Deduplicate CI runs and finish full matrices

.github/workflows/check.yml

@@ -2,12 +2,18 @@ name: check
 on:
     push:
         branches:
-            - "*"
+            - main
     pull_request:
         branches:
-            - "*"
+            - "**"
 permissions:
     contents: read
+
+# Pull requests supersede their own earlier runs; pushes to main are keyed by
+# run_id so they always run to completion.
+concurrency:
+    group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+    cancel-in-progress: true
 jobs:
     format:
         runs-on: ubuntu-latest
@@ -97,6 +103,7 @@ jobs:
         runs-on: ubuntu-latest
         name: build
         strategy:
+            fail-fast: false
             matrix:
                 package: [nats-py, nats-core, nats-server, nats-jetstream, nats-key-value]
         steps:

.github/workflows/test.yml

@@ -3,14 +3,20 @@ name: test
 on:
     push:
         branches:
-            - "**"
+            - main
     pull_request:
         branches:
             - "**"
 
 permissions:
     contents: read
 
+# Pull requests supersede their own earlier runs; pushes to main are keyed by
+# run_id so they always run to completion.
+concurrency:
+    group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+    cancel-in-progress: true
+
 jobs:
     nats:
         runs-on: ubuntu-latest
@@ -58,6 +64,7 @@ jobs:
         name: ${{ matrix.project }} (python-${{ matrix.python-version }}, nats-server-${{ matrix.nats-server-version }}, ${{ matrix.os }})
         runs-on: ${{ matrix.os }}
         strategy:
+            fail-fast: false
             matrix:
                 python-version: ["3.13"]
                 os: ["ubuntu-latest", "macos-latest", "windows-latest"]