feat(dataflow): govern reusable definition updates

src/govoplan_dataflow/backend/schemas.py

@@ -122,6 +122,11 @@ class PipelineGovernanceResponse(BaseModel):
     derived_from_pipeline_id: str | None
     derived_from_revision: int | None
     derived_from_hash: str | None
+    source_available: bool = False
+    source_name: str | None = None
+    source_current_revision: int | None = None
+    source_current_hash: str | None = None
+    update_available: bool = False
     derivation_provenance: dict[str, Any] = Field(default_factory=dict)
     actions: dict[str, DefinitionActionDecisionResponse]
 
@@ -246,7 +251,23 @@ class PipelineDeriveRequest(BaseModel):
     allow_automation: bool = False
 
 
+class PipelineRebaseRequest(BaseModel):
+    expected_revision: int = Field(ge=1)
+    source_revision: int = Field(ge=1)
+    source_hash: str = Field(pattern=r"^[0-9a-f]{64}$")
+    reason: str = Field(min_length=3, max_length=4_000)
+
+    @field_validator("reason")
+    @classmethod
+    def validate_reason(cls, value: str) -> str:
+        cleaned = value.strip()
+        if len(cleaned) < 3:
+            raise ValueError("A meaningful rebase review reason is required.")
+        return cleaned
+
+
 class PipelineDraftRequest(BaseModel):
+    pipeline_id: str | None = Field(default=None, max_length=36)
     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)