Update golangci-lint to v2.12.2 with canonical config (#29)

Bumps golangci-lint from v2.1.6 (digest-only pin in the `Dockerfile` lint stage) to v2.12.2, pinned by tag and digest (Debian-based image).

Replaces `.golangci.yml` with the canonical strict config: all linters enabled except the standard disable list (`exhaustruct`, `depguard`, `godot`, `wsl`, `wrapcheck`, `varnamelen`), `lll` at 88, `funlen` 80/50, `cyclop` 15, `dupl` 100, and test files are now linted (the old config had `tests: false`, an enable-only list of ~20 linters, `lll` 120, and a blanket exclusion of `internal/macse`).

The stricter config surfaced ~1550 findings, all fixed:

- `wsl_v5` (439) / `nlreturn` (24): blank-line insertions
- `lll` (309): line wrapping at 88 columns; long literals split with `+` concatenation, values unchanged
- `noinlineerr` (130): `if err := ...` split into assignment plus check
- `paralleltest` (116): `t.Parallel()` added to tests without shared state; reasoned `//nolint` where `t.Setenv` or shared fixtures forbid it
- `err113` (97): package-level sentinel errors (new `internal/vault/errors.go`), `%w` wrapping, `errors.Is`
- `perfsprint` (74) / `modernize` (39) / `intrange`: `strconv`, `errors.New`, `slices.Contains`, `any`, `SplitSeq`
- `goconst` (40) / `dupword` (41) / `testifylint` (42) / `thelper` (33): constants, assertion fixes, `t.Helper()`
- `noctx` (22): `exec.CommandContext` for gpg/CLI invocations
- `testpackage` (18): black-box tests moved to `_test` packages where they use only exported identifiers; white-box files carry a reasoned `//nolint`
- `funlen`/`cyclop`/`gocognit`/`nestif`/`dupl`: behavior-preserving helper extraction
- assorted singletons: `gosec`, `gosmopolitan`, `funcorder`, `nonamedreturns`, `makezero`, `prealloc`, `godox`, `nolintlint`, `ireturn`, `nilnil`, `gochecknoinits`

## User-visible strings

**None changed.** Every error message this branch composes is byte-identical to the one `main` composes.

The `err113` sentinels are shaped so `fmt.Errorf` reassembles the original text around them: the sentinel carries the fixed words and the caller supplies the interpolated value in the position it has always occupied. Where the value sits mid-sentence the sentinel holds only a fragment (e.g. `vault.ErrVaultNotFound` is `"does not exist"`, composed by its caller as `vault <name> does not exist`); each such sentinel documents the message it participates in.

Verified mechanically, not by inspection: every `fmt.Errorf` and `errors.New` call site in both trees is parsed, the `Error()` text of any sentinel passed to `%w` is substituted in, and the resulting sets of composed message templates are compared. All 350 templates `main` produces are still produced, character for character. The set of lost or altered messages is empty.

## `unlocker list`

`findUnlockerIDByMetadata` returns `(string, error)` rather than signalling failure with an empty ID, so an unreadable `unlockers.d` is no longer indistinguishable from "no matching entry". `UnlockersList` skips such an entry with a warning naming the directory — its behavior before the scan was extracted into a helper — instead of emitting a row under a synthesized fallback ID that no `unlocker remove` or `unlocker select` can match and that suppresses the current-unlocker marker. The duplicate-check and shell-completion callers skip on the same condition, matching their pre-extraction behavior. Covered by `internal/cli/unlockers_list_test.go`.

`TODO.md` records the change plus follow-ups (version-completion TODOs formerly in code comments, darwin-gated files exceeding 88 columns that Linux CI does not lint).

`make check` is green and the pinned v2.12.2 image reports `0 issues.` Note the test suite needs the memlock ulimit from `script/cibuild` for the 10MB memguard test; that requirement is pre-existing.

Not changed: `script/bootstrap` installs golangci-lint via the system package manager (no version pin to bump), and `script/lint` invokes whatever `golangci-lint` is on PATH. golangci-lint v2.12 deprecates `gomodguard` in favor of `gomodguard_v2` (warning only); the canonical config owns that decision.

Co-authored-by: sneak <sneak@sneak.berlin>
Reviewed-on: #29
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

TODO.md

@@ -25,6 +25,20 @@ Bring the repo into policy compliance in one commit:
 
 # Completed Steps
 
+- 2026-08-07: Updated golangci-lint to v2.12.2 with the canonical
+  `.golangci.yml` (all linters enabled minus the standard disable
+  list, `lll` 88, tests linted); bumped the `Dockerfile` lint-stage
+  image to the tagged v2.12.2 Debian digest; fixed all ~1550 new
+  findings across `internal/` and `pkg/` (line wrapping, `wsl_v5`
+  blank lines, sentinel errors for `err113`, `t.Parallel()` where
+  safe, `_test` package conversions, complexity/`dupl` helper
+  extraction) on branch `golangci-v2.12.2`. Reworked after review:
+  the `err113` sentinels in `internal/vault`, `internal/secret`,
+  `internal/cli` and `pkg/bip85` were reshaped so every composed
+  error message is byte-identical to `main`, and
+  `findUnlockerIDByMetadata` now returns an error so `unlocker list`
+  skips an unreadable `unlockers.d` entry with a warning instead of
+  emitting a fabricated fallback ID.
 - 2026-07-07 Adopted scripts-to-rule-them-all: `script/` entrypoints,
   Makefile shims, README Entrypoints section
 - 2026-03-11: Secure Enclave unlocker for hardware-backed secret
@@ -50,6 +64,17 @@ Bring the repo into policy compliance in one commit:
 
 - Compliance (after Next Step lands): keep main green under the new
   .gitea workflow; run make check before every merge.
+- Implement version-number shell completion for the second arg of
+  `secret version promote` and `secret version rm`
+  (`internal/cli/version.go`; was an in-code TODO removed for godox).
+- Cover mnemonic-vs-xprv identity consistency in
+  `pkg/agehd/agehd_test.go` `TestMnemonicVsXPRVConsistency` (was an
+  in-code FIXME removed for godox).
+- Darwin-gated files (`internal/secret/keychainunlocker.go`,
+  `seunlocker_darwin.go`, `internal/macse/macse_darwin.go`, related
+  tests) are not linted on the Linux CI runner and still contain lines
+  over the new 88-column limit; they will surface if lint ever runs on
+  macOS.
 - Merge secure-enclave-unlocker to main once review is done.
 - 1.0 critical security blockers (from repo TODO.md):
     - Command injection: GPG key IDs passed unescaped to exec.Command