Unit tests fail when .env.local is sourced

[crtahlin]

Problem

Unit tests fail (15 failures) when .env.local environment variables are exported in the shell. This happens because .env.local overrides values that unit tests expect to be unset or at defaults:

• PROVENANCE_GATEWAY_URL=http://localhost:8000 breaks test_default_url (expects production URL)
• X402_PRIVATE_KEY being set breaks test_x402_status_shows_no_private_key and test_x402_balance_fails_without_private_key
• Real X402_PRIVATE_KEY causes x402 client tests to bypass mocks and hit real Web3 providers

Current workaround

Run unit and integration tests separately:

# Unit tests — clean environment (no .env.local)
pytest --ignore=tests/test_integration.py

# Integration tests — need .env.local for wallet keys
export $(grep -v '^#' .env.local | xargs)
pytest tests/test_integration.py -v

Expected behavior

Unit tests should pass regardless of what environment variables are set, since they mock all external dependencies.

Possible solutions

1. Fixture-based env isolation: Add a conftest.py autouse fixture that saves and clears sensitive env vars (PROVENANCE_GATEWAY_URL, X402_PRIVATE_KEY, PROVENANCE_WALLET_KEY, etc.) before each unit test, restoring them after
2. monkeypatch in affected tests: Use monkeypatch.delenv() in the specific tests that assume unset env vars
3. Reload config module: Mock or reload config.py in unit tests so module-level os.getenv() calls pick up test values instead of shell env

Affected tests

Test file	Failures	Cause
test_gateway_client.py	1	PROVENANCE_GATEWAY_URL override
test_cli.py	2	X402_PRIVATE_KEY set
test_x402_client.py	12	X402_PRIVATE_KEY bypasses mocks

[crtahlin]

Resolved. Unit tests (604 passed, 18 skipped) now pass with .env.local sourced. The gateway test pollution was fixed in PR #80, and subsequent test improvements ensure proper isolation.