Streaming replies are silently dropped when the provider emits 'data:' without a trailing space

[pengzh1]

Symptom

When FastClaw talks to an OpenAI/Anthropic-compatible streaming endpoint through an LLM gateway (DeepSeek, GLM, self-hosted gateways, etc.), the model's reply is completely lost and the agent reports:

model returned an empty response

Non-gateway endpoints work fine, which makes this look random and very hard to debug.

Root cause

The SSE spec (MDN — event stream format) makes the single space after the data: field name optional:

If the value contains a leading space, it is ignored... the colon and space are both optional.

Many gateways emit data:{...} with no space. All four stream parsers match the literal prefix data: and skip every such line, so the assembled content ends up empty:

• internal/provider/openai.go — ChatStream (~line 340) and parseSSE (~line 520)
• internal/provider/anthropic.go — streaming loop (~line 515) and parseSSE (~line 650)

Verified with curl -N against the gateway: the body is well-formed SSE, just without the space.

Fix

Accept data: with or without the space and TrimSpace the payload — proposed in #112 (includes unit tests).