fix(copilot): adapt catalog endpoint routing across current runtimes

[Chenkeliang]

What does this PR do?

Fix Copilot models that advertise only /responses but are routed to /chat/completions. Grok 4.6 currently fails with HTTP 400 unsupported_api_for_model; with this change, the primary agent, auxiliary clients, and fallback activation use the shared catalog-aware resolver.

This is a current-main adaptation of #88538, not an independent claim of the same fix. Its commit was cherry-picked without committing, conflicts from subsequent function extraction were resolved, and the resulting commit retains Eleanor Berger's authorship. The dual-endpoint regression from that PR is included. The original PR credits earlier work in #58835; related work also includes #74377, #85224, and #86075. Maintainers may prefer to incorporate this adaptation and validation into the existing PR.

Related Issue

Fixes #96902

Type of Change

• Bug fix

Changes Made

• hermes_cli/models.py: upgrade non-GPT models when their catalog entry advertises /responses without /chat/completions. Keep existing GPT heuristics, Claude chat transport, dual-endpoint behavior, and missing-catalog fallback.
• agent/agent_init.py and run_agent.py: pass the initialization credential to the shared resolver before client construction.
• agent/auxiliary_client.py: resolve catalog capabilities before constructing request headers and wrap Responses-only clients appropriately.
• agent/chat_completion_helpers.py: pass the fallback credential through the extracted API-mode resolver. Explicit API-mode overrides still win.
• Reuse the upstream regressions for catalog routing, auxiliary requests, and fallback activation.

How to Test

On base 437116f9497c80d242ce034ff7f5d81dc277a337, the upstream catalog test reproduced the bug: 1 failed, 4 passed, with a Responses-only model resolving to chat_completions.

After the fix, run:

scripts/run_tests.sh \
  tests/hermes_cli/test_copilot_model_api_mode.py \
  tests/hermes_cli/test_copilot_runtime_api_mode.py \
  tests/hermes_cli/test_model_switch_copilot_api_mode.py \
  tests/hermes_cli/test_models.py \
  tests/hermes_cli/test_runtime_provider_resolution.py \
  tests/agent/test_auxiliary_main_first.py \
  tests/agent/test_fallback_api_mode_preservation.py \
  tests/agent/test_copilot_initiator.py \
  tests/agent/test_copilot_native_vision_headers.py -q

Result: 209 passed, 0 failed across nine files. Ruff 0.15.10, git diff --check, and the Windows-footgun check on all eight changed files also passed.

Live verification on Linux ARM64, with real imports and a temporary HERMES_HOME, no model.api_mode override, and a minimal Reply exactly OK prompt:

Case	Selected transport	Result
Copilot Grok 4.6	codex_responses	OK, completed, no fallback
Copilot Gemini 3.5 Flash	chat_completions	OK, completed, no fallback
Force Grok onto its unsupported chat endpoint in an isolated agent	Automatic fallback to a configured custom chat provider	OK, completed, fallback activated

No messaging-channel test messages were sent. Auxiliary and Copilot-as-fallback routing are covered by regression tests; the live fallback test exercises Copilot-to-custom failover.

Checklist

• Read CONTRIBUTING.md and applicable AGENTS.md files.
• Conventional commit; original contributor authorship retained.
• Searched open and merged PRs/issues; overlapping work is explicitly acknowledged above.
• Only this repair is included; one commit on the verified official main base.
• Relevant regression tests passed through scripts/run_tests.sh.
• Full repository test suite run locally (not run; targeted results above).
• Tested on Linux ARM64 in OrbStack.
• Relevant docstring updated; no new config keys, dependencies, tools, or architecture changes.
• Cross-platform impact checked; no new OS-specific behavior.

The existing explicit model.api_mode setting remains authoritative. Users who previously pinned chat_completions or codex_responses must remove that override to opt into automatic routing.

[alt-glitch]

This was generated by AI during triage.

Related: this is a current-main rebase of open #88538 (same commit, authorship retained), which is the canonical PR for the Responses-only Copilot routing fix for #96902; the broader Copilot api_mode routing cluster is led by #57625. Maintainers may prefer to take this rebase into #88538 rather than review two copies.

[Chenkeliang]

Closing this duplicate in favor of the canonical #88538, following the triage suggestion. The tested adaptation, retained contributor attribution, patch link, and validation evidence are being transferred to #88538 for integration by its author/maintainers.

The branch Chenkeliang/hermes-agent:fix/copilot-catalog-endpoints and commit c95ccc28a81db24c64cd3fb2036f9825208e2954 remain available; no branch deletion or history rewrite is requested.