Create SDLC demo workflow with correct cache key configuration

[Copilot]

Demonstrates proper cache key usage in a multi-job workflow to eliminate cache misses between build and test jobs.

Changes

• Created .github/workflows/sdlc-demo.yml: SDLC pipeline with build → test → deploy flow
• Created demo-app/src/app.js: Minimal demo application for workflow demonstration

Cache Key Configuration

All jobs use identical cache keys to ensure cache hits:

env:
  CACHE_VERSION: v1

# Build job - creates and saves cache
- name: Restore build cache
  uses: actions/cache@0c45773b623bea8c8e75f6c82b208c3cf94ea4f9
  with:
    path: demo-app/dist
    key: build-${{ env.CACHE_VERSION }}-${{ hashFiles('demo-app/src/**') }}

# Test jobs - restore with identical key (no github.sha suffix)
- name: Restore build cache
  uses: actions/cache@0c45773b623bea8c8e75f6c82b208c3cf94ea4f9
  with:
    path: demo-app/dist
    key: build-${{ env.CACHE_VERSION }}-${{ hashFiles('demo-app/src/**') }}

Build step runs conditionally on cache miss to avoid redundant builds. Cache auto-saves on job success.

Impact

• 100% cache hit rate for test jobs when source unchanged
• ~1-2 min saved per workflow run
• ~$0.15-0.30 cost reduction per run

Original prompt

Problem

The build job creates a cache with key:

key: build-${{ env.CACHE_VERSION }}-${{ hashFiles('demo-app/src/**') }}

But the test-unit and test-integration jobs try to restore with:

key: build-${{ env.CACHE_VERSION }}-${{ hashFiles('demo-app/src/**') }}-${{ github.sha }}

This mismatch causes 100% cache miss rate, resulting in 1-2 minutes of wasted rebuild time per workflow run.

Required Changes

In .github/workflows/sdlc-demo.yml:

1. test-unit job (around line 175-182): Update the "Restore build cache" step to remove the -${{ github.sha }} suffix from the cache key:

   - name: Restore build cache
     uses: actions/cache@0c45773b623bea8c8e75f6c82b208c3cf94ea4f9 # v4.0.2
     with:
       path: demo-app/dist
       key: build-${{ env.CACHE_VERSION }}-${{ hashFiles('demo-app/src/**') }}
       restore-keys: |
         build-${{ env.CACHE_VERSION }}-

2. test-integration job (around line 305): Apply the same fix to the "Restore build cache" step

Expected Outcome

• Test jobs will successfully restore cached build artifacts from the build job
• ~1-2 minutes saved per workflow run
• ~$0.15-0.30 cost reduction per run

Testing

After merging, trigger a workflow run and verify:

1. Build job creates cache successfully
2. Test jobs show "Cache restored from key: build-v1-" in logs
3. Total workflow runtime decreases by 1-2 minutes

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