feat(milestone): SSE live-updating progress bars (#14)

modules/sessiontag/sessiontag.go

@@ -0,0 +1,38 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+// Package sessiontag carries a per-page-load identifier from the
+// originating HTTP request down to the service- and model-layer SSE
+// publishers. The publishers echo the tag back inside event payloads so
+// the originating browser tab can suppress its own event after it has
+// already applied the optimistic update locally.
+//
+// It is deliberately tiny and dependency-free so any feature that emits
+// Server-Sent Events (project boards, milestones, ...) can share one
+// context key without importing one another.
+package sessiontag
+
+import "context"
+
+// sessionTagCtxKey is the context key under which the X-Session-Tag
+// value from the originating HTTP request is stashed.
+type sessionTagCtxKey struct{}
+
+// WithSessionTag returns ctx decorated with the provided session tag.
+// Web/API middleware reads the X-Session-Tag header and calls this so
+// service- and model-layer publishers can pull the tag back out.
+func WithSessionTag(ctx context.Context, tag string) context.Context {
+	if tag == "" {
+		return ctx
+	}
+	return context.WithValue(ctx, sessionTagCtxKey{}, tag)
+}
+
+// SessionTagFromContext returns the session tag previously stored via
+// WithSessionTag, or "" when none was set.
+func SessionTagFromContext(ctx context.Context) string {
+	if v, ok := ctx.Value(sessionTagCtxKey{}).(string); ok {
+		return v
+	}
+	return ""
+}