fix: correct invite URL path and fetch document from owner's PDS on accept

internal/handler/handler.go

···
 	"html/template"
 	"log"
 	"net/http"
+	"net/url"
 	"regexp"
 	"strings"
 	"time"
···
 		return
 	}
 
-	inviteLink := fmt.Sprintf("%s/doc/%s?invite=%s", h.BaseURL, rkey, invite.Token)
+	inviteLink := fmt.Sprintf("%s/docs/%s/accept?invite=%s", h.BaseURL, rkey, invite.Token)
 	h.jsonResponse(w, map[string]string{"inviteLink": inviteLink}, http.StatusOK)
 }
 
···
 func (h *Handler) AcceptInvite(w http.ResponseWriter, r *http.Request) {
 	user := h.currentUser(r)
 	if user == nil {
-		http.Redirect(w, r, "/auth/login", http.StatusSeeOther)
+		// Preserve invite token through the login redirect.
+		http.Redirect(w, r, "/auth/login?next="+url.QueryEscape(r.URL.String()), http.StatusSeeOther)
 		return
 	}
 
···
 		return
 	}
 
-	session, err := h.DB.GetATProtoSession(user.ID)
-	if err != nil || session == nil {
-		http.Redirect(w, r, "/auth/atproto", http.StatusSeeOther)
+	// The collaborator's session — needed to get their DID.
+	collabSession, err := h.DB.GetATProtoSession(user.ID)
+	if err != nil || collabSession == nil {
+		http.Redirect(w, r, "/auth/atproto?next="+url.QueryEscape(r.URL.String()), http.StatusSeeOther)
+		return
+	}
+
+	// Fetch and update the document from the OWNER's PDS, not the collaborator's.
+	// The invite records the owner's DID in CreatedBy.
+	ownerUser, err := h.DB.GetUserByDID(invite.CreatedBy)
+	if err != nil {
+		log.Printf("AcceptInvite: get owner by DID %s: %v", invite.CreatedBy, err)
+		http.Error(w, "Document owner not found", http.StatusInternalServerError)
 		return
 	}
 
-	client, err := h.xrpcClient(user.ID)
+	ownerClient, err := h.xrpcClient(ownerUser.ID)
 	if err != nil {
-		log.Printf("AcceptInvite: xrpc client: %v", err)
+		log.Printf("AcceptInvite: owner xrpc client: %v", err)
 		http.Error(w, "Failed to connect to ATProto", http.StatusInternalServerError)
 		return
 	}
 
-	doc, err := client.GetDocument(rKey)
+	doc, err := ownerClient.GetDocument(rKey)
 	if err != nil {
+		log.Printf("AcceptInvite: get document: %v", err)
 		http.Error(w, "Document not found", http.StatusNotFound)
 		return
 	}
 
+	// Already a collaborator — just redirect.
 	for _, c := range doc.Collaborators {
-		if c == session.DID {
+		if c == collabSession.DID {
 			http.Redirect(w, r, "/docs/"+rKey, http.StatusSeeOther)
 			return
 		}
 	}
 
-	doc.Collaborators = append(doc.Collaborators, session.DID)
-	_, _, err = client.PutDocument(rKey, doc)
-	if err != nil {
-		log.Printf("AcceptInvite: add collaborator: %v", err)
+	// Add collaborator DID and PUT back to owner's PDS.
+	doc.Collaborators = append(doc.Collaborators, collabSession.DID)
+	if _, _, err = ownerClient.PutDocument(rKey, doc); err != nil {
+		log.Printf("AcceptInvite: put document: %v", err)
 		http.Error(w, "Failed to add collaborator", http.StatusInternalServerError)
 		return
 	}