Fix retry phase-goal continuation

[yvette-carlisle]

Summary:

• Resume retry attempts from the immediately previous unterminated phase-goal state instead of resetting to implementation.
• Shadow stale older attempts from current-lane projection when a newer attempt holds the lease.
• Update runtime specs and operator reference docs for the retry/current-lane invariants.

Validation:

• cargo make fmt
• cargo make lint-fix
• cargo make test (1189 passed, 1 skipped)