fix(credits): seed cold-start usage gauge from subscription.credits_remaining

[entropy-0x]

The cold-start credits seed computed the subscription usage fraction from a
mismatched pair of fields: the numerator came from
paid_service_access_info.subscription_credits_remaining while the
denominator came from subscription.monthly_credits. The canonical /usage
gauge (build_nous_credits_snapshot) pairs subscription.credits_remaining
with subscription.monthly_credits, and the two remaining-balance fields can
hold different values. As a result the cold-start usage-band notices (50/75/90%)
were derived from a different balance than the gauge and could fire at the wrong
threshold or stay silent when the user was actually over a band.

This aligns the seed's numerator with its denominator so the session-open band
notice matches what /usage displays.

What does this PR do?

Fixes the field source used to compute the subscription used_fraction in the
cold-start credits seed. _credits_state_from_account now reads the subscription
remaining balance from subscription.credits_remaining — the same object that
supplies the denominator subscription.monthly_credits — instead of the
unrelated paid_service_access_info.subscription_credits_remaining. This makes
the session-open usage-band notices consistent with the /usage gauge.

Related Issue

N/A

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 🔒 Security fix
• 📝 Documentation update
• ✅ Tests (adding or improving test coverage)
• ♻️ Refactor (no behavior change)
• 🎯 New skill (bundled or hub)

Changes Made

• agent/credits_tracker.py: in _credits_state_from_account, read the
  subscription remaining balance from subscription.credits_remaining (paired
  with subscription.monthly_credits) for both subscription_micros and
  subscription_usd, instead of paid_service_access_info.subscription_credits_remaining.
• tests/agent/test_credits_cold_start.py: add two regression tests that build
  an account where the two remaining-balance fields differ and assert the seed's
  used_fraction matches the subscription-object pairing and fires the usage band.

How to Test

1. python -m pytest tests/agent/test_credits_cold_start.py -q — passes.
2. Revert the one-line field change and rerun: the two new tests fail
   (used_fraction is 0.10 instead of 0.75, and no credits.usage notice fires).
3. python -m pytest tests/agent/test_credits_tracker.py tests/agent/test_credits_policy.py tests/agent/test_nous_credits_gauge.py tests/agent/test_nous_credits_snapshot.py tests/agent/test_credits_fixture_snapshot.py -q — 166 tests pass.

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature (no unrelated commits)
• I've run the affected suites (tests/agent/test_credits_*, 166 tests) and they pass
• I've added tests for my changes (required for bug fixes, strongly encouraged for features)
• I've tested on my platform: macOS 15 (Darwin 25.5)

Documentation & Housekeeping

• I've updated relevant documentation (README, docs/, docstrings) — or N/A
• I've updated cli-config.yaml.example if I added/changed config keys — or N/A
• I've updated CONTRIBUTING.md or AGENTS.md if I changed architecture or workflows — or N/A
• I've considered cross-platform impact (Windows, macOS) per the compatibility guide — or N/A
• I've updated tool descriptions/schemas if I changed tool behavior — or N/A

[teknium1]

Thanks for the focused regression fix. The premise remains valid on current main: agent/credits_tracker.py:705-706 derives the cold-start subscription balance from paid_service_access_info, while /usage derives its gauge from subscription.credits_remaining at agent/account_usage.py:172-181. The patch aligns those sources and its differing-balance tests exercise both the computed fraction and usage-band outcome.

Automated hermes-sweeper review.