ci: defer cargo, integration, and coverage lanes to nightly

.github/workflows/coverage.yaml

@@ -2,16 +2,17 @@
 name: Coverage
 
 on:
+  # Coverage is expensive (xlarge runner, 180-min cap) and non-gating (no
+  # floor), so it runs nightly / on-demand instead of on every PR. push:main is
+  # kept so the GitHub-Pages coverage trend still updates on merge.
   push:
     branches: [main]
     paths-ignore:
       - '.github/styles/**'
       - 'web/**'
-  pull_request:
-    branches: [main]
-    paths-ignore:
-      - '.github/styles/**'
-      - 'web/**'
+  schedule:
+    - cron: '0 7 * * *' # 07:00 UTC daily (off-peak)
+  workflow_dispatch:
 
 permissions: read-all
 

.github/workflows/native-cargo.yaml

@@ -2,16 +2,12 @@
 name: Cargo Native
 
 on:
-  push:
-    branches: [main]
-    paths-ignore:
-      - '.github/styles/**'
-      - 'web/**'
-  pull_request:
-    branches: [main]
-    paths-ignore:
-      - '.github/styles/**'
-      - 'web/**'
+  # Cargo Native (Linux + Windows) is deferred to a nightly schedule +
+  # on-demand. Per-PR build/test signal is covered by the Nix (Bazel Dev) lane;
+  # this keeps full cargo and cross-platform coverage running daily against main.
+  schedule:
+    - cron: '0 7 * * *' # 07:00 UTC daily (off-peak)
+  workflow_dispatch:
 
 permissions: read-all
 

.github/workflows/nix.yaml

@@ -12,6 +12,12 @@ on:
     paths-ignore:
       - '.github/styles/**'
       - 'web/**'
+  # The Cargo Dev lane (nix-cargo) runs nightly only — see its per-job `if`. The
+  # other jobs here (Bazel Dev, installation, integration, RBE) stay on the
+  # per-PR path and are skipped on the schedule via `if: != 'schedule'`.
+  schedule:
+    - cron: '0 7 * * *' # 07:00 UTC daily (off-peak)
+  workflow_dispatch:
 
 permissions: read-all
 
@@ -21,6 +27,7 @@ concurrency:
 
 jobs:
   nix-bazel:
+    if: ${{ github.event_name != 'schedule' }}
     strategy:
       fail-fast: false
       matrix:
@@ -75,7 +82,9 @@ jobs:
         with:
           nativelink_attic_token: ${{ secrets.NATIVELINK_ATTIC_TOKEN }}
 
+  # Cargo Dev (Linux-only) moved off the per-PR critical path: nightly / on-demand only.
   nix-cargo:
+    if: ${{ github.event_name == 'schedule' || github.event_name == 'workflow_dispatch' }}
     strategy:
       fail-fast: false
       matrix:
@@ -109,6 +118,7 @@ jobs:
           nativelink_attic_token: ${{ secrets.NATIVELINK_ATTIC_TOKEN }}
 
   installation:
+    if: ${{ github.event_name != 'schedule' }}
     strategy:
       fail-fast: false
       matrix:
@@ -139,6 +149,7 @@ jobs:
           nativelink_attic_token: ${{ secrets.NATIVELINK_ATTIC_TOKEN }}
 
   integration:
+    if: ${{ github.event_name == 'schedule' || github.event_name == 'workflow_dispatch' }}
     name: ${{ matrix.test-name }}
     strategy:
       matrix:
@@ -168,6 +179,7 @@ jobs:
 
   # rbe-toolchain is slow because it has many subcommands, so split it out
   generate-rbe-commands:
+    if: ${{ github.event_name != 'schedule' }}
     runs-on: ubuntu-24.04
     outputs:
       matrix: ${{ steps.set-matrix.outputs.matrix }}
@@ -188,6 +200,7 @@ jobs:
         id: set-matrix
 
   rbe-toolchain:
+    if: ${{ github.event_name != 'schedule' }}
     name: rbe ${{ matrix.command}}
     needs: [generate-rbe-commands]
     strategy: