Run Dockerfile build, test and lint steps at nice -n 19 (closes #63)

The owner ordered every build, test and lint step in every Dockerfile to
run at the lowest priority. REPO_POLICIES.md gains that rule in one
line, and both Dockerfiles this repo hands out follow it: its own, and
the canonical Go example in REPO_POLICIES.md. Installs, dependency
downloads and the runtime entrypoint are left at normal priority.

Model: opus-5-5

Dockerfile

@@ -13,7 +13,7 @@ RUN script/bootstrap
 
 COPY . .
 
-RUN yarn run prettier --check '**/*.md' --tab-width 4 --prose-wrap always
+RUN nice -n 19 yarn run prettier --check '**/*.md' --tab-width 4 --prose-wrap always
 
 # Test phase, same shape and for the same reason.
 #
@@ -28,7 +28,7 @@ RUN script/bootstrap
 
 COPY . .
 
-RUN echo "No tests defined."
+RUN nice -n 19 echo "No tests defined."
 
 # Development environment, and the last stage: a plain `docker build .`
 # names no target and so builds this one. Nothing is wanted from the two

TODO.md

@@ -21,6 +21,10 @@ fmt-check, and commit.
 
 # Completed Steps
 
+- 2026-09-29: Every `Dockerfile` step that builds, tests or lints now runs at
+  `nice -n 19`, per the owner's order on issue 63: the rule is one line in
+  `REPO_POLICIES.md`, and this repo's `Dockerfile` and the canonical Go
+  `Dockerfile` there follow it.
 - 2026-09-08: Moved linting and testing into Docker as phases of the main
   `Dockerfile`, per the owner ruling on issue 40. `script/lint` and
   `script/test` build one phase each by name with `--no-cache` — the same answer

prompts/REPO_POLICIES.md

@@ -1,6 +1,6 @@
 ---
 title: Repository Policies
-last_modified: 2026-09-08
+last_modified: 2026-09-29
 ---
 
 This document covers repository structure, tooling, and workflow standards. Code
@@ -109,6 +109,10 @@ style conventions are in separate documents:
   manifests (`package.json` + `yarn.lock`, `go.mod` + `go.sum`, etc.) before
   running it.
 
+- Every `Dockerfile` `RUN` step that builds, tests or lints runs at the lowest
+  priority, as `RUN nice -n 19 <command>`; installs, downloads, copies and the
+  runtime `CMD`/`ENTRYPOINT` are not niced.
+
 - **Linting and testing run in Docker, as phases of the `Dockerfile`.** There is
   no separate lint file. `script/lint` and `script/test` each build one phase
   and nothing else:
@@ -171,7 +175,7 @@ style conventions are in separate documents:
     COPY go.mod go.sum ./
     RUN go mod download
     COPY . .
-    RUN golangci-lint run --config .golangci.yml ./...
+    RUN nice -n 19 golangci-lint run --config .golangci.yml ./...
 
     # Test phase
     # golang:1.x-alpine, YYYY-MM-DD
@@ -180,9 +184,9 @@ style conventions are in separate documents:
     COPY go.mod go.sum ./
     RUN go mod download
     COPY . .
-    RUN go test -timeout 90s -race -cover ./... || \
+    RUN nice -n 19 go test -timeout 90s -race -cover ./... || \
         { echo "--- Rerunning with -v for details ---"; \
-          go test -timeout 90s -race -v ./...; exit 1; }
+          nice -n 19 go test -timeout 90s -race -v ./...; exit 1; }
 
     # Build stage. Nothing is wanted from either phase above; the copies
     # are what make BuildKit build them first, so this stage cannot run
@@ -197,7 +201,7 @@ style conventions are in separate documents:
     COPY . .
 
     ARG VERSION=dev
-    RUN CGO_ENABLED=0 go build -trimpath \
+    RUN CGO_ENABLED=0 nice -n 19 go build -trimpath \
         -ldflags="-s -w -X main.Version=${VERSION}" \
         -o /app ./cmd/app/