Test pages CSS cache key inputs

[gianfrancopiana]

What

Add regression checks that the pages CSS cache tag changes when its build script, CSS input, package lock, or rake task changes.

Why

PR #8312 added the pages CSS cache. Its tests covered restore and save behavior, but did not prove that representative build inputs invalidate the cache key.

Before/After

Before: cache-key input changes had no direct regression coverage.

After: the shell harness checks each representative input independently and confirms unrelated changes keep the key stable.

Test Results

• bash .buildkite/scripts/main_asset_cache_compile_test.sh — 63 passed, 0 failed
• Mutation controls — removing each tested input from the key produced its intended failure
• bin/test-confidence --strict — no tests selected because the diff only changes the shell harness
• Private Claude Sonnet 5.5 high-effort review — clean

QA

No manual QA needed. This is test-only coverage for the existing cache key.

---

Implemented with Claude Sonnet 5.5.

[gianfrancopiana]

@greptileai

[greptile-apps]

Confidence Score: 5/5

[Low impact] This test-only change appears safe to merge.

Summary

Adds regression checks for the pages CSS cache key.

• The cache test checks which pages CSS inputs change its tag.

_{Reviews (1) · Last reviewed commit: "Test pages CSS cache key inputs" · Reviewed by Greptile}