---
id: GLAS-WP-0003
title: "First channel extension: formalize the CLI channel contract"
status: proposed
---

Scoped by `GLAS-WP-0002-T04`: of glas-harness's four charter pillars
(unified API, profile catalog, extension platform, observability),
"extension platform" is entirely unbuilt for channels — `glas_harness.cli`
is a channel in substance (a way a caller invokes a harness session) but
not in form (no `Channel` contract exists; it's just a CLI module).

This workplan does **one thing**: formalize the CLI as the first
channel extension, so the *contract* exists before a second channel
(Slack, HTTP, whatever) is attempted — not build a second channel now.
Same discipline as ADR-002/ADR-004: generalize from a real second
example, not in anticipation of one.

## Task: Define the Channel contract

A `Channel` mirrors `Rein`'s shape at a different layer: it turns an
external invocation (CLI args, a Slack message, an HTTP request) into
the `sandbox_profile`/`repo`/`title`/`description`/`rein` inputs
`run_task_through_rein` needs, and turns its `dict[str, Any]` result back
into whatever the invocation medium expects (stdout JSON for CLI, a
Slack reply, an HTTP response body). Minimal ABC:

```python
class Channel(ABC):
    @abstractmethod
    def parse_invocation(self, raw: Any) -> GatewayInvocation: ...

    @abstractmethod
    def render_result(self, result: dict[str, Any]) -> Any: ...
```

Document in `docs/channel-contract.md`, parallel to
`docs/harness-contract.md`.

```task
id: GLAS-WP-0003-T01
status: todo
priority: medium
```

## Task: Refactor glas_harness.cli into a CLIChannel

`src/glas_harness/channels/cli_channel.py`: `CLIChannel(Channel)`
implementing `parse_invocation` (argparse → `GatewayInvocation`) and
`render_result` (→ `json.dumps(..., indent=2)`, matching today's output
exactly — this is a refactor, not a behavior change). `cli.py` becomes a
thin `main()` that constructs a `CLIChannel` and calls it; existing CLI
usage and output are unchanged.

```task
id: GLAS-WP-0003-T02
status: todo
priority: medium
```

## Task: Tests + verify no behavior change

Unit tests for `CLIChannel.parse_invocation`/`render_result` in
isolation, plus re-running the existing live-proof commands (both
reins) to confirm identical CLI output before/after the refactor.

```task
id: GLAS-WP-0003-T03
status: todo
priority: medium
```

## Task: Document the pattern for a second channel

A short section in `docs/channel-contract.md` sketching what a second
channel (e.g. a Slack or HTTP channel) would need to implement,
without building one — this workplan stops at "the contract exists and
one real implementation proves it," matching the discipline applied
throughout this session's other deferred-until-a-second-example
decisions.

```task
id: GLAS-WP-0003-T04
status: todo
priority: low
```