Resume workflow runs from explicit durable signals

[taras]

Story

As a workflow user, I want a host to resume runs on explicit durable signals, so local scheduling today and cloud delegation later share the same lifecycle without embedding file watchers or hidden transcript reconstruction in the workflow contract.

Scope

Build scheduling around the public lifecycle from #366 and #367. A suspended or interrupted run may be reacquired by one authorized host when its recorded signal becomes available. The host calls the same resume operation used by the CLI and streams or retains output through its own transport.

The first implementation needs explicit user-input delivery and explicit resume scheduling. Configured source-file watching, unattended iteration-completion arbitration, and a public remote-host selector are deferred until a concrete workflow needs them.

The CLI reserves host-neutral command semantics but does not expose --context or another remote-host selector yet.

Acceptance

• Scheduling acquires the same single-executor lease as foreground resume.
• A durable input is correlated to the exact suspended request and cannot satisfy another run or attempt.
• Process exit requires no hidden Agent transcript or in-memory waiter.
• Duplicate or late signals are rejected or reconciled deterministically.
• Cancellation at acquisition, input delivery, and resumed execution has a durable outcome.
• Local and future remote hosts can implement the same contextual lifecycle API without changing documents.
• No file watcher, implicit branch movement, or document-path lookup is required for resumption.

Dependencies

• Add workflow inspection, cancellation, suspension, and deletion #367 supplies inspection, suspension, cancellation, and executor ownership.
• Store WorkflowRuns and filtered journals in SQLite #291 supplies retained run lookup.
• Compose the supervised adversarial implementation workflow #301 supplies the supervised workflow that consumes explicit continuation.
• End goal: Document adversarial implementation workflow WIP #181.