# Source Adapter Contract

## Purpose

This document pins the v1 contract for source-format adapters. It is the
handoff from `MKTT-WP-0019` to `MKTT-WP-0018`: `markitect-tool` implements the
contract, registry, CLI, public API, and tests; `markitect-filter` implements
concrete adapters, starting with EPUB3.

The v1 contract is intentionally read-only. It normalizes heterogeneous source
formats into canonical Markitect Markdown plus metadata, provenance, quality
signals, and diagnostics. Writer/export adapters are future scope.

## Scope

The v1 source adapter layer supports:

- local filesystem source inputs
- deterministic inspection and normalization
- package-provided read adapters discovered through Python entry points
- optional dependencies isolated in adapter packages
- JSON-serializable normalized Markdown outputs
- contract tests with fake adapters and small fixtures

The v1 layer does not support:

- EPUB3, PDF, DOCX, ODT, OCR, browser, or archive parsing in `markitect-tool`
- write/export adapters
- network fetching for source URIs
- durable ingestion, permissions, retrieval, or governance
- hidden AI-assisted repair or enrichment

URI fields appear in the model so adapters can preserve source identity, but
v1 CLI/API inputs are local paths unless a later workplan opens remote source
loading explicitly.

## Package Shape

External adapter packages should depend on `markitect-tool` and register one or
more read adapter descriptors through the entry point group
`markitect_tool.source_adapters`.

Recommended `markitect-filter` shape:

```text
markitect_filter/
  src/markitect_filter/
    __init__.py
    epub3.py
    adapters.py
  tests/
    fixtures/epub3/
    test_epub3_adapter.py
  pyproject.toml
```

The package should expose a lightweight descriptor function that does not
import heavyweight format dependencies until the adapter is instantiated or
used. For example:

```toml
[project.entry-points."markitect_tool.source_adapters"]
epub3 = "markitect_filter.adapters:epub3_adapter_descriptor"
```

Adapter packages may use extras such as `markitect-filter[epub3]` or
`markitect-filter[pdf]`. Missing optional dependencies must be reported through
structured diagnostics; they must not surface as raw import errors.

## Descriptor Contract

`MKTT-WP-0018` should implement a `SourceAdapterDescriptor` dataclass and map
it into the existing `ExtensionDescriptor` catalog with kind `source-adapter`.

Required descriptor fields:

| Field | Type | Meaning |
| --- | --- | --- |
| `id` | `str` | Stable adapter id, for example `source.epub3`. |
| `version` | `str` | Adapter contract implementation version. |
| `name` | `str` | Human-readable adapter name. |
| `operations` | `list[str]` | V1 must contain only `read`. |
| `media_types` | `list[str]` | Supported media types, lower-case. |
| `extensions` | `list[str]` | Supported file suffixes including dots. |
| `factory` | callable | Returns a `SourceReadAdapter`. |

Optional descriptor fields:

| Field | Type | Meaning |
| --- | --- | --- |
| `summary` | `str | None` | Short description for CLI and docs. |
| `option_schema` | `dict` | JSON-schema-like adapter options. |
| `optional_dependencies` | `list[OptionalDependency]` | Runtime libraries needed by the adapter. |
| `safety` | `dict` | Reads files, network, external processes, and related flags. |
| `quality_profile` | `dict` | Known extraction quality behavior. |
| `metadata` | `dict` | Adapter-specific metadata. |

The corresponding `ExtensionDescriptor` should use:

```text
id: same as SourceAdapterDescriptor.id
kind: source-adapter
input_contract: SourceInspectRequest | SourceReadRequest
output_contract: SourceInspectResult | SourceReadResult
diagnostics_namespace: source
provenance_prefix: source.<adapter>
```

Capabilities should include:

```text
source read
markdown normalize
diagnostics emit
provenance emit
filesystem read
```

Descriptor IDs are globally unique. Duplicate IDs from external packages are
registry errors. Descriptors from package entry points are sorted by ID for
deterministic listing.

## Entry Point Contract

The entry point group is:

```text
markitect_tool.source_adapters
```

Each entry point may load to one of:

- a `SourceAdapterDescriptor`
- an iterable of `SourceAdapterDescriptor`
- a callable returning either of the above

Discovery must not instantiate adapters unless the loaded object itself is a
descriptor factory. Descriptors should remain cheap enough to list without
format-specific imports.

Discovery errors should produce diagnostics with code
`source.discovery_failed`. Missing optional dependencies declared by a
descriptor should produce `source.missing_dependency` and mark that adapter
unavailable for reads until the dependency is installed.

## Data Model

All model objects must support stable `to_dict()` serialization. Serialization
rules:

- omit `None`, empty lists, empty dicts, and empty strings
- preserve `False`, `0`, and empty Markdown content where semantically valid
- use UTF-8 text
- use canonical JSON with sorted keys and compact separators when computing
  hashes or cache keys
- keep all timestamps and dates as strings unless they are filesystem metadata
  such as `mtime_ns`

### `SourceAsset`

| Field | Required | Type | Meaning |
| --- | --- | --- | --- |
| `uri` | yes | `str` | Stable source URI. For local files, use a normalized path URI or path string. |
| `path` | no | `str` | Local path when available. |
| `name` | no | `str` | Display name or basename. |
| `media_type` | no | `str` | Detected or declared media type. |
| `extension` | no | `str` | Lower-case suffix including the dot. |
| `size` | no | `int` | Byte size for local files. |
| `mtime_ns` | no | `int` | Local file modification timestamp in nanoseconds. |
| `digest` | no | `str` | `sha256:<hex>` of source bytes when available. |
| `metadata` | no | `dict` | Source asset metadata that is not document metadata. |

### `SourceMetadata`

| Field | Required | Type | Meaning |
| --- | --- | --- | --- |
| `title` | no | `str` | Source title. |
| `creators` | no | `list[str]` | Authors or creators in source order. |
| `language` | no | `str` | BCP 47 language tag when known. |
| `rights` | no | `str` | Rights or license text from the source. |
| `source_url` | no | `str` | Original public URL when known. |
| `publication_date` | no | `str` | Source publication date string. |
| `publisher` | no | `str` | Publisher name. |
| `identifiers` | no | `dict[str, str]` | ISBN, DOI, package IDs, and similar identifiers. |
| `raw` | no | `dict` | Adapter-preserved raw metadata. |

### `SourceProvenance`

| Field | Required | Type | Meaning |
| --- | --- | --- | --- |
| `source_uri` | yes | `str` | Source asset URI. |
| `source_path` | no | `str` | Local source path. |
| `source_href` | no | `str` | Package-internal href or document-relative reference. |
| `package_path` | no | `str` | Archive/package member path, such as EPUB XHTML. |
| `anchor` | no | `str` | Source anchor or fragment. |
| `page` | no | `str` | Page label or number where available. |
| `section` | no | `str` | Chapter, section, or nav label. |
| `start_offset` | no | `int` | Adapter-defined start offset. |
| `end_offset` | no | `int` | Adapter-defined end offset. |
| `digest` | no | `str` | Digest of the specific source component. |
| `metadata` | no | `dict` | Adapter-specific provenance details. |

### `NormalizedMarkdownSegment`

| Field | Required | Type | Meaning |
| --- | --- | --- | --- |
| `segment_id` | yes | `str` | Stable ID unique within the document. |
| `order` | yes | `int` | Zero-based reading order. |
| `markdown` | yes | `str` | Canonical Markdown for the segment. |
| `heading` | no | `str` | Primary heading text for the segment. |
| `heading_level` | no | `int` | Markdown heading level when known. |
| `anchors` | no | `list[str]` | Source anchors covered by the segment. |
| `provenance` | no | `list[SourceProvenance]` | Source spans contributing to the segment. |
| `metadata` | no | `dict` | Adapter-specific segment metadata. |

Segment IDs should be deterministic. Prefer source anchors when they are stable
and unique. Otherwise use ordinal IDs such as `seg-0001`, `seg-0002`, and so
on. Segment order is always authoritative for reading order.

### `NormalizationQuality`

| Field | Required | Type | Meaning |
| --- | --- | --- | --- |
| `lossiness` | yes | `str` | One of `none`, `low`, `medium`, `high`, or `unknown`. |
| `confidence` | no | `float` | Adapter confidence from `0.0` to `1.0`. |
| `skipped_items` | no | `int` | Count of skipped source items. |
| `warnings` | no | `int` | Count of warning diagnostics. |
| `metadata` | no | `dict` | Adapter-specific quality details. |

### `NormalizedMarkdownDocument`

| Field | Required | Type | Meaning |
| --- | --- | --- | --- |
| `schema_version` | yes | `str` | V1 uses `markitect.source.v1`. |
| `document_id` | yes | `str` | Stable normalized document ID. |
| `asset` | yes | `SourceAsset` | Original source identity. |
| `metadata` | yes | `SourceMetadata` | Source document metadata. |
| `markdown` | yes | `str` | Full normalized Markdown. |
| `segments` | yes | `list[NormalizedMarkdownSegment]` | Ordered segment list. |
| `quality` | yes | `NormalizationQuality` | Extraction quality summary. |
| `diagnostics` | no | `list[Diagnostic]` | Existing Markitect diagnostic shape. |
| `provenance` | no | `list[SourceProvenance]` | Document-level provenance. |
| `attachments` | no | `list[SourceAsset]` | Referenced binary assets; v1 metadata only. |
| `adapter` | yes | `dict` | Adapter id, version, and options. |
| `cache_key` | yes | `str` | Deterministic normalization cache key. |

The full `markdown` field should be equal to the ordered segment Markdown joined
with exactly two newlines, unless an adapter has a documented reason to emit
document-level frontmatter or separators.

## Hashing And Cache Keys

Source asset digests use the source bytes:

```text
sha256:<hex>
```

Document IDs should be stable across machines and based on:

- normalized source asset URI or path
- source asset digest when available
- adapter ID
- adapter version

Normalization cache keys should be based on canonical JSON containing:

- source asset URI or path
- source asset digest
- adapter ID
- adapter version
- normalized model version
- read options

Use this prefix:

```text
source-normalize:sha256:<hex>
```

## Read Adapter Protocol

`MKTT-WP-0018` should implement Python `Protocol` classes equivalent to:

```python
class SourceReadAdapter(Protocol):
    descriptor: SourceAdapterDescriptor

    def can_read(self, request: SourceAdapterMatchRequest) -> SourceAdapterMatch:
        ...

    def inspect(self, request: SourceInspectRequest) -> SourceInspectResult:
        ...

    def read(self, request: SourceReadRequest) -> SourceReadResult:
        ...
```

Request and result objects:

| Type | Required fields | Meaning |
| --- | --- | --- |
| `SourceAdapterMatchRequest` | `asset`, `options` | Cheap matching request. |
| `SourceAdapterMatch` | `adapter_id`, `matched`, `confidence`, `reason`, `diagnostics` | Match result. Confidence is `0` to `100`. |
| `SourceInspectRequest` | `asset`, `options` | Metadata-only inspection request. |
| `SourceInspectResult` | `valid`, `asset`, `adapter`, `metadata`, `capabilities`, `diagnostics`, `quality` | Inspection result without full Markdown conversion. |
| `SourceReadRequest` | `asset`, `options` | Full normalization request. |
| `SourceReadResult` | `valid`, `document`, `diagnostics` | Normalized read result. |

`inspect` must not perform full conversion. It may open enough of the source to
validate structure and collect metadata. `read` may perform full extraction.

Options must be JSON-serializable. Adapter-specific options should be declared
in `option_schema`. Unknown options should produce
`source.unknown_option` unless the descriptor explicitly permits free-form
options.

## Adapter Selection

Selection is deterministic:

1. If an explicit adapter ID is provided, use only that descriptor.
2. Prefer media type matches over extension-only matches.
3. Prefer higher `can_read().confidence`.
4. Prefer descriptors with required optional dependencies available.
5. Break remaining ties by descriptor ID in ascending lexical order and emit
   warning `source.adapter_ambiguous`.

No matching adapter returns an error diagnostic:

```text
source.unsupported_format
```

Malformed sources return an error diagnostic:

```text
source.malformed
```

Missing required optional dependencies return:

```text
source.missing_dependency
```

Warnings do not make a result invalid. Any error diagnostic makes `valid`
false.

## CLI Contract

The public commands are:

```bash
mkt source adapters
mkt source inspect <path>
mkt source normalize <path> --format markdown
```

Common options:

```text
--adapter <adapter-id>       Explicit adapter selection.
--format text|json|yaml      For adapters and inspect.
--format markdown|json|yaml  For normalize.
--option key=value           Adapter-specific option, repeatable.
--output <path>              Write normalized output.
```

Exit behavior:

| Exit | Meaning |
| --- | --- |
| `0` | Operation valid; warning diagnostics may exist. |
| `1` | Operation completed with error diagnostics. |
| `2` | CLI usage error from Click. |

JSON output must contain a top-level `valid` field for operations that can
fail. Markdown output writes only normalized Markdown to stdout or `--output`;
diagnostics for Markdown output go to stderr. If normalization is invalid, do
not emit partial Markdown unless a future option explicitly requests it.

## API Contract

`MKTT-WP-0018` should export these names from `markitect_tool`:

```text
SourceAsset
SourceMetadata
SourceProvenance
NormalizedMarkdownSegment
NormalizedMarkdownDocument
NormalizationQuality
SourceAdapterDescriptor
SourceReadAdapter
SourceAdapterRegistry
SourceAdapterMatchRequest
SourceAdapterMatch
SourceInspectRequest
SourceInspectResult
SourceReadRequest
SourceReadResult
default_source_adapter_registry
discover_source_adapters
inspect_source
normalize_source
```

Direct API helpers should accept an optional registry and adapter ID so tests
and sibling repos can avoid global discovery when they need deterministic
fixtures.

## Contract Tests For MKTT-WP-0018

Implementation should add tests for:

- `SourceAsset`, metadata, provenance, quality, segment, and document
  serialization
- source document cache-key determinism
- fake in-tree adapter registration and read behavior
- fake external entry point discovery
- optional dependency diagnostics
- unsupported format diagnostics
- malformed source diagnostics
- adapter selection tie behavior
- CLI `source adapters` JSON fixture
- CLI `source inspect` JSON fixture
- CLI `source normalize --format json` fixture
- CLI `source normalize --format markdown` fixture
- public API exports

Fixtures live in `examples/source-adapters/` and should be reused by tests where
practical.

## Markitect-filter Handoff

The first `markitect-filter` implementation should provide an EPUB3 descriptor:

```text
id: source.epub3
name: EPUB3
operations: read
media_types: application/epub+zip
extensions: .epub
entry_point: markitect_filter.adapters:epub3_adapter_descriptor
```

The EPUB3 adapter should inspect and normalize:

- `META-INF/container.xml`
- the OPF package document
- Dublin Core and package metadata
- spine reading order
- navigation labels
- body XHTML as ordered Markdown segments
- source hrefs, anchors, sections, and page references where available

It should classify or skip cover, navigation, table-of-contents, header,
footer, license, and transcriber-note material through explicit options and
diagnostics. It should report unsupported media, malformed package structure,
skipped assets, and lossy extraction.