tests : add fusion baseline README and broaden fusion CI triggers (#28893)

* tests : add README for updating the per-backend fusion baselines

Assisted-by: pi:llama.cpp/Qwen3.8-27B

* ci : trigger fusion on changes to test-llama-archs.cpp and src/models

the dummy models and their architectures drive the fusion baselines, so a
change to either can alter the per-fusion counters and should re-run the
fusion job.

Assisted-by: pi:llama.cpp/Qwen3.8-27B

* tests : merge the fusion build commands in the README

assisted-by: pi:llama.cpp/Qwen3.8-27B

* pi : require explicit permission before posting PR/issue comments

assisted-by: pi:llama.cpp/Qwen3.8-27B

.github/workflows/fusion.yml

@@ -9,7 +9,9 @@ on:
       '.github/workflows/fusion.yml',
       'ggml/**',
       'tests/fusion/**',
-      'tests/test-fusion.cpp'
+      'tests/test-fusion.cpp',
+      'tests/test-llama-archs.cpp',
+      'src/models/**'
     ]
 
   pull_request:
@@ -18,7 +20,9 @@ on:
       '.github/workflows/fusion.yml',
       'ggml/**',
       'tests/fusion/**',
-      'tests/test-fusion.cpp'
+      'tests/test-fusion.cpp',
+      'tests/test-llama-archs.cpp',
+      'src/models/**'
     ]
 
 concurrency:

.pi/gg/SYSTEM.md

@@ -23,6 +23,7 @@ Pull requests (PRs):
 - For the AI usage disclosure section, write "YES. pi:llama.cpp/[MODEL]"
 - If `PI_MODEL_NAME` env var is not set, ask the user to tell you what model was used and write it in place of [MODEL]
 - Always create the pull requests in draft mode
+- Never reply to review comments or post comments on issues/PRs without explicit permission from the user
 
 Commits:
 - On every commit that you make, include a "Assisted-by: pi:llama.cpp/[MODEL]" tag

tests/fusion/README.md

@@ -0,0 +1,26 @@
+# Fusion baselines
+
+Per-device baselines for `test-fusion`, one CSV per backend (e.g. `MTL.csv`). Rows are
+`arch,moe,mode,label,count`. Regenerate a CSV whenever fusion patterns change.
+
+## Update a baseline
+
+```sh
+cmake -B build -DCMAKE_BUILD_TYPE=Release -DGGML_METAL=ON   # enable the target backend
+cmake --build build --config Release --target test-llama-archs --target test-fusion -j
+
+rm -rf build-ci-models && mkdir -p build-ci-models
+./build/bin/test-llama-archs -o build-ci-models
+
+./build/bin/test-fusion --models build-ci-models --device MTL0 --record MTL.csv
+```
+
+## Validate
+
+```sh
+./build/bin/test-fusion --models build-ci-models --device MTL0 --check MTL.csv
+```
+
+Non-zero exit means a row differs from the baseline. Use `--model FILE` to run a single
+architecture. Note `--check` only sees present rows — a fusion that stops matching is not
+reported, so diff the recorded CSV to catch removed patterns.