fix(detector): detect functools.partial bound-state replay

[prasannakotyal]

Summary

Targets KG red #77, where custom_kernel = functools.partial(_impl, {}) hides replay state as a bound mutable argument. The helper fills that bound state from the input and later returns it on an input-independent fast path.

This adds a narrow PARTIAL_BOUND_STATE_REPLAY detector. It requires:

• a top-level custom_kernel assignment using functools.partial or imported partial
• a concrete helper function as the first partial argument
• at least one bound helper parameter acting as state
• mutation of that bound state from input-derived values
• a call-free early return from that same state under a guard that does not reference input parameters

Legitimate partial use for constants, callable caches, and workspace buffers stays out of scope.

KernelGuard-Red-Submission: 77

Local verification

• red_03_partial_replay -> PARTIAL_BOUND_STATE_REPLAY, should_filter=True
• clean_partial_scalar -> stays valid
• clean_partial_cached_fn -> stays valid
• clean_partial_workspace -> stays valid
• python -m py_compile kernelguard.py

[github-actions]

KernelGuard Blue Evaluation

• Evaluation job: 42
• Blue submission: 31
• Result: passed
• Target red submission caught: True
• Validation suite: TP 20/20, FP 20/20
• Surgicalness score: 1.0
• Workflow run: https://github.com/SinatrasC/kernelguard/actions/runs/25227738453

[SinatrasC]

Thanks for the KernelGuard Flywheel Campaign contribution. We are not merging this narrow variant separately because the consolidated rule-family implementation in #273 is the merge path for this detector area.