refactor(encryption): collapse redundant AES cfg split in detect_hardware_acceleration (LAB-6353)

[27Bslash6]

This refactor simplifies the private helper ZeroKnowledgeEncryptor::detect_hardware_acceleration in src/encryption/core.rs. No public API signatures change, and the reported flag stays the same on every target.

Changes

• x86 / x86_64 arm: The #[cfg(target_feature = "aes")] return true; short-circuit is removed, along with its #[cfg(not(target_feature = "aes"))] fallback. The arm now evaluates is_x86_feature_detected!("aes") directly.
• AArch64 arm: The same compile-time/runtime split is removed. The arm now evaluates std::arch::is_aarch64_feature_detected!("aes") directly.
• NEON comment: The existing comment is kept. It explains why a cfg!(target_feature = "neon") check would be meaningless for AES detection.
• Other architectures: The software fallback path is unchanged.
• Test comment: The comment on test_hardware_acceleration_matches_platform_probe now says the reported flag is exactly the platform AES probe. It no longer mentions the removed cfg short-circuit.

Rationale

• The short-circuit was redundant. Both detection macros already resolve to a constant true when AES is enabled at compile time.
• It broke strict builds. With -C target-feature=+aes -D warnings, the x86 arm never used the is_x86_feature_detected import, so the build failed with an unused import error. After this change, each arm has a single expression that is used in every configuration, so no #[allow] attribute is needed.

Impact

• There is no behavioral change on any target, and no public interface changes.
• Builds under -C target-feature=+aes -D warnings now compile.

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• src/encryption/core.rs

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Walkthrough

The hardware-acceleration check now uses runtime AES feature probes on x86, x86_64, and AArch64. The test comment now describes the reported flag as the platform AES probe.

Changes

AES feature detection

Layer / File(s)	Summary
Runtime AES probing src/encryption/core.rs	The detection function uses runtime AES probes on x86, x86_64, and AArch64. The hardware-acceleration test comment describes the reported flag as the platform AES probe.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Refactor

Merge Risk: ⚪ Minimal · up to a97e2

AES capability reporting retains its compile-time behavior and uses runtime detection otherwise, with the result still reaching metrics. No material merge-blocking risk is indicated.

Security Architecture Review

Security architecture risk: 🔵 Low · up to a97e2

The reported AES capability can change on AArch64, but the flag does not select the encryption implementation. No security regression was identified; the effect on external consumers of the public status remains unknown.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The observed change is limited to the reported capability and its existing metrics path; no change to encryption dispatch was found in the checked local consumers.

Trust Boundaries and Controls

• observed — The changed detection method is private and called during construction; the public getter returns its stored boolean without accepting input.

🚥 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 clearly and accurately summarises the main change: removing the redundant AES configuration split in detect_hardware_acceleration. It is specific and concise.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 1 files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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