+  "Return the current pi chat buffer for running a slash command.
+Signal `user-error' when no live chat buffer is linked to the current buffer."
+  (let ((chat-buf (pi-coding-agent--get-chat-buffer)))
+    (unless (and chat-buf (buffer-live-p chat-buf))
+      (user-error "No pi session in current buffer"))
+    chat-buf))
+
+(defun pi-coding-agent-run-command (name &optional args)
+  "Run pi slash command NAME with optional ARGS in the current session.
+NAME is the command name without the leading slash.  ARGS, when
+non-nil and non-empty, is appended after one space.
+
+This command sends through the pi session associated with the current
+pi chat buffer or its linked input buffer.  Signal `user-error' when the
+current buffer is not part of a pi session."
+  (interactive
+   (progn
+     (pi-coding-agent--command-chat-buffer-or-error)
+     (list (completing-read "Pi command: "
+                            (mapcar (lambda (cmd) (plist-get cmd :name))
+                                    pi-coding-agent--commands)
+                            nil t)
+           (read-string "Args: "))))
+  (let ((chat-buf (pi-coding-agent--command-chat-buffer-or-error)))
+    (let ((full-command (if (or (null args) (string-empty-p args))
+                            (format "/%s" name)
+                          (format "/%s %s" name args))))
+      (with-current-buffer chat-buf
+        (pi-coding-agent--prepare-and-send full-command)))))
+
 (defun pi-coding-agent--run-custom-command (cmd)
   "Execute custom command CMD.
 Always prompts for arguments - user can press Enter if none needed.
 Sends the literal /command text to pi, which handles expansion."
-  (when-let* ((chat-buf (pi-coding-agent--get-chat-buffer)))
-    (let* ((name (plist-get cmd :name))
-           (args-string (read-string (format "/%s: " name)))
-           (full-command (if (string-empty-p args-string)
-                             (format "/%s" name)
-                           (format "/%s %s" name args-string))))
-      (with-current-buffer chat-buf
-        (pi-coding-agent--prepare-and-send full-command)))))
+  (let* ((name (plist-get cmd :name))
+         (args-string (read-string (format "/%s: " name))))
+    (pi-coding-agent-run-command name args-string)))
 
 (defun pi-coding-agent-run-custom-command ()
   "Select and run a custom command.

test/pi-coding-agent-menu-test.el

@@ -810,6 +810,71 @@ BINDING-SPEC is (DIR CHAT-NAME INPUT-NAME PROC).  DIR is evaluated once."
         (should (member "fix-tests" (nth 2 completion)))
         (should (member "review" (nth 2 completion)))))))
 
+(ert-deftest pi-coding-agent-test-run-command-formats-command-text ()
+  "run-command builds literal slash commands from NAME and optional args."
+  (let ((sent-messages nil)
+        (fake-proc (start-process "test" nil "cat")))
+    (set-process-query-on-exit-flag fake-proc nil)
+    (unwind-protect
+        (with-temp-buffer
+          (pi-coding-agent-chat-mode)
+          (let ((pi-coding-agent--process fake-proc))
+            (cl-letf (((symbol-function 'pi-coding-agent--rpc-async)
+                       (lambda (_proc msg _cb)
+                         (push (plist-get msg :message) sent-messages))))
+              (pi-coding-agent-run-command "greet")
+              (pi-coding-agent-run-command "greet" "")
+              (pi-coding-agent-run-command "greet" "world")
+              (should (equal (nreverse sent-messages)
+                             '("/greet" "/greet" "/greet world"))))))
+      (delete-process fake-proc))))
+
+(ert-deftest pi-coding-agent-test-run-command-uses-linked-input-session ()
+  "run-command sends through the chat buffer linked to current input."
+  (let ((sent-message nil)
+        (fake-proc (start-process "test" nil "cat"))
+        (chat-buf (generate-new-buffer " *pi-command-chat*"))
+        (input-buf (generate-new-buffer " *pi-command-input*")))
+    (set-process-query-on-exit-flag fake-proc nil)
+    (unwind-protect
+        (progn
+          (with-current-buffer chat-buf
+            (pi-coding-agent-chat-mode)
+            (setq pi-coding-agent--process fake-proc)
+            (pi-coding-agent--set-input-buffer input-buf))
+          (with-current-buffer input-buf
+            (pi-coding-agent-input-mode)
+            (pi-coding-agent--set-chat-buffer chat-buf)
+            (cl-letf (((symbol-function 'pi-coding-agent--rpc-async)
+                       (lambda (_proc msg _cb)
+                         (setq sent-message (plist-get msg :message)))))
+              (pi-coding-agent-run-command "greet" "world")))
+          (should (equal sent-message "/greet world")))
+      (pi-coding-agent-test--kill-live-buffers input-buf chat-buf)
+      (delete-process fake-proc))))
+
+(ert-deftest pi-coding-agent-test-run-command-requires-current-session ()
+  "run-command reports a missing current pi session."
+  (with-temp-buffer
+    (should-error (pi-coding-agent-run-command "greet")
+                  :type 'user-error)))
+
+(ert-deftest pi-coding-agent-test-run-command-interactive-requires-session-first ()
+  "run-command reports a missing session before prompting interactively."
+  (with-temp-buffer
+    (let (prompted)
+      (cl-letf (((symbol-function 'completing-read)
+                 (lambda (&rest _args)
+                   (setq prompted t)
+                   "greet"))
+                ((symbol-function 'read-string)
+                 (lambda (&rest _args)
+                   (setq prompted t)
+                   "")))
+        (should-error (call-interactively #'pi-coding-agent-run-command)
+                      :type 'user-error)
+        (should-not prompted)))))
+
 (ert-deftest pi-coding-agent-test-run-custom-command-sends-literal ()
   "run-custom-command sends literal /command text, not expanded."
   (let* ((sent-message nil)