feat: add provider downgrade command (PRA-226)

src/pragma_cli/commands/providers.py

@@ -766,7 +766,7 @@ def upgrade(
     console.print()
 
     if not yes:
-        confirm = typer.confirm("Proceed with upgrade?")
+        confirm = typer.confirm(f"Upgrade {name} to v{target}?")
 
         if not confirm:
             console.print("[dim]Cancelled.[/dim]")
@@ -792,6 +792,62 @@ def upgrade(
     console.print(f"[green]Upgraded:[/green] {name} -> v{result.installed_version}")
 
 
+@app.command()
+def downgrade(
+    name: Annotated[str, typer.Argument(help="Provider name (org/name format)")],
+    version: Annotated[str, typer.Option("--version", "-v", help="Target version to downgrade to")],
+    yes: Annotated[
+        bool,
+        typer.Option("--yes", "-y", help="Skip confirmation prompt"),
+    ] = False,
+) -> None:
+    """Downgrade an installed provider to a previous version.
+
+    Requires an explicit target version. Migrations run sequentially
+    through each intermediate version in reverse order.
+
+    Examples:
+        pragma providers downgrade pragmatiks/qdrant --version 1.0.0
+        pragma providers downgrade pragmatiks/postgres -v 1.2.0 -y
+    """  # noqa: DOC501
+    client = get_client()
+    _require_auth(client)
+
+    console.print(f"[bold]Downgrading:[/bold] {name} -> v{version}")
+    console.print()
+
+    if not yes:
+        confirm = typer.confirm(f"Downgrade {name} to v{version}?")
+
+        if not confirm:
+            console.print("[dim]Cancelled.[/dim]")
+            raise typer.Exit(0)
+
+    try:
+        result = _fetch_with_spinner(
+            "Downgrading provider...",
+            lambda: client.downgrade_provider(name, target_version=version),
+        )
+    except httpx.HTTPStatusError as e:
+        if e.response.status_code == 404:
+            console.print(f"[red]Error:[/red] Provider '{name}' is not installed.")
+            raise typer.Exit(1) from e
+
+        if e.response.status_code == 409:
+            console.print(f"[yellow]Warning:[/yellow] Provider '{name}' is already on v{version}.")
+            raise typer.Exit(1) from e
+
+        if e.response.status_code == 422:
+            console.print(f"[red]Error:[/red] {_format_api_error(e)}")
+            console.print("[dim]The version chain between current and target may be broken.[/dim]")
+            raise typer.Exit(1) from e
+
+        console.print(f"[red]Error:[/red] {_format_api_error(e)}")
+        raise typer.Exit(1) from e
+
+    console.print(f"[green]Downgraded:[/green] {name} -> v{result.installed_version}")
+
+
 @app.command("list")
 def list_providers(
     trust_tier: Annotated[

tests/test_providers.py

@@ -729,6 +729,64 @@ def test_upgrade_already_on_version(cli_runner, mock_pragma_client):
     assert "already on the requested version" in result.output
 
 
+# ---------------------------------------------------------------------------
+# Downgrade command tests
+# ---------------------------------------------------------------------------
+
+
+def test_downgrade_success(cli_runner, mock_pragma_client, mocker):
+    """Downgrade command downgrades provider to specified version."""
+    downgraded = mocker.Mock()
+    downgraded.installed_version = "1.0.0"
+    mock_pragma_client.downgrade_provider.return_value = downgraded
+
+    result = cli_runner.invoke(app, ["providers", "downgrade", "qdrant", "--version", "1.0.0", "-y"])
+
+    assert result.exit_code == 0
+    assert "Downgraded" in result.output
+    assert "1.0.0" in result.output
+    mock_pragma_client.downgrade_provider.assert_called_once_with("qdrant", target_version="1.0.0")
+
+
+def test_downgrade_already_on_version(cli_runner, mock_pragma_client):
+    """Downgrade command handles 409 (already on version)."""
+    mock_response = httpx.Response(409, json={"detail": "Already on version"})
+    mock_pragma_client.downgrade_provider.side_effect = httpx.HTTPStatusError(
+        "Conflict", request=httpx.Request("POST", "http://test"), response=mock_response
+    )
+
+    result = cli_runner.invoke(app, ["providers", "downgrade", "qdrant", "--version", "1.0.0", "-y"])
+
+    assert result.exit_code == 1
+    assert "already on v1.0.0" in result.output
+
+
+def test_downgrade_not_installed(cli_runner, mock_pragma_client):
+    """Downgrade command handles 404 (provider not installed)."""
+    mock_response = httpx.Response(404, json={"detail": "Not found"})
+    mock_pragma_client.downgrade_provider.side_effect = httpx.HTTPStatusError(
+        "Not Found", request=httpx.Request("POST", "http://test"), response=mock_response
+    )
+
+    result = cli_runner.invoke(app, ["providers", "downgrade", "qdrant", "--version", "1.0.0", "-y"])
+
+    assert result.exit_code == 1
+    assert "not installed" in result.output
+
+
+def test_downgrade_version_chain_broken(cli_runner, mock_pragma_client):
+    """Downgrade command handles 422 (version chain broken)."""
+    mock_response = httpx.Response(422, json={"detail": "Missing intermediate version 1.5.0"})
+    mock_pragma_client.downgrade_provider.side_effect = httpx.HTTPStatusError(
+        "Unprocessable Entity", request=httpx.Request("POST", "http://test"), response=mock_response
+    )
+
+    result = cli_runner.invoke(app, ["providers", "downgrade", "qdrant", "--version", "1.0.0", "-y"])
+
+    assert result.exit_code == 1
+    assert "version chain" in result.output.lower()
+
+
 # ---------------------------------------------------------------------------
 # List command tests (store browsing)
 # ---------------------------------------------------------------------------