docs: describe the workflow engine as worker-thread first

The outer ring catches up with the engine swap (the package's own
README/JSDoc rode the port commit):

- Seam module doc and README name the worker-thread engine as THE
  implementation, with isolated-vm/separate-process sandboxing as the
  deferred hardening; the seam service doc states the holder-owned-runs
  contract (engine-fiber disposal deliberately leaves live runs to
  their holders).
- Seam contract precision: agentsStarted documents the termination-path
  degradation to the host-observed count; the events section scopes the
  agent-start/agent-end pair to calls that STARTED a child run;
  WorkflowRun wording drops the vm-era abandonment language.
- The dynamic-workflows RFC is rewritten in place to the shipped
  mechanism (implemented-RFC rule): why worker threads, the thread's
  concrete buys, the in-process node:vm first cut recorded under
  alternatives considered; the tool section describes the usage policy
  as the tool's own prompt section.
- gen-doc-graphs: six workflow/* DYNAMIC_EVENT_DISPATCHERS entries (the
  catalog no longer claims nothing dispatches them) and the seam-note
  wording; core-data-structures gains its workflow.md index row;
  packages/README + AGENTS.md layout line + example cordis.yml comments
  say worker-thread; catalogs regenerated.

docs/cordis-catalog/services.md

@@ -238,12 +238,13 @@ Semantics every implementation must honor:
 - start throws synchronously for a request that cannot begin (an unparseable script, an invalid meta block). Once it returns a WorkflowRun, `result` NEVER rejects — every failure resolves with `stopReason: 'error'` (or `'cancelled'`) — and once the run is cancelled, `result` SETTLES within the implementation's bounded grace even if the script itself never settles (a consumer awaiting `result` must never be wedged past a cancellation).
 - The `workflow/*` events fire through emitWorkflowEvent (data snapshots, per-listener containment); `workflow/end` fires exactly once per started run, after `result` is settled or as it settles.
 - `dispose()` reaches quiescence within a bounded grace: it cancels, waits for the script to settle AND its started children to finish disposing, and abandons whatever is left rather than hanging its caller (the engine documents what abandonment leaves behind).
+- Runs are HOLDER-OWNED: the engine hands control (`cancel`/`dispose`) to the `start()` caller and does not track its live runs — disposing the engine's own fiber mid-run deliberately leaves those runs to their holders' teardown, so an engine reload cannot yank a run out from under the consumer awaiting it.
 
 ```ts cordis-catalog
 abstract start(request: WorkflowStartRequest): WorkflowRun
 ```
 
-Source: [`packages/workflow/workflow/src/index.ts:202`](../../packages/workflow/workflow/src/index.ts)
+Source: [`packages/workflow/workflow/src/index.ts:207`](../../packages/workflow/workflow/src/index.ts)
 
 ## Inherited `ctx` members (cordis core + loader/hmr/timer)