[rounds] ci: pin build workflow actions and add default permissions

[jhgaylor]

Carried over from the archived managoat/rounds#1 when the demo suite
was consolidated into this repository. The original repo has been deleted, so
this is the surviving copy.

• Originally opened by @app/fountain-rounds on 2026-08-24 (PR https://github.com/managoat/rounds/pull/1)
• Now lives at: (root workflows)
• Status: APPLIED to .github/workflows/ in the monorepo — same substance as mend#1. Kept for the record.

---

chant flagged 7 things in .github/workflows/build.yml. This pull request fixes them.

• actions/checkout not pinned to a SHA (GHA021) in build — Pinned actions/checkout to commit 3d3c42e5aac5ba805825da76410c181273ba90b1 (tag v7), keeping the # v7 comment for readability.
• Action not pinned to a commit SHA (GHA029) in build — Pinned oven-sh/setup-bun to commit 0c5077e51419868618aeaa5fe8019c62421857d6 (tag v2), keeping the # v2 comment for readability.
• Action not pinned to a commit SHA (GHA029) in build — Pinned docker/setup-qemu-action to commit 96fe6ef7f33517b61c61be40b68a1882f3264fb8 (tag v4), keeping the # v4 comment for readability.
• Action not pinned to a commit SHA (GHA029) in build — Pinned docker/setup-buildx-action to commit 37fe631027851001ddb9b187196cc803df7f5f0e (tag v4), keeping the # v4 comment for readability.
• Action not pinned to a commit SHA (GHA029) in build — Pinned docker/login-action to commit dbcb813823bdd20940b903addbd779551569679f (tag v4), keeping the # v4 comment for readability.
• Action not pinned to a commit SHA (GHA029) in build — Pinned docker/build-push-action to commit 53b7df96c91f9c12dcc8a07bcb9ccacbed38856a (tag v7), keeping the # v7 comment for readability.
• No explicit permissions block (GHA017) — Added a top-level permissions: contents: read block as the workflow default.

Verified by re-running the audit: merge-worthy findings 11 → 4.

---

Opened by Rounds, which audits this repository's configuration on a schedule. Close it without merging and this file will never be raised again.

---

Original diff

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 0f546b3..1c11a5d 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -20,6 +20,9 @@ concurrency:
 env:
   IMAGE: ghcr.io/${{ github.repository_owner }}/rounds
 
+permissions:
+  contents: read
+
 jobs:
   build:
     runs-on: ubuntu-latest
@@ -27,22 +30,22 @@ jobs:
       contents: write
       packages: write
     steps:
-      - uses: actions/checkout@v7
-      - uses: oven-sh/setup-bun@v2
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
+      - uses: oven-sh/setup-bun@0c5077e51419868618aeaa5fe8019c62421857d6 # v2
       - name: Test and build
         run: |
           bun install --frozen-lockfile
           bun test
           bun run build
-      - uses: docker/setup-qemu-action@v4
-      - uses: docker/setup-buildx-action@v4
-      - uses: docker/login-action@v4
+      - uses: docker/setup-qemu-action@96fe6ef7f33517b61c61be40b68a1882f3264fb8 # v4
+      - uses: docker/setup-buildx-action@37fe631027851001ddb9b187196cc803df7f5f0e # v4
+      - uses: docker/login-action@dbcb813823bdd20940b903addbd779551569679f # v4
         with:
           registry: ghcr.io
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
       - name: Build and push
-        uses: docker/build-push-action@v7
+        uses: docker/build-push-action@53b7df96c91f9c12dcc8a07bcb9ccacbed38856a # v7
         with:
           context: .
           platforms: linux/amd64,linux/arm64