passwords: Phase B browser/manager propagation engine (pwgen + pwstore + CLI)

Add the secondary-persona path from docs/BROWSER-ROTATION.md: ingest a password
manager / browser store, take a mandatory verified sealed backup, generate fresh
strong passwords, hand the human a ready-to-finish task at the MFA wall, and commit
the new value into the manager only after the site change is confirmed.

- internal/pwgen: crypto/rand generator (rejection sampling, per-class guarantee,
  vault-native — never returns plaintext as a Go string).
- internal/pwstore: Manager/ItemUpdater/BulkImporter contracts, secrets-free
  RedactIdentity, and five adapters — bitwarden (bw, stdin), keepassxc
  (keepassxc-cli, stdin), 1password (op, argv assignment with documented caveat),
  chrome/firefox (tmpfs CSV ingest-and-shred). All real code; validation status is
  data (MOCK-ONLY against fake binaries/CSVs, recorded in the design doc).
- internal/pwstore/stage.go: age-sealed staged-list (WriteStaged/ReadStaged) +
  StagedImporter — the only artifacts crossing the plan->commit gap, never plaintext.
- cmd/incredigo: passwords scan|plan|guide|commit. Backup gate seals + round-trip
  verifies before any commit; guide is interactive verify-before-commit; commit is
  headless over a sealed stage. Browser CSV writes are gated behind --allow-csv.

Hard rules honored: backup-before-commit, verify-before-commit, no plaintext on
disk (browser CSV is the flag-gated tmpfs+shred exception), MFA always a human
handoff. go vet + -race clean; end-to-end verified against a fake bw.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/pwstore/pwstore_test.go

@@ -0,0 +1,115 @@
+package pwstore
+
+import (
+	"os"
+	"strings"
+	"testing"
+
+	"incredigo/internal/vault"
+)
+
+func handleStr(t *testing.T, v *vault.Vault, h *vault.Handle) string {
+	t.Helper()
+	buf, err := v.Open(h)
+	if err != nil {
+		t.Fatalf("open: %v", err)
+	}
+	return string(buf.Bytes())
+}
+
+func TestParseLoginCSVChrome(t *testing.T) {
+	v := vault.New()
+	defer v.Purge()
+	data := []byte("name,url,username,password,note\n" +
+		"GitHub,https://github.com/login,alice@example.com,s3cr3t-old,\n" +
+		"Example,https://app.example.com/,bob,hunter2,a note\n")
+	accts, err := parseLoginCSV(v, data)
+	if err != nil {
+		t.Fatalf("parse: %v", err)
+	}
+	if len(accts) != 2 {
+		t.Fatalf("got %d accounts, want 2", len(accts))
+	}
+	if accts[0].Site != "github.com" || accts[0].Username != "alice@example.com" {
+		t.Errorf("account0 = %+v", accts[0])
+	}
+	if pw := handleStr(t, v, accts[0].Secret); pw != "s3cr3t-old" {
+		t.Errorf("account0 password = %q", pw)
+	}
+	if accts[1].Site != "app.example.com" || accts[1].Meta["name"] != "Example" {
+		t.Errorf("account1 = %+v", accts[1])
+	}
+}
+
+func TestParseLoginCSVNoPasswordColumn(t *testing.T) {
+	v := vault.New()
+	defer v.Purge()
+	if _, err := parseLoginCSV(v, []byte("name,url,username\nx,y,z\n")); err == nil {
+		t.Error("expected error when csv has no password column")
+	}
+}
+
+func TestRedactIdentity(t *testing.T) {
+	cases := []struct{ site, url, user, want string }{
+		{"github.com", "", "alice@example.com", "github.com / a…@example.com"},
+		{"", "https://app.example.com/login", "bob", "app.example.com / b…"},
+		{"site.test", "", "", "site.test"},
+		{"", "", "", "(unknown login)"},
+	}
+	for _, c := range cases {
+		got := RedactIdentity(Account{Site: c.site, URL: c.url, Username: c.user})
+		if got != c.want {
+			t.Errorf("RedactIdentity(%q,%q,%q) = %q, want %q", c.site, c.url, c.user, got, c.want)
+		}
+	}
+}
+
+func TestRedactIdentityNeverLeaksPassword(t *testing.T) {
+	// The password is not even a field RedactIdentity sees, but assert the label
+	// for a realistic account contains no secret-looking material beyond masked user.
+	id := RedactIdentity(Account{Site: "bank.test", Username: "verylongusername@mail.test"})
+	if strings.Contains(id, "verylongusername") {
+		t.Errorf("identity %q leaked the full username", id)
+	}
+}
+
+func TestWriteShreddableCSVAndShred(t *testing.T) {
+	v := vault.New()
+	defer v.Purge()
+	accts := []Account{
+		{URL: "https://a.test/", Username: "u1", Secret: v.Store([]byte("old1")), Meta: map[string]string{"name": "A"}},
+		{URL: "https://b.test/", Username: "u2", Secret: v.Store([]byte("old2")), Meta: map[string]string{"name": "B"}},
+	}
+	newPw := map[int]*vault.Handle{0: v.Store([]byte("NEW-pw-1"))}
+
+	path, cleanup, err := writeShreddableCSV(v, accts, newPw)
+	if err != nil {
+		t.Fatalf("writeShreddableCSV: %v", err)
+	}
+	// Read it back BEFORE shred to confirm new pw substituted, old kept where absent.
+	raw, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("read csv: %v", err)
+	}
+	s := string(raw)
+	if !strings.Contains(s, "NEW-pw-1") {
+		t.Errorf("csv missing substituted new password:\n%s", s)
+	}
+	if !strings.Contains(s, "old2") {
+		t.Errorf("csv missing untouched old password for second account:\n%s", s)
+	}
+	if !strings.HasPrefix(s, "name,url,username,password,note") {
+		t.Errorf("csv header wrong:\n%s", s)
+	}
+
+	cleanup() // shred + remove
+	if _, err := os.Stat(path); !os.IsNotExist(err) {
+		t.Errorf("expected file removed after shred, stat err = %v", err)
+	}
+}
+
+func TestShredMissingFileNoError(t *testing.T) {
+	if err := Shred("/dev/shm/incredigo/does-not-exist-xyz.csv"); err != nil {
+		t.Errorf("Shred of missing file should be nil, got %v", err)
+	}
+}