feat(runtime): expand concurrency strategies — debounce, burst, concurrent, lockScope, preemption (ADR 0012)

[ThomasK33]

Expand runtime concurrency handling beyond ConcurrencyDrop and ConcurrencyQueue to the remaining strategies specified in ADR 0012.

Motivation

Under deferred dispatch (DispatchDeferred, ADR 0002), long-running LLM/tool work needs richer concurrency control than drop/queue: debouncing rapid human message bursts, batching, lock-free concurrent reads, channel-scoped locking, and preemption of in-flight handlers.

Acceptance

• ConcurrencyDebounce, ConcurrencyBurst, ConcurrencyConcurrent implemented in the runtime per ADR 0012.
• Configurable lock scope (thread default, channel opt-in).
• Handler preemption / steerability hook with force-release-lock coordination via chat.State.
• Conformance + hardening tests for every new strategy lifecycle, matching the existing test style (queue_edge_test.go, dispatch_deferred_test.go).

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[ThomasK33]

Status update — partial delivery via a maintainer-directed split of #38:

Merging via #38 (reduced): ConcurrencyDebounce, ConcurrencyConcurrent, configurable LockScope (thread default / channel opt-in), and universal lease-loss cancellation for deferred handlers (chat.ErrPreempted cause, preempted outcome), with hardening test suites for each lifecycle, race-detector-clean across all workspace modules.

Staged (not merging yet): ConcurrencyBurst and the OnLockConflict force/steerability hook (plus the LockForcer State capability). Nine codex review rounds converged everywhere except these two areas, whose remaining P1s (atomic remote-force validation, stallable burst refresh, mixed sync/deferred fencing) are structural consequences of key-only force-release and unbounded deferred admission. They live on draft PR #53 and re-enter after the design pass tracked in #44 (admission bound) and #50 (fenced coordination: cross-instance coalescing + token-bound force).

This issue stays open until the staged surface lands.

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