Adopt JoinSet supervision in JobManager

[josecelano]

Goal

Adopt tokio::task::JoinSet for JobManager so the application directly owns its named top-level component tasks, observes their completion concurrently, and applies explicit cooperative-cancellation and escalation policies.

The detailed, versioned implementation specification is maintained in docs/issues/open/1586-evaluate-job-manager-join-set/ISSUE.md.

Context

The shutdown architecture for parent EPIC #1488 is finalized: JobManager supervises direct named top-level components under a root CancellationToken; each component owns and completes or deliberately aborts its own child tasks. This issue implements only the supervisor layer.

Required design

• Register direct component futures through a spawn(name, future) API. Do not accept already-spawned JoinHandles or add wrapper tasks that only await them.
• Keep component names associated with every completion, failure, panic, cancellation, timeout, and deliberate-abort outcome.
• After cancellation is requested, observe all direct components concurrently under one process-wide deadline, rather than applying a timeout sequentially per component.
• On deadline expiry, deliberately abort every remaining direct component, join it, and report a named abnormal outcome. No component may be silently detached.
• Do not flatten component-owned child tasks into JobManager; each component retains its lifecycle responsibility for those children.

Acceptance criteria

• JobManager directly owns its top-level component tasks through JoinSet and has no wrapper around an already-spawned handle.
• The direct registration API and all application callers use spawn(name, future).
• Supervisor outcomes retain component names and distinguish normal completion, failure, panic, cooperative cancellation, deadline expiry, and deliberate abort as supported by the component contract.
• The supervisor uses a single concurrent overall deadline.
• Remaining direct components are deliberately aborted and joined after deadline expiry.
• Deterministic focused tests cover completion order, panic/failure, cooperative cancellation, deadline expiry, escalation, and retained names.
• linter all passes.

Scope boundary and rollback

This issue does not migrate individual components to token cancellation; those vertical slices remain separately sequenced #1488 work items. A coherent revert restores the prior supervisor implementation without changing component-owned child lifecycles.

[copilot-swe-agent]

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