Release v0.10.0

[dangra]

Bumps VERSION and every in-tree require to v0.10.0.

After merge, run the tag-release workflow with version v0.10.0 to tag every module at the merge commit, publish the GitHub release, and verify the modules resolve for consumers.

Migration from v0.9.0

durable owes no compatibility to earlier releases; this release breaks the generated API, the handler contract, the proto options, and the cancel model.

• Regenerate every pipeline proto (Extension numbers 1374 and 1375, durable's registered allocation #99). The durable.v1.step and durable.v1.pipeline options are now extensions 1374 and 1375, durable's registered numbers; a descriptor compiled against 51841/51842 is invisible to the generator and the runtime.
• Steps nest in their pipeline message (Steps nest in their pipeline message; the steps list is gone #95). A step is a message declared directly inside the pipeline message, in topology order; the steps list option is gone. Generated step types are Pipeline_Step.
• One handler interface per pipeline (Generated pipelines: one handler interface, one typed invocation #93, Generated handlers: Reduce is ReduceOutput #96). NewXxx(h XxxHandlers) takes one implementation with a method per step, Unwind<Step> per unwinding step, and ReduceOutput / ReduceFailure when the pipeline declares outputs. Per-step handler types and XxxFunc adapters are gone; handler methods receive XxxInvocation, a durable.TypedInvocation[*XxxInput].
• Per-pipeline middleware (Per-pipeline middleware, composed once at Bind #97). NewXxx(h, xxxpb.WithMiddleware(mw...)) installs middleware on one pipeline, composed inside the engine chain once at Bind; hand-rolled definitions set pipelinedef.Config.Middleware.
• Cancellation (Cancellation: resolve the pending operation, cut the running one, cascade to children #92, A cancel request racing an attempt's registration still cuts it #98). A dormant or parked operation resolves as canceled at once with no handler run; a running attempt's context is canceled with a *durable.PreemptedError cause and anything but success resolves it as canceled; reduction is uncancellable; a park cascades to its targets only with durable.WithCancelCascade(). CancelRequested, FailFastOnCancel, and Yield are removed.
• Shutdown interrupts, it does not fail (Shutdown interrupts an attempt; it does not fail it #89). An attempt cut by Stop that returns an ordinary error records no last error and no retry backoff; observers see AttemptInterrupted.
• Run classes and unbounded workers (Run classes: a run-scoped counting bound with an eligibility-ordered line #87, Unbounded workers by default #88). run_class on a pipeline plus engine.WithRunClass bound started nonterminal Runs with an eligibility-ordered line; workers are unbounded unless WithConcurrency is set.

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