fix(core): ensure nested transient provider isolation

[mag123c]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

When a transient provider depends on another transient provider, each parent consumer should receive its own dedicated instance of the nested transient provider. However, in request/durable scoped contexts, nested transient providers are incorrectly shared across different parents, causing context pollution.

Issue Number: #15689

What is the new behavior?

Each parent now receives its own isolated instance of nested transient providers. The fix adds a getEffectiveInquirer() helper method that uses parentInquirer instead of inquirer when resolving transient-to-transient dependency chains in non-static contexts (REQUEST/DURABLE scopes).

Key changes:

• Added getEffectiveInquirer() helper method in injector.ts
• Applied to 4 injection points: constructor params, properties, metadata loading, scoped component resolution
• Only affects TRANSIENT→TRANSIENT chains in REQUEST/DURABLE contexts
• Preserves existing behavior for DEFAULT scope

Does this PR introduce a breaking change?

• Yes
• No

Other information

Similar but distinct from: #15553 / #15571: Lifecycle hook phantom instance bug (different root cause)

[coveralls]

Pull Request Test Coverage Report for Build f21074a3-8fcf-4ec1-a93c-75675d264f01

Details

• 7 of 7 (100.0%) changed or added relevant lines in 1 file are covered.
• 52 unchanged lines in 5 files lost coverage.
• Overall coverage decreased (-0.2%) to 88.726%

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Files with Coverage Reduction	New Missed Lines	%
packages/websockets/gateway-metadata-explorer.ts	1	95.24%
packages/common/module-utils/configurable-module.builder.ts	6	90.16%
packages/microservices/client/client-rmq.ts	7	65.84%
packages/websockets/web-sockets-controller.ts	9	87.67%
packages/microservices/server/server-rmq.ts	29	68.9%

Totals
Change from base Build daf86254-cf7e-4ef4-bff5-de9bcb9f9199:	-0.2%
Covered Lines:	7280
Relevant Lines:	8205

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💛 - Coveralls

[kamilmysliwiec]

Would you like to add an integration test for this, too?

[KamalAman]

Oooh man, i think i've been fighting with this bug for 2 days now....

My symptoms are tenant databases are getting mixed up (in a sandbox env), and they are all resolving as the same latest database initialized for our durable database providers.

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Update: My bad, i've isolated my bug to updating "@nestjs-cls/transactional" "2.5.1" -> "2.6".

Papooch/nestjs-cls#404

[kamilmysliwiec]

LGTM