[ben-reitz]

A host module sometimes needs to know who a run is for, such as the conversation that started it, so it can keep separate state for each. The run's env and input can't carry that: the run's code reads both, and a model writing that code could change them.

runtime.exec() now takes metadata, a record of strings, and host module calls read it as context.execution.metadata. The run's code never sees it. Host code reads it as WorkspaceExecutionMetadata, whose values may be undefined, since a run may have been started without metadata, by other code, or before metadata existed.

await workspace.runtime.exec(source, {
  backend: "worker-javascript",
  metadata: { conversation: conversationId },
});

WorkerJavaScriptBackend validates it like env and caps it at a fixed 16 KiB, which is plenty for identifiers; it can become an option if someone needs more. The Workspace stub and the client pass it through, and backends without host modules ignore it.

A replayable run saves its metadata with the rest of its start, so it keeps it when it resumes. The field is optional in the saved start, and a run saved by an earlier version resumes with empty metadata, so JOURNAL_VERSION stays the same and runs in flight during a deploy still resume. runtime.pending() and onWait list each waiting call with its run's metadata, which lets an app that queues work per conversation see that a paused run holds a conversation's place.

Unit tests cover validation, the byte cap, resuming with and without saved metadata, and pending(). Workerd tests check that host modules see the metadata, that the run's code can't find it in process.env or its input, that it reaches the backend through the stub, and that it survives a restart while a run waits. docs/05_runtime_interface.md and docs/17_isolate_javascript.md describe the option.

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Latest commit: bcf2f52

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 4 packages

Name	Type
@cloudflare/computer	Minor
@cloudflare/dofs	Minor
@cloudflare/computer-rpc	Minor
@cloudflare/computerd	Minor

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