Stream Hubble UI responses without proxy disk buffering #5534

🤖 Generated by the Agentic Engineer

Description

The Hubble UI reverse proxy buffers its long-lived API responses and can spill them to temporary files. This adds unnecessary disk work and can delay updates reaching the UI. The fix must address streaming behavior while preserving visibility of real failures.

Reproduction

The pinned Cilium 1.20.3 chart's Hubble UI proxy template forwards the API with HTTP/1.1 but leaves response buffering at its default. Runtime observations are retained privately. The configuration establishes the suspected cause; a controlled slow-stream regression is still required before claiming an executed reproduction.

Expected Behavior

API response chunks reach the client promptly without temporary-file buffering. Ordinary frontend assets, health checks, request headers and error responses continue to behave correctly.

Acceptance Criteria

• Reproduce delayed or buffered delivery with the actual pinned frontend runtime and controlled upstream responses.
• Make the narrowest declarative correction, retaining the upstream configuration's routing and health behavior. Change no log severity, alert rule or security permission.
• Test the actual rendered chart configuration, including a negative control using the original buffering behavior; retain proper error/status propagation and request handling.
• Limit rollout to the UI and validate both supported overlays and existing production authorization checks.
• Complete substantive review and protected deployment, then verify prompt updates and the absence of new buffering warnings over a fresh observation window.

Part of #2043