fix(auth): show Codex device retry guidance

[ehz0ah]

Description

When the initial Codex device-code request is rate-limited, OpenViking currently reports only the HTTP status. This change preserves valid Retry-After guidance from the response so users know when to try again. It does not retry automatically or invent a delay when the server omits the header.

Human Involvement

• A human participated in the implementation or review loop
• This PR was generated entirely by AI agents without human participation in the loop

Related Issue

Fixes #6224

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 not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test update

Changes Made

• Parse standard Retry-After delta-seconds and HTTP-date values.
• Append valid retry timing to the initial Codex device-login error.
• Keep the existing status-only error for missing or invalid headers.

Testing

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have tested this on the following platforms:
  • Linux
  • macOS
  • Windows

Commands:

uv run --native-tls --isolated --no-default-groups --with pytest --with pytest-cov --with pytest-asyncio python -m pytest -q -o addopts='' tests/unit/test_codex_vlm.py -k device_login_reports_valid_retry_after
uv run --native-tls --isolated --no-default-groups --with pytest --with pytest-cov --with pytest-asyncio python -m pytest -q -o addopts='' tests/unit/test_codex_vlm.py
uv tool run --native-tls ruff@0.14.14 check openviking/models/vlm/backends/codex_auth.py tests/unit/test_codex_vlm.py
uv tool run --native-tls ruff@0.14.14 format --check openviking/models/vlm/backends/codex_auth.py tests/unit/test_codex_vlm.py

Results: 5 focused cases passed, all 34 Codex VLM unit tests passed, and Ruff check and format passed.

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Screenshots (if applicable)

Not applicable.

Additional Notes

The motivating external report is anomalyco/opencode#56499. The OpenViking change is independently implemented and limited to the supported openviking-server init Codex login path.