fix: improve error handling and empty config behavior in TailContextInput

- Add warning log when tail_context command fails with exit status
- Change empty config behavior from break to sleep+continue for hot-reload support
- Update RBS type definitions for detector and tail_context_input
- Add tests for error logging and empty config loop behavior

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: iberianpig

lib/fusuma/plugin/inputs/tail_context_input.rb

@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require "open3"
 require_relative "input"
 
 module Fusuma
@@ -30,15 +31,19 @@ def start(reader, writer)
         # Returns nil on failure
         #: (String) -> String?
         def execute_command(command)
-          result = `#{command}`
-          return nil unless $?.success?
+          stdout, stderr, status = Open3.capture3(command)
+          unless status.success?
+            MultiLogger.warn "tail_context command failed: #{command} (exit status: #{status.exitstatus})"
+            MultiLogger.warn "  stderr: #{stderr}" unless stderr.empty?
+            return nil
+          end
 
-          result.strip
+          stdout.strip
         end
 
         # Reads the tail_context section from the config file
         # Returns an empty Hash if no config is found
-        #: () -> Hash[untyped, untyped]
+        #: () -> (String | Hash[untyped, untyped] | Integer | Float)
         def tail_contexts
           Config.search(Config::Index.new(:tail_context)) || {}
         end
@@ -70,10 +75,14 @@ def create_io
           IO.pipe
         end
 
+        #: (StringIO) -> void
         def watch_loop(writer)
           loop do
             contexts = tail_contexts
-            break if contexts.empty?
+            if contexts.empty?
+              sleep DEFAULT_INTERVAL
+              next
+            end
 
             contexts.each do |name, config|
               command = config[:command]

sig/generated/lib/fusuma/plugin/detectors/detector.rbs

@@ -29,8 +29,8 @@ module Fusuma
 
         # @param record [Events::Records::Record]
         # @return [Events::Event]
-        # : (record: Fusuma::Plugin::Events::Records::IndexRecord) -> Fusuma::Plugin::Events::Event
-        def create_event: (record: Fusuma::Plugin::Events::Records::IndexRecord) -> Fusuma::Plugin::Events::Event
+        # : (record: Fusuma::Plugin::Events::Records::Record) -> Fusuma::Plugin::Events::Event
+        def create_event: (record: Fusuma::Plugin::Events::Records::Record) -> Fusuma::Plugin::Events::Event
 
         # : () -> Time
         def last_time: () -> Time

sig/generated/lib/fusuma/plugin/inputs/tail_context_input.rbs

@@ -19,8 +19,8 @@ module Fusuma
 
         # Reads the tail_context section from the config file
         # Returns an empty Hash if no config is found
-        # : () -> Hash[untyped, untyped]
-        def tail_contexts: () -> Hash[untyped, untyped]
+        # : () -> (String | Hash[untyped, untyped] | Integer | Float)
+        def tail_contexts: () -> (String | Hash[untyped, untyped] | Integer | Float)
 
         # Executes the specified command periodically and
         # writes to writer in "name:value" format only when the value changes
@@ -36,7 +36,8 @@ module Fusuma
 
         def create_io: () -> untyped
 
-        def watch_loop: (untyped writer) -> untyped
+        # : (StringIO) -> void
+        def watch_loop: (StringIO) -> void
 
         def find_min_interval: (untyped contexts) -> untyped
       end

spec/fusuma/plugin/inputs/tail_context_input_spec.rb

@@ -44,6 +44,17 @@ module Inputs
             result = @input.execute_command("exit 1")
             expect(result).to be_nil
           end
+
+          it "logs warning with MultiLogger.warn when command fails" do
+            expect(MultiLogger).to receive(:warn).with(/tail_context command failed:.*exit 1.*exit status: 1/)
+            @input.execute_command("exit 1")
+          end
+
+          it "logs stderr when command fails with error output" do
+            expect(MultiLogger).to receive(:warn).with(/tail_context command failed:/)
+            expect(MultiLogger).to receive(:warn).with(/stderr:.*error message/)
+            @input.execute_command("echo 'error message' >&2 && exit 1")
+          end
         end
 
         describe "#tail_contexts" do
@@ -130,6 +141,33 @@ module Inputs
             expect(@writer.read).to eq ""
           end
         end
+
+        describe "#watch_loop (private)" do
+          before do
+            @writer = StringIO.new
+            @input.reset_last_values
+          end
+
+          it "sleeps DEFAULT_INTERVAL and continues loop when config is empty" do
+            call_count = 0
+            allow(@input).to receive(:tail_contexts) do
+              call_count += 1
+              raise StopIteration if call_count > 2
+              {}
+            end
+            allow(@input).to receive(:sleep).with(1.0)
+
+            expect(@input).to receive(:sleep).with(1.0).at_least(:once)
+
+            begin
+              @input.send(:watch_loop, @writer)
+            rescue StopIteration
+              # expected
+            end
+
+            expect(call_count).to be > 1
+          end
+        end
       end
     end
   end