fix(primary): preserve routed client headers on auto-routed provider init

[GabriWar]

Bug

When the primary agent client is built via the auto-routed path (provider auto-detected, no explicit API key in config.yaml), run_agent.py checks hasattr(_routed_client, '_default_headers') to copy provider-specific headers into self._client_kwargs. The OpenAI SDK actually stores headers passed via default_headers= on the constructor in _custom_headers, so the check silently fails and _client_kwargs is saved without any headers.

Every subsequent request-client rebuild via _create_request_openai_client then constructs a bare OpenAI(api_key, base_url) client that drops the Copilot-required Editor-Version and Copilot-Integration-Id headers, causing hard 400 model_not_supported responses from api.githubcopilot.com/chat/completions on every tool-call round after the first request.

The gateway path (WhatsApp, Telegram, Discord, etc.) is the easiest repro because each turn spawns a fresh AIAgent that immediately rebuilds its request client before any assistant output. The CLI path can be mostly unaffected for single-shot queries because the first request uses the original client directly.

Reproduction

1. model.default: gemini-3.1-pro-preview + model.provider: copilot in config.yaml
2. No COPILOT_API_KEY env var — rely on gh auth token / ghu_* github user token, so the auto-route path at line ~914 is taken
3. Start hermes gateway run, send a message via a messaging platform that triggers a tool call
4. Gateway log:

⚠️ Non-retryable error (HTTP 400) — trying fallback...
❌ Non-retryable error (HTTP 400): HTTP 400: The requested model is not supported.
   📋 Details: {'message': 'The requested model is not supported.', 'code': 'model_not_supported', 'param': 'model', 'type': 'invalid_request_error'}

Inspecting the dumped outgoing request headers shows only Authorization and Content-Type — Editor-Version / Copilot-Integration-Id are missing, confirming the rebuilt client dropped them.

Root cause

from agent.auxiliary_client import resolve_provider_client
c, _ = resolve_provider_client("copilot", model="gemini-3.1-pro-preview", raw_codex=True)
print(hasattr(c, "_default_headers"))  # False
print(hasattr(c, "_custom_headers"))   # True
# _custom_headers contains: Editor-Version, User-Agent, Copilot-Integration-Id,
#                           Openai-Intent, x-initiator

resolve_provider_client() in auxiliary_client.py correctly passes the full copilot header set via default_headers= when constructing the OpenAI client, but the OpenAI SDK stashes them on _custom_headers, not _default_headers.

Fix

Prefer _custom_headers and fall back to _default_headers for forward-compat with any routed client type that uses the older attribute name:

_rh = getattr(_routed_client, '_custom_headers', None) or getattr(_routed_client, '_default_headers', None)
if _rh:
    client_kwargs["default_headers"] = dict(_rh)

This mirrors the pattern used in #6076, which fixed the same class of bug in _try_activate_fallback(). That PR only covered the fallback activation path — the auto-routed primary path was missed.

Verified

After applying the patch + systemctl --user restart hermes-gateway.service + clearing __pycache__, repeated multi-tool-call sessions on gemini-3.1-pro-preview via Copilot now complete cleanly with zero 400 model_not_supported errors. Primary no longer needs to hand off to the fallback chain on every request.

Related

• [Bug]: Provider-specific headers (e.g. KimiCLI User-Agent) lost after fallback activation #6075 — Original bug report (fallback path)
• fix(fallback): preserve provider-specific headers when activating fallback #6076 — Fallback path fix (merged)

[Copilot]

Pull request overview

Fixes a regression where auto-routed provider initialization failed to persist provider-specific HTTP headers (notably GitHub Copilot headers) into _client_kwargs, causing rebuilt request clients to drop required headers on subsequent turns.

Changes:

• Update auto-routed client initialization to copy headers from the OpenAI SDK’s _custom_headers (with fallback) into client_kwargs["default_headers"].
• Add explanatory comments tying the fix to the prior fallback-path fix (#6076) and documenting the OpenAI SDK behavior.

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