Add comprehensive unit tests for agenthooks guardrails (AST-165778) - #1537

Add extensive unit tests and test helpers for agenthooks guardrails. hooks_test.go: introduce sampleJWT, recordingTelemetry, and helpers (resetHookGlobals, setHomeDir, writePolicy, currentOS); add tests for session IDs, tool-call rules (blacklist, tool rules, SCA), file-edit rules (secrets, blast radius, total size, KICS, SCA manifest), fullAfterContent/newline normalization, prompt handling, RegisterGuardrails/RegisterPassThrough, telemetry logging, and agent string mapping. guardrails/asca_test.go: add tests for ASCA-supported extensions, highestSeverity, existing ignore file path, shouldUpdateVersion flag, ASCA telemetry, and ScanFileEdit early-return cases. No production code changed.

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Description

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Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Related Issues

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Checklist

• I have performed a self-review of my code
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in downstream modules
• I have updated the CLI help for new/changed functionality in this PR (if applicable)
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used

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