improved s3 hydration (#997)

- Improvement: Hub shares a single S3 client and IMDS credential provider across all modules, reducing IMDS load and surviving transient IMDS blips during bulk provisioning
- Improvement: Hub validates hydration config at startup; bad `--hub-hydration-target-spec` or `--hub-hydration-target-config` now fails `zen hub` at boot instead of per-module at first hydrate
- Improvement: S3 hydration multipart chunk size configurable via `settings.chunk-size` (default 32 MiB)
- Improvement: S3 client extracts `<Error><Code>` and `<Message>` from XML error bodies (previously logged as `<unhandled content format>`)
- Improvement: S3 client fails fast with a "no credentials available" error when AWS credentials are missing, instead of sending an unsigned request that S3 rejects with a generic 400
- Improvement: IMDS credential provider retries transient connection failures (up to 3 attempts with backoff)
- Improvement: HTTP clients with `RetryCount > 0` also retry on `CURLE_COULDNT_CONNECT`

1 files changed, 1 insertions, 0 deletions

diff --git a/src/zenutil/cloud/imdscredentials.cpp b/src/zenutil/cloud/imdscredentials.cpp
index 433afdc3c..a23cb9c28 100644
--- a/src/zenutil/cloud/imdscredentials.cpp
+++ b/src/zenutil/cloud/imdscredentials.cpp
@@ -64,6 +64,7 @@ ImdsCredentialProvider::ImdsCredentialProvider(const ImdsCredentialProviderOptio
 				   .LogCategory	   = "imds",
 				   .ConnectTimeout = Options.ConnectTimeout,
 				   .Timeout		   = Options.RequestTimeout,
+				   .RetryCount	   = 3,
 			   })
 {
 	ZEN_INFO("IMDS credential provider configured (endpoint: {})", m_HttpClient.GetBaseUri());