fix(config): warn when active provider shadows llm settings

[amh1k]

Description

Warns users when they configure llm.* settings while an active provider takes precedence over them.

Adds ocr config unset provider, which clears the active provider and top-level model so OCR can fall back to legacy llm.* configuration. Saved provider entries and credentials remain intact for later reuse.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Refactoring (no functional changes)
• Documentation update
• CI / Build / Tooling

How Has This Been Tested?

• make test passes locally

• Manual testing (describe below)

• Ran focused configuration and resolver tests:

  go test ./cmd/opencodereview ./internal/llm

• Ran the full race-enabled suite:

  make test

• Ran formatting, dependency, and vet checks:

  make check

• Added test coverage for warnings on shadowed llm.* settings and for ocr config unset provider.

Checklist

• My code follows the project's coding style (go fmt, go vet)
• I have performed a self-review of my code
• I have added tests that prove my fix is effective or my feature works
• New and existing unit tests pass locally with my changes
• I have updated the documentation accordingly (if applicable)
• I have signed the CLA

Related Issues

Closes #583

[github-actions]

🔍 OpenCodeReview found 2 issue(s) in this PR.

• ✅ Successfully posted inline: 1 comment(s)
• 📝 In summary (no line info): 1 comment(s)

---

[bug · medium]

📄 cmd/opencodereview/flags.go

⚠️ GitHub could not post this as an inline comment: No line information provided

Bug: The warning always suggests providers.<name>.<field> even when the active provider is a custom provider. For custom providers, the correct config path is custom_providers.<name>.<field>. You should use llm.LookupProvider(provider) (already used elsewhere in this file) to determine whether the provider is built-in or custom, and adjust the suggested prefix accordingly.

💡 Suggested Change

Before:

	return fmt.Sprintf("[ocr] WARNING: provider %q is active and takes precedence over llm.* settings.\n"+
		"[ocr] Use 'ocr config set providers.%s.<field> <value>' to configure the active provider,\n"+
		"[ocr] or run 'ocr config unset provider' to disable provider-based config.\n", provider, provider)

After:

	prefix := "providers"
	if _, isPreset := llm.LookupProvider(provider); !isPreset {
		prefix = "custom_providers"
	}
	return fmt.Sprintf("[ocr] WARNING: provider %q is active and takes precedence over llm.* settings.\n"+
		"[ocr] Use 'ocr config set %s.%s.<field> <value>' to configure the active provider,\n"+
		"[ocr] or run 'ocr config unset provider' to disable provider-based config.\n", provider, prefix, provider)

[lizhengfeng101]

Nice PR — two small issues:

1. legacyLLMShadowWarning: the strings.ToLower on the key causes false-positive warnings

   The config system is case-sensitive, so LLM.url or Llm.model won't actually set a valid config field. But strings.HasPrefix(strings.ToLower(key), "llm.") still matches them and emits the shadow warning, which is misleading. Should just be strings.HasPrefix(key, "llm.") without the ToLower.

2. flags.go:282: the unset usage error message lost helpful examples

   The original error text listed examples for both custom_providers.<name> and mcp_servers.<name>. The new version only shows ocr config unset provider as an example, making it harder for users to discover the other unset targets. Consider keeping at least one example per supported key type.

[amh1k]

Nice PR — two small issues:

1. **`legacyLLMShadowWarning`: the `strings.ToLower` on the key causes false-positive warnings**
   The config system is case-sensitive, so `LLM.url` or `Llm.model` won't actually set a valid config field. But `strings.HasPrefix(strings.ToLower(key), "llm.")` still matches them and emits the shadow warning, which is misleading. Should just be `strings.HasPrefix(key, "llm.")` without the ToLower.

2. **`flags.go:282`: the unset usage error message lost helpful examples**
   The original error text listed examples for both `custom_providers.<name>` and `mcp_servers.<name>`. The new version only shows `ocr config unset provider` as an example, making it harder for users to discover the other unset targets. Consider keeping at least one example per supported key type.

Done

[lizhengfeng101]

LGTM