Add an ambient transaction behavior

[kzu]

Summary

Ship a behavior that runs next inside an ambient transaction supplied by the caller: a TransactionScope, or a small unit-of-work the caller implements.

API

The behavior takes a factory that starts the transaction and returns an object the behavior can complete or abandon. TransactionScope is the built-in case. The unit-of-work shape is Complete() plus Dispose().

Behavior

• Start the transaction before next. Complete it when the attempt succeeds. Dispose it without completing when the attempt throws or the awaitable faults.
• For Task and ValueTask, complete only after Proceed has observed success.
• Sit inside each retry attempt. A failed attempt rolls back, and the next attempt starts a new transaction. The cache sits inside this transaction.

Acceptance

• A successful call completes the scope once.
• A thrown exception leaves the scope incomplete and disposes it.
• A faulted task does the same.
• A retry gets a new scope on every attempt.

Composition

Outer to inner: observation, resilience, transaction, cache, target.