add agent tool use formatter

lib/roast/cogs/agent/providers/claude/tool_use.rb

@@ -266,6 +266,33 @@ def format_task
               details.empty? ? "TASK #{description}" : "TASK #{description} (#{details})"
             end
 
+            # Formats an Agent tool-use line.
+            #
+            # Input fields:
+            #   :description       (String) – short label for the work        [required]
+            #   :run_in_background (bool)   – run the agent asynchronously     [optional]
+            #   :subagent_type     (String) – which agent type to spawn        [optional]
+            #
+            # Output: "AGENT <description>", with " (<details>)" appended when any
+            # optional field is set: "background" (when :run_in_background is set),
+            # then :subagent_type — joined with " · " in that order and shown as raw
+            # values (no key= labels). :description is truncated to TRUNCATE_LIMIT
+            # chars; :subagent_type is not.
+            #
+            # Examples:
+            #   AGENT Find all callers (background · Explore)
+            #   AGENT Summarize the diff
+            #
+            #: () -> String
+            def format_agent
+              description = truncate(input[:description])
+              details = [
+                ("background" if input[:run_in_background]),
+                input[:subagent_type],
+              ].compact.join(" · ")
+              details.empty? ? "AGENT #{description}" : "AGENT #{description} (#{details})"
+            end
+
             #: () -> String
             def format_unknown
               "UNKNOWN [#{name}] #{input.inspect}"

test/roast/cogs/agent/providers/claude/tool_use_test.rb

@@ -338,6 +338,36 @@ class ToolUseTest < ActiveSupport::TestCase
               assert_equal "TASK #{truncated} (#{long} · #{long})", output
             end
 
+            # format_agent
+
+            test "format_agent renders the description alone with no optional fields" do
+              tool_use = ToolUse.new(name: :agent, input: { description: "Find all callers" })
+
+              output = tool_use.format
+
+              assert_equal "AGENT Find all callers", output
+            end
+
+            test "format_agent renders the description with all optional fields" do
+              input = { description: "Audit", run_in_background: true, subagent_type: "Explore" }
+              tool_use = ToolUse.new(name: :agent, input: input)
+
+              output = tool_use.format
+
+              assert_equal "AGENT Audit (background · Explore)", output
+            end
+
+            test "format_agent truncates the description but not the subagent type" do
+              long = "a" * (ToolUse::TRUNCATE_LIMIT + 10)
+              truncated = "#{"a" * (ToolUse::TRUNCATE_LIMIT - 3)}..."
+              input = { description: long, subagent_type: long }
+              tool_use = ToolUse.new(name: :agent, input: input)
+
+              output = tool_use.format
+
+              assert_equal "AGENT #{truncated} (#{long})", output
+            end
+
             test "format calls format_unknown for unknown tool" do
               tool_use = ToolUse.new(name: :unknown_tool, input: { arg: "value" })