feat: checkpointWhen is required on Durable document definitions

Breaking change: defineDoc and defineDocFamily now require an explicit checkpointWhen predicate; no default is supplied. Set policies on built-in documents, examples, tests, and triage state, and document the required API.

packages/durable/test/examples/01-documents.ts

@@ -12,6 +12,7 @@ const session = createSession(new MemoryStorage());
 // looked like when a particular entry was written.
 // `fork` says what a forked copy of the conversation starts with (see 02-forks.ts).
 const Notes = defineDoc<{ text: string }>({
+	checkpointWhen: () => false,
 	kind: "example.notes",
 	version: 1,
 	scope: "conversation",

packages/durable/test/examples/02-forks.ts

@@ -8,6 +8,7 @@ const context = BACKGROUND_CONTEXT;
 const session = createSession(new MemoryStorage());
 
 const Notes = defineDoc<{ text: string }>({
+	checkpointWhen: () => false,
 	kind: "example.notes",
 	version: 1,
 	scope: "conversation",

packages/durable/test/examples/03-owned-conversations.ts

@@ -29,6 +29,7 @@ const Supervisor = defineTask<null, { phase: "ready" }, null>({
 const AgentRegistry = defineDoc<{
 	agents: Record<string, { conversationId: ConversationId; requestId: string }>;
 }>({
+	checkpointWhen: () => false,
 	kind: "example.agent-registry",
 	version: 1,
 	scope: "conversation",

packages/durable/test/examples/04-chord-state.ts

@@ -8,6 +8,7 @@ const context = BACKGROUND_CONTEXT;
 const session = createSession(new MemoryStorage());
 
 const Notes = defineDoc<{ text: string }>({
+	checkpointWhen: () => false,
 	kind: "example.notes",
 	version: 1,
 	scope: "conversation",

packages/durable/test/examples/05-watches.ts

@@ -8,6 +8,7 @@ const context = BACKGROUND_CONTEXT;
 const session = createSession(new MemoryStorage());
 
 const Notes = defineDoc<{ text: string }>({
+	checkpointWhen: () => false,
 	kind: "example.notes",
 	version: 1,
 	scope: "conversation",

packages/durable/test/examples/06-harness.ts

@@ -34,6 +34,7 @@ registry.install(Files);
 const harness = await Harness.open(new MemoryStorage(), { models: createModels(), registry }, context);
 
 const Notes = defineDoc<{ text: string }>({
+	checkpointWhen: () => false,
 	kind: "example.notes",
 	version: 1,
 	scope: "conversation",

packages/durable/test/examples/11-extension-state.ts

@@ -20,6 +20,7 @@ const context = BACKGROUND_CONTEXT;
 // A todo list per conversation. Rewindable with `asOf`, so a fork starts with
 // the todos its parent had at the fork entry.
 const Todos = defineDoc<{ items: string[] }>({
+	checkpointWhen: () => false,
 	kind: "example.todos",
 	version: 1,
 	scope: "conversation",

packages/durable/test/examples/23-subagent-background.ts

@@ -44,6 +44,7 @@ type Subagent = {
 	reported: EntryId[];
 };
 const Subagents = defineDoc<{ agents: Record<string, Subagent>; reporters: Record<string, TaskId> }>({
+	checkpointWhen: () => false,
 	kind: "app.subagents",
 	version: 1,
 	scope: "conversation",

packages/durable/test/examples/27-plan-mode.ts

@@ -27,6 +27,7 @@ const context = BACKGROUND_CONTEXT;
 
 // The current plan of a conversation. A fork keeps the plan it had at the fork entry.
 const PlanDoc = defineDoc<{ steps: string[] }>({
+	checkpointWhen: () => false,
 	kind: "app.plan",
 	version: 1,
 	scope: "conversation",

packages/durable/test/examples/29-sandbox-per-conversation.ts

@@ -17,6 +17,7 @@ const context = BACKGROUND_CONTEXT;
 
 // Which sandbox a conversation runs in. `fork: "initial"`: a fork gets no sandbox until the app assigns one.
 const Sandbox = defineDoc<{ path?: string }>({
+	checkpointWhen: () => false,
 	kind: "app.sandbox",
 	version: 1,
 	scope: "conversation",