Fix Bedrock streaming dropping all chunks when Faraday env is nil

[chen-anders]

What this does

Fixes a bug where Bedrock ConverseStream responses come back completely empty (zero chunks, blank content, nil token counts) even though the HTTP request succeeds with status 200.

The Faraday 2 on_data callback gates chunk parsing on env&.status == 200. With the net_http adapter, env is nil during streaming (the status is not yet known when chunks arrive), so this condition is false for every chunk. Each valid AWS event-stream frame is then routed to the failed-response handler, which tries to JSON.parse binary eventstream bytes, fails, logs a "failed stream error chunk" debug line, and silently drops it. The result is an empty streamed response.

This affects any app on Faraday 2.x + the net_http adapter (Faraday's default) using Bedrock streaming.

Fix: invert the guard so a nil env (status unknown) falls through to normal chunk parsing, and only a present env reporting a non-200 status is treated as a failure. Applied in both spots that build the v2 on_data proc:

• RubyLLM::Streaming::FaradayHandlers.v2_on_data (shared SSE handler)
• RubyLLM::Protocols::Converse::Streaming#stream_response (Bedrock ConverseStream)

Reproduction

chat = RubyLLM.chat(model: "us.anthropic.claude-sonnet-4-6", provider: "bedrock", assume_model_exists: true)

# Non-streaming — works:
chat.ask("Say BANANA only.").content          # => "BANANA"

# Streaming — broken before this fix:
chunks = []
resp = chat.ask("Say BANANA only.") { |c| chunks << c }
chunks.size    # => 0   (expected: > 0)
resp.content   # => ""   (expected: "BANANA")

With Faraday 2.x + net_http, the debug log shows the data arriving fine ({"delta":{"text":"BANANA"}}, usage tokens, status 200) but every frame hitting "Failed Bedrock stream error chunk". After the fix: chunks.size => 5, resp.content => "BANANA", tokens populated.

Type of change

• Bug fix
• New feature
• Breaking change
• Documentation
• Performance improvement

Scope check

• I read the Contributing Guide
• This aligns with RubyLLM's focus on LLM communication
• This isn't application-specific logic that belongs in user code
• This benefits most users, not just my specific use case

Quality check

• I ran overcommit --install and all hooks pass
• I tested my changes thoroughly
  • For provider changes: Re-recorded VCR cassettes with bundle exec rake vcr:record[provider_name]
  • Added unit tests covering nil-env / 200 / non-200 routing for both code paths (spec/ruby_llm/streaming_spec.rb, spec/ruby_llm/protocols/converse/streaming_spec.rb)
• I updated documentation if needed
• I didn't modify auto-generated files manually (models.json, aliases.json)

AI-generated code

• I used AI tools to help write this code
• I have reviewed and understand all generated code (required if above is checked)

API changes

• Breaking change
• New public methods/classes
• Changed method signatures
• No API changes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.34%. Comparing base (3998b05) to head (a0f7bf5).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #813      +/-   ##
==========================================
+ Coverage   83.29%   83.34%   +0.05%     
==========================================
  Files         172      172              
  Lines        8281     8282       +1     
  Branches     1347     1347              
==========================================
+ Hits         6898     6903       +5     
- Misses        887      888       +1     
+ Partials      496      491       -5     

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[crmne]

The bug fix and test coverage look right. Please tighten the shape before merging: keep the Faraday status-routing rule in one helper, and keep the comment/predicate small.

[crmne]

Let's keep this short, and treat unknown status the same whether env is nil or env.status is nil.

# Some adapters do not expose response status during on_data.
status = env&.status

if status && status != 200
  on_failed_response.call(chunk, env)
else
  on_chunk.call(chunk, env)
end

[crmne]

Converse needs its own AWS Event Stream parser, but it can still use the existing Faraday on_data wrapper so this routing rule lives in one place.

faraday_v1 = Faraday::VERSION.start_with?('1')
on_data = RubyLLM::Streaming::FaradayHandlers.build(
  faraday_v1: faraday_v1,
  on_chunk: ->(chunk, _env) { parse_stream_chunk(decoder, chunk, accumulator, &block) },
  on_failed_response: ->(chunk, env) { handle_failed_stream(chunk, env) }
)

if faraday_v1
  req.options[:on_data] = on_data
else
  req.options.on_data = on_data
end