workflow: drop the determinism bans (unimplemented-resume pre-support)

The Date.now()/Math.random()/argless-new-Date() bans existed solely to
keep scripts resume-compatible for the deferred journaling/resume
feature. Pre-support for an unimplemented feature is speculative cost:
scripts may now read the clock freely; implementing resume reintroduces
the bans as a script-contract tightening. The RFC's shipped-state
description is updated in place, the tool DESCRIPTION drops the
constraint sentence (the pinned text-turn header follows), and the
engine README's trust-premise paragraph now leans on absent globals
alone.

packages/workflow/workflow-vm/README.md

@@ -4,13 +4,13 @@ The first [`WorkflowService`](../workflow/README.md) implementation: an in-proce
 
 ## Trust premise
 
-Workflow scripts are **model-written** — the same trust level as the model's existing bash access — so this engine defends against **buggy** scripts, never hostile ones. vm is NOT a security boundary and no attempt is made to contain adversarial values: property reads on script values may run script code (a getter, a `toString`, a proxy trap) on the host stack, and a script determined to hang the process can simply spin past its first await (see the limitations below). Concretely, the context is **escapable by construction**: `node:vm` shares object machinery with the host, so a script can reach the host `Function` constructor (`globalThis.constructor.constructor`) and from it `process` and every Node builtin — the absent globals and determinism bans are API surface that keeps honest scripts portable and resume-compatible, not walls. What the engine DOES guarantee, because benign scripts hit these constantly: `result` never rejects, a dropped hook promise never becomes an unhandled rejection (the app boot layer exits the process on those), values that JSON cannot carry are rejected **loud** instead of silently mangled, and hook misuse is fatal instead of dissolving into a per-item `null`. Genuine sandboxing is an engine swap behind the seam (worker-thread/isolated-vm, where the boundary is serialization by construction), not incremental host-side defenses here.
+Workflow scripts are **model-written** — the same trust level as the model's existing bash access — so this engine defends against **buggy** scripts, never hostile ones. vm is NOT a security boundary and no attempt is made to contain adversarial values: property reads on script values may run script code (a getter, a `toString`, a proxy trap) on the host stack, and a script determined to hang the process can simply spin past its first await (see the limitations below). Concretely, the context is **escapable by construction**: `node:vm` shares object machinery with the host, so a script can reach the host `Function` constructor (`globalThis.constructor.constructor`) and from it `process` and every Node builtin — the absent globals are API surface that keeps honest scripts portable, not walls. What the engine DOES guarantee, because benign scripts hit these constantly: `result` never rejects, a dropped hook promise never becomes an unhandled rejection (the app boot layer exits the process on those), values that JSON cannot carry are rejected **loud** instead of silently mangled, and hook misuse is fatal instead of dissolving into a per-item `null`. Genuine sandboxing is an engine swap behind the seam (worker-thread/isolated-vm, where the boundary is serialization by construction), not incremental host-side defenses here.
 
 ## The script contract it executes
 
 - **Meta extraction** (`extractMeta`): a string/comment-aware brace scanner finds the leading `export const meta` literal (template interpolation rejected — the literal must be pure), evaluates it ALONE in an empty timed vm context, materializes the result to plain JSON data, validates the shape (`name`/`description` required; unknown fields rejected loud), and blanks the statement line-preservingly so error stacks keep the script's own line numbers.
 - **Hooks**: `agent(prompt, {label, phase, schema, model})` (schema = the [structured-output subset](../../core/tools/README.md), forwarded as `outputSchema`; result = validated object, or final text without a schema; a failed child resolves `null`), `parallel(thunks)`, `pipeline(items, ...stages)` with NO cross-stage barrier and `(prev, item, index)` stage callbacks, `phase(title)`, `log(message)`, and the `args` global. Anything else — `effort`/`isolation`/`agentType`, unknown options, malformed arguments, schemas outside the subset — throws a FATAL `WorkflowError` that `parallel`/`pipeline` re-throw rather than nulling (see the seam README's failure discipline).
-- **Determinism bans**: `Date.now()`, `Math.random()`, and argless `new Date()` throw (kept even though resume is deferred, so scripts stay resume-compatible); no timers, filesystem, or Node APIs are injected into the context (absence is API surface, not containment — see the trust premise).
+- **No ambient APIs**: no timers, filesystem, or Node APIs are injected into the context (absence is API surface, not containment — see the trust premise).
 
 ## The value boundary