Document producer upload client behavior

docs/integrations/http-upload.md

@@ -106,6 +106,28 @@ Archive entry rules:
 
 The uploaded archive size and extracted bundle size are bounded by the selected pipeline's `source.max_upload_size`. Extracted file count is also bounded by the implementation.
 
+## Go Producer Helper
+
+Go producers can use `gitea.maximumdirect.net/eric/distributor/pkg/upload` to build or validate source bundles, package them as gzip-compressed tar archives, and submit them to this API:
+
+```go
+client, err := upload.NewClient(upload.ClientOptions{
+	Endpoint: "http://127.0.0.1:8080",
+	Token:    token,
+})
+if err != nil {
+	return err
+}
+result, err := client.UploadBundle(ctx, upload.UploadBundleOptions{
+	Root:           "examples/source-bundle",
+	IdempotencyKey: "reports.example.20260604T120000Z",
+})
+```
+
+`Endpoint` is the server base URL; the package derives `/upload` and `/runs/<run-id>`. `UploadBundle` validates a local bundle by default and uploads only `manifest.json` plus manifest-listed files. `UploadFiles` creates a temporary bundle from explicit `bundle.BundleFile` values before uploading. When `IdempotencyKey` is omitted, the package generates one random 128-bit lowercase hex key for the upload operation and reuses it across retries.
+
+The helper retries only safe cases: `503 Service Unavailable`, temporary network errors, and ambiguous mid-upload failures. It does not retry after `202 Accepted` and does not retry `400`, `401`, `409`, `413`, or `415`. Bearer token values are redacted from returned errors.
+
 ## Queue And Retention
 
 `server.http.queue_size` bounds accepted-but-not-started uploads plus uploads being staged. `server.http.max_concurrency` bounds publishing concurrency. The coordinator does not run two uploads for the same pipeline concurrently.
@@ -123,5 +145,5 @@ The HTTP API does not expose pipeline selection by request parameter, TLS, publi
 Before changing this contract, inspect and run:
 
 ```sh
-go test ./internal/app ./internal/ingest
+go test ./internal/app ./internal/ingest ./pkg/upload
 ```