release 1.9.3

Features:

• Return structured introspection failure details from introspect, so callers can distinguish invalid requests and tokens from endpoint unavailability, invalid responses, and configuration errors (#576; thanks @shreemaan-abhishek).

Compatibility:

• Require introspection responses to include a boolean active claim; truthy non-boolean values are treated as invalid responses.

Tests:

• Cover structured failure details for negative-cache hits and concurrent requests sharing an introspection endpoint failure.
• CI passes: 1 build job succeeded.

Full changelog: v1.9.2...v1.9.3