Check gofumpt formatting with the pinned version in CI and lint

golangci-lint bundles gofumpt v0.8.0, which formats code differently
from the v0.9.2 we pin in go.mod. Enforcing formatting through
golangci-lint may therefore disagree with `just format`.

Remove gofumpt from golangci-lint's formatters and instead run the
pinned `go tool gofumpt` as a standalone check via a new
scripts/gofumpt-check.sh, wired into CI, `just lint`, and `make lint`.
goimports stays in golangci-lint; it's stable across versions and
nothing runs a competing copy of it.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -167,7 +167,12 @@ jobs:
         uses: actions/setup-go@v6
         with:
           go-version: 1.25.x
+      - name: Check formatting
+        run: ./scripts/gofumpt-check.sh
       - name: Lint
+        # Run even if the formatting check failed, so that both sets of
+        # problems are reported in a single CI run.
+        if: ${{ !cancelled() }}
         uses: golangci/golangci-lint-action@ba0d7d2ec06a0ea1cb5fa41b2e4a3ab91d21278a # v9
         with:
           # If you change this, make sure to also update scripts/golangci-lint-shim.sh

.golangci.yml

@@ -102,7 +102,9 @@ linters:
       - vendor/
 formatters:
   enable:
-    - gofumpt
+    # gofumpt is intentionally not listed here: golangci-lint bundles its own
+    # gofumpt version, which drifts from the one we pin in go.mod. We run that
+    # pinned version separately via scripts/gofumpt-check.sh instead.
     - goimports
   exclusions:
     generated: lax

Makefile

@@ -40,6 +40,7 @@ format:
 
 .PHONY: lint
 lint:
+	./scripts/gofumpt-check.sh
 	./scripts/golangci-lint-shim.sh run
 
 # For more details about integration test, see https://github.com/jesseduffield/lazygit/blob/master/pkg/integration/README.md.

justfile

@@ -37,6 +37,7 @@ format:
     go tool gofumpt -l -w .
 
 lint:
+    ./scripts/gofumpt-check.sh
     ./scripts/golangci-lint-shim.sh run
 
 e2e-test-command := "go test pkg/integration/clients/*.go"

scripts/gofumpt-check.sh

@@ -0,0 +1,22 @@
+#!/bin/sh
+
+# Checks that all Go files are gofumpt-formatted, and fails if any aren't.
+# Used by `just lint`, `make lint`, and CI. We run gofumpt with the version
+# pinned in go.mod (via `go tool`) rather than the one bundled with
+# golangci-lint, so that formatting is identical across all of them and the
+# editor.
+
+set -e
+
+script_dir=$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)
+repo_root=$(dirname "$script_dir")
+
+cd "$repo_root"
+
+unformatted=$(go tool gofumpt -l .)
+if [ -n "$unformatted" ]; then
+  echo "The following files are not formatted correctly:"
+  echo "$unformatted"
+  echo "Run 'just format' (or 'make format') and commit the result."
+  exit 1
+fi