## ADDED Requirements

### Requirement: TGZ adapter composes tar over a codec

The package SHALL export `TgzArchiveStorage` implementing the structural `DriveStorage` view by composing a tar adapter over a pluggable codec. The default constructor MUST accept `codec: ArchiveCodec` and SHALL ship a convenience `openTarGz(source, opts)` that defaults to `gzipCodec` from `@suaveplan/drive-storage-gz`.

#### Scenario: Default tar.gz opens with gzip codec

- **WHEN** `openTarGz(bytes, { mode: "read-only" })` is called on valid `.tar.gz` bytes
- **THEN** entries from the inner tar are listed and read correctly

### Requirement: Codec slot for tar.bz2, tar.xz, tar.zst

The package SHALL accept any object satisfying the `ArchiveCodec` interface (`compress`, `decompress`). Codecs for bzip2, xz, and zstd are NOT shipped in v0.1.0 but the slot MUST be functional so consumers can plug them in. Construction with no codec MUST raise `ARCHIVE_CODEC_MISSING`.

#### Scenario: Custom xz codec works

- **WHEN** `new TgzArchiveStorage(bytes, { codec: customXzCodec })` is constructed and the bytes are a valid `.tar.xz`
- **THEN** entries are listed and read correctly using the custom codec's `decompress`

#### Scenario: Missing codec rejects clearly

- **WHEN** `new TgzArchiveStorage(bytes, {})` is constructed without a codec
- **THEN** construction throws `ARCHIVE_CODEC_MISSING`

### Requirement: Read-mostly with full re-encode on write

The adapter SHALL support `read-only`, `copy-on-write`, and `rewrite` modes. Writes MUST re-encode the full tar and then the full codec output. The cost MUST be documented and `pendingMutationCount` exposed.

#### Scenario: Round-trip write

- **WHEN** an adapter in `copy-on-write` mode adds one entry and calls `flush()`
- **THEN** the host bytes contain a valid codec-wrapped tar whose entry list contains the new entry

### Requirement: Error code registry

The package SHALL register stable codes including `TGZ_CODEC_FAILED`, `TGZ_INNER_TAR_INVALID`. Format-specific errors from the underlying tar and codec packages MUST be propagated unchanged.

#### Scenario: Inner tar corruption surfaces

- **WHEN** the codec decompresses successfully but the resulting tar bytes fail header checksum validation
- **THEN** the error chain contains both `TGZ_INNER_TAR_INVALID` and the underlying `TAR_HEADER_CHECKSUM_INVALID`