Format Go with gofmt, then golines -m 77 (closes #160)

REPO_POLICIES names gofmt then golines -m 77 as the Go formatter, says
what script/fmt, script/fmt-check and script/bootstrap do, and pins
golines v0.13.0 by commit hash. The Go style guide and both checklists
agree. lll stays at 88: golines leaves long strings and comments alone.

Model: opus-5-5

TODO.md

@@ -21,6 +21,11 @@ fmt-check, and commit.
 
 # Completed Steps
 
+- 2026-11-07: Go code is now formatted with `gofmt` and then `golines -m 77`
+  (https://git.eeqj.de/sneak/prompts/issues/160). `prompts/REPO_POLICIES.md`
+  says how `script/fmt`, `script/fmt-check` and `script/bootstrap` do it and
+  pins `golines`. The Go style guide and both checklists say the same. `lll`
+  stays at 88, since `golines` leaves long strings and comments as they are.
 - 2026-11-06: The pinning rule in `prompts/REPO_POLICIES.md` now opens with its
   scope: what we download and install ourselves in scripts and Dockerfiles
   (https://git.eeqj.de/sneak/prompts/issues/154). Distribution packages are

prompts/CODE_STYLEGUIDE_GO.md

@@ -1,13 +1,16 @@
 ---
 title: Code Styleguide — Go
-last_modified: 2026-10-18
+last_modified: 2026-11-07
 ---
 
-1.  Try to hard wrap long lines at 77 characters or less.
+1.  Format Go code with `gofmt` and then `golines -m 77`, through `make fmt`.
+    Don't commit anything `make fmt` would change. The only exception is when
+    committing things that aren't yet syntactically valid, which should only
+    happen pre-v0.0.1 or on a non-`main` branch.
 
-1.  Don't commit anything that hasn't been `go fmt`'d. The only exception is
-    when committing things that aren't yet syntactically valid, which should
-    only happen pre-v0.0.1 or on a non-`main` branch.
+1.  Hard wrap long lines at 77 characters or less. `golines` does this for code.
+    Wrap comments and long string literals by hand, since `golines` leaves them
+    as they are.
 
 1.  Even if you are planning to deal with only positive integers, use
     `int`/`int64` types instead of `uint`/`uint64` types. This is for

prompts/EXISTING_REPO_CHECKLIST.md

@@ -1,6 +1,6 @@
 ---
 title: Existing Repo Checklist
-last_modified: 2026-11-06
+last_modified: 2026-11-07
 ---
 
 Use this checklist when beginning work in a repo that may not yet conform to our
@@ -259,8 +259,13 @@ with your task.
 
 # Formatting
 
-- [ ] Platform-standard formatter is configured (`black`, `prettier`, `go fmt`)
-- [ ] Default formatter config, only exception: four-space indents (except Go)
+- [ ] Platform-standard formatter is configured (`black`, `prettier`, and for Go
+      `gofmt` then `golines -m 77`)
+- [ ] Default formatter config, except four-space indents (not Go) and the Go
+      77-column limit
+- [ ] Go: `script/bootstrap` installs `golines` with `go install` pinned to a
+      commit hash; `script/fmt-check` fails when `gofmt` or `golines -m 77`
+      would change a file
 - [ ] All files pass `make fmt-check`
 
 # Git Hygiene

prompts/NEW_REPO_CHECKLIST.md

@@ -1,6 +1,6 @@
 ---
 title: New Repo Checklist
-last_modified: 2026-11-06
+last_modified: 2026-11-07
 ---
 
 Use this checklist when creating a new repository from scratch. Follow the steps
@@ -233,9 +233,11 @@ are thin shims calling them. Model scripts:
       which writes no image. No lint verdict may come from a host invocation of
       the linter.
 - [ ] `script/fmt` / `make fmt` — formats code (writes; native, never in a
-      container)
+      container). Go code gets `gofmt`, then `golines -m 77`.
 - [ ] `script/fmt-check` / `make fmt-check` — checks formatting (read-only;
-      native)
+      native). Fails when `gofmt` or `golines -m 77` would change a Go file.
+- [ ] Go: `script/bootstrap` installs `golines` with `go install` pinned to a
+      commit hash
 - [ ] `script/check` / `make check` — runs `test`, `lint`, `fmt-check`; must not
       modify files
 - [ ] `script/projectname` — outputs the project name (used by `script/docker`

prompts/REPO_POLICIES.md

@@ -1,6 +1,6 @@
 ---
 title: Repository Policies
-last_modified: 2026-11-06
+last_modified: 2026-11-07
 ---
 
 This document covers repository structure, tooling, and workflow standards. Code
@@ -675,11 +675,31 @@ style conventions are in separate documents:
 - Use platform-standard formatters:
     - `black` for Python
     - `prettier` for JS/CSS/Markdown/HTML
-    - `go fmt` for Go
+    - `gofmt`, then `golines -m 77`, for Go
 
-    Always use default configuration, with two exceptions:
+    Always use default configuration, with three exceptions:
     - four-space indents (except Go)
     - `proseWrap: always` for Markdown (hard-wrap at 80 columns)
+    - a 77-column limit for Go, set by `golines -m 77`
+
+    `script/fmt` runs `gofmt` and then `golines -m 77` on Go code.
+    `script/fmt-check` fails when either of them would change a file. `golines`
+    comes from `github.com/segmentio/golines`. `script/bootstrap` installs it
+    with `go install`, pinned to a commit hash as below:
+
+    ```sh
+    # golines v0.13.0, 2025-08-21
+    go install github.com/segmentio/golines@8f32f0f7e89c30f572c7f2cd3b2a48016b9d8bbf
+    ```
+
+    `script/bootstrap` reads the installed version from the `mod` line of
+    `go version -m "$(command -v golines)"`, which reports `v0.13.0`. It does
+    not use `golines --version`, which prints `golines vdev` for a binary that
+    `go install` built.
+
+    `golines` cannot shorten every line: long string literals and comments stay
+    as they are. golangci-lint's `lll` limit therefore stays at 88 columns, so
+    it fails only lines far past the formatter's limit.
 
     Documentation and writing repos (Markdown, HTML, CSS) should also have
     `.prettierrc` and `.prettierignore`.