diff --git a/.github/copilot-instructions.md b/.github/copilot-instructions.md
index c8c1501..2e17755 100644
--- a/.github/copilot-instructions.md
+++ b/.github/copilot-instructions.md
@@ -113,7 +113,7 @@ Task<T>              — Base: result, exception, isComplete, isFailed, parent r
 │   ├── RetryableTask     — Policy-driven retries (exponential backoff)
 │   └── RetryHandlerTask  — Custom retry handler function
 └── CompositeTask    — Holds children with parent backlinks
-    ├── WhenAllTask  — Completes when ALL children done; fails fast on first failure
+    ├── WhenAllTask  — Completes when ALL children are terminal (waits for every child)
     └── WhenAnyTask  — Completes when ANY child done
 ```
 
@@ -123,11 +123,15 @@ Task<T>              — Base: result, exception, isComplete, isFailed, parent r
 **Important:** `CompositeTask` checks already-complete children in its constructor.
 A composite task can be **immediately complete upon construction** — callers must handle this.
 
-### WhenAll Fail-Fast Behavior
+### WhenAll Wait-All Behavior
 
-`WhenAllTask` marks itself complete on the **first** failed child. Other children may still
-be in flight. The `isComplete` guard prevents double-completion, but the mental model is:
-one failure = whole task fails immediately, remaining results ignored.
+`WhenAllTask` completes only when **every** child is terminal (`_completedTasks == _tasks.length`) —
+a failing child does **not** complete it early. This prevents a later failing sibling's `TaskFailed`
+from being dropped against an already-terminal instance (issue #301). `_exception` is set only at
+completion, so `isFailed` and `isComplete` flip together — otherwise `resume()` (which checks
+`isFailed` before `isComplete`) would throw into the generator before the other siblings finish,
+re-introducing fail-fast. On failure, all child exceptions are aggregated into an `AggregateError`
+whose message inlines each child message.
 
 ---
 
diff --git a/packages/azure-functions-durable/README.md b/packages/azure-functions-durable/README.md
index 3d642a0..801cf01 100644
--- a/packages/azure-functions-durable/README.md
+++ b/packages/azure-functions-durable/README.md
@@ -40,10 +40,13 @@ changed:
   **`client.startNew()` supports the `version` option.**
 - **Entity locking / critical sections moved to the core context.** v3's `context.df.lock(...)` /
   `context.df.isLocked()` and the `DurableLock` / `LockState` / `LockingRulesViolationError` exports
-  are removed. Acquire locks with the core `context.entities.lockEntities(...entityIds)` (returns a
-  `LockHandle` — call `release()`, ideally in a `finally`) and query with
-  `context.entities.isInCriticalSection()`. Restoring the v3 `df.lock` / `isLocked` surface is tracked
-  in [#317](https://github.com/microsoft/durabletask-js/issues/317).
+  are removed. Locks live on the core-native `context.entities` surface, which the classic
+  `{ df, log }` context does **not** expose — an orchestrator that needs locks must first migrate to
+  the core-native orchestrator/context shape, then acquire locks with
+  `context.entities.lockEntities(...entityIds)` (returns a `LockHandle` — call `release()`, ideally
+  in a `finally`) and query with `context.entities.isInCriticalSection()`. Reintroducing the v3
+  `df.lock` / `isLocked` surface is **not supported and not planned**
+  ([#317](https://github.com/microsoft/durabletask-js/issues/317), closed as not planned).
 - **`context.df.callHttp(...)` is restored** as a worker-side durable HTTP call
   ([#318](https://github.com/microsoft/durabletask-js/issues/318)) — though **not** as a drop-in, fully
   v3-equivalent replacement: the known incompatibilities and behavior differences listed below are
@@ -106,6 +109,19 @@ changed:
   sync **generators** (`function*`) using `context.df.*` — are unaffected; convert any non-generator
   classic orchestrator to generator form, or to the core-native `ctx.*` API.
 
+## Requirements
+
+This provider reaches the Durable Task backend over the Functions host's **gRPC** channel, which
+exists only in newer durable-extension builds. Your app's `host.json` must reference one of:
+
+- GA bundle — `Microsoft.Azure.Functions.ExtensionBundle` at **`[4.36.0, 5.0.0)`**, or
+- Preview bundle — `Microsoft.Azure.Functions.ExtensionBundle.Preview` at **`[4.29.0, 5.0.0)`**.
+
+Earlier GA v4 bundles (**<= 4.32.0**) predate that gRPC endpoint, so orchestration starters **hang
+for ~60 seconds and time out with no error**. A fresh app on the default GA range (`[4.*, 5.0.0)`)
+resolves to the latest GA (>= 4.36.0) and works — the trap is an **explicit** pin at or below
+4.32.0.
+
 ## Getting started
 
 ```typescript
@@ -170,4 +186,6 @@ are `@deprecated`):
 
 ## Status
 
-This package is an early preview (`4.0.0`); APIs may change before the stable release.
+This rewritten `durable-functions` v4 provider is in **preview**, published under the `preview` npm
+dist-tag — install it with `npm install durable-functions@preview`. APIs may change before the
+GA `4.0.0` release.