diff --git a/routers/api/v1/api.go b/routers/api/v1/api.go
index e0f89656fd..55c625c174 100644
--- a/routers/api/v1/api.go
+++ b/routers/api/v1/api.go
@@ -875,6 +875,7 @@ func Routes() *web.Router {
 		}))
 	}
 
+	m.AfterRouting(common.SessionTagMiddleware())
 	m.AfterRouting(context.APIContexter())
 	m.AfterRouting(checkDeprecatedAuthMethods)
 
diff --git a/routers/common/session_tag.go b/routers/common/session_tag.go
new file mode 100644
index 0000000000..bd91fc2421
--- /dev/null
+++ b/routers/common/session_tag.go
@@ -0,0 +1,34 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package common
+
+import (
+	"net/http"
+
+	"code.gitea.io/gitea/services/project_events"
+)
+
+// SessionTagHeader is the HTTP header browser tabs use to broadcast a
+// per-page-load identifier with every mutation request. The server
+// echoes it back inside SSE event payloads so the originating tab
+// can suppress its own event after applying the optimistic update.
+const SessionTagHeader = "X-Session-Tag"
+
+// SessionTagMiddleware decorates each incoming request's context with
+// the X-Session-Tag header value when present. Service- and model-
+// layer publishers read the value via project_events.SessionTagFromContext.
+//
+// Empty / missing headers are a no-op.
+func SessionTagMiddleware() func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			tag := r.Header.Get(SessionTagHeader)
+			if tag != "" {
+				ctx := project_events.WithSessionTag(r.Context(), tag)
+				r = r.WithContext(ctx)
+			}
+			next.ServeHTTP(w, r)
+		})
+	}
+}
diff --git a/routers/web/web.go b/routers/web/web.go
index ecd75250d2..62927df442 100644
--- a/routers/web/web.go
+++ b/routers/web/web.go
@@ -295,7 +295,7 @@ func Routes() *web.Router {
 	routes.Get("/ssh_info", misc.SSHInfo)
 	routes.Get("/api/healthz", healthcheck.Check)
 
-	mid = append(mid, common.MustInitSessioner(), context.Contexter())
+	mid = append(mid, common.SessionTagMiddleware(), common.MustInitSessioner(), context.Contexter())
 
 	// Get user from session if logged in.
 	webAuth := newWebAuthMiddleware()