chore(detector): remove stale fnm not-implemented comment, sentinel.go pkg-doc collision, dead config.FileOverlay

internal/config/resolve.go

@@ -68,8 +68,10 @@ func applyOverlay(dst *Config, src *Overlay) {
 // Resolve can distinguish "user said no" from "user said nothing".
 //
 // Build one Overlay per source (CLI, env, file). Pass all of them to
-// Resolve. The file overlay is normally built by FileOverlay(*Config)
-// from a loaded Config, which marks every present field as set.
+// Resolve. The file overlay is normally built by FileOverlayFromNode
+// (see internal/config/fileoverlay.go) from a loaded Config and its
+// parsed yaml.Node; that form preserves "key absent" vs "key present
+// with zero value" — a distinction FileOverlay alone cannot make.
 type Overlay struct {
 	C *Config
 
@@ -90,36 +92,6 @@ type Overlay struct {
 // NewOverlay returns an empty Overlay (no fields set).
 func NewOverlay() *Overlay { return &Overlay{C: &Config{}} }
 
-// FileOverlay returns an Overlay that marks every field of cfg as set.
-// This is the right way to turn a loaded Config into the "file" layer
-// for Resolve — it preserves explicit zeros like track.lts: false.
-//
-// Nil cfg produces an overlay that sets nothing.
-//
-// Caveat: yaml.v3 cannot distinguish "key absent" from "key present
-// with zero value" for non-pointer fields, so a few set-flags use a
-// heuristic ("non-zero means set"). Manager empty-string is treated
-// as "not set" — meaning `manager: ""` in the file behaves like
-// omitting `manager` entirely. That matches the docs, which only
-// define "empty Manager" to mean auto-detect.
-func FileOverlay(cfg *Config) *Overlay {
-	if cfg == nil {
-		return NewOverlay()
-	}
-	o := &Overlay{C: cfg}
-	o.ManagerSet = cfg.Manager != ""
-	o.TrackLTSSet = true
-	o.TrackCurrentSet = true
-	o.PackagesMigrateSet = true
-	o.PackagesStrategySet = cfg.Packages.Strategy != ""
-	o.PackagesSkipSet = cfg.Packages.Skip != nil
-	o.CleanupAutoSet = true
-	o.CleanupPromptSet = true
-	o.CacheTTLSet = cfg.Cache.TTL != 0
-	o.SchemaVersionSet = cfg.SchemaVersion != 0
-	return o
-}
-
 // SetManager records an explicit manager override.
 func (o *Overlay) SetManager(name string) {
 	if o == nil || o.C == nil {

internal/detector/fnm.go

@@ -18,14 +18,23 @@ import (
 // FNM is the Fast Node Manager implementation. See
 // internal/detector/detector.go for the Manager interface contract.
 //
-// Phase 1 implements the detection surface only:
-//   - Detect       : cheap PATH probe via exec.LookPath
-//   - Version      : `fnm --version`, parsed to drop the leading "fnm "
-//   - ListInstalled: `fnm list`, parsed into sorted []semver.Version
+// Detection:
+//   - Detect        : cheap PATH probe via exec.LookPath
+//   - Version       : `fnm --version`, parsed to drop the leading "fnm "
+//   - ListInstalled : `fnm list`, parsed into sorted []semver.Version
+//   - Current       : `fnm current`, parsed via parseFNMCurrent
 //
-// Mutation methods (Install, Uninstall, Use, SetDefault, GlobalNpmPrefix)
-// return an explicit "not implemented" error so callers can detect them
-// at runtime instead of getting a silent zero-value result.
+// Mutations shell out to the `fnm` binary directly:
+//   - Install       : `fnm install <v>`
+//   - Uninstall     : `fnm uninstall <v>` (refuses if <v> is the default;
+//     callers must SetDefault elsewhere first)
+//   - Use           : `fnm use <v>` (current shell only)
+//   - SetDefault    : `fnm default <v>` (persists for new shells)
+//
+// Layout queries:
+//   - GlobalNpmPrefix : resolves $FNM_DIR/node-versions/<v>/installation/lib/node_modules,
+//     with a fallback to the older .../lib/node_modules
+//     layout used before fnm 1.30.
 type FNM struct{}
 
 // NewFNM constructs a fresh fnm detector. Returned by value so each
@@ -41,13 +50,6 @@ func (f *FNM) Name() string { return "fnm" }
 // Signature matches platform.RunShell so a direct assignment works.
 var runShell = platform.RunShell
 
-// ErrFNMNotImplemented is returned by FNM mutation methods that have not
-// yet been implemented in Phase 1 (Install, Uninstall, Use, SetDefault,
-// GlobalNpmPrefix). Returning this error instead of a zero value lets
-// callers distinguish "I haven't done it yet" from "user passed a bad
-// version" via errors.Is.
-var ErrFNMNotImplemented = errors.New("fnm mutation commands not yet implemented")
-
 // Detect returns true when an fnm executable can be located on PATH.
 // Per the Manager contract, it MUST be cheap — exec.LookPath does a
 // directory walk but no subprocess spawn.
@@ -158,9 +160,7 @@ func parseFNMInstalled(stdout string) ([]semver.Version, error) {
 // --- Mutation methods ----------------------------------------------------
 //
 // Install, Uninstall, Use, SetDefault, GlobalNpmPrefix, and Current all
-// shell out to the `fnm` binary through runShell. They were left as
-// stubs in Phase 1; filling them in was deferred until the upgrade
-// command (Phase 4) actually needed them.
+// shell out to the `fnm` binary through runShell.
 //
 // All shell-outs follow the same error-wrapping convention: a non-zero
 // exit becomes a wrapped error containing the captured stderr, so the

internal/packages/sentinel.go

@@ -1,4 +1,4 @@
-// Package sentinel implements the upgrade-in-progress sentinel file.
+// Sentinel file handling: tracks when `nodeup upgrade` is mid-migration.
 //
 // When `nodeup upgrade` starts a migration that involves snapshotting global
 // npm packages, installing new Node versions, and restoring packages onto