Store finish_reason in LLMResult

[Copilot]

LLM refusals and other completion states were not propagated, forcing users to rely on not result.text which is unreliable and ambiguous.

Changes

• Added finish_reason field to LLMResult - optional string capturing completion state (stop, length, tool_calls, refusal, etc.)
• Non-streaming path - captures choice.finish_reason from response and passes to LLMResult
• Streaming path - extracts finish_reason from final chunk; also fixed potential NameError if stream is empty by initializing choice = None
• Tests - added coverage for both streaming and non-streaming paths with various finish reasons

Usage

result = await llm.call_single(messages)

# Before: unreliable and ambiguous
if not result.text:
    # Could be empty response OR refusal OR error
    pass

# After: explicit and reliable
if result.finish_reason == "refusal":
    # Definitively a refusal
    pass
elif result.finish_reason == "length":
    # Hit token limit
    pass

Fully backward compatible - field defaults to None.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• astral.sh
  • Triggering command: /usr/bin/curl curl -LsSf REDACTED (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Store finish reason in LLMResult</issue_title>
<issue_description>We don't store the finish reason, which is fine most times.

However, in the event of a LLM refusal, the refusal isn't propagated, so users can only do not result.text.

We should propagate the finish reason.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Store finish reason in LLMResult #396

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.

[jamesbraza]

This seems to be an unused local?

[jamesbraza]

Don't we know the type here, do we need this getattr?

[jamesbraza]

Talk about why it would be None