Summary

Phase 5 of the ecosystem-wide directory structure standardization. monitoring_system has a 997-line root CMakeLists.txt that maintains a legacy/new dual structure with 13 hardcoded .cpp paths as fallback. Remove the legacy fallback, regularize the src/{context,core,impl,platform,plugins}/ layout, and decompose the CMake configuration per the canonical template.

Part of kcenon/common_system#657 (master EPIC).

Why

• The 997-line root CMakeLists.txt is bloated primarily because it supports two structural layouts simultaneously (legacy fallback path)
• 13 hardcoded .cpp file paths in build config drift silently as files move
• The flat 37 test files under tests/ do not mirror src/, making test-to-source navigation harder than it needs to be

Scope

1. Identify and remove the legacy/fallback branch in CMakeLists.txt
2. Reorganize src/{context,core,impl,platform,plugins}/ to match the standard (consolidate impl/ into feature directories)
3. Replace 13 hardcoded .cpp paths with glob or feature-grouped target sources
4. Decompose 997-line root CMakeLists.txt into cmake/*.cmake modules per canonical template
5. Reorganize tests/ to mirror src/ (or document deliberate flat layout)

Child Issues

• [#674-1/5] Consolidate src/impl/ into feature directories #675 — Consolidate src/impl/ into feature directories
• [#674-2/5] Remove legacy CMake fallback branch #676 — Remove legacy CMake fallback branch
• [#674-3/5] Replace remaining hardcoded .cpp lists with structured globbing #677 — Replace remaining hardcoded .cpp lists with structured globbing
• [#674-4/5] Decompose 996-line CMakeLists.txt into cmake/ modules #678 — Decompose 996-line CMakeLists.txt into cmake/ modules
• [#674-5/5] Reorganize tests/ to mirror src/ (or document deliberate flat layout) #679 — Reorganize tests/ to mirror src/ (or document deliberate flat layout)

Execution order: #675 → #676 → #677 → #678 → #679 (sequential, dependency-ordered).

Acceptance Criteria

• Single CMake build path; no legacy/new branch in any CMakeLists.txt
• No hardcoded .cpp file lists in build config
• cmake modules match the canonical template
• Test files organized to mirror src/ or with documented rationale
• All downstream consumers (pacs, network) build unchanged