Allow multiple projects per issue and pull requests (#36784)

Add ability to add and remove multiple projects per issue
and pull request.

Resolve #12974

---------

Signed-off-by: Icy Avocado <avocado@ovacoda.com>
Co-authored-by: Tyrone Yeh <siryeh@gmail.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: OpenCode (gpt-5.2-codex) <opencode@openai.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>

services/convert/issue.go

@@ -95,6 +95,13 @@ func toIssue(ctx context.Context, doer *user_model.User, issue *issues_model.Iss
 		apiIssue.Milestone = ToAPIMilestone(issue.Milestone)
 	}
 
+	if err := issue.LoadProjects(ctx); err != nil {
+		return &api.Issue{}
+	}
+	if len(issue.Projects) > 0 {
+		apiIssue.Projects = ToAPIProjectList(issue.Projects)
+	}
+
 	if err := issue.LoadAssignees(ctx); err != nil {
 		return &api.Issue{}
 	}

services/convert/project.go

@@ -0,0 +1,37 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package convert
+
+import (
+	project_model "code.gitea.io/gitea/models/project"
+	api "code.gitea.io/gitea/modules/structs"
+)
+
+// ToAPIProject converts a Project to API format
+func ToAPIProject(p *project_model.Project) *api.Project {
+	apiProject := &api.Project{
+		ID:          p.ID,
+		Title:       p.Title,
+		Description: p.Description,
+		OwnerID:     p.OwnerID,
+		RepoID:      p.RepoID,
+		CreatorID:   p.CreatorID,
+		IsClosed:    p.IsClosed,
+		Created:     p.CreatedUnix.AsTime(),
+		Updated:     p.UpdatedUnix.AsTime(),
+	}
+	if p.IsClosed && p.ClosedDateUnix > 0 {
+		apiProject.Closed = p.ClosedDateUnix.AsTimePtr()
+	}
+	return apiProject
+}
+
+// ToAPIProjectList converts a list of Projects to API format
+func ToAPIProjectList(projects []*project_model.Project) []*api.Project {
+	result := make([]*api.Project, len(projects))
+	for i := range projects {
+		result[i] = ToAPIProject(projects[i])
+	}
+	return result
+}