ci: run make test on every PR and push to main

Add .github/workflows/ci.yml (Nim + gcc → make test). Keep selfhost-loop
as an optional/weekly job. Document CI layout; reformat hir_lower for fmt-check.

.github/workflows/ci.yml

@@ -0,0 +1,52 @@
+# Default PR / main CI: full `make test` (not selfhost fixed-point — see selfhost-loop.yml).
+name: ci
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+  workflow_dispatch:
+
+concurrency:
+  group: ci-${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  test:
+    name: make test
+    runs-on: ubuntu-latest
+    timeout-minutes: 90
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Install Nim
+        uses: jiro4989/setup-nim-action@v2
+        with:
+          nim-version: "2.0.x"
+          repo-token: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Install build deps
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y --no-install-recommends \
+            gcc make binutils libssl-dev python3
+
+      - name: Bootstrap + full test suite
+        env:
+          # Ensure registry / selfhost smokes see a clean env
+          BUX_NO_LINE: ""
+        run: |
+          unset BUX_DEBUG_FILE || true
+          unset BUX_SELFHOST_FIXED_POINT || true
+          make test
+
+      - name: Upload selfhost artifacts on failure
+        if: failure()
+        uses: actions/upload-artifact@v4
+        with:
+          name: ci-failure-logs
+          path: |
+            build/selfhost/build/main.c
+            _test_tmp_pkg/**
+          if-no-files-found: ignore

.github/workflows/selfhost-loop.yml

@@ -1,13 +1,13 @@
 # Optional / not on every PR: bootstrap selfhost determinism (make selfhost-loop).
-# Triggers: manual, weekly, or push to main that touches compiler/stdlib/loop.
-# Fixed-point buxc2→buxc3 is opt-in via BUX_SELFHOST_FIXED_POINT=1 (experimental).
+# Default PR CI is .github/workflows/ci.yml (`make test`).
+# Fixed-point gen2 vs gen3: BUX_SELFHOST_FIXED_POINT=1 (workflow_dispatch input).
 name: selfhost-loop
 
 on:
   workflow_dispatch:
     inputs:
       fixed_point:
-        description: "Also run experimental buxc2→buxc3 fixed-point"
+        description: "Also run fixed-point buxc2→buxc3→buxc4 (gen2 vs gen3)"
         type: boolean
         default: false
   schedule: