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/pypi_registry.go

@@ -126,20 +126,10 @@ func (i *PypiRegistryInterceptor) HandleRequest(ctx *proxy.RequestContext) (*pro
 		// for version resolution. JSON API requests (/pypi/{pkg}/json) are allowed through;
 		// they have a different response structure and pip does not use them for installs.
 		if depCooldownConfig.Enabled && strings.HasPrefix(ctx.URL.Path, "/simple/") {
-			// Match the skip list against the normalized name (lowercase, _/. → -),
-			// the same canonical form used for pinned-version lookups, so a PURL
-			// like pkg:pypi/My_Pkg reliably matches the resolved request name.
-			skip := pmgconfig.CooldownSkip(packagev1.Ecosystem_ECOSYSTEM_PYPI, denormalizePyPIPackageName(pkgInfo.GetName()))
-			if skip.SkipAll {
-				// Whole package is on the cooldown skip list: pass metadata through
-				// unmodified. The tarball download still hits analyzePackage, so
-				// malware analysis is preserved.
-				log.Infof("[%s] Cooldown: package %s is on the skip list (dependency_cooldown.skip); malware analysis still applies", ctx.RequestID, pkgInfo.GetName())
+			if pmgconfig.IsTrustedPackageAllVersions(packagev1.Ecosystem_ECOSYSTEM_PYPI, denormalizePyPIPackageName(pkgInfo.GetName())) {
 				return &proxy.InterceptorResponse{Action: proxy.ActionAllow}, nil
 			}
-
-			// Version-pinned skip entries (if any) are preserved during stripping.
-			return i.cooldownHandler.HandleMetadataRequest(ctx, pkgInfo.GetName(), depCooldownConfig.Days, i.execContext.PinnedVersions[pkgInfo.GetName()], skip.Versions)
+			return i.cooldownHandler.HandleMetadataRequest(ctx, pkgInfo.GetName(), depCooldownConfig.Days, i.execContext.PinnedVersions[pkgInfo.GetName()])
 		}
 
 		log.Debugf("[%s] Skipping analysis for metadata request: %s", ctx.RequestID, pkgInfo.GetName())
@@ -153,6 +143,14 @@ func (i *PypiRegistryInterceptor) HandleRequest(ctx *proxy.RequestContext) (*pro
 		return &proxy.InterceptorResponse{Action: proxy.ActionAllow}, nil
 	}
 
+	// Canonical name is used for identity checks (trusted, cooldown); raw name
+	// is kept for analyzePackage so malware analysis sees the original form.
+	canonicalName := denormalizePyPIPackageName(pkgInfo.GetName())
+
+	if resp, ok := i.fastAllow(ctx, packagev1.Ecosystem_ECOSYSTEM_PYPI, canonicalName, pkgInfo.GetVersion()); ok {
+		return resp, nil
+	}
+
 	// Get file type for logging if available
 	fileType := ""
 	if pypiInfo, ok := pkgInfo.(*pypiPackageInfo); ok {