fix: make SSE buffer size configurable to prevent overflow during multi-round searches (#664) (#665)

* fix: make SSE buffer size configurable to prevent overflow during multi-round searches (Issue #664)

- Add NEXT_PUBLIC_MAX_STREAM_BUFFER_SIZE environment variable for frontend SSE stream buffer
- Default to 1MB for backward compatibility, users can increase to 5-10MB for large searches
- Enhance error message with actual buffer sizes and guidance on configuration
- Add validation schema in env.js with positive integer requirement
- Document configuration in .env.example with clear examples and use cases

* Apply suggestions from code review

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

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Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

web/.env.example

@@ -41,3 +41,17 @@ NEXT_PUBLIC_API_URL=http://localhost:8000/api
 # Github OAuth Token (optional)
 GITHUB_OAUTH_TOKEN=xxxx
 
+# Stream Buffer Size Configuration (optional)
+# Controls the maximum buffer size for SSE (Server-Sent Events) streams in bytes.
+# Default: 1MB (1048576 bytes)
+# Increase this if you experience buffer overflow errors during large searches.
+# Use cases for increasing:
+# - Performing multi-round web searches with large content results
+# - Handling responses with many search results or images
+# - Systems with sufficient memory to handle larger buffers
+# Examples:
+# - 5MB: NEXT_PUBLIC_MAX_STREAM_BUFFER_SIZE=5242880
+# - 10MB: NEXT_PUBLIC_MAX_STREAM_BUFFER_SIZE=10485760
+# Note: Very large buffers may increase memory usage. Start with 5-10MB if needed.
+# NEXT_PUBLIC_MAX_STREAM_BUFFER_SIZE=1048576
+