fix: improve import, evidence indexing and material-scoped grading

Preserve document revisions and evidence, harden indexing and export behavior, add explicit material selection and direct-folder import, validate model JSON schemas with safe error messages, and retain student selection while loading scoring data.

backend/migrations/versions/0007_index_defaults.py

@@ -0,0 +1,21 @@
+"""Align new document defaults; existing documents stay stale until rebuilt.
+
+Revision ID: 0007
+Revises: 0006
+"""
+from alembic import op
+
+revision = "0007"
+down_revision = "0006"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    with op.batch_alter_table("knowledge_documents") as batch:
+        batch.alter_column("index_version", server_default="4")
+
+
+def downgrade():
+    with op.batch_alter_table("knowledge_documents") as batch:
+        batch.alter_column("index_version", server_default="1")

backend/migrations/versions/0008_document_revisions.py

@@ -0,0 +1,46 @@
+"""Keep immutable document revisions for reindex and historical citations.
+
+Revision ID: 0008
+Revises: 0007
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "0008"
+down_revision = "0007"
+branch_labels = None
+depends_on = None
+
+SOURCE_COLUMNS = ["course_version_id", "project_id", "submission_file_id", "source_hash"]
+REVISION_CONSTRAINT = "uq_knowledge_document_revision"
+NAMING = {"uq": "uq_%(table_name)s_%(column_0_name)s"}
+
+
+def upgrade():
+    inspector = sa.inspect(op.get_bind())
+    columns = {column["name"] for column in inspector.get_columns("knowledge_documents")}
+    constraints = inspector.get_unique_constraints("knowledge_documents")
+    # Migration 0001 uses current metadata for fresh installs; handle both fresh
+    # schema and a deployed 0007 schema without a revision column.
+    with op.batch_alter_table("knowledge_documents", naming_convention=NAMING) as batch:
+        if "revision" not in columns:
+            batch.add_column(sa.Column("revision", sa.Integer(), nullable=False, server_default="1"))
+        for constraint in constraints:
+            if constraint["column_names"] == SOURCE_COLUMNS:
+                batch.drop_constraint(constraint["name"] or "uq_knowledge_documents_course_version_id", type_="unique")
+        if not any(c["column_names"] == SOURCE_COLUMNS + ["revision"] for c in constraints):
+            batch.create_unique_constraint(REVISION_CONSTRAINT, SOURCE_COLUMNS + ["revision"])
+
+
+def downgrade():
+    # Restoring the old uniqueness would require deleting citation sources. Stop
+    # before schema changes rather than silently choosing a surviving revision.
+    duplicates = op.get_bind().execute(sa.text(
+        "SELECT 1 FROM knowledge_documents GROUP BY course_version_id, project_id, "
+        "submission_file_id, source_hash HAVING COUNT(*) > 1 LIMIT 1")).first()
+    if duplicates:
+        raise RuntimeError("存在同源文档的历史修订，不能无损降级；请保留 0008 或恢复完整升级前备份")
+    with op.batch_alter_table("knowledge_documents", naming_convention=NAMING) as batch:
+        batch.drop_constraint(REVISION_CONSTRAINT, type_="unique")
+        batch.create_unique_constraint("uq_knowledge_documents_source", SOURCE_COLUMNS)
+        batch.drop_column("revision")

backend/migrations/versions/0009_navigation_index.py

@@ -0,0 +1,21 @@
+"""New navigation policy requires rebuilding existing indexes explicitly.
+
+Revision ID: 0009
+Revises: 0008
+"""
+from alembic import op
+
+revision = "0009"
+down_revision = "0008"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    with op.batch_alter_table("knowledge_documents") as batch:
+        batch.alter_column("index_version", server_default="5")
+
+
+def downgrade():
+    with op.batch_alter_table("knowledge_documents") as batch:
+        batch.alter_column("index_version", server_default="4")