Problem

resolve_provider('custom') silently returned 'openrouter' due to a combined set check:

if normalized in {"openrouter", "custom"}:
    return "openrouter"

This caused:

• /model showing "via openrouter" when user set provider: custom
• /status showing the wrong provider
• No notice given to the user about the remapping

Fix

Split the set check so each provider returns its own name:

if normalized == "openrouter":
    return "openrouter"
if normalized == "custom":
    return "custom"

Also preserve provider: custom in the runtime dict returned by resolve_runtime_provider() so all display layers receive the correct name.

What is not changed

• The OpenRouter code path continues to handle custom base_url requests correctly — _resolve_openrouter_runtime() is still called for custom, only the provider key in the returned dict changes
• Local model support via custom + base_url in config.yaml is unaffected
• resolve_provider('openrouter') behavior is unchanged

Tests

5 new tests in tests/test_runtime_provider_resolution.py:

• test_resolve_provider_custom_returns_custom — verifies the core fix against the actual resolve_provider() function
• test_resolve_provider_openrouter_unchanged — regression guard
• test_resolve_runtime_provider_custom_preserves_provider_name — runtime dict has provider: custom
• test_resolve_runtime_provider_custom_base_url_preserved — base_url passes through correctly
• test_resolve_runtime_provider_openrouter_not_affected — openrouter regression guard

Fixes #2562