refactor(toolkit-lib): batch asset-active lookups in cdk gc with a multi-pattern search

[Adityaj0]

fixes #1860

Reason for this change

cdk gc's ActiveAssetCache.contains() checked whether an asset is still referenced by any stack via a linear per-stack String.includes() scan, called once per asset:

public contains(asset: string): boolean {
  for (const stack of this.stacks) {
    if (stack.includes(asset)) {
      return true;
    }
  }
  return false;
}

garbageCollectEcr/garbageCollectS3 call this once per asset in every batch (batch size 1000), so for an account with S stacks and A accumulated orphaned assets, the lookup phase alone costs O(A x S x avg template size) — every single asset re-scans every stack template from scratch. In a long-lived account with hundreds of stacks and tens of thousands of orphaned S3 objects / ECR images, this dominates cdk gc runtime.

Description of changes

• Added ActiveAssetCache.containsAny(assets: string[]), which builds a single Aho-Corasick multi-pattern search index over a batch of candidate asset identifiers and scans each remembered stack template exactly once, regardless of how many candidates are in the batch. This brings the cost down to O(stacks x avg template size + sum of candidate lengths) per batch.
• garbageCollectEcr/garbageCollectS3 now call containsAny() once per batch (of up to 1000 assets/tags) instead of calling contains() once per asset.
• Kept contains(asset) as a thin wrapper around containsAny([asset]) for any other/future single-item callers.
• The multi-pattern search is exact substring matching — same semantics as before, so results are byte-for-byte identical to the old implementation. This matters a lot here: a false negative would mean deleting an asset that's actually still referenced by a live stack.

Testing

• Added test/api/garbage-collection/stack-refresh.test.ts, including:
  • basic contains/containsAny behavior across multiple stacks
  • overlapping/substring patterns (one candidate being a substring of another)
  • a template-boundary false-positive regression test (concatenating templates without a separator could otherwise create a spurious match spanning two templates)
  • a randomized-workload test that cross-checks containsAny() against the naive per-candidate contains() for exact agreement (no false negatives, no false positives)
• Existing garbage-collection.test.ts suite passes unchanged (40/40 tests).

Metrics

Synthetic benchmark modeling a large, long-lived account (500 stacks x ~20KB templates, 50,000 orphaned assets processed in batches of 1000, matching cdk gc's real batch size):

	Before	After	Speedup
Asset-lookup phase	~13.3s	~5.3s	~2.5x

Results were identical between old and new implementations across all benchmarked scales (3,000 / 20,000 / 50,000 assets) — verified via direct set comparison, not just count.

Checklist

• Unit tests added/updated
• Integration tests added/updated (not applicable — algorithmic change, no new AWS resource types or cross-service interactions)
• No manual edits to generated files

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.13%. Comparing base (2845174) to head (5a3bd8f).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1861      +/-   ##
==========================================
+ Coverage   90.93%   91.13%   +0.19%     
==========================================
  Files          80       80              
  Lines       12250    12205      -45     
  Branches     1756     1744      -12     
==========================================
- Hits        11140    11123      -17     
+ Misses       1073     1046      -27     
+ Partials       37       36       -1     

Flag	Coverage Δ
suite.unit	91.13% <ø> (+0.19%)	⬆️

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