Fix authentication test API key formats and resolve test failures

[Copilot]

Problem

The authentication package tests were failing due to invalid API key formats that didn't match the validation requirements. The validator expects API keys to follow the pattern sk-ant-[a-zA-Z0-9\-_]+, but test cases were using keys like test-api-key-not-real-valid-test-key-123456789 which lack the required sk-ant- prefix.

This was causing systematic test failures across the auth package:

=== FAIL: TestNewAPIKeyAuthenticator/valid_api_key (0.00s)
    auth_test.go:47: NewAPIKeyAuthenticator() error = invalid API key: invalid API key format: API key must match pattern, wantErr false

Solution

Updated all test API keys across the authentication package to use proper sk-ant- prefixed formats while maintaining test coverage and security:

• auth_test.go: Updated API key test cases to use sk-ant-api03-validtestkey1234567890abcdefghijklmnopqrstuvwxyz
• manager_test.go: Fixed API key patterns in credential management tests
• validator_test.go: Updated validation test cases to use compliant formats

The new test keys:

• Follow the required sk-ant- prefix pattern
• Are clearly marked as test keys with api03- and validtest prefixes
• Meet length requirements (20-200 characters)
• Pass entropy and security validation checks
• Are safe for use in tests (not real API keys)

Testing

All authentication tests now pass successfully:

$ go test -v ./pkg/auth/
=== RUN   TestNewAPIKeyAuthenticator
=== RUN   TestAPIKeyAuthenticator_Authenticate  
=== RUN   TestValidator_ValidateAPIKey
--- PASS: TestValidator_ValidateAPIKey (0.00s)
PASS
ok      github.com/jonwraymond/go-claude-code-sdk/pkg/auth    0.006s

Full test suite also passes with no failures across all packages (auth, client, errors, mocks, types).

Impact

• ✅ Resolves all authentication test failures
• ✅ Maintains existing test coverage and functionality
• ✅ Enables CI/CD pipeline to proceed with other pending PRs
• ✅ No breaking changes to public API
• ✅ Test keys are clearly identified as non-production values

This fix unblocks the repository for merging other pending dependency updates and improvements.

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