refactor(ai-term): split into sessions, display, and EAT-backend layers

ai-term.el had grown to ~1,215 lines mixing project/tmux session discovery, window display policy, the EAT terminal backend, and the public commands, so a change to any one risked coupling to the others.

I extracted three layers, following the calendar-sync split shape: ai-term-sessions.el (discovery, tmux naming and parsing, launch command, picker ordering), ai-term-display.el (display-buffer actions and rule, toggle state, server-window routing), and ai-term-backend-eat.el (terminal create/reattach, pty send, EAT keymap). The backend file is named for its backend so a future one lands as a sibling. ai-term.el stays the public face (options, commands, keymap, shutdown), every name unchanged, so existing (require 'ai-term) callers and all 30 test files work as before.

The extracted layers forward-declare the face's defcustoms rather than requiring it, keeping the graph acyclic. I dropped the unused cl-lib and host-environment requires and added the three modules to the header-contract list.

1 files changed, 93 insertions, 0 deletions

diff --git a/modules/ai-term-backend-eat.el b/modules/ai-term-backend-eat.el
new file mode 100644
index 00000000..6d512831
--- /dev/null
+++ b/modules/ai-term-backend-eat.el
@@ -0,0 +1,93 @@
+;;; ai-term-backend-eat.el --- EAT terminal backend for ai-term -*- lexical-binding: t; -*-
+
+;; Author: Craig Jennings <c@cjennings.net>
+
+;;; Commentary:
+;;
+;; Layer: 3 (Domain Workflow).
+;; Category: D.
+;; Load shape: library.
+;; Top-level side effects: binds M-SPC in `eat-semi-char-mode-map' after EAT
+;;   loads.
+;; Runtime requires: ai-term-sessions.
+;; Direct test load: yes.
+;;
+;; EAT backend of ai-term: terminal buffer creation and tmux reattach, the
+;; pty send helper, and the EAT keymap integration.  The name is
+;; backend-specific on purpose -- a future terminal backend lands as a
+;; sibling ai-term-backend-<name>.el and everything above this layer stays
+;; put.  The display routing the created buffer goes through lives in
+;; ai-term-display (the display-buffer-alist rule); this module only calls
+;; `display-buffer'.
+
+;;; Code:
+
+(require 'ai-term-sessions)
+
+(declare-function eat "eat" (&optional program arg))
+(declare-function cj/ai-term-next "ai-term" ())
+(defvar eat-buffer-name)
+(defvar eat-semi-char-mode-map)
+
+(defun cj/--ai-term-send-string (buffer string)
+  "Send STRING to BUFFER's terminal process (the agent's shell).
+Sends to the pty directly so the launch command reaches the shell EAT runs."
+  (let ((proc (get-buffer-process buffer)))
+    (when (process-live-p proc)
+      (process-send-string proc string))))
+
+(defun cj/--ai-term-show-or-create (dir name)
+  "Show or create the AI-term buffer for project DIR with buffer NAME.
+
+If a buffer named NAME exists with a live process, display it.  If
+the buffer exists but its process is dead, kill it and recreate.  If
+no such buffer exists, create a new EAT terminal in DIR and send
+the project's tmux launch command (see `cj/--ai-term-launch-command') so
+the same project basename reattaches across Emacs restarts.
+
+EAT runs a plain shell with no auto-tmux hook, so the named
+`tmux new-session -A' launch command is the only thing that starts the
+session -- the spike confirmed EAT + tmux detach and reattach exactly
+like ghostel + tmux did.
+
+Records DIR in `cj/--ai-term-mru' (whichever branch runs) so the
+project picker can list recently-opened projects first.  Returns the
+buffer."
+  (cj/--ai-term-record-mru dir)
+  (let ((existing (get-buffer name)))
+    (cond
+     ((and existing (cj/--ai-term-process-live-p existing))
+      (display-buffer existing)
+      existing)
+     (t
+      (when existing
+        (kill-buffer existing))
+      ;; `eat' switches to its buffer in the selected window before our
+      ;; display-buffer-alist rule can route it; `save-window-excursion'
+      ;; reverts that, and the explicit display-buffer below routes the buffer
+      ;; through the alist into the agent slot.  `eat-buffer-name' is bound to
+      ;; NAME so the terminal is created under the agent name; EAT (unlike
+      ;; ghostel) does not rename the buffer from the terminal's OSC title, so
+      ;; the "agent [" prefix that buffer detection and the display rule key on
+      ;; stays put.
+      (save-window-excursion
+        (let ((default-directory dir)
+              (eat-buffer-name name))
+          (eat)))
+      (let ((buf (get-buffer name)))
+        (with-current-buffer buf
+          (cj/--ai-term-send-string
+           buf (concat (cj/--ai-term-launch-command dir) "\n")))
+        (display-buffer buf)
+        buf)))))
+
+;; In EAT's semi-char mode, keys not bound in `eat-semi-char-mode-map' are
+;; forwarded to the pty.  M-SPC (swap to the next agent) must reach Emacs from
+;; inside an agent buffer, so bind it in that map -- no exception-list or rebuild
+;; dance like ghostel needed.  C-; is already bound there (eat-config), so the
+;; C-; a family resolves through the global prefix without extra wiring.
+(with-eval-after-load 'eat
+  (keymap-set eat-semi-char-mode-map "M-SPC" #'cj/ai-term-next))
+
+(provide 'ai-term-backend-eat)
+;;; ai-term-backend-eat.el ends here