Document CI cache strategy for build artifacts

- Explain how idempotent extraction scripts support caching
- Provide GitHub Actions configuration example
- Document performance impact: ~450-950ms savings per build
- Include cache invalidation strategies and manual cleanup instructions

Author: jdalton

packages/cli/.cache-strategy.md

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+# CI Cache Strategy for Build Artifacts
+
+This document describes how to configure CI caching for Socket CLI build artifacts to avoid regenerating files on every build.
+
+## Cached Files
+
+The `external/` directory contains auto-generated files that should be cached:
+
+- `external/yoga-sync.mjs` - Yoga layout WASM wrapper
+- `external/onnx-sync.mjs` - ONNX Runtime wrapper
+- `external/minilm-sync.mjs` - MiniLM model/tokenizer loader
+
+## How Caching Works
+
+All extraction scripts are **idempotent** and include built-in cache checking:
+
+1. On first build: Scripts generate files from source packages
+2. On subsequent builds: Scripts detect cached files and skip regeneration
+3. Cache validation: Each script verifies file content before using cache
+
+### Extraction Scripts
+
+- `scripts/extract-yoga-wasm.mjs` - Extracts Yoga layout WASM
+- `scripts/extract-onnx-runtime.mjs` - Creates ONNX Runtime wrapper
+- `scripts/extract-minilm-model.mjs` - Creates MiniLM model/tokenizer loader
+
+Each script:
+- Checks if file exists in `external/`
+- Validates file content (not corrupted)
+- Skips regeneration if cache is valid
+- Logs `✓ Using cached` message when cache hit
+
+## CI Configuration
+
+### GitHub Actions
+
+Add cache configuration to your workflow:
+
+```yaml
+- name: Cache build artifacts
+  uses: actions/cache@v4
+  with:
+    path: packages/cli/external
+    key: socket-cli-external-${{ hashFiles('packages/cli/package.json') }}
+    restore-keys: |
+      socket-cli-external-
+```
+
+This caches the `external/` directory and invalidates when `package.json` changes (e.g., dependency updates).
+
+### Other CI Systems
+
+For other CI systems (GitLab CI, CircleCI, etc.), cache the `packages/cli/external/` directory between builds. The cache is safe to reuse because:
+
+1. Files are deterministically generated from locked dependencies
+2. Cache is invalidated when dependencies change (`package.json` hash)
+3. Built-in validation prevents corrupted cache usage
+
+## Performance Impact
+
+**Without cache:**
+- First build: ~500ms-1s (extract Yoga, ONNX, MiniLM)
+- Subsequent builds: ~500ms-1s (regenerate all files)
+
+**With cache:**
+- First build: ~500ms-1s (generate files)
+- Subsequent builds: ~50ms (detect cache, skip regeneration)
+
+**CI savings:** ~450-950ms per build on cache hit
+
+## Cache Invalidation
+
+Cache is automatically invalidated when:
+
+1. `package.json` changes (dependency updates)
+2. Extraction scripts are modified
+3. Manual cache clear in CI settings
+
+To manually clear cache in development:
+
+```bash
+rm -rf packages/cli/external/*.mjs
+pnpm run build
+```
+
+## Notes
+
+- Cache files should NOT be committed to git (they're auto-generated)
+- Cache is specific to this project layout - do not share across repos
+- Extraction scripts handle missing npm packages gracefully
+- Invalid/corrupted cache is automatically regenerated