computer, docs: Mark restart and replay as experimental

The journal format, event log and fingerprint check will change as
replay develops, and a run interrupted across such a change fails
rather than resuming. WorkerJavaScriptBackend and workspace.runtime are
now listed as stable, so give resuming its own experimental row in the
package's status table, and say so in the docs, the onInterrupt JSDoc
and the changeset. The changeset also notes the new required callId on
host module call contexts.

A comment on the durable tables records why a change to their shape
should rename them rather than migrate: every backend creates them when
it connects, and CREATE TABLE IF NOT EXISTS leaves an older table as it
was.

Author: scuffi

.changeset/durable-javascript.md

@@ -2,4 +2,4 @@
 "@cloudflare/computer": minor
 ---
 
-`WorkerJavaScriptBackend` can restart or replay runs interrupted by a deploy or crash, with the `onInterrupt` option and `runtime.recover()`. Host module functions can opt out of running twice with `unsafeToRepeat()`.
+`WorkerJavaScriptBackend` can restart or replay runs interrupted by a deploy or crash, with the experimental `onInterrupt` option and `runtime.recover()`. Host module functions can opt out of running twice with `unsafeToRepeat()`. Host module call contexts now carry a required `callId`.

docs/17_isolate_javascript.md

@@ -147,7 +147,7 @@ A deploy or a crash still ends a run. A deploy shuts the old instance down a few
 
 ## Interrupted executions
 
-A run that was in flight when its Durable Object restarted is settled by its `onInterrupt` policy. Set a default on the backend and override it per run:
+A run that was in flight when its Durable Object restarted is settled by its `onInterrupt` policy. Set a default on the backend and override it per run. The `"restart"` and `"replay"` policies are [experimental](../packages/computer/README.md#status): their behavior and stored format may change in any release, and a run interrupted across such an upgrade fails rather than resuming.
 
 ```ts
 const backend = new WorkerJavaScriptBackend({ loader: env.LOADER, onInterrupt: "replay" });

packages/computer/README.md

@@ -31,6 +31,7 @@ removed in a future release; each one names its replacement.
 | Observability hook and its Cloudflare adapter | `@cloudflare/computer`, `@cloudflare/computer/observe/cloudflare` | Stable |
 | `ContainerBackend` and `withWorkspaceContainer` | `@cloudflare/computer/backends/container` | Experimental |
 | `LegacyContainerBackend` and `withLegacyWorkspaceContainer` | `@cloudflare/computer/backends/container-legacy` | Deprecated: use `ContainerBackend` |
+| Resuming interrupted isolate JavaScript: `onInterrupt: "restart"` and `"replay"`, `workspace.runtime.recover()`, and `unsafeToRepeat()` | `@cloudflare/computer`, `@cloudflare/computer/backends/worker-javascript` | Experimental |
 | `WorkerShellBackend` and the shell command groups | `@cloudflare/computer/backends/worker-shell`, `@cloudflare/computer/shell/*` | Experimental |
 | The `ws:container` host module | `@cloudflare/computer/modules/container` | Experimental |
 | `workspace.push()`, `workspace.pull()`, and the sync protocol between the durable object and `computerd` | `@cloudflare/computer` | Experimental |

packages/computer/src/backends/worker-javascript/journal.ts

@@ -104,6 +104,10 @@ export const DURABLE_TABLES = [
 /** Most events one log chunk may carry. */
 const MAX_LOG_CHUNK = 65536;
 
+// The tables hold state for running executions only. A change to their
+// shape should rename them rather than migrate: every backend creates
+// them on connect, whether or not it uses them, and CREATE TABLE IF NOT
+// EXISTS leaves an older table as it was.
 export function createDurableTables(db: Database): void {
   db.run(`
     CREATE TABLE IF NOT EXISTS workspace_runtime_durable (

packages/computer/src/backends/worker-javascript/worker-javascript.ts

@@ -107,6 +107,9 @@ export interface WorkerJavaScriptBackendOptions {
    * attempts and must finish within its original timeout. A call in
    * flight at the interruption runs again, unless it's marked with
    * `unsafeToRepeat()`.
+   *
+   * `"restart"` and `"replay"` are experimental and may change in any
+   * release.
    */
   onInterrupt?: WorkspaceRuntimeInterruptPolicy;
   /**

packages/computer/src/runtime/types.ts

@@ -278,7 +278,8 @@ export interface ModuleExecutionInput {
  * What a backend does with a run its Durable Object restarted under.
  * `fail` settles it as failed. `restart` runs it again from the start.
  * `replay` runs it again and answers the calls it already made from a
- * journal, so their effects aren't repeated.
+ * journal, so their effects aren't repeated. `restart` and `replay` are
+ * experimental and may change in any release.
  */
 export type WorkspaceRuntimeInterruptPolicy = "fail" | "restart" | "replay";