Fixed
Deterministic workflow time no longer shares mutable Carbon objects with callers. Deriving a deadline with Workflow::now()->addHour() cannot advance the workflow clock or expire that deadline immediately. Mutating an object supplied to WorkflowFiberContext::setTime() also cannot change stored time.
Timestamp precision, timezones, Carbon mutable/immutable types, history-based advancement, and the wall-clock fallback outside workflows are preserved. No wire-format or database-schema change.
Upgrade the durable-workflow/workflow dependency and restart long-running PHP workers so they load the fix.
Implementation and regression evidence: #512 (fixes #511).
Source validation: https://github.com/durable-workflow/workflow/actions/runs/34685503210 . Full MySQL, PostgreSQL, MariaDB, supported Laravel-major upgrades, static analysis, regression corpus and coverage passed. Published-package verification follows through the repository release workflow.