Set the lint digest and .golangci.yml together; state the Go version rule

The canonical .golangci.yml now names exhaustruct_v5, which v2.12.2
rejects, so a repo that re-vendors the file on the old digest gets a
lint phase that fails before checking any code. REPO_POLICIES now says
a repo sets the lint phase digest and re-vendors .golangci.yml in one
commit, whichever prompted the change, and both repo checklists point
to that rule. It also replaces "a new Go version needs a golangci-lint
built with it" with the rule golangci-lint applies: the go directive
must not name a newer Go minor version than the one it was built with.

Model: opus-5-5

.gitignore

@@ -20,8 +20,26 @@ Thumbs.db
 # Node
 node_modules/
 
-# Environment / secrets
-.env
-.env.*
-*.pem
-*.key
+# Secrets. Unanchored like every entry above, so each matches at every
+# depth. Matching is case-sensitive on Linux, so names use character
+# ranges rather than a lowercase form that misses `Server.Key`.
+
+# Environment files. `*.env` covers bare `.env` and the `prod.env`
+# convention. Only the templates `example.env` and `sample.env` are
+# re-included below. A repository that commits any other template adds
+# its own negation after these lines, for example `!.env.example`.
+*.[eE][nN][vV]
+.[eE][nN][vV].*
+.[eE][nN][vV][rR][cC]
+!example.env
+!sample.env
+
+# Private keys and the bundles carrying them.
+*.[pP][eE][mM]
+*.[kK][eE][yY]
+*.[pP]12
+*.[pP][fF][xX]
+[iI][dD]_[rR][sS][aA]
+[iI][dD]_[dD][sS][aA]
+[iI][dD]_[eE][cC][dD][sS][aA]
+[iI][dD]_[eE][dD]25519

TODO.md

@@ -28,6 +28,11 @@ fmt-check, and commit.
   `.golangci.yml` now disables `exhaustruct_v5` beside `exhaustruct`. v2.12.2
   rejects that file, so `REPO_POLICIES.md` and both repo checklists now say a
   repo sets the lint phase digest and re-vendors `.golangci.yml` in one commit.
+- 2026-10-03: Brought the canonical `.gitignore` level with `.dockerignore` on
+  secrets (issue 38): it now also ignores `prod.env`-style `*.env` files,
+  `.envrc`, `*.p12`, `*.pfx` and the extensionless SSH private keys, written to
+  `.gitignore`'s own rules (no `**/` prefix) and case-folded with character
+  ranges. `example.env` and `sample.env` stay trackable through negations.
 - 2026-10-02: The image version now comes from git inside the build (issues 69
   and 71), superseding the 2026-09-08 entry that excluded `.git`. The canonical
   `.dockerignore` sends `.git` but keeps out `.git/config`, which can hold a