fix(core): prevent duplicate middleware registrations in function chains

[alwaysprince05]

Problem

A middleware instance could appear more than once in a function's middleware chain when it was both explicitly configured for the function and later auto-registered by a DynamicFunctionMiddleware. The middleware then executed multiple times per invocation — causing repeated pre/post handling, duplicate logs, extra latency, and incorrect behavior for non-idempotent middleware.

Reproduced on develop @ ad7f4a4:

after explicit config    : [<DynamicMiddleware object at 0x...>]
after runtime discovery  : [<DynamicMiddleware object at 0x...>, <DynamicMiddleware object at 0x...>]  # same instance twice
middleware executions for one call: 2

Root cause

All middleware configuration paths (explicit per-function config, function-group config, and dynamic auto-registration) flow through validate_middleware in packages/nvidia_nat_core/src/nat/middleware/function_middleware.py, which validated types and final-middleware ordering but never checked for duplicate instances. DynamicFunctionMiddleware._register_function appends itself to the function's existing chain without a membership check, so a middleware already present in the chain via explicit configuration was added a second time.

Solution

Deduplicate middleware instances by identity in validate_middleware (the single choke point for every configuration path). The first occurrence keeps its position, so an explicitly configured middleware wins over a later auto-registered duplicate. Repeated registrations log a warning instead of silently duplicating chain entries. The final-middleware ordering guarantees are now evaluated on the deduplicated list. No public API changes.

Tests

• test_register_function_does_not_duplicate_middleware_already_in_chain — regression test reproducing the exact collision (explicit config + dynamic registration); asserts the chain contains the instance once and it executes exactly once per invocation. Failed before the fix, passes after.
• test_validate_middleware_deduplicates_repeated_instances
• test_validate_middleware_keeps_distinct_instances_of_same_class
• test_validate_middleware_deduplicated_final_is_accepted

Validation

• pytest packages/nvidia_nat_core → 2842 passed, 54 skipped, 0 failed (Python 3.13)
• pre-commit (yapf, ruff, uv-lock, etc.) → all pass on changed files
• ci/scripts/copyright.py --verify-apache-v2, documentation_checks.sh (nbconvert + vale: 0 errors), path_checks.sh → all pass

Limitations

• Integration tests not run (change is not covered by them); CI will cover Python 3.11–3.13.

Closes #2093

Summary by CodeRabbit

• Bug Fixes
  • Prevented duplicate middleware from running more than once during a function invocation.
  • Preserved the order of configured middleware while removing repeated references.
  • Correctly handles duplicated final middleware after deduplication.
  • Keeps separate middleware instances independent, even when they share the same type.
  • Added logging when duplicate middleware entries are ignored.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

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Reviewing files that changed from the base of the PR and between d787336 and ec14a46.

📒 Files selected for processing (2)

• packages/nvidia_nat_core/tests/nat/middleware/test_dynamic_middleware.py
• packages/nvidia_nat_core/tests/nat/middleware/test_middleware_components.py

🚧 Files skipped from review as they are similar to previous changes (2)

• packages/nvidia_nat_core/tests/nat/middleware/test_middleware_components.py
• packages/nvidia_nat_core/tests/nat/middleware/test_dynamic_middleware.py

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Walkthrough

Middleware validation now removes repeated references to the same middleware instance before applying final-middleware ordering checks. Tests cover dynamic registration, identity-based deduplication, order preservation, distinct instances, and duplicated final middleware.

Changes

Middleware deduplication

Layer / File(s)	Summary
Validation deduplication packages/nvidia_nat_core/src/nat/middleware/function_middleware.py	validate_middleware removes repeated middleware instances in first-seen order, logs ignored duplicates, and validates final-middleware ordering after deduplication.
Deduplication regression coverage packages/nvidia_nat_core/tests/nat/middleware/test_dynamic_middleware.py, packages/nvidia_nat_core/tests/nat/middleware/test_middleware_components.py	Tests verify that dynamic and explicit registration keep one middleware entry, preserve distinct instances, retain order, accept duplicated final middleware, and execute pre_invoke once.

Estimated code review effort: 2 (Simple) | ~15 minutes

Merge Risk: ⚪ Minimal · up to ec14a

This change prevents duplicate middleware execution through a localized validation fix, with the reported test suite and checks passing; no actionable merge-blocking risk remains beyond normal review.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title is concise, descriptive, imperative, and accurately describes duplicate middleware prevention.
Linked Issues check	✅ Passed	The changes satisfy issue #2093 by deduplicating identical middleware instances and adding regression coverage.
Out of Scope Changes check	✅ Passed	The implementation and tests remain focused on duplicate middleware registration and related chain validation.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches 💡 1

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• Create stacked PR
• Commit on current branch

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[coderabbitai]

Actionable comments posted: 2

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Inline comments:
In `@packages/nvidia_nat_core/tests/nat/middleware/test_dynamic_middleware.py`:
- Around line 588-593: Add type annotations to
_CountingDynamicMiddleware.__init__ parameters compatible with
DynamicFunctionMiddleware, annotate pre_invoke’s context parameter as
InvocationContext, and add return annotations for both methods according to the
project’s Python typing conventions.
- Around line 585-586: Update the docstring for _CountingDynamicMiddleware in
packages/nvidia_nat_core/tests/nat/middleware/test_dynamic_middleware.py lines
585-586 to wrap pre_invoke in backticks. Also update each validate_middleware
reference in
packages/nvidia_nat_core/tests/nat/middleware/test_middleware_components.py
lines 423-447 with backticks; make no other changes.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
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📒 Files selected for processing (3)

• packages/nvidia_nat_core/src/nat/middleware/function_middleware.py
• packages/nvidia_nat_core/tests/nat/middleware/test_dynamic_middleware.py
• packages/nvidia_nat_core/tests/nat/middleware/test_middleware_components.py

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[alwaysprince05]

Hi — thank you for the quick review feedback; both nits are addressed in ec14a46 (type hints + docstring code identifiers). The branch is also synced with develop.

Could a vetter/maintainer add the bug and non-breaking labels (I don't have permission to label this repo, and the required Label Checker needs them) so the pipeline can run? Thanks!