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/chromecsv_test.go

@@ -0,0 +1,95 @@
+package pwstore
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"incredigo/internal/vault"
+)
+
+func writeTempCSV(t *testing.T, body string) string {
+	t.Helper()
+	p := filepath.Join(t.TempDir(), "chrome-export.csv")
+	if err := os.WriteFile(p, []byte(body), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	return p
+}
+
+func TestChromeExportFromCSV(t *testing.T) {
+	v := vault.New()
+	defer v.Purge()
+	path := writeTempCSV(t,
+		"name,url,username,password,note\n"+
+			"GitHub,https://github.com/login,alice@example.com,old1,\n"+
+			"App,https://app.example.com/,bob,old2,\n")
+	c := &ChromeCSV{ExportPath: path}
+
+	if !c.Available() {
+		t.Fatal("Available should be true when export file exists")
+	}
+	accts, err := c.Export(context.Background(), v)
+	if err != nil {
+		t.Fatalf("Export: %v", err)
+	}
+	if len(accts) != 2 {
+		t.Fatalf("got %d accounts, want 2", len(accts))
+	}
+	if accts[0].Site != "github.com" {
+		t.Errorf("site = %q", accts[0].Site)
+	}
+	if pw := handleStr(t, v, accts[0].Secret); pw != "old1" {
+		t.Errorf("password = %q, want old1", pw)
+	}
+}
+
+func TestChromeUnavailableWithoutPath(t *testing.T) {
+	c := &ChromeCSV{}
+	if c.Available() {
+		t.Error("Available should be false with no export path")
+	}
+	if _, err := c.Export(context.Background(), vault.New()); err == nil {
+		t.Error("Export should error with no export path")
+	}
+}
+
+func TestChromeBareImportRefuses(t *testing.T) {
+	c := &ChromeCSV{}
+	if err := c.Import(context.Background(), vault.New(), nil); err == nil {
+		t.Error("bare Import must refuse and direct callers to ImportStaged")
+	}
+}
+
+func TestChromeImportStagedWritesThenShreds(t *testing.T) {
+	v := vault.New()
+	defer v.Purge()
+	c := &ChromeCSV{}
+	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-1"))}
+
+	path, cleanup, err := c.ImportStaged(v, accts, newPw)
+	if err != nil {
+		t.Fatalf("ImportStaged: %v", err)
+	}
+	raw, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("read staged csv: %v", err)
+	}
+	s := string(raw)
+	if !strings.Contains(s, "NEW-1") {
+		t.Errorf("staged csv missing substituted new password:\n%s", s)
+	}
+	if !strings.Contains(s, "old2") {
+		t.Errorf("staged csv missing untouched second password:\n%s", s)
+	}
+	cleanup()
+	if _, err := os.Stat(path); !os.IsNotExist(err) {
+		t.Errorf("staged csv should be shredded+removed after cleanup, stat err = %v", err)
+	}
+}