Fix inconsistent inputs access pattern in build.yaml

[Copilot]

The workflow mixes inputs.cache_buster with github.event.inputs.* for accessing workflow_dispatch inputs. Both work, but inconsistency hurts maintainability.

Changes

• Unified input access to use github.event.inputs.cache_buster pattern, matching existing usage for backend_ref and frontend_ref

# Before
CACHE_BUSTER: ${{ inputs.cache_buster || '' }}

# After  
CACHE_BUSTER: ${{ github.event.inputs.cache_buster || '' }}

Note: The cache mechanism and cache buster functionality are correct—this is purely a consistency fix.

Original prompt

当前build.yml中的缓存机制是否存在问题？Cache buster是否有效？

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[Nativu5]

@copilot Cache buster在指纹计算和缓存查找中被使用并生效了吗？

[Copilot]

@copilot Cache buster在指纹计算和缓存查找中被使用并生效了吗？

是的，cache buster 在指纹计算和缓存查找中被正确使用并生效：

1. 指纹计算 (第194行): FINGERPRINT="${CRANE_SHA}-${FE_REF}-${FE_SHA}-${CI_DIGEST}-${CACHE_BUSTER}" - CACHE_BUSTER 作为指纹组成部分

2. 缓存键生成 (第196行): KEY_SHA256=$(printf '%s' "$FINGERPRINT" | sha256sum) - 指纹被哈希为缓存键

3. 缓存路径 (第197-198行): CACHE_TGZ="${LOCAL_CACHE_DIR}/${KEY_SHA256}.tar.gz" - 缓存文件使用此键定位

当提供非空的 cache_buster 时，会产生不同的 KEY_SHA256，导致缓存未命中（第225行的 if [ -f "${CACHE_TGZ}" ] 检查失败），从而触发重新构建。