fix(genai): correct Anthropic SSE event-type filtering and text path …

[Irfan-del-droid]

Summary

Fixes #1592 — Anthropic streaming was silently broken in two ways:

1. AnthropicModel.streamOutputFormatter returned x['text'] which is
   always null. The actual text lives at x['delta']['text'].
2. streamGenAIRequest ignored SSE event: field lines entirely and
   forwarded every data: line to the formatter — including ping,
   message_start, content_block_start, etc. — causing null noise
   in the output stream.

Changes

📦 Files Changed — packages/genai/

lib/models/model_provider.dart

• Added optional {String? eventType} parameter to streamOutputFormatter

lib/models/ai_request_model.dart

• Updated getFormattedStreamOutput to accept and forward eventType

lib/utils/ai_request_utils.dart

• Track SSE event: type across chunk boundaries using lastEventType
• Pass eventType to getFormattedStreamOutput
• Reset lastEventType on empty lines (SSE block boundaries)
• Handle \r\n line endings with trimRight()
• Suppress null / empty formatter results before sink.add

lib/interface/model_providers/anthropic.dart ⭐ Core fix

• Added two guard constants: _kContentBlockDelta, _kTextDelta
• Fast-path: skip payload inspection if eventType is not content_block_delta
• Check x['type'] as fallback when eventType is absent
• Validate delta is a Map
• Check delta['type'] == 'text_delta' before extracting text
• Fix extraction path: x['text'] → x['delta']['text']
• Return null for all non-text events (ping, message_start, etc.)

lib/interface/model_providers/openai.dart

• Signature alignment: added {String? eventType} (unused, no logic change)

lib/interface/model_providers/gemini.dart

• Signature alignment: added {String? eventType} (unused, no logic change)

lib/interface/model_providers/azureopenai.dart

• Signature alignment: added {String? eventType} (unused, no logic change)

test/genai_test.dart

• Removed two dead unused imports from empty placeholder file

test/streaming/anthropic_stream_formatter_test.dart

• 35 new unit tests across 7 groups:
  • Valid content_block_delta events
  • Ignored events via SSE event: fast-path
  • Ignored events via payload type field
  • Malformed / edge-case payloads
  • Multi-chunk sequential streaming simulation
  • Fast-path vs payload-check consistency
  • Full JSON encode → decode → format round-trip

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Root pubspec.yaml

• Added missing flutter_driver: sdk: flutter dev dependency
• Fixes integrationDriver being undefined in test_driver/integration_test.dart

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Root Cause

Anthropic's SSE wire format emits multiple event types per response: