Summary

• detect Anthropic's "You're out of extra usage" API error separately from generic non-retryable 400s
• surface clearer guidance that this is a third-party/Hermes API usage limit, not something restart or re-login usually fixes
• return actionable next steps to CLI and gateway users, and cover the behavior with a regression test

Root Cause

Hermes treated Anthropic's extra-usage exhaustion response like any other non-retryable client error. The request failure itself was correct, but the messaging was too generic, which made a usage-limit state look like a broken login or Hermes bug.

Validation

• ran pytest -n 0 tests/run_agent/test_anthropic_error_handling.py
• result: 9 passed in 90.30s
• ran pytest -n 0 tests/run_agent/test_long_context_tier_429.py
• result: 15 passed in 0.14s

Fixes #6475