feat(cooldown): respect trusted_packages in dependency cooldown (#342)

* feat(cooldown): respect trusted_packages in dependency cooldown

Trusted packages are now treated as a superset waiver that bypasses every
PMG control (malware analysis, cooldown, and any future controls). A
globally trusted package is automatically exempt from the cooldown window
and no longer needs a duplicate entry in dependency_cooldown.skip.

The skip list remains the narrower, cooldown-only waiver for packages
that must bypass the cooldown wait but still be malware-scanned.

* refactor(cooldown): tag skip reason and audit-log skipped packages

Address review feedback on #342:

- Restore cooldownSkip to a pure single-list function (SRP); the merge
  into trusted_packages now happens in a separate mergeCooldownSkip step,
  driven by the exported CooldownSkip wrapper.
- Extend CooldownSkipInfo with a CooldownSkipReason (TrustedPackage /
  CooldownSkipList) on both SkipAll and per-version entries, so callers
  can tell apart the broad waiver from the cooldown-only one. When both
  lists match the same package, trusted_packages wins.
- Add audit.LogCooldownSkipped and emit it from the npm and PyPI
  interceptors on the SkipAll path, alongside the existing info log,
  carrying the source list as the reason.

* refactor(cooldown): inline list merge, audit per-version exemptions

Address further review feedback:

- Drop the separate mergeCooldownSkip helper; cooldownSkip now writes
  into a shared *CooldownSkipInfo and is called twice from CooldownSkip
  (cooldown skip list first, trusted_packages on top so trusted entries
  override the reason on overlap).
- Audit log every exemption, not just SkipAll: a new auditCooldownSkip
  helper in proxy/interceptors/cooldown.go emits one event per match
  (package-wide or per-version), each tagged with its source list.
  LogCooldownSkipped gains a version argument for the per-version case.
- Cover the trusted_packages reason path in TestCooldownSkip.

* fix(cooldown): avoid double-auditing trusted package exemptions

auditCooldownSkip now only emits EventTypeCooldownSkipped for entries
that came from dependency_cooldown.skip. Trusted-package exemptions
already get an EventTypeInstallTrustedAllowed event at tarball-download
time (proxy/interceptors/base_registry.go), so emitting a cooldown event
for them too would double-count the same waiver.

* emit trusted and cooldown skip events to cloud

* fix tests

* refactor(cooldown): return value from collectCooldownSkip, short-circuit on trusted SkipAll

Address PR review feedback:
- Rename cooldownSkip to collectCooldownSkip and return CooldownSkipInfo
  instead of mutating an input pointer.
- Add mergeCooldownSkip to combine per-list results with trusted_packages
  taking precedence on overlap.
- CooldownSkip now consults trusted_packages first and returns immediately
  on a package-wide trusted exemption (DC skip list cannot add anything).
- Extend tests to cover disjoint pinned entries across both lists and the
  case where DC version-less subsumes a trusted pinned entry.

* fix(audit): address cooldown review feedback

* fix(cooldown): audit cooldown skips at download time with concrete version

Backend rejects PackageVersion messages without a version, and audit logs
should reflect the runtime fact (a specific version was skipped) rather
than the config rule. Move the audit emission from metadata-request
handling to download-request handling, where the concrete version is
known, and require version in LogCooldownSkipped.

* chore(audit): drop dead scope assignment in LogCooldownSkipped

* refactor(cooldown): move skip-list logic into cooldown handlers

Registry interceptors no longer compute CooldownSkip or branch on SkipAll;
they just call HandleMetadataRequest. The npm and pypi cooldown handlers
own the skip lookup, the package-wide exemption short-circuit, and (for
pypi) the canonical-name denormalization. Also align LogCooldownSkipped
with other LogXxx signatures by taking *packagev1.PackageVersion.

* fix: Simplify audit logging for dependency cooldown skip

* refactor: Simplify cooldown handling and maintain separation of concepts for trusted and DC skip packages

* fix: Code review fixes

* fix: Emit cooldown skipped audit event ONLY when an in-window version is skipped

---------

Co-authored-by: Abhisek Datta <abhisek.datta@gmail.com>

proxy/interceptors/base_registry.go

@@ -71,6 +71,36 @@ func (b *baseRegistryInterceptor) HandleRequest(ctx *proxy.RequestContext) (*pro
 	return &proxy.InterceptorResponse{Action: proxy.ActionAllow}, nil
 }
 
+// fastAllow short-circuits the request when no security control should run for
+// this concrete version: insecure-installation mode (analysis globally off) or a
+// trusted package (waives every control). It returns (response, true) when it
+// handled the request; (nil, false) otherwise. Insecure is checked first to
+// preserve the previous ordering inside analyzePackage.
+func (b *baseRegistryInterceptor) fastAllow(
+	ctx *proxy.RequestContext,
+	ecosystem packagev1.Ecosystem,
+	name, version string,
+) (*proxy.InterceptorResponse, bool) {
+	pkgVersion := &packagev1.PackageVersion{
+		Package: &packagev1.Package{Ecosystem: ecosystem, Name: name},
+		Version: version,
+	}
+
+	if config.Get().InsecureInstallation {
+		log.Debugf("[%s] Skipping insecure installation", ctx.RequestID)
+		audit.LogInstallInsecureBypass(pkgVersion)
+		return &proxy.InterceptorResponse{Action: proxy.ActionAllow}, true
+	}
+
+	if config.IsTrustedPackageRef(ecosystem, name, version) {
+		log.Debugf("[%s] Skipping trusted package: %s/%s@%s", ctx.RequestID, ecosystem.String(), name, version)
+		audit.LogInstallTrustedAllowed(pkgVersion)
+		return &proxy.InterceptorResponse{Action: proxy.ActionAllow}, true
+	}
+
+	return nil, false
+}
+
 // analyzePackage analyzes a package using the configured analyzer with caching
 // This method is ecosystem-agnostic and can be used by any registry interceptor
 func (b *baseRegistryInterceptor) analyzePackage(
@@ -79,7 +109,6 @@ func (b *baseRegistryInterceptor) analyzePackage(
 	packageName string,
 	packageVersion string,
 ) (*analyzer.PackageVersionAnalysisResult, error) {
-	// Check if package is trusted before analyzing
 	pkgVersion := &packagev1.PackageVersion{
 		Package: &packagev1.Package{
 			Ecosystem: ecosystem,
@@ -88,29 +117,6 @@ func (b *baseRegistryInterceptor) analyzePackage(
 		Version: packageVersion,
 	}
 
-	if cfg := config.Get(); cfg.InsecureInstallation {
-		log.Debugf("[%s] Skipping insecure installation", ctx.RequestID)
-
-		audit.LogInstallInsecureBypass(pkgVersion)
-
-		return &analyzer.PackageVersionAnalysisResult{
-			PackageVersion: pkgVersion,
-			Action:         analyzer.ActionAllow,
-		}, nil
-	}
-
-	if config.IsTrustedPackage(pkgVersion) {
-		log.Debugf("[%s] Skipping trusted package: %s/%s@%s",
-			ctx.RequestID, ecosystem.String(), packageName, packageVersion)
-
-		audit.LogInstallTrustedAllowed(pkgVersion)
-
-		return &analyzer.PackageVersionAnalysisResult{
-			PackageVersion: pkgVersion,
-			Action:         analyzer.ActionAllow,
-		}, nil
-	}
-
 	if cached, ok := b.cache.Get(ecosystem.String(), packageName, packageVersion); ok {
 		log.Debugf("[%s] Using cached analysis result for %s@%s", ctx.RequestID, packageName, packageVersion)
 		return cached, nil