fix: multi-provider hook context management (#1282)

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## This PR
Fixing an issue with the MultiProvider where hook contexts and hints
were being lost due to copies of the context data being created in the
OpenFeature sdk evaluation.

Since key evaluation of Maps using objects is done by reference, the
lookup of the context during evaluation was failing, leading to errors.

- adds this new feature

### Related Issues

Fixes #1268

### Notes

### Follow-up Tasks

### How to test

---------

Signed-off-by: Mike Kitzman <[email protected]>

Author: mdkitzman

packages/server/src/client/internal/open-feature-client.ts

@@ -332,7 +332,7 @@ export class OpenFeatureClient implements Client {
     mergedContext: EvaluationContext,
     options: FlagEvaluationOptions,
   ) {
-    let accumulatedContext = mergedContext;
+    const accumulatedContext = mergedContext;
 
     for (const [index, hook] of hooks.entries()) {
       const hookContextIndex = hooks.length - 1 - index; // reverse index for before hooks
@@ -343,10 +343,7 @@ export class OpenFeatureClient implements Client {
 
       const hookResult = await hook?.before?.(hookContext, Object.freeze(options.hookHints));
       if (hookResult) {
-        accumulatedContext = {
-          ...accumulatedContext,
-          ...hookResult,
-        };
+        Object.assign(accumulatedContext, hookResult);
 
         for (let i = 0; i < hooks.length; i++) {
           Object.assign(hookContexts[hookContextIndex].context, accumulatedContext);

packages/server/test/client.spec.ts

@@ -811,6 +811,40 @@ describe('OpenFeatureClient', () => {
         client.setContext({ [KEY]: VAL });
         expect(client.getContext()[KEY]).toEqual(VAL);
       });
+
+      it('context object is reference stable between hook and evaluation calls', async () => {
+        let hookContextRef;
+        const contextMap = new WeakMap<EvaluationContext, HookContext>();
+        const contextStabilityProvider = {
+          metadata: {
+            name: 'evaluation-context',
+          },
+          hooks: [
+            {
+              before: jest.fn((hookContext: HookContext) => {
+                contextMap.set(hookContext.context, hookContext);
+                return hookContext.context;
+              })
+            }
+          ],
+          resolveBooleanEvaluation: jest.fn((_flagKey, _defaultValue, context): Promise<ResolutionDetails<boolean>> => {
+            // We expect that the context object reference is the same as that captured in the hook
+            hookContextRef = contextMap.get(context);
+            return Promise.resolve({
+              value: true,
+            });
+          }),
+        } as unknown as Provider;
+
+        await OpenFeature.setProviderAndWait(contextStabilityProvider);
+        const client = OpenFeature.getClient();
+        
+        const context = { data: 1, value: '2' };
+        await client.getBooleanValue('some-other-flag', false, context);
+        expect(contextStabilityProvider.resolveBooleanEvaluation).toHaveBeenCalled();
+        expect(contextStabilityProvider.hooks?.[0].before).toHaveBeenCalled();
+        expect(hookContextRef).toBeDefined();
+      });
     });
   });