feat(opencode): add session tracking and update default model

configs/init-ai.el

@@ -47,10 +47,35 @@
                   (json-parse-buffer :object-type 'alist))))
       (alist-get 'key (alist-get 'opencode-go auth))))
 
+  (defvar-local kj-opencode-session-id nil
+    "Stable OpenCode session id for this conversation buffer.")
+
+  (defun kj-opencode-go-new-session-id ()
+    "Generate a new stable-enough random id for x-opencode-session."
+    (md5 (format "opencode-go-%s-%s" (random) (float-time))))
+
+  (defun kj-opencode-go-session-id (info)
+    "Return a stable x-opencode-session id for the buffer in INFO."
+    (let ((buf (or (plist-get info :buffer) (current-buffer))))
+      (if (buffer-live-p buf)
+          (with-current-buffer buf
+            (or kj-opencode-session-id
+                (setq-local kj-opencode-session-id
+                            (kj-opencode-go-new-session-id))))
+        (kj-opencode-go-new-session-id))))
+
+  (defun kj-opencode-go-header (info)
+    "Auth plus per-conversation session header for the OpenCode Go backends."
+    (append
+     (when-let* ((key (gptel--get-api-key)))
+       `(("Authorization" . ,(concat "Bearer " key))))
+     `(("x-opencode-session" . ,(kj-opencode-go-session-id info)))))
+
   (gptel-make-openai "OpenCode Go"
     :host "opencode.ai"
     :endpoint "/zen/go/v1/chat/completions"
     :key #'kj-opencode-go-key
+    :header #'kj-opencode-go-header
     :stream t
     :models '(minimax-m3 minimax-m2.7 minimax-m2.5
                          kimi-k3 kimi-k2.7-code kimi-k2.6 longcat-2.0 kimi-k2.5
@@ -67,6 +92,7 @@
     :host "opencode.ai"
     :endpoint "/zen/v1/chat/completions"
     :key #'kj-opencode-go-key
+    :header #'kj-opencode-go-header
     :stream t
     :models '(big-pickle deepseek-v4-flash-free muse-spark-1.2-contributor-free
                          mimo-v2.5-free hy3-free nemotron-3-ultra-free
@@ -191,7 +217,7 @@ content do not break gptel-magit."
   :config
   (setq agent-shell-opencode-authentication
         (agent-shell-opencode-make-authentication :none t))
-  (setq agent-shell-opencode-default-model-id "opencode-go/mimo-v2.5")
+  (setq agent-shell-opencode-default-model-id "opencode-go/qwen3.8-flash")
 
   ;; Header compacto
   (setq agent-shell-header-style 'text)