fix(openai): enable function calling for DeepSeek models

[yusiwen]

Summary

• Remove the special-case that forces plain text completion for DeepSeek models in GetSummaryPrefix, enabling OpenAI-compatible function calling instead.

Problem

When using a DeepSeek model, GetSummaryPrefix in provider/openai/openai.go skips function calling and falls back to CreateChatCompletion due to this check:

if checkOSeriesModels.MatchString(c.model) ||
    strings.Contains(strings.ToLower(c.model), "deepseek") {
    resp, err = c.CreateChatCompletion(ctx, content)

The conventional_commit.tmpl prompt asks the model two questions:

1. What's the best label for the commit?
2. What's the best scope for the commit?

Since function calling is bypassed, the model responds with plain text like:

feat
auth

This raw text is returned directly as summarize_prefix (see openai.go:167-171 — the ToolCalls == 0 branch returns msg.Content without any post-processing), resulting in "feat\nauth" instead of the expected "feat(auth)" format.

This causes the final commit message to break across lines:

feat
auth: add new authentication module

Instead of the correct:

feat(auth): add new authentication module

Solution

DeepSeek models now officially support OpenAI-compatible function calling. Removing the strings.Contains(strings.ToLower(c.model), "deepseek") condition allows DeepSeek models to use the function calling path, which returns structured prefix and scope arguments that are properly formatted as prefix(scope).

Test Plan

• Verify codegpt commit with a DeepSeek model produces a commit message with prefix(scope) format (e.g., feat(auth): ...)
• Verify codegpt commit with OpenAI o-series models still falls back to plain text completion as expected
• Verify other providers (Anthropic, Gemini) are unaffected

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 17.31%. Comparing base (0125d86) to head (1510983).
⚠️ Report is 281 commits behind head on main.

Files with missing lines	Patch %	Lines
provider/openai/openai.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #266      +/-   ##
==========================================
- Coverage   21.96%   17.31%   -4.66%     
==========================================
  Files           8       36      +28     
  Lines         346     2374    +2028     
==========================================
+ Hits           76      411     +335     
- Misses        264     1929    +1665     
- Partials        6       34      +28     

Flag	Coverage Δ
go-1.25	17.31% <0.00%> (?)
go-1.26	17.31% <0.00%> (?)
macos-latest	17.31% <0.00%> (?)
ubuntu-latest	17.31% <0.00%> (?)

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