Client does not respect SSE retry field or send Last-Event-ID on reconnection #590

• Target: client
• Component: sdk-client
• Scenarios: sse-retry

Root cause

When the server closes an SSE stream to trigger reconnection, StreamableHttpClientTransport reconnects immediately instead of waiting the duration specified by the SSE retry field (e.g. 500 ms). It also does not send the Last-Event-ID header on the reconnection GET request. The Ktor SSE client manages reconnection internally and the transport does not propagate the retry timing or last event ID into its own reconnection logic

Client-side subset of #420