Give each failure one error value (closes #113)

internal/cli's copies of vault.ErrSecretNotFound, ErrVaultNotFound,
ErrVersionNotFound and ErrSecretExists are removed; the commands wrap the
vault errors. errUnsupportedUnlockerType is removed for
errInvalidUnlockerType, which names the same failure. Every error of
secret.ReadPassphrase wraps ErrPassphraseNotRead, so its callers no longer
add those words. ResolveGPGKeyFingerprint returns ErrGPGKeyNotFound for a
key the keyring lacks, recognised by gpg's status line. storeInKeychain
returns errNilDataBuffer. bip85's ErrPasswordTooShort and
ErrEncodedTooShort go with their unreachable checks. Tests that matched
these errors' text use errors.Is.

Model: opus-5-5

internal/cli/errors_test.go

@@ -0,0 +1,62 @@
+package cli_test
+
+import (
+	"testing"
+
+	"git.eeqj.de/sneak/secret/internal/cli"
+	"git.eeqj.de/sneak/secret/internal/vault"
+	"github.com/spf13/cobra"
+)
+
+// TestMissingSecretOrVaultErrors checks that a command that finds no such
+// secret or vault returns the vault package's error for it, as `secret get`
+// does, and leaves the vaults unchanged. "default" is the current vault, and
+// both vaults hold the secret "x".
+func TestMissingSecretOrVaultErrors(t *testing.T) {
+	t.Parallel()
+
+	before := snapshotStateDir(t, newTwoVaultFs(t))
+
+	tests := []struct {
+		command string
+		want    error
+		run     func(c *cli.Instance) error
+	}{
+		{
+			"rm --force nosuch", vault.ErrSecretNotFound,
+			func(c *cli.Instance) error {
+				return c.RemoveSecret(&cobra.Command{}, "nosuch", true)
+			},
+		},
+		{
+			"version rm --force nosuch", vault.ErrSecretNotFound,
+			func(c *cli.Instance) error {
+				return c.RemoveVersion(&cobra.Command{}, "nosuch", "20260101.001", true)
+			},
+		},
+		{
+			"mv --force work:nosuch default", vault.ErrSecretNotFound,
+			func(c *cli.Instance) error {
+				return c.MoveSecret(&cobra.Command{}, "work:nosuch", "default", true)
+			},
+		},
+		{
+			"decrypt nosuch", vault.ErrSecretNotFound,
+			func(c *cli.Instance) error { return c.Decrypt("nosuch", "", "") },
+		},
+		{
+			"vault rm --force nosuch", vault.ErrVaultNotFound,
+			func(c *cli.Instance) error {
+				return c.RemoveVault(&cobra.Command{}, "nosuch", true)
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.command, func(t *testing.T) {
+			t.Parallel()
+
+			requireRejectedAndUnchanged(t, before, tt.want, tt.run)
+		})
+	}
+}