fix(bridge): do not surface numbered SSE metadata as assistant text

[drewstone]

Problem

@tangle-network/agent-runtime@0.128.0 treats valid numbered Server-Sent Events metadata from CLI Bridge as model text.

CLI Bridge emits an id-only comment frame for internal session metadata:

id: 1
: bridge-metadata

A real runAgentTaskStream call through createOpenAICompatibleBackend returned final text beginning with:

id: 1
: bridge-metadata

before the actual model response. The same run emitted three text_delta events although the model produced one response token string.

Root cause

streamResponseEvents drains any first line that does not begin with data: before waiting for the blank-line SSE event boundary. It therefore sends id: 1 through parseStreamChunk; the non-JSON fallback converts protocol metadata into text_delta.

Expected

• Ignore comment-only and id-only frames as assistant output.
• Parse id: plus data: as one SSE event.
• Preserve numbered CLI Bridge replay frames without leaking metadata.
• Remain correct when CRLF or event lines are split across transport chunks.

Completion criteria

• Add regressions for id plus comment, id plus JSON data, comment-only heartbeat, split CRLF, and split frame boundaries.
• Prove final assistant text contains only model content.
• Either fix the published OpenAI-compatible path or prove the canonical profile execution replacement in refactor(runtime): enforce canonical model execution boundary #736 handles the exact CLI Bridge bytes before releasing it.

Live reproduction

Observed 2026-08-04 with Runtime 0.128.0, CLI Bridge on localhost, Pi 0.83.0, and pi/tangle-router/glm-5.2. The request completed successfully in 15.176 seconds, which rules out an error-body fallback.