improvement(sandbox): delegate timers to Node, add phase timings + saturation logs

Follow-ups on top of the isolated-vm migration (da14027):

Timer delegation (laverdet/isolated-vm#136 recommended pattern):
 - setTimeout / setInterval / clearTimeout / clearImmediate delegate to
   Node's real timer heap via ivm.Reference. Real delays are honored;
   clearTimeout actually cancels; ms is clamped to the script timeout
   so callbacks can't fire after the isolate is disposed.
 - Per-execution timer tracking + dispose-sweep in finally. Zero stale
   callbacks post-dispose.
 - unwrapPrimitive helper normalizes ivm.Reference-wrapped primitives
   (arguments: { reference: true } applies uniformly to all args).
 - _polyfills.ts shrinks from ~130 lines to the global->globalThis alias.
   Timers / TextEncoder / TextDecoder / console all install per-execution
   from the worker via ivm bridges.

AbortSignal race fix (pre-existing bug surfaced by the timer smoke):
 - Listener is registered after await tryAcquireDistributedLease. If the
   signal aborted during that ~200ms window (Redis down), AbortSignal
   doesn't fire listeners registered after the fact — the abort was
   silently missed. Now re-checks signal.aborted synchronously after
   addEventListener.

Observability:
 - executeTask returns IsolatedVMTaskTimings (setup, runtimeBootstrap,
   bundles, brokerInstall, taskBootstrap, harden, userCode, finalize,
   total) in every success + error path. run-task.ts logs these with
   workspaceId + queueMs so 'which tenant is slow' is queryable.
 - Pool saturation events now emit structured logger.warn with reason
   codes: queue_full_global, queue_full_owner, queue_wait_timeout,
   distributed_lease_limit. Matches the existing broker reject pattern.

Security policy:
 - New .cursor/rules/sim-sandbox.mdc codifies the hard rules for the
   worker process: no app credentials, all credentialed work goes
   through host-side brokers, every broker scopes by workspaceId.
   Pre-merge checklist for future changes to isolated-vm-worker.cjs.

Measured phase breakdown (local smoke, Redis down): pptx wall=~310ms
with bundles=~16ms, finalize=~83ms; docx ~290ms / 17ms / 70ms; pdf
~235ms / 17ms / 5ms. Bundle compilation is not the bottleneck —
library finalize is.

Made-with: Cursor

Author: icecrasher321

.cursor/rules/sim-sandbox.mdc

@@ -0,0 +1,85 @@
+---
+description: Isolated-vm sandbox worker security policy. Hard rules for anything that lives in the worker child process that runs user code.
+globs: ["apps/sim/lib/execution/isolated-vm-worker.cjs", "apps/sim/lib/execution/isolated-vm.ts", "apps/sim/lib/execution/sandbox/**", "apps/sim/sandbox-tasks/**"]
+---
+
+# Sim Sandbox — Worker Security Policy
+
+The isolated-vm worker child process at
+`apps/sim/lib/execution/isolated-vm-worker.cjs` runs untrusted user code inside
+V8 isolates. The process itself is a trust boundary. Everything in this rule is
+about what must **never** live in that process.
+
+## Hard rules
+
+1. **No app credentials in the worker process**. The worker must not hold, load,
+   or receive via IPC: database URLs, Redis URLs, AWS keys, Stripe keys,
+   session-signing keys, encryption keys, OAuth client secrets, internal API
+   secrets, or any LLM / email / search provider API keys. If you catch yourself
+   `require`'ing `@/lib/auth`, `@sim/db`, `@/lib/uploads/core/storage-service`,
+   or anything that imports `env` directly inside the worker, stop and use a
+   host-side broker instead.
+
+2. **Host-side brokers own all credentialed work**. The worker can only access
+   resources through `ivm.Reference` / `ivm.Callback` bridges back to the host
+   process. Today the only broker is `workspaceFileBroker`
+   (`apps/sim/lib/execution/sandbox/brokers/workspace-file.ts`); adding a new
+   one requires co-reviewing this file.
+
+3. **Host-side brokers must scope every resource access to a single tenant**.
+   The `SandboxBrokerContext` always carries `workspaceId`. Any new broker that
+   accesses storage, DB, or an external API must use `ctx.workspaceId` to scope
+   the lookup — never accept a raw path, key, or URL from isolate code without
+   validation.
+
+4. **Nothing that runs in the isolate is trusted, even if we wrote it**. The
+   task `bootstrap` and `finalize` strings in `apps/sim/sandbox-tasks/` execute
+   inside the isolate. They must treat `globalThis` as adversarial — no pulling
+   values from it that might have been mutated by user code. The hardening
+   script in `executeTask` undefines dangerous globals before user code runs.
+
+## Why
+
+A V8 JIT bug (Chrome ships these roughly monthly) gives an attacker a native
+code primitive inside the process that owns whatever that process can reach.
+If the worker only holds `isolated-vm` + a single narrow workspace-file broker,
+a V8 escape leaks one tenant's files. If the worker holds a Stripe key or a DB
+connection, a V8 escape leaks the service.
+
+The original `doc-worker.cjs` vulnerability (CVE-class, 225 production secrets
+leaked via `/proc/1/environ`) was the forcing function for this architecture.
+Keep the blast radius small.
+
+## Checklist for changes to `isolated-vm-worker.cjs`
+
+Before landing any change that adds a new `require(...)` or `process.send(...)`
+payload or `ivm.Reference` wrapper in the worker:
+
+- [ ] Does it load a credential, key, connection string, or secret? If yes,
+      move it host-side and expose as a broker.
+- [ ] Does it import from `@/lib/auth`, `@sim/db`, `@/lib/uploads/core/*`,
+      `@/lib/core/config/env`, or any module that reads `process.env` of the
+      main app? If yes, same — move host-side.
+- [ ] Does it expose a resource that's workspace-scoped without taking a
+      `workspaceId`? If yes, re-scope.
+- [ ] Did you update the broker limits (`IVM_MAX_BROKER_ARGS_JSON_CHARS`,
+      `IVM_MAX_BROKER_RESULT_JSON_CHARS`, `IVM_MAX_BROKERS_PER_EXECUTION`) if
+      the new broker can emit large payloads or fire frequently?
+
+## What the worker *may* hold
+
+- `isolated-vm` module
+- Node built-ins: `node:fs` (only for reading the checked-in bundle `.cjs`
+  files) and `node:path`
+- The three prebuilt library bundles under
+  `apps/sim/lib/execution/sandbox/bundles/*.cjs`
+- IPC message handlers for `execute`, `cancel`, `fetchResponse`,
+  `brokerResponse`
+
+The worker deliberately has **no host-side logger**. All errors and
+diagnostics flow through IPC back to the host, which has `@sim/logger`. Do
+not add `createLogger` or console-based logging to the worker — it would
+require pulling the main app's config / env, which is exactly what this
+rule is preventing.
+
+Anything else is suspect.