#+TITLE: SKILL: Embedding Gateway (org-skill-embedding-gateway.org)
#+AUTHOR: Agent
#+FILETAGS: :skill:system:embedding:
#+PROPERTY: header-args:lisp :tangle ../lisp/system-model-embedding.lisp

* Architectural Intent

~system-model-embedding~ converts text into vector representations for semantic search and memory retrieval. It provides three backends:

- ~:local~ — any OpenAI-compatible ~/api/embeddings~ endpoint (Ollama, vLLM, etc.)
- ~:openai~ — the OpenAI ~/v1/embeddings~ API with an API key
- ~:hashing~ — a zero-dependency fallback that produces deterministic vectors from SHA-256 hashes. No server, no config, works offline.

The embedding queue (~embed-queue-object~ / ~embed-all-pending~) decouples document indexing from the main loop. On each heartbeat tick, ~embed-all-pending~ drains the queue and embeds all accumulated objects. This prevents indexing traffic from blocking conversational responses.

The default provider is ~:hashing~ — useful for bootstrapping with zero configuration and for deployments where embedding quality isn't critical. Switch to ~:local~ or ~:openai~ when you have an embedding server available.

This replaces the old ~system-embedding-gateway~ with the same logic but renamed to ~system-model-embedding~ to live alongside the other ~system-model-*~ skills.

* Implementation

** State
#+begin_src lisp
(in-package :passepartout)

(defvar *embedding-provider* :hashing
  "Active embedding provider: :hashing, :local, :openai.")

(defvar *embedding-queue* nil
  "Queue of text objects awaiting embedding.")

(defvar *embedding-batch-size* 10
  "Maximum texts per embedding API call.")
#+end_src

** Local backend (OpenAI-compatible)
#+begin_src lisp
(defun embedding-backend-local (text)
  "Generate embeddings via a local OpenAI-compatible endpoint."
  (let* ((url (or (uiop:getenv "LOCAL_BASE_URL") (format nil "http://~a" (or (uiop:getenv "OLLAMA_HOST") "localhost:11434"))))
         (model (or (uiop:getenv "EMBEDDING_MODEL") "nomic-embed-text"))
         (body (cl-json:encode-json-to-string
                `((model . ,model) (input . ,text)))))
    (handler-case
        (let* ((response (dex:post (format nil "~a/api/embeddings" url)
                                   :headers '(("Content-Type" . "application/json"))
                                   :content body :connect-timeout 5 :read-timeout 30))
               (json (cl-json:decode-json-from-string response))
               (data (car (cdr (assoc :data json)))))
          (or (cdr (assoc :embedding data))
              (list :error "No embedding in response")))
      (error (c)
        (list :error (format nil "Embedding failed: ~a" c))))))
#+end_src

** OpenAI backend
#+begin_src lisp
(defun embedding-backend-openai (text)
  "Generate embeddings via OpenAI compatible /v1/embeddings endpoint."
  (let* ((api-key (uiop:getenv "OPENAI_API_KEY"))
         (base-url (or (uiop:getenv "EMBEDDING_BASE_URL") "https://api.openai.com/v1"))
         (model (or (uiop:getenv "EMBEDDING_MODEL") "text-embedding-3-small"))
         (body (cl-json:encode-json-to-string
                `((model . ,model) (input . ,text)))))
    (handler-case
        (let* ((response (dex:post (format nil "~a/embeddings" base-url)
                                    :headers `(("Content-Type" . "application/json")
                                               ("Authorization" . ,(format nil "Bearer ~a" api-key)))
                                    :content body :connect-timeout 5 :read-timeout 30))
               (json (cl-json:decode-json-from-string response))
               (data (car (cdr (assoc :data json)))))
          (or (cdr (assoc :embedding data))
              (list :error "No embedding in response")))
      (error (c)
        (list :error (format nil "OpenAI Embedding failed: ~a" c))))))
#+end_src

** Hashing fallback
#+begin_src lisp
(defun embedding-backend-hashing (text)
  "Fallback: produces a deterministic vector from the text hash."
  (let* ((digest (ironclad:digest-sequence :sha256 (babel:string-to-octets text)))
         (vec (make-array 8 :element-type 'single-float :initial-element 0.0)))
    (dotimes (i (min (length digest) 8))
      (setf (aref vec i) (float (/ (aref digest i) 255.0) 0.0)))
    vec))
#+end_src

** Object embedding and queuing
#+begin_src lisp
(defun embed-object (text)
  "Embed a single text string using the active backend."
  (let* ((selected (or *embedding-provider* :hashing))
         (backend (case selected
                    (:local #'embedding-backend-local)
                    (:openai #'embedding-backend-openai)
                    (t #'embedding-backend-hashing))))
    (if backend
        (progn
          (log-message "EMBEDDING: Provider ~a, backend=~a" selected backend)
          (funcall backend text))
        (progn
          (log-message "EMBEDDING: No backend for provider ~a, using hashing" selected)
          (embedding-backend-hashing text)))))

(defun embed-queue-object (object)
  "Queue a text object for async embedding."
  (push object *embedding-queue*)
  (log-message "EMBEDDING: Queued object"))

(defun embed-all-pending ()
  "Drain the embedding queue, batch-process all queued objects."
  (let ((batch (nreverse *embedding-queue*)))
    (setf *embedding-queue* nil)
    (dolist (item batch)
      (handler-case
          (let ((text (if (stringp item) item (format nil "~a" item))))
            (embed-object text))
        (error (c)
          (log-message "EMBEDDING: Failed to embed object: ~a" c))))))

(log-message "EMBEDDING: Gateway loaded with provider ~a" *embedding-provider*)
#+end_src