Added code for backend glue

backend/internal/glue/completion.go

@@ -0,0 +1,39 @@
+package glue
+
+import (
+	"context"
+)
+
+type CompletionReq struct {
+	ConversationID int64  `json:"conversation_id"`
+	BranchName     string `json:"branch"`
+	Prompt         string `json:"prompt"`
+}
+
+type CompletionResp struct {
+	PromptNodeID   int64  `json:"prompt_node_id"`
+	AnswerNodeID   int64  `json:"answer_node_id"`
+	Answer         string `json:"answer"`
+}
+
+// For v0 we stub the answer as a simple echo with a prefix.
+func (g *Glue) AppendCompletion(ctx context.Context, req CompletionReq) (CompletionResp, error) {
+	b, err := g.repo.GetBranch(ctx, req.ConversationID, req.BranchName)
+	if err != nil { return CompletionResp{}, err }
+
+	// 1) create user prompt node
+	promptID, err := g.repo.CreateNode(ctx, req.ConversationID, "user", req.Prompt)
+	if err != nil { return CompletionResp{}, err }
+	if err := g.repo.Link(ctx, b.HeadNodeID, promptID); err != nil { return CompletionResp{}, err }
+
+	// 2) create assistant answer node (stub)
+	answerText := "(stub) You said: " + req.Prompt
+	answerID, err := g.repo.CreateNode(ctx, req.ConversationID, "assistant", answerText)
+	if err != nil { return CompletionResp{}, err }
+	if err := g.repo.Link(ctx, promptID, answerID); err != nil { return CompletionResp{}, err }
+
+	// 3) move branch head
+	if err := g.repo.MoveBranchHead(ctx, b.ID, answerID); err != nil { return CompletionResp{}, err }
+
+	return CompletionResp{PromptNodeID: promptID, AnswerNodeID: answerID, Answer: answerText}, nil
+}