Fix for race condition in RPC connection

.changeset/rpc-method-tracking.md

@@ -0,0 +1,5 @@
+---
+'@cloudflare/sandbox': patch
+---
+
+Keep RPC sessions alive while method calls are pending to avoid intermittent `RPC session was shut down by disposing the main stub` failures during concurrent sandbox startup.

.changeset/surface-container-unavailable.md

@@ -0,0 +1,5 @@
+---
+'@cloudflare/sandbox': patch
+---
+
+Surface container capacity failures as retryable `ContainerUnavailableError` (with a `reason`) instead of masking them as `utils.createSession` interruptions or raw transport errors, make `destroy()` an idempotent no-op when the container was never admitted, and record the wrapped error `.cause` chain on RPC trace spans so the true startup failure (e.g. container not listening, network loss) is visible instead of the generic "no container instance" wrapper.

packages/sandbox/src/bridge/warm-pool.ts

@@ -42,7 +42,7 @@ export interface PoolStats {
 // Container RPC shapes (inherited by Sandbox from Container)
 // ---------------------------------------------------------------------------
 
-interface ContainerRpc {
+interface ContainerRPC {
   startAndWaitForPorts(): Promise<void>;
   stop(signal?: string): Promise<void>;
   renewActivityTimeout(): void;
@@ -205,7 +205,7 @@ export class WarmPool extends DurableObject<WarmPoolEnv> {
     for (const containerUUID of [...this.warmContainers]) {
       try {
         const stub = this.getSandboxStub(containerUUID);
-        await (stub as unknown as ContainerRpc).stop();
+        await (stub as unknown as ContainerRPC).stop();
         this.warmContainers.delete(containerUUID);
       } catch (error) {
         console.error({
@@ -296,7 +296,7 @@ export class WarmPool extends DurableObject<WarmPoolEnv> {
 
     try {
       const stub = this.getSandboxStub(containerUUID);
-      await (stub as unknown as ContainerRpc).startAndWaitForPorts();
+      await (stub as unknown as ContainerRPC).startAndWaitForPorts();
       console.info({
         message: 'Container started',
         component: 'warm-pool',
@@ -364,7 +364,7 @@ export class WarmPool extends DurableObject<WarmPoolEnv> {
     for (const containerUUID of this.warmContainers) {
       try {
         const stub = this.getSandboxStub(containerUUID);
-        (stub as unknown as ContainerRpc).renewActivityTimeout();
+        (stub as unknown as ContainerRPC).renewActivityTimeout();
       } catch (error) {
         console.error({
           message: 'Failed to renew activity timeout',
@@ -455,7 +455,7 @@ export class WarmPool extends DurableObject<WarmPoolEnv> {
       for (const uuid of toStop) {
         try {
           const stub = this.getSandboxStub(uuid);
-          await (stub as unknown as ContainerRpc).stop();
+          await (stub as unknown as ContainerRPC).stop();
           stopped.push(uuid);
         } catch (error) {
           console.error({