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

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`.