Added code for backend glue

backend/internal/glue/linearize.go

@@ -0,0 +1,41 @@
+package glue
+
+import (
+	"context"
+	"mind/internal/models"
+)
+
+type Linearized struct {
+	Nodes []models.Node `json:"nodes"`
+	Text  string        `json:"text"`
+}
+
+func (g *Glue) LinearizeByBranch(ctx context.Context, convID int64, branchName string) (Linearized, error) {
+	b, err := g.repo.GetBranch(ctx, convID, branchName)
+	if err != nil { return Linearized{}, err }
+	return g.linearizeFromHead(ctx, b.HeadNodeID)
+}
+
+func (g *Glue) linearizeFromHead(ctx context.Context, head int64) (Linearized, error) {
+	var seq []models.Node
+	// Walk parents by latest-created parent until none
+	curID := head
+	for {
+		n, err := g.repo.GetNode(ctx, curID)
+		if err != nil { return Linearized{}, err }
+		seq = append(seq, n)
+		p, ok, err := g.repo.LatestParent(ctx, curID)
+		if err != nil { return Linearized{}, err }
+		if !ok { break }
+		curID = p.ID
+	}
+	// Reverse seq to root→head, and stitch text
+	for i, j := 0, len(seq)-1; i < j; i, j = i+1, j-1 { seq[i], seq[j] = seq[j], seq[i] }
+	var txt string
+	for _, n := range seq {
+		role := "[user]"
+		if n.AuthorKind == "assistant" { role = "[assistant]" }
+		txt += role + "\n" + n.Content + "\n\n"
+	}
+	return Linearized{Nodes: seq, Text: txt}, nil
+}