fix(iflow): add connection error retry logic and silent context failure detection

[MasuRii]

Summary

Add robust connection error handling with retry logic and silent context failure detection for the iFlow provider, preventing quota waste from transient network issues and undetected empty responses.

Changes

• Connection error retry logic: Wrap stream_handler in a retry loop with exponential backoff (1s/2s/4s) for transient connection errors (RemoteProtocolError, ConnectError, ReadTimeout, NetworkError), retrying up to 3 times before re-raising
• Silent context failure detection: Detect and reject HTTP 200 responses that contain no choices, zero completion tokens with non-zero prompt tokens, empty assistant messages, or streams that complete without any data chunks — raising a non-retryable context_window_exceeded error
• Context window error detection: Surface token limit errors explicitly from HTTP error response bodies using pattern matching
• Error classification improvement: Add httpx.RemoteProtocolError to the api_connection error type classification in the global error handler
• Module-level constants: Extract CONNECTION_ERROR_TYPES, CONTEXT_WINDOW_ERROR_PATTERNS, MAX_CONNECTION_RETRIES, and RETRY_BACKOFF_BASE for clarity and reuse

Files Changed

File	Type	Impact
src/rotator_library/providers/iflow_provider.py	Modified	Added retry loop with backoff in stream_handler, silent context failure detection, helper methods, and module-level error constants (+219/-80 lines)
src/rotator_library/error_handler.py	Modified	Added httpx.RemoteProtocolError to api_connection classification tuple (+6/-1 lines)

Testing Instructions

1. Trigger iFlow requests with a large context that exceeds the model's window — verify the proxy surfaces a clear context window error instead of silently failing
2. Simulate a transient connection drop mid-stream — verify the proxy retries up to 3 times with backoff before failing
3. Verify normal iFlow streaming requests still complete successfully without unnecessary retries

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Important

Enhances iFlow provider with retry logic for connection errors and detection of silent context failures, updating error classifications and constants.

• Behavior:
  • Adds retry logic with exponential backoff in stream_handler in iflow_provider.py for connection errors (RemoteProtocolError, ConnectError, ReadTimeout, NetworkError), retrying up to 3 times.
  • Detects silent context failures in iflow_provider.py by checking for HTTP 200 responses with no choices, zero completion tokens, empty messages, or streams without data, raising context_window_exceeded.
  • Explicitly surfaces context window errors from HTTP error responses using pattern matching in iflow_provider.py.
• Error Handling:
  • Adds httpx.RemoteProtocolError to api_connection error classification in error_handler.py.
• Constants:
  • Extracts CONNECTION_ERROR_TYPES, CONTEXT_WINDOW_ERROR_PATTERNS, MAX_CONNECTION_RETRIES, and RETRY_BACKOFF_BASE in iflow_provider.py for clarity and reuse.

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