story-kit: create 318_refactor_split_mcp_rs_into_domain_specific_tool_modules

.story_kit/work/1_backlog/318_refactor_split_mcp_rs_into_domain_specific_tool_modules.md

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+---
+name: "Split mcp.rs into domain-specific tool modules"
+---
+
+# Refactor 318: Split mcp.rs into domain-specific tool modules
+
+## Current State
+
+- TBD
+
+## Desired State
+
+mcp.rs is 4,925 lines containing all MCP tool definitions and handlers in a single file. Split by domain:
+- mcp/mod.rs — JSON-RPC dispatch, tools list registration
+- mcp/story_tools.rs — create_story, update_story, check_criterion, add_criterion, accept_story, move_story
+- mcp/agent_tools.rs — start_agent, stop_agent, list_agents, get_agent_output, wait_for_agent
+- mcp/merge_tools.rs — merge_agent_work, get_merge_status, move_story_to_merge, report_merge_failure
+- mcp/qa_tools.rs — request_qa, approve_qa, reject_qa, launch_qa_app
+- mcp/diagnostics.rs — get_server_logs, get_pipeline_status, get_token_usage, rebuild_and_restart
+- Tests split into corresponding test modules
+
+## Acceptance Criteria
+
+- [ ] mcp.rs split into domain-specific modules under http/mcp/
+- [ ] JSON-RPC dispatch remains in mod.rs, delegates to domain handlers
+- [ ] All tool handler signatures unchanged
+- [ ] All existing tests pass
+- [ ] No public API changes
+
+## Out of Scope
+
+- TBD