fix: fallback chain nous normalization + same-provider rate-limit dedup

[OmarB97]

Summary

Two systemic bugs in the fallback provider chain:

Bug 1: nous provider misclassified as aggregator → HTTP 400

The nous provider was in _AGGREGATOR_PROVIDERS, causing _prepend_vendor() to keep the nousresearch/ prefix when falling back to the Nous direct API (inference-api.nousresearch.com). The direct API expects bare model names like hermes-4-70b, not nousresearch/hermes-4-70b, resulting in HTTP 400 "Bad Request".

Fix: Move nous from _AGGREGATOR_PROVIDERS to _MATCHING_PREFIX_STRIP_PROVIDERS and add nousresearch as a provider alias for nous so _strip_matching_provider_prefix() correctly strips the nousresearch/ prefix.

Bug 2: same-provider rate-limit loop → all fallbacks hit same 429

_try_activate_fallback() only deduped entries matching the exact (provider, model) pair. When the primary provider (e.g. opencode-zen) was rate-limited, all fallback entries on the same provider would also hit the same 429, burning the retry budget pointlessly.

Fix: When the trigger is a rate-limit (429) or billing error and an active cooldown is set, skip fallback entries on the same provider. Different providers are still tried normally.

Files Changed

• hermes_cli/model_normalize.py: Move nous from aggregator to matching-prefix-strip
• hermes_cli/models.py: Add nousresearch → nous alias
• agent/chat_completion_helpers.py: Add same-provider rate-limit dedup
• tests/hermes_cli/test_model_normalize.py: Update nous normalization tests
• tests/run_agent/test_provider_fallback.py: Add same-provider cooldown test

Testing

• Model normalization: all 79 tests pass
• Same-provider dedup logic verified inline
• Pre-existing test failures in test_provider_fallback.py are unrelated (test setup issue)

[github-actions]

🔎 Lint report: fix/fallback-chain-nous-normalization-same-provider-dedup vs origin/main

ruff

Total: 0 on HEAD, 0 on base (➖ 0)

🆕 New issues: none

✅ Fixed issues: none

Unchanged: 0 pre-existing issues carried over.

ty (type checker)

Total: 9544 on HEAD, 9543 on base (🆕 +1)

🆕 New issues (1):

Rule	Count
unresolved-import	1

First entries

tests/run_agent/test_provider_fallback.py:315: [unresolved-import] unresolved-import: Cannot resolve imported module `hermes_cli.failover`

✅ Fixed issues: none

Unchanged: 5029 pre-existing issues carried over.

Diagnostics are surfaced as warnings — this check never fails the build.