docs: add v1 to v2 migration guide

Add docs/migration-1.x-to-2.x.md covering the 2.x breaking changes: typed
per-operation error hierarchy, first-run serialize/deserialize round trip,
removed config types and fields, construction-time config validation, and
wait_for_condition changes; plus the optional should_complete feature.
Also document the initial_state serdes requirement on WaitForConditionConfig.

Author: ayushiahjolia

docs/migration-1.x-to-2.x.md

@@ -0,0 +1,209 @@
+# Migrating from 1.x to 2.x
+
+`2.x` is a breaking major release. Every change is a bug fix or brings Python to
+parity with the JavaScript and Java SDKs. The two changes most likely to touch
+your code are the typed, per-operation **error hierarchy** and the
+**serialize/deserialize round trip on the first run**.
+
+There is no compatibility shim: removed names (for example `CallableRuntimeError`)
+are gone with no alias. If you are not ready to migrate, stay on `1.x`.
+
+> Instrumentation plugins are out of scope here. The experimental `plugins=` hook
+> already existed in `1.x`; `2.x` adds opt-in auto-discovery and `PluginLoadError`.
+> Because plugins are opt-in and still evolving, they are documented with the
+> plugin/OpenTelemetry feature rather than in this guide.
+
+## What Changed and What to Do
+
+| Change | What you must do |
+| --- | --- |
+| `CallableRuntimeError`, `UserlandError`, `CallableRuntimeErrorSerializableDetails` removed; typed per-operation errors added | Catch `StepError`, `InvokeError`, `ChildContextError`, or `WaitForConditionError` (or the base `DurableOperationError`) instead of `CallableRuntimeError`. |
+| `CallbackError` moved out of the termination tree; graded subtypes added | Remove any `termination_reason == TerminationReason.CALLBACK_ERROR` check (the enum member is gone). Optionally catch `CallbackTimeoutError` / `CallbackExternalError` / `CallbackSubmitterError`. |
+| `BatchResult.throw_if_error()` now raises a typed error | Replace `except CallableRuntimeError` with `ChildContextError` (ordinary item failure), `SerDesError` (item serialize/deserialize failure), and `BatchCompletionError` (custom `should_complete` failed the batch with no item error). `ChildContextError` and `BatchCompletionError` share the base `DurableOperationError`, but `SerDesError` does not, so catch `(DurableOperationError, SerDesError)` or list all three. |
+| Serialization/deserialization failures surface as `SerDesError`, a direct child of `DurableExecutionsError` (not `ExecutionError`) | If you caught serdes failures with `except ExecutionError`, catch `SerDesError` (or `DurableExecutionsError`) instead. |
+| First-run serialize/deserialize round trip for `step`, child contexts, `map`/`parallel`, and `wait_for_condition` | On the first run these now return `deserialize(serialize(x))`, the same canonical value replay returns. If you relied on the raw pre-serialization object, use the deserialized shape instead (or make your `SerDes` round-trip identity). Ensure `wait_for_condition` `initial_state` is serializable by the configured serdes. For a transient serdes failure, raise the new `RetryableSerDesError` (retries) instead of `SerDesError` (permanent). |
+| `InvokeConfig.timeout` and `InvokeConfig.timeout_seconds` removed | Remove them. Enforce any timeout inside the invoked function or as a separate timer. |
+| Removed `ItemBatcher`, `ItemsPerBatchUnit`, `BatchedInput`, `TerminationMode`, `StepFuture`, `MapConfig.item_batcher`, `ChildConfig.item_serdes`; also `ChainedInvokeFailedToStartType`, `ChainedInvokeTimeoutType`, `ChainedInvokeStopType` (from `lambda_service`) | Remove all uses. Replace `ChildConfig.item_serdes` with `ChildConfig.serdes`. |
+| `MapConfig` / `ParallelConfig` / `CompletionConfig` validate arguments at construction (e.g. `max_concurrency=0` or `min_successful=0` now raise `ValidationError`); `min_successful > total` is validated at the `map()`/`parallel()` call, not at construction | Wrap config construction, and the `map()`/`parallel()` call, in `try/except ValidationError` when inputs are external. |
+| `CompletionConfig.all_completed()` now actually tolerates all failures | If you hand-built the old all-`None` config, use the factory instead. |
+| `BatchResult.all` now omits never-started branches, so `total_count` and positional iteration differ for early-completed batches | If you index `.all` by original position or expect `total_count` to include unstarted branches, update that logic. |
+| For `map`/`parallel`, a custom `summary_generator` output is now stored under a `"summary"` key in an SDK-owned envelope (it no longer replaces the checkpoint payload). `ChildConfig.summary_generator` is unchanged: its output is still checkpointed verbatim | If you parse `map`/`parallel` summary payloads from execution history, read the `"summary"` key from the envelope. Child-context summary consumers need no change. |
+| `WaitDecision` removed; `WaitStrategyConfig.timeout` / `timeout_seconds` removed | Use `WaitForConditionDecision` (`stop_polling()` / `continue_waiting(delay)`). |
+| `wait_for_condition` raises `WaitForConditionError` when it exhausts `max_attempts` | Catch `WaitForConditionError` instead of inspecting the returned state. |
+
+Find affected code before upgrading:
+
+```bash
+rg -n "CallableRuntimeError|UserlandError|CallableRuntimeErrorSerializableDetails" .
+rg -n "CallbackError|CALLBACK_ERROR" .
+rg -n "InvokeConfig\(|\.timeout_seconds" .
+rg -n "WaitDecision|WaitStrategyConfig\(|item_batcher|ItemBatcher|ItemsPerBatchUnit" .
+rg -n "TerminationMode|BatchedInput|StepFuture|ChildConfig\(" .
+rg -n "ChainedInvoke|except ExecutionError" .
+```
+
+## Error Handling (the biggest change)
+
+In `1.x` nearly every user-land failure surfaced as one `CallableRuntimeError`,
+so a failed step was indistinguishable from a failed invoke or child branch. `2.x`
+raises a specific type per operation, all under a new base `DurableOperationError`.
+Inspect the failure through its fields, not `__cause__`: `error_type`, `message`,
+`data`, and `stack_trace`. Do not rely on `__cause__` being the original
+exception - the SDK reconstructs a `DurableOperationError` stand-in carrying
+those same fields (on both the first run and replay, for determinism), so the
+original type is not preserved (a `ValueError` does not stay a `ValueError`) and
+custom attributes are lost.
+
+For `StepError`, `InvokeError`, `ChildContextError`, and `WaitForConditionError`,
+`error_type` is the name of the error that escaped your code (e.g. `"ValueError"`).
+The graded callback errors are different: `CallbackTimeoutError`,
+`CallbackExternalError`, and `CallbackSubmitterError` are constructed without the
+originating `error_type`, so `error_type` is the callback class name, not the
+underlying cause. Use the specific callback exception type (and `message` /
+`data` / `stack_trace`) to distinguish those.
+
+```python
+# 1.x
+from aws_durable_execution_sdk_python.exceptions import CallableRuntimeError
+try:
+    result = context.step(charge_card, name="charge")
+except CallableRuntimeError as e:
+    context.logger.error("something failed: %s", e.message)
+
+# 2.x
+from aws_durable_execution_sdk_python import StepError, DurableOperationError
+try:
+    result = context.step(charge_card, name="charge")
+except StepError as e:               # or `except DurableOperationError` to catch any operation
+    context.logger.error("charge step failed: %s", e.message)
+```
+
+New types, all exported from the package root: `DurableOperationError` (base),
+`StepError`, `InvokeError`, `ChildContextError`, `WaitForConditionError`,
+`CallbackError` (+ `CallbackExternalError`, `CallbackTimeoutError`,
+`CallbackSubmitterError`), plus `SerDesError` (now exported) and
+`RetryableSerDesError`. `SerDesError` stays a direct child of
+`DurableExecutionsError`; `RetryableSerDesError` is a retryable `InvocationError`.
+
+### Callbacks
+
+`context.wait_for_callback(...)` returns the payload directly and raises the
+callback error from the call itself (there is no `callback.result()`):
+
+```python
+from aws_durable_execution_sdk_python import (
+    CallbackError, CallbackTimeoutError, CallbackSubmitterError,
+)
+try:
+    payload = context.wait_for_callback(submit_approval, name="approval")
+except CallbackTimeoutError:
+    ...                               # timeout / heartbeat expiry
+except CallbackSubmitterError:
+    ...                               # the submitter step failed
+except CallbackError as e:            # external + internal
+    context.logger.error("callback failed: %s", e.message)
+```
+
+### map / parallel
+
+`throw_if_error()` can raise three types: `ChildContextError` for the ordinary
+item/branch failure, `SerDesError` if an item result failed to serialize or
+deserialize, and `BatchCompletionError` when a custom `should_complete` predicate
+marked the batch failed with no failed item (see the completion-predicate section
+below). `ChildContextError` and `BatchCompletionError` share the base
+`DurableOperationError`, but `SerDesError` does not, so catch
+`(DurableOperationError, SerDesError)` or list all three explicitly.
+
+```python
+from aws_durable_execution_sdk_python import (
+    ChildContextError, SerDesError, BatchCompletionError,
+)
+
+result = context.map(items, process_item)
+try:
+    result.throw_if_error()
+except (ChildContextError, SerDesError, BatchCompletionError):
+    for err in result.get_errors():   # every failed item's ErrorObject
+        context.logger.error("%s: %s", err.type, err.message)
+```
+
+## Serialize/Deserialize Round Trip
+
+`1.x` returned the raw in-memory result on the first run but the deserialized
+result on replay, so a non-identity custom `SerDes` produced different values.
+`2.x` round-trips (`serialize` then `deserialize`) on the first run for `step`,
+child contexts, `map`/`parallel`, and `wait_for_condition` (which also feeds the
+deserialized state to the wait strategy). Non-identity serdes (for example
+canonicalizing) is fully supported: the first run now returns the canonical
+`deserialize(serialize(x))` value, matching replay. If your code depended on the
+raw pre-serialization object on the first run, switch to the deserialized shape
+(or make the serdes round-trip identity). This also surfaces genuine
+serialization bugs on the first run instead of later on replay.
+
+`invoke` and `wait` are unaffected. `wait_for_callback` is implemented via a
+child context, so its result is serialized and deserialized before it returns:
+do not rely on callback-result object identity. The enclosing child context uses
+the default (extended-type) serdes, not `WaitForCallbackConfig.serdes`, so the
+value your callback deserializer returns must itself be serializable by the
+default serdes; otherwise the child raises `SerDesError`.
+
+`wait_for_condition` also round-trips `initial_state` through the serdes before
+the first check, so `initial_state` must now be serializable by the configured
+serdes.
+
+## New in 2.x: Custom Completion Predicate (Optional)
+
+`2.x` adds a `should_complete` predicate to `CompletionConfig`, giving `map` and
+`parallel` full control over when a batch completes early. This is a new feature,
+not a breaking change - no action is required unless you adopt it.
+
+```python
+from aws_durable_execution_sdk_python import complete_batch, continue_batch
+from aws_durable_execution_sdk_python.config import CompletionConfig
+
+config = CompletionConfig(
+    should_complete=lambda status: (
+        complete_batch() if status.success_count >= 2 else continue_batch()
+    )
+)
+```
+
+The predicate receives a `CompletionStatus` snapshot (counts plus per-item
+statuses) and returns a `CompletionDecision` - `continue_batch()`, or
+`complete_batch(CompletionOutcome.SUCCEEDED)` / `complete_batch(CompletionOutcome.FAILED)`
+(the outcome defaults to `SUCCEEDED`). A `FAILED` outcome marks the whole batch
+failed; `throw_if_error()` then raises `BatchCompletionError` (a
+`DurableOperationError` subtype) even when no individual item failed. Individual
+item/branch failures still surface as `ChildContextError`. Notes:
+
+- It cannot be combined with `min_successful` or the `tolerated_failure_*`
+  fields; doing so raises `ValidationError` at construction.
+- The predicate must be deterministic, side-effect-free, and monotonic (once a
+  level of progress would complete the batch, more progress must not flip it back
+  to continue). Replaying an already-completed batch uses the checkpointed
+  decision, but a mid-run resume re-runs the batch live and re-evaluates the
+  predicate as completed branches replay, possibly in a different order.
+- New exports: `complete_batch`, `continue_batch`, `CompletionStatus`,
+  `CompletionDecision`, `CompletionOutcome`, `CompletionItemStatus`,
+  `BatchItemStatus`, `BatchCompletionError`.
+
+## New in 2.x: Attempt Number in Contexts (Optional)
+
+`StepContext` and `WaitForConditionCheckContext` now expose an `attempt` field
+(the current attempt number, starting at 1). Read it inside a step or a
+`wait_for_condition` check to branch on the retry count. The SDK injects these
+contexts, so normal usage needs no change. But `attempt` is a required
+dataclass field with no default: if you construct these contexts directly (in
+tests, fixtures, or wrappers), you must now pass `attempt` or construction fails
+with `TypeError`.
+
+## Recommended Validation After Upgrading
+
+1. Build and run your test suite against `2.x`, and grep for the removed names above.
+2. Trigger a failure in a `step`, an `invoke`, and a `map`/`parallel` branch;
+   confirm you catch `StepError`, `InvokeError`, and `ChildContextError`.
+3. Exercise a `wait_for_callback` timeout and a submitter-step failure
+   (`CallbackTimeoutError`, `CallbackSubmitterError`).
+4. Exercise a `wait_for_condition` that exhausts its attempts (`WaitForConditionError`).
+5. If you use a custom `SerDes`, run a workflow that checkpoints both a result and
+   an error payload and confirm first-run output equals replay output.

packages/aws-durable-execution-sdk-python/src/aws_durable_execution_sdk_python/waits.py

@@ -99,7 +99,17 @@ def wait_strategy(result: T, attempts_made: int) -> WaitForConditionDecision:
 
 @dataclass(frozen=True)
 class WaitForConditionConfig(Generic[T]):
-    """Configuration for wait_for_condition."""
+    """Configuration for wait_for_condition.
+
+    Attributes:
+        wait_strategy: Called after each poll with (state, attempts_made) and
+            returns a WaitForConditionDecision (continue_waiting or stop_polling).
+        initial_state: State passed to the first poll. It is round-tripped
+            through serdes (serialize then deserialize) before the first check,
+            so it must be serializable by the configured serdes.
+        serdes: SerDes used to serialize and deserialize the polled state at
+            each checkpoint. Defaults to the SDK's extended-type serdes when None.
+    """
 
     wait_strategy: Callable[[T, int], WaitForConditionDecision]
     initial_state: T