Fix caching gaps and reduce Pathname overhead in file lookups (#161)

Cache nil results in TeamFinder.for_file when RustCodeOwners returns nil,
preventing repeated uncached calls to the Rust layer for unowned files.
Memoize Pathname.pwd and use string prefix stripping instead of
Pathname#relative_path_from for the common case, eliminating costly
Pathname allocations and cleanpath operations.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: pharris2411

lib/code_ownership.rb

@@ -315,5 +315,7 @@ def self.for_package(package)
   sig { void }
   def self.bust_caches!
     Private::FilePathTeamCache.bust_cache!
+    Private::FilePathFinder.instance_variable_set(:@pwd, nil)
+    Private::FilePathFinder.instance_variable_set(:@pwd_prefix, nil)
   end
 end

lib/code_ownership/private/file_path_finder.rb

@@ -6,13 +6,29 @@ module Private
     module FilePathFinder
       extend T::Sig
 
+      sig { returns(String) }
+      def self.pwd_prefix
+        @pwd_prefix ||= T.let("#{Dir.pwd}/", T.nilable(String))
+      end
+
+      sig { returns(Pathname) }
+      def self.pwd
+        @pwd ||= T.let(Pathname.pwd, T.nilable(Pathname))
+      end
+
       # Returns a string version of the relative path to a Rails constant,
       # or nil if it can't find anything
       sig { params(klass: T.nilable(T.any(T::Class[T.anything], T::Module[T.anything]))).returns(T.nilable(String)) }
       def self.path_from_klass(klass)
         if klass
           path = Object.const_source_location(klass.to_s)&.first
-          (path && Pathname.new(path).relative_path_from(Pathname.pwd).to_s) || nil
+          return nil unless path
+
+          if path.start_with?(pwd_prefix)
+            path.delete_prefix(pwd_prefix)
+          else
+            Pathname.new(path).relative_path_from(pwd).to_s
+          end
         end
       rescue NameError
         nil
@@ -30,15 +46,15 @@ def self.from_backtrace(backtrace)
         #   ./app/controllers/some_controller.rb:43:in `block (3 levels) in create'
         #
         backtrace_line = if RUBY_VERSION >= '3.4.0'
-                           %r{\A(#{Pathname.pwd}/|\./)?
+                           %r{\A(#{pwd}/|\./)?
                                (?<file>.+)       # Matches 'app/controllers/some_controller.rb'
                                :
                                (?<line>\d+)      # Matches '43'
                                :in\s
                                '(?<function>.*)' # Matches "`block (3 levels) in create'"
                              \z}x
                          else
-                           %r{\A(#{Pathname.pwd}/|\./)?
+                           %r{\A(#{pwd}/|\./)?
                                (?<file>.+)       # Matches 'app/controllers/some_controller.rb'
                                :
                                (?<line>\d+)      # Matches '43'

lib/code_ownership/private/team_finder.rb

@@ -13,9 +13,8 @@ def self.for_file(file_path, allow_raise: false)
         return FilePathTeamCache.get(file_path) if FilePathTeamCache.cached?(file_path)
 
         result = T.let(RustCodeOwners.for_file(file_path), T.nilable(T::Hash[Symbol, String]))
-        return if result.nil?
 
-        if result[:team_name].nil?
+        if result.nil? || result[:team_name].nil?
           FilePathTeamCache.set(file_path, nil)
         else
           FilePathTeamCache.set(file_path, T.let(find_team!(T.must(result[:team_name]), allow_raise: allow_raise), T.nilable(CodeTeams::Team)))

spec/lib/code_ownership/private/team_finder_spec.rb

@@ -20,11 +20,16 @@
       expect(CodeOwnership::Private::FilePathTeamCache.cached?(file_path)).to be true
     end
 
-    it 'does not cache when rust returns nil' do
-      allow(RustCodeOwners).to receive(:for_file).with(file_path).and_return(nil)
+    it 'caches nil when rust returns nil' do
+      allow(RustCodeOwners).to receive(:for_file).with(file_path)
+        .and_return(nil, { team_name: 'Bar' })
 
-      expect(described_class.for_file(file_path)).to be_nil
-      expect(CodeOwnership::Private::FilePathTeamCache.cached?(file_path)).to be false
+      first = described_class.for_file(file_path)
+      second = described_class.for_file(file_path)
+
+      expect(first).to be_nil
+      expect(second).to be_nil
+      expect(CodeOwnership::Private::FilePathTeamCache.cached?(file_path)).to be true
     end
 
     it 'caches nil when team_name is nil' do