feat(mcp): embed Python engine and extract to user cache
U2 of the Claude Desktop .mcpb bundle plan. - internal/engine/embed.go embeds the vendored Python tree at build time via //go:embed all:vendored. The engine package owns the embed because Go's directive cannot reach outside its own package directory; sync and gitignore paths are updated to match (internal/engine/vendored/ in place of mcp/vendored/). - internal/engine/extract.go materializes the embed into <cache>/last30days-pp-mcp/<version>/ with a .version sentinel that short-circuits re-extraction. Atomic rename from a .tmp sibling means a partial extraction can never be mistaken for complete. Concurrent first-call extractions serialize behind a per-cache-dir sync.Once. - EnsureUserCache honors a LAST30DAYS_CACHE_DIR env override for locked-down filesystems; the override is named in extract errors. - internal/engine/extract_test.go covers happy path, sentinel skip, version bump, 10-goroutine race, empty-version rejection, unwritable cache parent, and the env override (7 tests, all passing). - A tracked vendored/.gitkeep anchors the embed path so the directive matches even before scripts/sync-engine.sh runs.
This commit is contained in:
Matt Van Horn
+4
-1
@@ -1,6 +1,9 @@
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# Mirror of skills/last30days/scripts/, populated by scripts/sync-engine.sh.
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# Source of truth lives in the Python skill; never commit the mirror.
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vendored/
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# Lives inside internal/engine/ because //go:embed cannot reach outside
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# its own package directory.
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internal/engine/vendored/*
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!internal/engine/vendored/.gitkeep
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# Local build output: cross-compiled binaries and packaged .mcpb files.
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build/
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+1
-1
@@ -9,7 +9,7 @@ The MCP server exposes a single `research` tool that mirrors the `/last30days <t
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- `cmd/last30days-pp-mcp/` - server entry point
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- `internal/engine/` - `embed.FS` of the Python engine + cache extractor + subprocess wrapper
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- `internal/tools/` - MCP tool handlers (currently `research`)
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- `vendored/` - mirror of `skills/last30days/scripts/`, generated by `scripts/sync-engine.sh` (gitignored)
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- `internal/engine/vendored/` - mirror of `skills/last30days/scripts/`, generated by `scripts/sync-engine.sh` (gitignored). Lives inside the engine package because `//go:embed` cannot reach files outside its own package directory.
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- `manifest.json` - MCPB v0.3 manifest consumed by Claude Desktop and `printing-press bundle`
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## Local build
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@@ -0,0 +1,26 @@
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// Package engine wraps the vendored Python last30days engine. The engine
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// is embedded at build time via //go:embed and extracted into a per-user
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// cache directory on first use, then invoked through python3 in a
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// subprocess. Consumers should call EnsureUserCache to materialize the
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// engine and Run to execute it.
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package engine
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import (
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"embed"
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"io/fs"
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)
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// EngineSourceDir is the embed root inside the binary. scripts/sync-engine.sh
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// mirrors skills/last30days/scripts/ into this directory before each build.
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// The all: prefix preserves files starting with "." or "_" so the .gitkeep
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// anchor file survives - without it the embed would error before sync runs.
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//
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//go:embed all:vendored
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var vendored embed.FS
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// EngineFS returns the embedded engine as a filesystem rooted at the
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// vendored/ directory contents (so callers see "last30days.py" at the
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// root, not "vendored/last30days.py").
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func EngineFS() (fs.FS, error) {
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return fs.Sub(vendored, "vendored")
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}
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@@ -0,0 +1,168 @@
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package engine
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import (
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"errors"
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"fmt"
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"io"
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"io/fs"
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"os"
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"path/filepath"
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"sync"
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)
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// SentinelFilename names the file Ensure writes inside the cache directory
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// after a successful extraction. Its contents are compared to the requested
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// version; a match short-circuits re-extraction on subsequent calls.
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const SentinelFilename = ".version"
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// cacheSubdir namespaces our cache under the OS user cache directory so
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// multiple printing-press-style bundles can coexist.
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const cacheSubdir = "last30days-pp-mcp"
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// CacheEnvOverride lets users redirect the cache directory when the default
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// OS cache location is read-only (locked-down corp images, ephemeral CI
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// containers). Pointed at by extract errors via the documented escape hatch.
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const CacheEnvOverride = "LAST30DAYS_CACHE_DIR"
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// Ensure extracts src into baseDir/last30days-pp-mcp/<version> and returns
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// the cache path. If the sentinel file already records the same version the
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// directory is reused without rewriting. version must be non-empty so the
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// cache layout always namespaces by version.
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//
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// Extraction writes to a sibling .tmp directory and renames it on success
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// so a partial extraction can never be mistaken for a complete one. Concurrent
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// callers within the same process serialize behind a per-cache-dir sync.Once
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// so the rename happens exactly once.
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func Ensure(src fs.FS, baseDir, version string) (string, error) {
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if version == "" {
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return "", errors.New("engine: version is required")
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}
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cacheDir := filepath.Join(baseDir, cacheSubdir, version)
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once := getOnce(cacheDir)
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var extractErr error
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once.Do(func() {
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extractErr = ensureLocked(src, cacheDir, version)
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})
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if extractErr != nil {
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// Reset the sync.Once so a follow-up call can retry rather than
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// permanently caching the error. Retry is the right default when
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// the failure is transient (e.g., disk full, parent dir restored).
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resetOnce(cacheDir)
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return "", extractErr
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}
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return cacheDir, nil
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}
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// EnsureUserCache wraps Ensure with the OS user cache dir (or the
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// LAST30DAYS_CACHE_DIR override) as base. Production callers use this; tests
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// use Ensure with an explicit temp dir.
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func EnsureUserCache(src fs.FS, version string) (string, error) {
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if override := os.Getenv(CacheEnvOverride); override != "" {
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return Ensure(src, override, version)
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}
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base, err := os.UserCacheDir()
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if err != nil {
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return "", fmt.Errorf("engine: resolve user cache dir (set %s to override): %w", CacheEnvOverride, err)
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}
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return Ensure(src, base, version)
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}
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func ensureLocked(src fs.FS, cacheDir, version string) error {
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if sentinelMatches(cacheDir, version) {
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return nil
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}
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tmpDir := cacheDir + ".tmp"
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if err := os.RemoveAll(tmpDir); err != nil {
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return fmt.Errorf("engine: clean tmp cache: %w", err)
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}
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if err := os.MkdirAll(tmpDir, 0o755); err != nil {
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return fmt.Errorf("engine: create tmp cache (%s, set %s to override): %w", tmpDir, CacheEnvOverride, err)
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}
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if err := extractAll(src, tmpDir); err != nil {
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_ = os.RemoveAll(tmpDir)
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return err
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}
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sentinel := filepath.Join(tmpDir, SentinelFilename)
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if err := os.WriteFile(sentinel, []byte(version), 0o644); err != nil {
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_ = os.RemoveAll(tmpDir)
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return fmt.Errorf("engine: write sentinel: %w", err)
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}
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if err := os.RemoveAll(cacheDir); err != nil {
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_ = os.RemoveAll(tmpDir)
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return fmt.Errorf("engine: clean old cache: %w", err)
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}
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if err := os.Rename(tmpDir, cacheDir); err != nil {
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_ = os.RemoveAll(tmpDir)
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return fmt.Errorf("engine: promote tmp cache: %w", err)
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}
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return nil
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}
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func sentinelMatches(cacheDir, version string) bool {
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data, err := os.ReadFile(filepath.Join(cacheDir, SentinelFilename))
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if err != nil {
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return false
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}
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return string(data) == version
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}
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func extractAll(src fs.FS, dst string) error {
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return fs.WalkDir(src, ".", func(path string, d fs.DirEntry, err error) error {
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if err != nil {
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return err
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}
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if path == "." {
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return nil
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}
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target := filepath.Join(dst, path)
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if d.IsDir() {
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return os.MkdirAll(target, 0o755)
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}
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return copyEmbeddedFile(src, path, target)
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})
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}
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func copyEmbeddedFile(src fs.FS, srcPath, dst string) error {
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in, err := src.Open(srcPath)
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if err != nil {
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return fmt.Errorf("engine: open %s: %w", srcPath, err)
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}
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defer func() { _ = in.Close() }()
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if err := os.MkdirAll(filepath.Dir(dst), 0o755); err != nil {
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return fmt.Errorf("engine: ensure parent of %s: %w", dst, err)
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}
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out, err := os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0o644)
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if err != nil {
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return fmt.Errorf("engine: create %s: %w", dst, err)
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}
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defer func() { _ = out.Close() }()
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if _, err := io.Copy(out, in); err != nil {
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return fmt.Errorf("engine: write %s: %w", dst, err)
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}
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return nil
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}
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// onceRegistry serializes first-call extraction per cache directory so the
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// rename in ensureLocked happens exactly once across goroutines.
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var (
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onceMu sync.Mutex
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onceRegistry = map[string]*sync.Once{}
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)
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func getOnce(cacheDir string) *sync.Once {
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onceMu.Lock()
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defer onceMu.Unlock()
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if o, ok := onceRegistry[cacheDir]; ok {
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return o
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}
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o := &sync.Once{}
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onceRegistry[cacheDir] = o
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return o
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}
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func resetOnce(cacheDir string) {
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onceMu.Lock()
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defer onceMu.Unlock()
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delete(onceRegistry, cacheDir)
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}
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@@ -0,0 +1,167 @@
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package engine
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import (
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"os"
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"path/filepath"
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"sync"
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"testing"
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"testing/fstest"
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)
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func newTestFS() fstest.MapFS {
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return fstest.MapFS{
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"last30days.py": &fstest.MapFile{Data: []byte("# last30days entry\n"), Mode: 0o644},
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"lib/__init__.py": &fstest.MapFile{Data: []byte(""), Mode: 0o644},
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"lib/env.py": &fstest.MapFile{Data: []byte("# env helpers\n"), Mode: 0o644},
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}
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}
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func TestEnsureExtractsEngine(t *testing.T) {
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src := newTestFS()
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base := t.TempDir()
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cacheDir, err := Ensure(src, base, "v1")
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if err != nil {
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t.Fatalf("Ensure: %v", err)
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}
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if cacheDir != filepath.Join(base, cacheSubdir, "v1") {
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t.Fatalf("cacheDir = %q, want %q", cacheDir, filepath.Join(base, cacheSubdir, "v1"))
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}
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mustReadFile(t, filepath.Join(cacheDir, "last30days.py"), "# last30days entry\n")
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mustReadFile(t, filepath.Join(cacheDir, "lib/env.py"), "# env helpers\n")
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mustReadFile(t, filepath.Join(cacheDir, SentinelFilename), "v1")
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}
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func TestEnsureSkipsWhenSentinelMatches(t *testing.T) {
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src := newTestFS()
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base := t.TempDir()
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cacheDir, err := Ensure(src, base, "v1")
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if err != nil {
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t.Fatalf("first Ensure: %v", err)
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}
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target := filepath.Join(cacheDir, "last30days.py")
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info1, err := os.Stat(target)
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if err != nil {
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t.Fatalf("stat: %v", err)
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}
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// Reset the sync.Once so a second call would re-extract if not for the
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// sentinel short-circuit. Without the reset, sync.Once would skip the
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// extraction regardless of sentinel state.
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resetOnce(cacheDir)
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if _, err := Ensure(src, base, "v1"); err != nil {
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t.Fatalf("second Ensure: %v", err)
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}
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info2, err := os.Stat(target)
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if err != nil {
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t.Fatalf("stat second: %v", err)
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}
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if !info2.ModTime().Equal(info1.ModTime()) {
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t.Fatalf("expected file untouched on sentinel match; got mtime %v -> %v", info1.ModTime(), info2.ModTime())
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}
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}
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func TestEnsureReExtractsOnVersionChange(t *testing.T) {
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v1 := fstest.MapFS{
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"last30days.py": &fstest.MapFile{Data: []byte("v1\n"), Mode: 0o644},
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}
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v2 := fstest.MapFS{
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"last30days.py": &fstest.MapFile{Data: []byte("v2\n"), Mode: 0o644},
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}
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base := t.TempDir()
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cache1, err := Ensure(v1, base, "v1")
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if err != nil {
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t.Fatalf("Ensure v1: %v", err)
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}
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cache2, err := Ensure(v2, base, "v2")
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if err != nil {
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t.Fatalf("Ensure v2: %v", err)
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}
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if cache1 == cache2 {
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t.Fatalf("expected distinct cache dirs per version, got %q == %q", cache1, cache2)
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}
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mustReadFile(t, filepath.Join(cache1, "last30days.py"), "v1\n")
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mustReadFile(t, filepath.Join(cache2, "last30days.py"), "v2\n")
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}
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func TestEnsureConcurrentFirstCall(t *testing.T) {
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src := newTestFS()
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base := t.TempDir()
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const goroutines = 10
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var wg sync.WaitGroup
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wg.Add(goroutines)
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results := make([]string, goroutines)
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errs := make([]error, goroutines)
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for i := 0; i < goroutines; i++ {
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i := i
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go func() {
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defer wg.Done()
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results[i], errs[i] = Ensure(src, base, "v1")
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}()
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}
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wg.Wait()
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for i, err := range errs {
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if err != nil {
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t.Fatalf("goroutine %d: %v", i, err)
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}
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}
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for i := 1; i < goroutines; i++ {
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if results[i] != results[0] {
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t.Fatalf("goroutine 0 saw %q, goroutine %d saw %q", results[0], i, results[i])
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}
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}
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mustReadFile(t, filepath.Join(results[0], "last30days.py"), "# last30days entry\n")
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}
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func TestEnsureRejectsEmptyVersion(t *testing.T) {
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if _, err := Ensure(newTestFS(), t.TempDir(), ""); err == nil {
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t.Fatal("expected error for empty version")
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}
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}
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func TestEnsureReturnsErrorWhenCacheUnwritable(t *testing.T) {
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// Place the cache root at a path that cannot exist (a regular file).
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// MkdirAll will refuse and Ensure must surface a wrapped error.
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base := t.TempDir()
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blocker := filepath.Join(base, "blocker")
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if err := os.WriteFile(blocker, []byte("not a dir"), 0o644); err != nil {
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t.Fatalf("setup: %v", err)
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}
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_, err := Ensure(newTestFS(), blocker, "v1")
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if err == nil {
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t.Fatal("expected error when cache parent is not a directory")
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}
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}
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func TestEnsureUserCacheHonorsOverride(t *testing.T) {
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override := t.TempDir()
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t.Setenv(CacheEnvOverride, override)
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src := newTestFS()
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cacheDir, err := EnsureUserCache(src, "v1")
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if err != nil {
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t.Fatalf("EnsureUserCache: %v", err)
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}
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want := filepath.Join(override, cacheSubdir, "v1")
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if cacheDir != want {
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t.Fatalf("cacheDir = %q, want %q", cacheDir, want)
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}
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mustReadFile(t, filepath.Join(cacheDir, "last30days.py"), "# last30days entry\n")
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}
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func mustReadFile(t *testing.T, path, want string) {
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t.Helper()
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data, err := os.ReadFile(path)
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if err != nil {
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t.Fatalf("read %s: %v", path, err)
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}
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if string(data) != want {
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t.Fatalf("%s: got %q, want %q", path, string(data), want)
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}
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}
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@@ -0,0 +1,2 @@
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Populated at build time by scripts/sync-engine.sh.
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Source of truth: skills/last30days/scripts/.
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@@ -11,15 +11,18 @@ SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
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MCP_DIR="$(cd "${SCRIPT_DIR}/.." && pwd)"
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REPO_ROOT="$(cd "${MCP_DIR}/.." && pwd)"
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ENGINE_SRC="${REPO_ROOT}/skills/last30days/scripts"
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VENDORED="${MCP_DIR}/vendored"
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# Embed path must live inside the consuming package (Go //go:embed cannot
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# reach outside its own directory tree), so vendored/ sits under engine/.
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VENDORED="${MCP_DIR}/internal/engine/vendored"
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if [ ! -f "${ENGINE_SRC}/last30days.py" ]; then
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echo "sync-engine: ${ENGINE_SRC}/last30days.py not found" >&2
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exit 1
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fi
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rm -rf "${VENDORED}"
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mkdir -p "${VENDORED}"
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# Clear stale content while keeping the .gitkeep that anchors the embed path.
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find "${VENDORED}" -mindepth 1 -not -name ".gitkeep" -delete
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# Copy the entry script and the lib/ tree (modules + lib/vendor/).
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cp "${ENGINE_SRC}/last30days.py" "${VENDORED}/last30days.py"
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|
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Reference in New Issue
Block a user