🪭 feat: Add opt-in Langfuse fanout gateway + collector (#13872)

* feat: add opt-in Langfuse fanout collector

* feat: fan out Langfuse feedback scores

* docs: prepare Langfuse fanout for OSS setup

* fix: clarify Langfuse fanout collector config

* test: stabilize librechat suite

* test: fix upload dialog import order

* fix: omit empty Langfuse tenant fields

* fix: gate tenant Langfuse fanout

* test: cover central Langfuse env fallback

* style: format Langfuse fanout config

* feat: route langfuse fanout by destination

* docs: clarify langfuse compose destination scope

* test: remove unrelated suite stabilization

* style: sort agent imports

* fix: treat blank tenant fanout toggle as disabled

* fix: rename tenant fanout emergency toggle

* test: guard langfuse fanout collector config drift

* feat: tune langfuse fanout batching

* test: render fanout helm tests without dependencies

* fix: narrow remote agent run config

* refactor: share string normalization helper

* fix: align langfuse fanout env parsing

* fix(langfuse): align score fanout toggles with traces

* fix(langfuse): keep central fanout config collector-only

* fix(langfuse): type fanout collector config

* fix(langfuse): harden tenant fanout config

* feat(langfuse): support media fanout gateway

* fix(langfuse): route tenant fanout through destination URL

* fix(langfuse): harden fanout routing checks

* ci(langfuse): test fanout gateway changes

* ci(langfuse): check fanout go formatting

* fix(langfuse): satisfy api typecheck

.github/workflows/langfuse-fanout.yml

@@ -0,0 +1,43 @@
+name: Langfuse Fanout
+
+on:
+  workflow_dispatch:
+  pull_request:
+    paths:
+      - '.github/workflows/langfuse-fanout.yml'
+      - 'otel/langfuse-fanout/**'
+
+permissions:
+  contents: read
+
+concurrency:
+  group: langfuse-fanout-${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  go-tests:
+    name: Go tests
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version-file: otel/langfuse-fanout/go.mod
+          cache-dependency-path: otel/langfuse-fanout/go.sum
+
+      - name: Check Go formatting
+        working-directory: otel/langfuse-fanout
+        run: |
+          unformatted="$(gofmt -l .)"
+          if [ -n "$unformatted" ]; then
+            echo "::error::Go files are not gofmt-formatted:"
+            echo "$unformatted"
+            exit 1
+          fi
+
+      - name: Run Go tests
+        working-directory: otel/langfuse-fanout
+        run: go test ./...