[IDE-1514] delta issue counts incorrect

[andrewrobinsonhodges-snyk]

Description

This PR fixes two issues with the delta scan issue counts, and adds more robust logging so we can debug these issues more easily in the future.

1. Issue caches were not getting cleared when reference branches/folders were being set. As the cache was only populated after a scan completes, this meant that changing a base/reference branch/folder would potentially give different results depending on whether or not the new base/reference branch/folder had been scanned before.

2. When we enrich issues with isNew after a delta scan, we set isNew to true if they were in the diff, however we did not set isNew to false if they were not in the diff. Depending on the order of scans and base/reference branch changes, the same issue list could be diffed multiple times, giving different results as it would contain old state.

Checklist

• Tests added and all succeed
• Regenerated mocks, etc. (make generate)
• Linted (make lint-fix)
• [n/a] README.md updated, if user-facing
• [n/a] License file updated, if new 3rd-party dependency is introduced

[snyk-io]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scanner	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues
✅	Licenses	0	0	0	0	0 issues
✅	Code Security	0	0	0	0	0 issues

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[gemini-code-assist]

Summary of Changes

Hello @andrewrobinsonhodges-snyk, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses critical inaccuracies in delta scan issue counts by ensuring that cached scan results are properly invalidated and that the 'isNew' status of issues is correctly determined. It also significantly improves the observability of the delta scanning process through comprehensive logging, enhancing the reliability and debuggability of the feature.

Highlights

• Delta Cache Clearing: The system now correctly clears the persisted scan cache for a folder when its base branch or reference folder path changes. This prevents stale delta scan results from being used.
• Corrected 'isNew' Flag Logic: The logic for enriching issues with the 'isNew' flag has been fixed. Issues that are no longer present in the current scan's diff are now explicitly marked as 'isNew: false', resolving a bug where old issues could incorrectly retain a 'new' status.
• Enhanced Logging for Debugging: Extensive debug and info level logging has been added across the persistence layer, scanner, and product-specific scanners. This provides much greater visibility into the delta scan process, cache operations, and issue enrichment, making future debugging significantly easier.
• Improved Delta Matching Robustness: New test cases have been introduced to ensure the delta calculation correctly identifies identical issues even when their content roots differ (e.g., between a temporary base branch directory and the working directory), preventing false positives for 'new' issues.

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[gemini-code-assist]

Code Review

This pull request effectively resolves two key issues concerning incorrect delta scan issue counts and enhances logging for improved future debugging. The first fix correctly invalidates issue caches upon changes to reference branches or folders. The second fix refines the logic for marking issues as new, ensuring that issues no longer present in the delta are appropriately updated. The introduction of more detailed and structured logging is a commendable improvement for observability. The added tests are thorough, particularly those for cache clearing and cross-directory diffing. I've identified a minor logging format issue in internal/vcs/checkout_handler.go and have provided suggestions for correction.

[rrama]

LGTM. I think I wrapped my head around "new", "base", "current", "delta", etc.