fix(detector): replace n.Current()'s silent-download call site

[dipto0321]

Summary

internal/detector/n.go's N.Current() shells out to n current — an undocumented subcommand in upstream tj/n (bin/n). The string current is not a first-class case arm in the script's dispatch block; it falls through to the default *) arm install "$1"; exit ;;. Inside install, "current" matches the version-label branch in display_remote_versions (same as "latest"), which downloads the latest Node.js tarball, extracts it, and activates it. So every Current() invocation would silently side-effect-install the newest available Node version on the user's machine — every run, every n-using machine.

Callers treat Current() errors as "active version unknown, don't exclude it" (the safe-by-convention default per the Manager interface doc). That meant the cleanup safety net never fired on any n install: the active version was always "unknown," and --cleanup / --yes / cfg.Cleanup.Auto could happily auto-delete whatever was actually powering the user's shell.

This PR replaces the call site with <N_PREFIX>/bin/node --version. n's activate function (bin/n) copies the active node binary into that path, so its --version IS the active version — side-effect-free, and matches every supported n install. The pre-fix tests (TestParseNCurrent_*, TestNCurrent_InvokesShell) codified the buggy behavior; they're deleted.

Linked issues

Fixes #59

Type of change

• fix — bug fix (PATCH bump)
• feat — new feature (MINOR bump)
• refactor — no behavior change
• perf — performance improvement
• docs — documentation only
• test — tests only
• chore — maintenance / dependency bump
• ci — CI/CD only
• build — build system only
• Breaking change (MAJOR bump) — explain below

Checklist

• Title follows Conventional Commits (feat(scope): subject)
• I ran make ci locally and it passes (tidy/fmt/vet/test all green; make lint fails locally with the documented build(lint): .golangci.yml v1 schema incompatible with golangci-lint v2 (brew installs v2, make lint fails to even parse config) #62 golangci v1/v2 schema issue — CI uses the pinned v1.64.8 which is unaffected)
• I added or updated tests for the change
• I updated relevant docs (README, docs/, inline godoc)
• No new linter warnings
• If breaking: I documented the migration path in the PR body and updated CHANGELOG.md

Screenshots / output

Pre-fix behavior on an n-using machine, every nodeup invocation:

$ nodeup upgrade --cleanup
# in n.go: Current() calls `n current`
# upstream `n current` resolves to "latest", downloads
# the new tarball, and activates it. The user's machine
# now has a version they didn't ask for.
# Then the all-or-nothing cleanup deletes whichever
# version happens to be on PATH, including the user's
# currently-active Node.js.

Post-fix behavior:

$ nodeup upgrade --cleanup
# in n.go: Current() runs `/usr/local/bin/node --version`
# — pure read, no side effects.
# If /usr/local/bin/node is missing, the error propagates
# and the upgrade flow treats Current() as "unknown,"
# which (combined with #58's ForcePerVersion safety net)
# means per-version y/N guards every delete.

Files touched

• internal/detector/n.go —
  • N.Current() rewritten to shell out to <N_PREFIX>/bin/node --version via the existing nPrefix() helper. The pre-fix runShell(ctx, "n", "current") is gone.
  • parseNCurrent (the pre-fix n current parser) is renamed to parseNNodeVersion and its doc comment is rewritten to explain <node --version>'s output format and why n current is not used.
  • The mutation-methods doc block (the long comment listing every Current strategy) is updated to spell out the reasoning and link fix(detector): n manager's Current() relies on unverified 'n current' subcommand #59.
• internal/detector/n_test.go —
  • Tests TestParseNCurrent_Bare, TestParseNCurrent_WithPrefix, TestParseNCurrent_Empty, TestNCurrent_InvokesShell (which all pinned n current invocation / parsing): deleted.
  • New tests in their place:
    • TestParseNNodeVersion_VPrefixedReal, TestParseNNodeVersion_Bare, TestParseNNodeVersion_LeadingTrailingWhitespace, TestParseNNodeVersion_Empty, TestParseNNodeVersion_Unparseable — parser coverage for both common shapes (vX.Y.Z) and defensive shapes (bare X.Y.Z, whitespace, garbage).
    • TestN_Current_InvokesNodeVersionNotNCurrent — integration test that fails the test if the literal n current request re-appears in any future regression. The fixture's t.Fatalf cites the request so the diagnosis is immediate.
    • TestN_Current_PropagatesRunShellError, TestN_Current_PropagatesParseError — error-path coverage.
  • New import: "strings".
• CHANGELOG.md — ### Fixed entry under [Unreleased] documenting the change with the fix(detector): n manager's Current() relies on unverified 'n current' subcommand #59 reference.

[cocogitto-bot]

✔️ 01c528a - Conventional commits check succeeded.