Classify the unmigrated settings instead of just counting them

A production rehearsal reported 12,182 settings not carried over by
migrate_v016.py. As a bare number that reads as an impossible amount of
manual reconstruction, and it is misleading. Snapshotting a v0.16.14 store
migrated from a real v0.15.5 showed what those settings actually are:

    8547  regenerates         server.blocked-ip
    3337  shipped with v0.16  lookup.url-redirectors, lookup.trusted-domains,
                              spam-filter.list, spam-filter.rule,
                              spam-filter.dnsbl, lookup.surbl-hashbl
     224  already carried     server.listener, signature.* (DKIM)
     293  NEED YOUR REVIEW    queue.schedule, config.local-keys,
                              server.auto-ban, spam-filter.llm, queue.tls, ...

server.blocked-ip is auto-ban state that repopulates from live traffic. The
stock groups are data v0.16 provides itself - 2,084 MemoryLookupKey, 66
SpamRule and 18 SpamDnsblServer objects were already present in the migrated
store. DKIM came across as DkimSignature objects with private keys intact,
verified on that instance. So the real worklist is ~293 keys, not 12,182.

backup.UnmigratedReport.Classify encodes this and the rehearsal now reports
the categorised view. Rules match longest-prefix-first, because
server.blocked-ip is runtime state while server.auto-ban beside it is
configuration, and an unrecognized prefix defaults to "needs review" -
assuming an unknown setting is safe to ignore is the wrong default.

This also retired the lookup and spam-filter generators that were the
planned next step. v0.15's rules are stwt_rbl_senderscore_ip; v0.16's are
STWT_RBL_SENDERSCORE_IP - the same stock set, already installed. Generating
them from v0.15 would duplicate every rule and revert upstream updates, so
they were deliberately not written. The targets worth generating are the
small site-specific groups instead: queue.schedule, queue.tls,
session.auth, server.auto-ban.

No production data in this commit: the test fixture uses the real group
names and counts with example.com standing in for customer domains.

internal/backup/settingsdump_test.go

@@ -262,3 +262,118 @@ func TestRunSettingsConvertRunsInTheGivenWorkDir(t *testing.T) {
 		t.Errorf("unmigrated.txt should land in WorkDir, not the caller's cwd: %v", err)
 	}
 }
+
+// The numbers here are the real ones from a production instance, because
+// the point of classifying is what it does to those numbers: 12,182 reads
+// as impossible, and is mostly nothing to do.
+const productionUnmigrated = `# Unmigrated v0.15 settings
+
+Total unmigrated keys: 12182 across 69 prefixes.
+
+  server.blocked-ip                     8547 keys
+  lookup.url-redirectors                1076 keys
+  lookup.trusted-domains                 828 keys
+  spam-filter.list                       537 keys
+  spam-filter.rule                       424 keys
+  spam-filter.dnsbl                      292 keys
+  lookup.surbl-hashbl                    180 keys
+  queue.schedule                          41 keys
+  server.listener                         26 keys
+  signature.rsa-example.com               22 keys
+  server.auto-ban                         16 keys
+  session.auth                            14 keys
+`
+
+func classifyProduction(t *testing.T) *ClassifiedReport {
+	t.Helper()
+	path := filepath.Join(t.TempDir(), "unmigrated.txt")
+	if err := os.WriteFile(path, []byte(productionUnmigrated), 0o640); err != nil {
+		t.Fatal(err)
+	}
+	report, err := ReadUnmigratedReport(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return report.Classify()
+}
+
+func TestClassifySeparatesWorkFromNoise(t *testing.T) {
+	c := classifyProduction(t)
+
+	// Runtime state: auto-ban repopulates it.
+	if got := c.Counts[DispositionRegenerates]; got != 8547 {
+		t.Errorf("regenerates = %d, want 8547 (server.blocked-ip)", got)
+	}
+	// Stock data v0.16 ships: restoring v0.15's would revert it.
+	if got := c.Counts[DispositionShipped]; got != 1076+828+537+424+292+180 {
+		t.Errorf("shipped = %d, want the stock spam/lookup groups", got)
+	}
+	// Carried by another route.
+	if got := c.Counts[DispositionCarried]; got != 22+26 {
+		t.Errorf("carried = %d, want the signature and listener groups", got)
+	}
+	// What's actually left for a human.
+	if got := c.Counts[DispositionReview]; got != 41+16+14 {
+		t.Errorf("needs review = %d, want %d", got, 41+16+14)
+	}
+}
+
+// server.blocked-ip is runtime state; server.auto-ban sitting right next to
+// it is configuration. A shortest-prefix match would get this wrong.
+func TestClassifyPrefersTheMoreSpecificRule(t *testing.T) {
+	c := classifyProduction(t)
+	for _, g := range c.Groups {
+		switch g.Prefix {
+		case "server.blocked-ip":
+			if g.Disposition != DispositionRegenerates {
+				t.Errorf("server.blocked-ip = %q, want regenerates", g.Disposition)
+			}
+		case "server.auto-ban":
+			if g.Disposition != DispositionReview {
+				t.Errorf("server.auto-ban = %q, want review - it is configuration, not runtime state", g.Disposition)
+			}
+		case "server.listener":
+			if g.Disposition != DispositionCarried {
+				t.Errorf("server.listener = %q, want carried - the apply plan regenerates it", g.Disposition)
+			}
+		}
+	}
+}
+
+func TestClassifyReviewListIsTheActualWorklist(t *testing.T) {
+	review := classifyProduction(t).NeedsReview()
+	if len(review) != 3 {
+		t.Fatalf("review groups = %d, want 3", len(review))
+	}
+	if review[0].Prefix != "queue.schedule" {
+		t.Errorf("first review group = %q, want the largest (queue.schedule)", review[0].Prefix)
+	}
+	for _, g := range review {
+		if g.Disposition != DispositionReview {
+			t.Errorf("%s is in the review list with disposition %q", g.Prefix, g.Disposition)
+		}
+	}
+}
+
+func TestClassifySummaryLeadsWithWhatMatters(t *testing.T) {
+	summary := classifyProduction(t).Summary("/var/lib/stalwart-migrator/runs/x/unmigrated.txt")
+	if !strings.Contains(summary, "NEED YOUR REVIEW") {
+		t.Errorf("summary should call out the review bucket:\n%s", summary)
+	}
+	if !strings.Contains(summary, "71 needing review are work") {
+		t.Errorf("summary should say how much is actually work:\n%s", summary)
+	}
+	if !strings.Contains(summary, "would revert them") {
+		t.Errorf("summary should warn against restoring stock data:\n%s", summary)
+	}
+}
+
+func TestClassifyUnknownPrefixesDefaultToReview(t *testing.T) {
+	d, note := classifyPrefix("something.nobody.has.seen")
+	if d != DispositionReview {
+		t.Errorf("unknown prefix = %q, want review - guessing that an unknown setting is safe to ignore is the wrong default", d)
+	}
+	if note != "" {
+		t.Errorf("note = %q, want empty for an unclassified prefix", note)
+	}
+}

internal/backup/unmigrated_classify.go

@@ -0,0 +1,176 @@
+// SPDX-FileCopyrightText: 2026 LINUXexpert-org
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package backup
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+)
+
+// Disposition is what an operator actually has to do about a group of
+// settings migrate_v016.py didn't carry over.
+//
+// The raw count is misleading on its own, and alarmingly so. A real
+// production instance reported 12,182 unmigrated settings, which reads as
+// an impossible amount of manual work. Categorised, 8,547 of them
+// repopulate themselves, 3,337 ship with v0.16, ~198 had already been
+// carried by another mechanism, and roughly 290 genuinely needed a human.
+// The difference between those two framings is the difference between a
+// migration nobody attempts and an afternoon's review.
+type Disposition string
+
+const (
+	// DispositionRegenerates: runtime state, not configuration. Nothing to
+	// do; it rebuilds itself in normal operation.
+	DispositionRegenerates Disposition = "regenerates"
+	// DispositionShipped: v0.16 provides its own copy, and restoring
+	// v0.15's would duplicate it or replace newer definitions with older
+	// ones.
+	DispositionShipped Disposition = "shipped with v0.16"
+	// DispositionCarried: the substance came across by another route even
+	// though these particular keys are listed as unmigrated.
+	DispositionCarried Disposition = "already carried"
+	// DispositionReview: genuinely site-specific. This is the real work.
+	DispositionReview Disposition = "needs review"
+)
+
+// dispositionRule maps a setting prefix to what to do about it.
+//
+// Every entry here was checked against a v0.16.14 instance migrated from a
+// real v0.15.5 - by snapshotting the migrated store and counting what was
+// already in it - not inferred from documentation. Rules are matched
+// longest-prefix-first, because "server.blocked-ip" is runtime state while
+// "server.auto-ban" right next to it is configuration.
+type dispositionRule struct {
+	prefix      string
+	disposition Disposition
+	note        string
+}
+
+var dispositionRules = []dispositionRule{
+	{"server.blocked-ip", DispositionRegenerates,
+		"auto-ban repopulates these from live traffic; a migrated instance simply starts with an empty list"},
+
+	{"lookup.url-redirectors", DispositionShipped,
+		"v0.16 ships this list itself (observed as MemoryLookupKey/SpamUrlRedirector entries in a migrated store)"},
+	{"lookup.trusted-domains", DispositionShipped,
+		"v0.16 ships this list itself (MemoryLookupKey/SpamTrustedDomain)"},
+	{"lookup.surbl-hashbl", DispositionShipped,
+		"v0.16 ships this list itself (MemoryLookupKey)"},
+	{"spam-filter.rule", DispositionShipped,
+		"v0.16 ships its own rules - 66 SpamRule objects were present in a migrated store, the same stock set under v0.16's naming (stwt_x -> STWT_X). Restoring v0.15's would duplicate them and revert a year of updates"},
+	{"spam-filter.dnsbl", DispositionShipped,
+		"v0.16 ships its own DNSBL servers (18 SpamDnsblServer objects present after migration)"},
+	{"spam-filter.list", DispositionShipped,
+		"stock lists (file extensions and similar) that v0.16 provides itself"},
+
+	{"signature.", DispositionCarried,
+		"DKIM: carried across as DkimSignature objects, private keys included - verified on a migrated instance"},
+	{"server.listener", DispositionCarried,
+		"regenerated by this tool's own apply plan (see the supplement)"},
+}
+
+// Classification is one group of unmigrated settings with its disposition.
+type Classification struct {
+	Prefix      string
+	Keys        int
+	Disposition Disposition
+	Note        string
+}
+
+// ClassifiedReport is an UnmigratedReport with each group's disposition
+// resolved, and totals per disposition.
+type ClassifiedReport struct {
+	TotalKeys int
+	Groups    []Classification
+	Counts    map[Disposition]int
+}
+
+// Classify resolves what to do about each group in the report.
+func (r *UnmigratedReport) Classify() *ClassifiedReport {
+	out := &ClassifiedReport{Counts: map[Disposition]int{}}
+	if r == nil {
+		return out
+	}
+	out.TotalKeys = r.TotalKeys
+	for _, p := range r.Prefixes {
+		disposition, note := classifyPrefix(p.Prefix)
+		out.Groups = append(out.Groups, Classification{
+			Prefix: p.Prefix, Keys: p.Keys, Disposition: disposition, Note: note,
+		})
+		out.Counts[disposition] += p.Keys
+	}
+	sort.Slice(out.Groups, func(i, j int) bool { return out.Groups[i].Keys > out.Groups[j].Keys })
+	return out
+}
+
+func classifyPrefix(prefix string) (Disposition, string) {
+	best := -1
+	var disposition Disposition = DispositionReview
+	var note string
+	for _, rule := range dispositionRules {
+		if !strings.HasPrefix(prefix, rule.prefix) {
+			continue
+		}
+		if len(rule.prefix) > best {
+			best, disposition, note = len(rule.prefix), rule.disposition, rule.note
+		}
+	}
+	return disposition, note
+}
+
+// NeedsReview returns just the groups a human has to deal with, largest
+// first - the actual worklist, as opposed to the raw count.
+func (c *ClassifiedReport) NeedsReview() []Classification {
+	var out []Classification
+	for _, g := range c.Groups {
+		if g.Disposition == DispositionReview {
+			out = append(out, g)
+		}
+	}
+	return out
+}
+
+// Summary renders the categorised report, leading with what needs a human
+// rather than with the total.
+func (c *ClassifiedReport) Summary(worklistPath string) string {
+	if c == nil || c.TotalKeys == 0 {
+		return "no unmigrated settings were reported"
+	}
+	var b strings.Builder
+	fmt.Fprintf(&b, "%d setting(s) were not carried over by migrate_v016.py. What they actually are:\n", c.TotalKeys)
+
+	for _, d := range []Disposition{DispositionRegenerates, DispositionShipped, DispositionCarried, DispositionReview} {
+		n := c.Counts[d]
+		if n == 0 {
+			continue
+		}
+		label := string(d)
+		if d == DispositionReview {
+			label = "NEED YOUR REVIEW"
+		}
+		fmt.Fprintf(&b, "\n      %6d  %-18s", n, label)
+		groups := []string{}
+		for _, g := range c.Groups {
+			if g.Disposition == d && g.Keys > 0 {
+				groups = append(groups, fmt.Sprintf("%s (%d)", g.Prefix, g.Keys))
+			}
+		}
+		shown := groups
+		if len(shown) > 6 {
+			shown = shown[:6]
+		}
+		fmt.Fprintf(&b, "  %s", strings.Join(shown, ", "))
+		if len(groups) > len(shown) {
+			fmt.Fprintf(&b, ", +%d more", len(groups)-len(shown))
+		}
+	}
+
+	review := c.Counts[DispositionReview]
+	fmt.Fprintf(&b, "\n\n      Only the %d needing review are work. The rest either rebuild themselves,\n", review)
+	fmt.Fprintf(&b, "      ship with v0.16 (restoring v0.15's copies would revert them), or came\n")
+	fmt.Fprintf(&b, "      across by another route. Full key list: %s", worklistPath)
+	return b.String()
+}