Fix duplicate key exception when using WithExplicitStart() on resources with environment callbacks

[Copilot]

Environment callbacks in hosting builder extensions were using Dictionary.Add(), which throws when invoked multiple times with the same key. Resources configured with WithExplicitStart() trigger these callbacks repeatedly during their lifecycle, causing crashes.

Example failure:

builder.AddKafka("events")
    .WithKafkaUI(ui => ui.WithExplicitStart());
// Throws: ArgumentException: An item with the same key has already been added. Key: KAFKA_CLUSTERS_0_NAME

Changes:

• Replace context.EnvironmentVariables.Add(key, value) with indexer syntax context.EnvironmentVariables[key] = value to allow idempotent callback execution
• Applied across all hosting builder extensions with environment callbacks:
  • Aspire.Hosting.Kafka
  • Aspire.Hosting.MongoDB
  • Aspire.Hosting.PostgreSQL
  • Aspire.Hosting.Redis
  • Aspire.Hosting.MySql
  • Aspire.Hosting.Milvus
  • Aspire.Hosting.Azure.EventHubs
  • Aspire.Hosting.Azure.ServiceBus
• Added idempotency tests for all resources to verify GetEnvironmentVariableValuesAsync can be called multiple times without errors:
  • KafkaEnvironmentCallbackIsIdempotent
  • KafkaUIEnvironmentCallbackIsIdempotent
  • MongoExpressEnvironmentCallbackIsIdempotent
  • PostgresEnvironmentCallbackIsIdempotent
  • RedisInsightEnvironmentCallbackIsIdempotent
  • PhpMyAdminEnvironmentCallbackIsIdempotent

This aligns with the existing pattern used in ProjectResourceBuilderExtensions and DashboardEventHandlers.

Fixes #12516

Original prompt

---

This section details on the original issue you should resolve

<issue_title>KafkaUI fails to start when configured with WithExplicitStart()</issue_title>
<issue_description>### Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

When configuring KafkaUI with WithExplicitStart(), attempting to start KafkaUI from the Dashboard results in an exception.
Without WithExplicitStart() and everything works fine.

Expected Behavior

KafkaUI start without error.

Steps To Reproduce

var events = builder
    .AddKafka("events")
    .WithKafkaUI(configureContainer =>
    {
        configureContainer.WithExplicitStart();
    });

Exceptions (if any)

fail: Aspire.Hosting.Dcp.DcpExecutor[0]
      Failed to start resource kafka-ui
      System.ArgumentException: An item with the same key has already been added. Key: KAFKA_CLUSTERS_0_NAME
         at System.Collections.Generic.Dictionary`2.TryInsert(TKey key, TValue value, InsertionBehavior behavior)
         at System.Collections.Generic.Dictionary`2.Add(TKey key, TValue value)
         at Aspire.Hosting.KafkaBuilderExtensions.<WithKafkaUI>g__ConfigureKafkaUIContainer|5_0(EnvironmentCallbackContext context, EndpointReference endpoint, Int32 index) in /_/src/Aspire.Hosting.Kafka/KafkaBuilderExtensions.cs:line 143
         at Aspire.Hosting.KafkaBuilderExtensions.<>c__DisplayClass5_1.<WithKafkaUI>b__2(EnvironmentCallbackContext context) in /_/src/Aspire.Hosting.Kafka/KafkaBuilderExtensions.cs:line 122
         at Aspire.Hosting.ApplicationModel.EnvironmentCallbackAnnotation.<>c__DisplayClass3_0.<.ctor>b__0(EnvironmentCallbackContext c) in /_/src/Aspire.Hosting/ApplicationModel/EnvironmentCallbackAnnotation.cs:line 59
         at Aspire.Hosting.ApplicationModel.ResourceExtensions.ProcessEnvironmentVariableValuesAsync(IResource resource, DistributedApplicationExecutionContext executionContext, Action`4 processValue, ILogger logger, String containerHostName, CancellationToken cancellationToken) in /_/src/Aspire.Hosting/ApplicationModel/ResourceExtensions.cs:line 352
         at Aspire.Hosting.Dcp.DcpExecutor.BuildEnvVarsAsync(ILogger resourceLogger, IResource modelResource, CancellationToken cancellationToken) in /_/src/Aspire.Hosting/Dcp/DcpExecutor.cs:line 1974
         at Aspire.Hosting.Dcp.DcpExecutor.CreateContainerAsync(AppResource cr, ILogger resourceLogger, CancellationToken cancellationToken) in /_/src/Aspire.Hosting/Dcp/DcpExecutor.cs:line 1506
         at Aspire.Hosting.Dcp.DcpExecutor.StartResourceAsync(IResourceReference resourceReference, CancellationToken cancellationToken) in /_/src/Aspire.Hosting/Dcp/DcpExecutor.cs:line 1829

.NET Version info

.NET SDK v9.0.306
Aspire v9.5.2

Anything else?

No response</issue_description>

<agent_instructions>Fix the code in WithKafkaUI to use the indexer for environment variables instead of .Add. Look for other environment variable callbacks that might be doing the same thing. Add tests for this as well.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@davidfowl Yea, this code is using Add instead of Set and these callback get run multiple times.

• Fixes KafkaUI fails to start when configured with WithExplicitStart() #12516

---

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[davidfowl]

@copilot We need to add unit tests that evaluate these callbacks using GetEnvironmentVariableValuesAsync multiple times to make sure we are idempotent for these resources.

[Copilot]

@copilot We need to add unit tests that evaluate these callbacks using GetEnvironmentVariableValuesAsync multiple times to make sure we are idempotent for these resources.

Added idempotency tests for all resources with environment callbacks. Each test calls GetEnvironmentVariableValuesAsync multiple times to verify callbacks can be invoked repeatedly without errors.

Tests added in commit a6209f3:

• KafkaEnvironmentCallbackIsIdempotent
• KafkaUIEnvironmentCallbackIsIdempotent
• MongoExpressEnvironmentCallbackIsIdempotent
• PostgresEnvironmentCallbackIsIdempotent
• RedisInsightEnvironmentCallbackIsIdempotent
• PhpMyAdminEnvironmentCallbackIsIdempotent

All tests pass ✅

[github-actions]

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

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Or

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[Copilot]

Pull Request Overview

This PR fixes environment callback idempotency issues where calling GetEnvironmentVariableValuesAsync() multiple times would fail due to duplicate key additions. The fix changes environment variable setting from .Add() to indexer assignment [] in multiple hosting extension methods, making callbacks idempotent.

• Changes environment variable assignments from .Add() to [] indexer syntax across multiple hosting extensions (Redis, PostgreSQL, MySQL, MongoDB, Kafka, Milvus, Azure Service Bus, Azure Event Hubs)
• Adds comprehensive test coverage verifying idempotent behavior when GetEnvironmentVariableValuesAsync() is called multiple times

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/Aspire.Hosting.Redis/RedisBuilderExtensions.cs	Changes RedisInsight environment variable assignments to use indexer syntax
src/Aspire.Hosting.PostgreSQL/PostgresBuilderExtensions.cs	Changes PgAdmin environment variable assignments to use indexer syntax
src/Aspire.Hosting.MySql/MySqlBuilderExtensions.cs	Changes PhpMyAdmin environment variable assignments to use indexer syntax
src/Aspire.Hosting.MongoDB/MongoDBBuilderExtensions.cs	Changes MongoExpress environment variable assignments to use indexer syntax
src/Aspire.Hosting.Milvus/MilvusBuilderExtensions.cs	Changes Attu environment variable assignments to use indexer syntax
src/Aspire.Hosting.Kafka/KafkaBuilderExtensions.cs	Changes Kafka and KafkaUI environment variable assignments to use indexer syntax
src/Aspire.Hosting.Azure.ServiceBus/AzureServiceBusExtensions.cs	Changes Service Bus emulator environment variable assignments to use indexer syntax
src/Aspire.Hosting.Azure.EventHubs/AzureEventHubsExtensions.cs	Changes Event Hubs emulator environment variable assignments to use indexer syntax
tests/Aspire.Hosting.Redis.Tests/AddRedisTests.cs	Adds test verifying RedisInsight environment callbacks are idempotent
tests/Aspire.Hosting.PostgreSQL.Tests/AddPostgresTests.cs	Adds test verifying PostgreSQL environment callbacks are idempotent
tests/Aspire.Hosting.MySql.Tests/AddMySqlTests.cs	Adds test verifying PhpMyAdmin environment callbacks are idempotent
tests/Aspire.Hosting.MongoDB.Tests/AddMongoDBTests.cs	Adds test verifying MongoExpress environment callbacks are idempotent
tests/Aspire.Hosting.Kafka.Tests/AddKafkaTests.cs	Adds tests verifying Kafka and KafkaUI environment callbacks are idempotent

[eerhardt]

/backport to release/13.0

[github-actions]

Started backporting to release/13.0: https://github.com/dotnet/aspire/actions/runs/19051646441