fix: add collaborator edit route and fix edit link for shared documents

cmd/server/main.go

···
 	mux.HandleFunc("GET /docs/{rkey}/edit", h.DocumentEdit)
 	// Collaborator-scoped routes (owner DID in path)
 	mux.HandleFunc("GET /docs/{did}/{rkey}", h.CollaboratorDocumentView)
+	mux.HandleFunc("GET /docs/{did}/{rkey}/edit", h.CollaboratorDocumentEdit)
 
 	// API
 	mux.HandleFunc("POST /api/render", h.APIRender)

internal/handler/handler.go

···
 	type DocumentViewData struct {
 		Doc      *model.Document
 		Rendered template.HTML
+		OwnerDID string // non-empty when viewing a collaborator's document
 	}
 	h.render(w, "document_view.html", PageData{
 		Title:   doc.Title,
 		User:    user,
-		Content: DocumentViewData{Doc: doc, Rendered: template.HTML(rendered)},
+		Content: DocumentViewData{Doc: doc, Rendered: template.HTML(rendered), OwnerDID: ownerDID},
 	})
 }
 
···
 	h.documentView(w, r, ownerUser.ID, ownerDID, rkey)
 }
 
-// DocumentEdit renders the editor for a document.
-func (h *Handler) DocumentEdit(w http.ResponseWriter, r *http.Request) {
-	user := h.currentUser(r)
-	if user == nil {
-		http.Redirect(w, r, "/auth/atproto", http.StatusSeeOther)
-		return
-	}
-
-	rkey := r.PathValue("rkey")
-	client, err := h.xrpcClient(user.ID)
+// documentEdit is the shared implementation for the edit page.
+// ownerUserID/ownerDID identify whose PDS holds the document; isOwner is true for the creator.
+func (h *Handler) documentEdit(w http.ResponseWriter, r *http.Request, user *model.User, ownerUserID, ownerDID, rkey string, isOwner bool) {
+	ownerClient, err := h.xrpcClient(ownerUserID)
 	if err != nil {
 		http.Error(w, "Could not connect to PDS", 500)
 		return
 	}
 
-	value, _, err := client.GetRecord(client.DID(), collectionDocument, rkey)
+	value, _, err := ownerClient.GetRecord(ownerDID, collectionDocument, rkey)
 	if err != nil {
 		http.NotFound(w, r)
 		return
···
 	}
 	doc.RKey = rkey
 
-	// Fetch ATProto session to pass access token to the WebSocket client.
-	// The user is always the owner here since we fetched the doc via client.DID().
-	editData := &DocumentEditData{Document: doc, IsOwner: true}
+	editData := &DocumentEditData{Document: doc, IsOwner: isOwner}
 	if session, err := h.DB.GetATProtoSession(user.ID); err == nil && session != nil {
 		editData.AccessToken = session.AccessToken
-		// Check if this user is listed as a collaborator on the doc.
 		userDID := session.DID
 		for _, did := range doc.Collaborators {
 			if did == userDID {
···
 		User:    user,
 		Content: editData,
 	})
+}
+
+// DocumentEdit renders the editor for a document (owner).
+func (h *Handler) DocumentEdit(w http.ResponseWriter, r *http.Request) {
+	user := h.currentUser(r)
+	if user == nil {
+		http.Redirect(w, r, "/auth/atproto", http.StatusSeeOther)
+		return
+	}
+
+	rkey := r.PathValue("rkey")
+	client, err := h.xrpcClient(user.ID)
+	if err != nil {
+		http.Error(w, "Could not connect to PDS", 500)
+		return
+	}
+
+	h.documentEdit(w, r, user, user.ID, client.DID(), rkey, true)
+}
+
+// CollaboratorDocumentEdit renders the editor for a document owned by another user.
+func (h *Handler) CollaboratorDocumentEdit(w http.ResponseWriter, r *http.Request) {
+	user := h.currentUser(r)
+	if user == nil {
+		http.Redirect(w, r, "/auth/atproto", http.StatusSeeOther)
+		return
+	}
+
+	ownerDID := r.PathValue("did")
+	rkey := r.PathValue("rkey")
+
+	ownerUser, err := h.DB.GetUserByDID(ownerDID)
+	if err != nil {
+		http.NotFound(w, r)
+		return
+	}
+
+	h.documentEdit(w, r, user, ownerUser.ID, ownerDID, rkey, false)
 }
 
 // APIDocumentSave saves a document to the PDS.

templates/document_view.html

···
             {{else if .Doc.CreatedAt}}<time>Created {{.Doc.CreatedAt | fmtdate}}</time>{{end}}
         </div>
         <div class="file-actions">
+            {{if .OwnerDID}}
+            <a href="/docs/{{.OwnerDID}}/{{.Doc.RKey}}/edit" class="btn btn-sm">Edit</a>
+            {{else}}
             <a href="/docs/{{.Doc.RKey}}/edit" class="btn btn-sm">Edit</a>
             <button class="btn btn-sm btn-outline btn-danger" onclick="deleteDocument('{{.Doc.RKey}}')">Delete</button>
+            {{end}}
         </div>
     </div>
     <div class="markdown-body">