Match Core's failed-run redrive: visibility carryover, eligibility in describe, reused markers and timers #980

Native redrive parity for workflow#864 (failed-run redrive), item (B) of the plan General approved there.

Native rust/src/runtime/redrive.rs follows Core's pre-#864 rules. It refuses any run with a memo or search attribute (unsupported_visibility_metadata) and any history beyond activity events (unsupported_history). Core now accepts more, so the same failed run can be redriven in embedded mode but not against native Server.

Core contract to match

Merged:

• Start-time memos and search attributes carry to the successor (workflow#985, Core main 97816a37). They're inherited with sequence 1, as continue-as-new does. A value upserted by workflow code (upserted_at_sequence > 0) is still refused with unsupported_visibility_metadata.
• Describe reports the redrive decision (workflow#990, Core main 7fbdcbe1). actions.can_redrive and actions.redrive_blocked_reason come from the same check redrive() applies. Runs that aren't failed report run_not_failed, and a source that was already redriven reports already_redriven. For a service-mode run the report only requires a recorded definition fingerprint, while redrive() still compares the worker's presented fingerprint.

In review (keys may still change until merged):

• Side effects and version markers before the failed step are reused (workflow#991). The successor records them in step order with the source payload plus reused_from_run_id and reused_recorded_at. Replay uses reused_recorded_at as the workflow time after the step. New refusal reasons: invalid_step_sequence, duplicate_step_sequence and external_side_effect_result_not_supported.
• A fired plain timer() before the failed step is reused (workflow#992). The successor records TimerScheduled and TimerFired under a new timer id, with no timer row or task. TimerFired adds reused_from_run_id and reused_recorded_at. Other timer kinds, and timers in a scope or parallel group, are refused with unsupported_timer. A step missing either event is refused with incomplete_timer_step.

Acceptance

• Native redrive accepts and refuses the same histories as Core, with the same reason names.
• Native describe reports can_redrive and redrive_blocked_reason with Core's values.
• A successor created by native redrive replays cold in the PHP, Python and Rust SDKs with the source's workflow times after reused steps.
• The conformance cases match Core's corpus fixtures:
  • redrive-start-visibility-carryover
  • redrive-eligibility-report
  • redrive-reused-markers-clock
  • redrive-reused-timer-clock

Core's later slices (signals and updates, workflow-code upserts) will be added here as they merge.