Add intermediate previews and graph reconnection

src/govoplan_dataflow/backend/schemas.py

@@ -184,6 +184,12 @@ class PipelinePreviewRequest(BaseModel):
     graph: PipelineGraph | None = None
     sql_text: str | None = Field(default=None, max_length=100_000)
     source_nodes: list[GraphNode] = Field(default_factory=list, max_length=20)
+    preview_node_id: str | None = Field(
+        default=None,
+        min_length=1,
+        max_length=100,
+        pattern=r"^[A-Za-z0-9_.:-]+$",
+    )
     row_limit: int = Field(default=100, ge=1, le=500)
 
 
@@ -203,6 +209,14 @@ class NodePreviewDiagnostic(BaseModel):
     messages: list[str] = Field(default_factory=list)
 
 
+class NodePreviewResult(BaseModel):
+    node_id: str
+    columns: list[PreviewColumn]
+    rows: list[dict[str, Any]]
+    total_rows: int
+    truncated: bool
+
+
 class PipelinePreviewResponse(BaseModel):
     run_id: str | None
     pipeline_id: str | None
@@ -214,6 +228,7 @@ class PipelinePreviewResponse(BaseModel):
     truncated: bool
     diagnostics: list[DataflowDiagnostic]
     node_diagnostics: list[NodePreviewDiagnostic]
+    node_preview: NodePreviewResult | None = None
     source_fingerprints: list[dict[str, Any]]
     input_row_count: int
     definition_hash: str