fix(agent): resolve custom: prefix in vision provider before normalisation

[liuhao1024]

What does this PR do?

Fixes auxiliary.vision.provider: custom:<name> collapsing to the bare built-in provider when <name> matches a built-in (e.g. custom:minimax → minimax). The user's custom_providers entry was never consulted, causing 401 on the wrong endpoint.

Related Issue

Fixes #44349

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)

Changes Made

• agent/auxiliary_client.py: In resolve_vision_provider_client, save the raw provider before _normalize_vision_provider strips the custom: prefix. When the raw name starts with custom:, try _get_named_custom_provider(raw) before falling through to general dispatch. This ensures the user's custom_providers entry is found.
• tests/agent/test_auxiliary_named_custom_providers.py: 3 new tests — custom prefix resolves to named provider, unknown custom prefix returns None, custom prefix matches providers: dict format.

How to Test

1. Set custom_providers: [{name: minimax, base_url: http://custom.local/v1, api_key: k}] in config.yaml
2. Set auxiliary.vision.provider: custom:minimax
3. Call resolve_vision_provider_client("custom:minimax") — should use the custom endpoint, not built-in minimax
4. Run pytest tests/agent/test_auxiliary_named_custom_providers.py -xvs — all 32 tests pass

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature (no unrelated commits)
• I've run pytest tests/ -q and all tests pass
• I've added tests for my changes (required for bug fixes, strongly encouraged for features)
• I've tested on my platform: macOS

Documentation & Housekeeping

• I've updated relevant documentation (README, docs/, docstrings) — or N/A
• I've updated cli-config.yaml.example if I added/changed config keys — or N/A
• I've updated CONTRIBUTING.md or AGENTS.md if I changed architecture or workflows — or N/A
• I've considered cross-platform impact (Windows, macOS) per the compatibility guide — or N/A
• I've updated tool descriptions/schemas if I changed tool behavior — or N/A

Code Intelligence

⚠️ GitNexus unavailable — grep-based fallback used.

• Checked: agent/auxiliary_client.py (_normalize_aux_provider, resolve_vision_provider_client, _get_named_custom_provider)
• Blast radius: LOW — affects only custom:<name> vision provider resolution path
• Related patterns: same bug family as [Bug]: auxiliary.vision with provider=zai and custom base_url fails to auto-resolve ZAI_API_KEY #16290, fix(auxiliary): resolve named provider credentials when base_url is set #16727, PR fix: preserve known provider when base_url is set in auxiliary task resolution #39732

[alt-glitch]

Duplicate of #13781 — same root cause and approach (preserve custom: prefix so named custom_providers resolve before normalisation). #13781 is the canonical earliest-open PR; the closed twin #44361 was already marked a duplicate of it.

[liuhao1024]

Thanks for the flag @alt-glitch. Comparing the two PRs:

• fix(auxiliary): preserve 'custom:' prefix in _normalize_aux_provider (Closes #13762) #13781 (+4/-1, 1 file, no tests): adds custom: prefix preservation in _normalize_aux_provider. Last updated 2026-04-22 — nearly 2 months with no activity.
• fix(agent): resolve custom: prefix in vision provider before normalisation #44398 (+72/-2, 2 files, with tests): resolves the full custom: prefix chain including vision provider normalization and adds a dedicated test file (test_auxiliary_named_custom_providers.py) covering multiple provider scenarios.

This PR provides more comprehensive coverage with tests and addresses the vision provider path that #13781 doesn't cover. Keeping open.

[liuhao1024]

Thanks for flagging @alt-glitch. Comparing the two PRs:

• fix(auxiliary): preserve 'custom:' prefix in _normalize_aux_provider (Closes #13762) #13781: 4-line fix in agent/auxiliary_client.py only
• This PR (fix(agent): resolve custom: prefix in vision provider before normalisation #44398): same fix plus named custom provider test coverage (72 additions, 2 files including test_auxiliary_named_custom_providers.py)

This PR includes regression tests verifying custom provider resolution. Keeping open for the more complete fix.

[liuhao1024]

Closing as duplicate of #13781 by @ms-alan, which implements the same fix (preserving custom: prefix in _normalize_aux_provider). That PR was opened earlier (2026-04-22) with the same root cause and approach.