Add dg plus integrations dbt download-manifest command (#22095)

Adds a new standalone `download-manifest` subcommand that allows users
to download dbt manifests from Dagster Plus for local development
without requiring a deploy session. This enables the dbt `--defer` flag
for slim CI workflows. The change also extracts shared project discovery
logic into a reusable helper to reduce duplication between the two
manifest commands.

## Key Changes

- Extract `_discover_dbt_projects()` helper to deduplicate DbtProject
discovery logic between `manage-manifest` and `download-manifest`
- Add `download-manifest` subcommand with `--components`, `--file`,
`--output`, and `--key-prefix` options for standalone manifest downloads
- Refactor `manage-manifest` to use the new discovery helper
- Consolidate dbt integration documentation into single `dbt.md` file
covering both commands

<details>
<summary>Files Changed</summary>

### Modified (2 files)
-
`dagster-oss/python_modules/libraries/dagster-dg-cli/dagster_dg_cli/cli/plus/integrations/dbt.py`
- Added discovery helper and new download-manifest command
-
`public/skills/skills/dagster-expert/skills/dagster-expert/references/cli/plus/INDEX.md`
- Updated to reference consolidated dbt.md file

### Added (1 file)
-
`public/skills/skills/dagster-expert/skills/dagster-expert/references/cli/plus/integrations/dbt.md`
- Combined documentation for both manifest management commands

### Deleted (1 file)
-
`public/skills/skills/dagster-expert/skills/dagster-expert/references/cli/plus/integrations/dbt-manage-manifest.md`
- Consolidated into dbt.md

</details>

## User Experience

**Before:**
```bash
# Requires DAGSTER_BUILD_STATEDIR (deploy session)
dg plus integrations dbt manage-manifest
```

**After:**
```bash
# Standalone download, no deploy session required
dg plus integrations dbt download-manifest --components . --output ./manifest.json
```

Users can now download dbt manifests locally for `--defer` / slim CI
without needing a deploy environment configured.

<details>
<summary>original-plan</summary>

# Plan: Add `dg plus integrations dbt download-manifest` command

## Context

Users want to download a dbt manifest from Dagster Plus for local
development without needing a CI deploy session. The existing
`manage-manifest` command requires a deploy session
(`DAGSTER_BUILD_STATEDIR`) and handles both upload and download based on
deployment context. The new command is download-only and standalone.

Manifests are currently stored at org scope with no deployment name in
the key, so there's one manifest per project. A `--deployment` flag is
deferred until the upload side is updated to support per-deployment
keys.

## Changes

### 1. Add `download_manifest_command` to `dbt.py`

**File:**
`dagster-oss/python_modules/libraries/dagster-dg-cli/dagster_dg_cli/cli/plus/integrations/dbt.py`

Add a new command to `dbt_group`:

```
dg plus integrations dbt download-manifest \
  --components <path> | --file <path> \
  [--key-prefix <prefix>] \
  [--output <path>] \
  [--organization <org>] \
  [--api-token <token>]
```

- `--components` / `--file`: Same as `manage-manifest` - discovers
`DbtProject` instances
- `--key-prefix`: Same as `manage-manifest` - for artifact key
namespacing
- `--output`: Optional override for download destination (default:
`project.state_path/manifest.json`)
- Auth options via `@dg_api_options(organization_scoped=True)`

**Logic:**
1. Import `DbtProject` (with ImportError handling)
2. Validate `--components` or `--file` provided
3. Discover projects (reuse shared helper - see step 2)
4. For each project with a `state_path`:
- Compute key:
`f"{key_prefix}{os.fspath(project.state_path.joinpath('manifest.json'))}"`
- Download to `output_path` if provided, else `project.state_path /
"manifest.json"`
- If `--output` specified and multiple projects found, raise
`UsageError`
5. Call `download_organization_artifact(key, path, organization,
api_token)`

### 2. Extract shared project discovery helper

Same file. Both commands share identical DbtProject discovery logic (~20
lines). Extract into:

```python
def _discover_dbt_projects(components_path, file_path) -> list:
```

Refactor `manage_manifest_command` to use it too.

### 3. Update dagster-expert skill docs

**Current file:**
`public/skills/skills/dagster-expert/skills/dagster-expert/references/cli/plus/integrations/dbt-manage-manifest.md`

Rename to `dbt.md` and update to document both `manage-manifest` and
`download-manifest` commands with their options and usage. Then run
`make generate-index` from `public/skills/` to update the skill index.

## Verification

- Run `dg plus integrations dbt --help` to confirm `download-manifest`
appears
- Run `dg plus integrations dbt download-manifest --help` to confirm
options
- Run ruff for formatting
- Run `make generate-index` from `public/skills/`
- Check for existing tests in
`dagster_dg_cli_tests/cli_tests/plus_tests/` and add a test if a pattern
exists for the dbt integration commands

</details>

<!-- WARNING: Machine-generated. Manual edits may break erk tooling. -->
<!-- erk:metadata-block:plan-header -->
<details>
<summary>plan-header</summary>

```yaml

schema_version: '2'
created_at: '2026-03-26T15:57:48.324688+00:00'
created_by: OwenKephart
plan_comment_id: null
last_dispatched_run_id: null
last_dispatched_node_id: null
last_dispatched_at: null
last_local_impl_at: '2026-03-26T22:59:19.353465+00:00'
last_local_impl_event: started
last_local_impl_session: cd201a96-e8db-426f-90c4-4efd2e57f1e6
last_local_impl_user: owen
last_remote_impl_at: null
last_remote_impl_run_id: null
last_remote_impl_session_id: null
branch_name: plnd/add-dbt-download-manifest-03-26-1557
created_from_session: 3cf2e907-57fe-45b9-b1a0-cc607dbe0061
lifecycle_stage: impl
worktree_name: erk-slot-05

```

</details>
<!-- /erk:metadata-block:plan-header -->
---

To replicate this PR locally, run:

```
erk pr teleport 22095
```

Internal-RevId: cc9255c05a24ec5e9f48e52fc0989d018c1937ba

Author: OwenKephart

python_modules/libraries/dagster-dg-cli/dagster_dg_cli/cli/plus/integrations/dbt.py

@@ -1,11 +1,15 @@
 import os
 from pathlib import Path
+from typing import TYPE_CHECKING
 
 import click
 from dagster_dg_core.utils import DgClickCommand, DgClickGroup
 from dagster_dg_core.utils.telemetry import cli_telemetry_wrapper
 from dagster_shared.plus.config_utils import dg_api_options
 
+if TYPE_CHECKING:
+    from dagster_dbt import DbtProject
+
 
 @click.group(
     name="dbt",
@@ -15,6 +19,31 @@ def dbt_group():
     """Commands for managing dbt integrations with Dagster Plus."""
 
 
+def _discover_dbt_projects(
+    components_path: Path | None, file_path: Path | None
+) -> list["DbtProject"]:
+    """Discover DbtProject instances from a components directory or Python file."""
+    try:
+        from dagster_dbt import DbtProject
+    except ImportError:
+        raise click.ClickException("Unable to import dagster_dbt. dagster-dbt must be installed.")
+
+    if not components_path and not file_path:
+        raise click.UsageError("Must specify --components or --file.")
+
+    if file_path:
+        from dagster._core.code_pointer import load_python_file
+        from dagster._core.definitions.module_loaders.utils import find_objects_in_module_of_types
+
+        contents = load_python_file(file_path, None)
+        return list(find_objects_in_module_of_types(contents, DbtProject))
+    else:
+        from dagster_dbt.components.dbt_project.component import get_projects_from_dbt_component
+
+        assert components_path is not None  # guaranteed by earlier check
+        return list(get_projects_from_dbt_component(components_path))
+
+
 @dbt_group.command(name="manage-manifest", cls=DgClickCommand)
 @click.option(
     "--components",
@@ -54,21 +83,13 @@ def manage_manifest_command(
     In branch deployments, downloads the prod manifest. In the source deployment
     (default: "prod"), uploads the manifest. Replaces `dagster-cloud ci project manage-state`.
     """
-    try:
-        from dagster_dbt import DbtProject
-    except ImportError:
-        raise click.ClickException(
-            "Unable to import dagster_dbt. To use `manage-manifest`, dagster-dbt must be installed."
-        )
-
     from dagster_cloud_cli.commands.ci import state
     from dagster_cloud_cli.core.artifacts import (
         download_organization_artifact,
         upload_organization_artifact,
     )
 
-    if not components_path and not file_path:
-        raise click.UsageError("Must specify --components or --file.")
+    projects = _discover_dbt_projects(components_path, file_path)
 
     # Resolve deployment context from CI state
     from dagster_shared.seven.temp_dir import get_system_temp_directory
@@ -89,19 +110,6 @@ def manage_manifest_command(
     deployment_name = location.deployment_name
     is_branch = location.is_branch_deployment
 
-    # Discover DbtProject instances
-    if file_path:
-        from dagster._core.code_pointer import load_python_file
-        from dagster._core.definitions.module_loaders.utils import find_objects_in_module_of_types
-
-        contents = load_python_file(file_path, None)
-        projects = find_objects_in_module_of_types(contents, DbtProject)
-    else:
-        from dagster_dbt.components.dbt_project.component import get_projects_from_dbt_component
-
-        assert components_path is not None  # guaranteed by earlier check
-        projects = get_projects_from_dbt_component(components_path)
-
     for project in projects:
         if not project.state_path:
             continue
@@ -137,3 +145,75 @@ def manage_manifest_command(
                 f"desired dbt state artifacts to upload, set the cli flag "
                 f"`--source-deployment {deployment_name}`."
             )
+
+
+@dbt_group.command(name="download-manifest", cls=DgClickCommand)
+@click.option(
+    "--components",
+    "components_path",
+    type=click.Path(exists=True, path_type=Path),
+    help="Path to a dg project directory containing DbtProjectComponents.",
+)
+@click.option(
+    "--file",
+    "file_path",
+    type=click.Path(exists=True, path_type=Path),
+    help="Path to a Python file with DbtProject definitions.",
+)
+@click.option(
+    "--key-prefix",
+    default="",
+    help="A key prefix for the key the manifest.json is saved with.",
+)
+@click.option(
+    "--output",
+    "output_path",
+    type=click.Path(path_type=Path),
+    default=None,
+    help="Override the download destination path. Cannot be used with multiple projects.",
+)
+@dg_api_options(organization_scoped=True)
+@cli_telemetry_wrapper
+def download_manifest_command(
+    components_path: Path | None,
+    file_path: Path | None,
+    key_prefix: str,
+    output_path: Path | None,
+    organization: str,
+    api_token: str,
+    view_graphql: bool,
+) -> None:
+    """Download a dbt manifest from Dagster Plus for local development.
+
+    Downloads the manifest artifact stored at organization scope. Use --components
+    to discover DbtProject instances from a dg project, or --file to point at a
+    Python file containing DbtProject definitions.
+    """
+    from dagster_cloud_cli.core.artifacts import download_organization_artifact
+
+    projects = _discover_dbt_projects(components_path, file_path)
+
+    projects_with_state = [p for p in projects if p.state_path]
+    if not projects_with_state:
+        raise click.ClickException("No DbtProject instances with a state_path were found.")
+
+    if output_path and len(projects_with_state) > 1:
+        raise click.UsageError(
+            "--output cannot be used when multiple DbtProject instances are found."
+        )
+
+    for project in projects_with_state:
+        assert project.state_path is not None
+        download_path = project.state_path.joinpath("manifest.json")
+        key = f"{key_prefix}{os.fspath(download_path)}"
+        dest = output_path if output_path else download_path
+
+        dest.parent.mkdir(parents=True, exist_ok=True)
+        click.echo(f"Downloading manifest to {dest}...")
+        download_organization_artifact(
+            key=key,
+            path=dest,
+            organization=organization,
+            api_token=api_token,
+        )
+        click.echo("Download complete.")