feat(skill): add Gecode CMake guidance

Author: zayenz

README.md

@@ -32,6 +32,7 @@ The skill routes internally to focused reference documents for:
 - memory management
 - built-in search engines
 - custom search engine implementation
+- downstream CMake consumption
 
 ## Contributing
 

evals/gecode-trigger-evals.json

@@ -15,6 +15,10 @@
     "query": "Can you help debug a Gecode issue where a stored choice seems invalid after recomputation? The model uses custom branchers and I suspect I'm breaking clone or commit invariants.",
     "should_trigger": true
   },
+  {
+    "query": "I am packaging a C++ solver that depends on Gecode 6.3+ and I want the downstream CMake project to use find_package(Gecode CONFIG) with a FetchContent fallback when it's not installed.",
+    "should_trigger": true
+  },
   {
     "query": "Please model this scheduling problem in Gecode with strong global constraints, sensible symmetry breaking, and a branching strategy that focuses on the cost-driving variables first.",
     "should_trigger": true
@@ -35,6 +39,10 @@
     "query": "I'm using Gecode with a mix of discrete choices and continuous tolerances. What should I watch out for when float vars are part of the model, especially compared with ordinary integer branching intuition?",
     "should_trigger": true
   },
+  {
+    "query": "I need to clean up a generic CMakeLists.txt for a small SDL app. There is no Gecode involved, I just want better target_link_libraries usage and install rules.",
+    "should_trigger": false
+  },
   {
     "query": "How would you model a nurse rostering problem in constraint programming? I'm open to any solver or even OR-Tools, I mainly want high-level CP advice.",
     "should_trigger": false
@@ -47,6 +55,10 @@
     "query": "Can you explain branch and bound versus depth-first search in general terms? I don't need implementation details for any particular library.",
     "should_trigger": false
   },
+  {
+    "query": "I have an old FindFoo.cmake module and want to migrate to package config usage. The library is our in-house SDK, not Gecode.",
+    "should_trigger": false
+  },
   {
     "query": "What are good heuristics for graph coloring in CP, and how do I think about symmetry? Solver-agnostic advice is fine.",
     "should_trigger": false

skills/gecode/SKILL.md

@@ -1,6 +1,6 @@
 ---
 name: gecode
-description: "Gecode architecture, modeling, cookbook-style modeling patterns, set/float/scheduling guidance, propagators, branchers, memory management, search engine usage and implementation, recomputation/cloning behavior, and debugging/performance diagnosis. Use for any materially Gecode-specific task: building or refining Gecode models, implementing custom constraints or branchers, tuning DFS/BAB/RBS/PBS/LDS search, diagnosing weak propagation or search pathologies, or reasoning about set/float/resource-style models."
+description: "Gecode architecture, modeling, cookbook-style modeling patterns, set/float/scheduling guidance, propagators, branchers, memory management, search engine usage and implementation, recomputation/cloning behavior, debugging/performance diagnosis, and downstream CMake consumption. Use for any materially Gecode-specific task: building or refining Gecode models, implementing custom constraints or branchers, tuning DFS/BAB/RBS/PBS/LDS search, diagnosing weak propagation or search pathologies, reasoning about set/float/resource-style models, or integrating Gecode into CMake projects."
 ---
 
 # Gecode
@@ -47,6 +47,7 @@ Use this skill as the entry point for any Gecode-specific task. Carry the univer
 - Read `references/memory-handling.md` for space/region/heap allocation, handles, clone footprint, and disposal obligations.
 - Read `references/search-engines.md` for using and tuning built-in engines such as `DFS`, `BAB`, `LDS`, restart, and portfolio search.
 - Read `references/search-engine-implementation.md` for custom engine orchestration, recomputation strategy, LAO, and completeness invariants.
+- Read `references/cmake-consumption.md` for `find_package(Gecode CONFIG)`, target usage, version checks, and vendored fallback patterns.
 - Read `references/general-knowledge.md` only for broad conceptual explanations, tracing/observability guidance, or staged model-improvement workflow discussion that goes beyond the always-on mental model.
 
 ## Operating Rules
@@ -68,3 +69,4 @@ Use this skill as the entry point for any Gecode-specific task. Carry the univer
 - `references/memory-handling.md`: memory areas, lazy vs eager allocation, shared/local handles, and `AP_DISPOSE` discipline.
 - `references/search-engines.md`: engine selection, restart/portfolio tradeoffs, no-goods, parallel semantics, and completeness caveats.
 - `references/search-engine-implementation.md`: custom engine state, replay/recomputation, ownership, branch-and-bound integration, and invariants.
+- `references/cmake-consumption.md`: package-config integration, exported targets, component selection, and fetch fallback.

skills/gecode/references/cmake-consumption.md

@@ -0,0 +1,39 @@
+# Gecode CMake Consumption
+
+## Core
+- Prefer config-package consumption: `find_package(Gecode CONFIG REQUIRED)`.
+- Link downstream targets to `Gecode::gecode` unless explicit component granularity is required.
+- Require `Gecode_VERSION >= 6.3.0` and use package version checks rather than parsing `gecode/support/config.hpp`.
+- Hint package location with `Gecode_ROOT` or `CMAKE_PREFIX_PATH`.
+- Keep `cmake_minimum_required(VERSION 3.21)` or newer for parity with Gecode's build.
+
+## Key Patterns
+- Minimal integration:
+  ```cmake
+  find_package(Gecode CONFIG REQUIRED)
+  target_link_libraries(app PRIVATE Gecode::gecode)
+  ```
+- Component-specific integration:
+  ```cmake
+  find_package(Gecode CONFIG REQUIRED COMPONENTS driver)
+  target_link_libraries(app PRIVATE Gecode::gecodedriver)
+  ```
+- Version guard:
+  ```cmake
+  if(SOME_STRICT_OPTION AND Gecode_VERSION VERSION_LESS "6.3.0")
+    message(FATAL_ERROR "Gecode >= 6.3.0 required, found ${Gecode_VERSION}")
+  endif()
+  ```
+- Try installed package first with `find_package(Gecode CONFIG QUIET)` when discovery is optional.
+- If the package is absent and project policy allows vendoring, use `FetchContent` and set Gecode cache options before `FetchContent_MakeAvailable(...)`.
+- Require `TARGET Gecode::gecode` after resolution and fail fast with actionable error text if it is missing.
+- Mark Gecode targets as `SYSTEM` in strict-warning projects to isolate third-party headers from local warning policy.
+- For pinned source fallbacks, prefer stable release tags or commits over long-lived feature branches.
+- When migrating away from custom discovery modules, remove manual imported-target composition and library probing once package config is the baseline.
+- Keep strict version toggles if desired, but enforce them against `Gecode_VERSION`.
+
+## Pitfalls
+- Calling `find_package(Gecode REQUIRED)` without `CONFIG` and accidentally resolving old module-mode shims.
+- Assuming optional components exist without checking enabled modules in the installed build.
+- Mixing custom imported-target composition with package-provided targets in the same code path.
+- Parsing headers for version when package metadata already provides `Gecode_VERSION`.