feat: enable Markdown (.md) file upload in KB Accelerator

Moved md from Phase 2 extensions to allowed formats, added extraction
handler (reuses txt handler), and updated plan_limits defaults to
include md for all plans.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/alembic/versions/056_add_md_to_kb_allowed_formats.py

@@ -0,0 +1,44 @@
+"""Add md to kb_allowed_formats defaults
+
+Revision ID: 056
+Revises: 055
+Create Date: 2026-03-12
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "056"
+down_revision = "055"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    # Update server default for new rows
+    op.alter_column(
+        "plan_limits",
+        "kb_allowed_formats",
+        server_default=sa.text("'[\"txt\",\"paste\",\"md\"]'::jsonb"),
+    )
+    # Add "md" to existing rows that have the old default ["txt","paste"]
+    op.execute(
+        """
+        UPDATE plan_limits
+        SET kb_allowed_formats = kb_allowed_formats || '["md"]'::jsonb
+        WHERE NOT kb_allowed_formats @> '"md"'::jsonb
+        """
+    )
+
+
+def downgrade() -> None:
+    op.alter_column(
+        "plan_limits",
+        "kb_allowed_formats",
+        server_default=sa.text("'[\"txt\",\"paste\"]'::jsonb"),
+    )
+    op.execute(
+        """
+        UPDATE plan_limits
+        SET kb_allowed_formats = kb_allowed_formats - 'md'
+        """
+    )

backend/app/api/endpoints/kb_accelerator.py

@@ -57,6 +57,7 @@ MAX_UPLOAD_SIZE = 10 * 1024 * 1024
 
 ALLOWED_EXTENSIONS = {
     "txt": ["text/plain"],
+    "md": ["text/markdown", "text/plain"],
     "docx": ["application/vnd.openxmlformats-officedocument.wordprocessingml.document"],
 }
 
@@ -64,7 +65,6 @@ ALLOWED_EXTENSIONS = {
 PHASE2_EXTENSIONS = {
     "pdf": ["application/pdf"],
     "html": ["text/html"],
-    "md": ["text/markdown", "text/plain"],
 }
 
 
@@ -110,7 +110,7 @@ async def _check_lifetime_limit(user: User, limits: PlanLimits, db: AsyncSession
 
 
 async def _check_format_allowed(source_format: str, limits: PlanLimits) -> None:
-    allowed = limits.kb_allowed_formats or ["txt", "paste"]
+    allowed = limits.kb_allowed_formats or ["txt", "paste", "md"]
     if source_format not in allowed:
         raise HTTPException(
             status_code=status.HTTP_403_FORBIDDEN,
@@ -205,7 +205,7 @@ async def get_quota(
             kb_accelerator_enabled=False,
             lifetime_conversions_used=committed_count,
             lifetime_conversions_limit=0,
-            allowed_formats=["txt", "paste"],
+            allowed_formats=["txt", "paste", "md"],
             detailed_analysis=False,
             conversational_refinement=False,
             step_library_matching=False,

backend/app/core/kb_extraction_service.py

@@ -159,6 +159,7 @@ def _extract_docx(content_bytes: bytes) -> ExtractResult:
 # Registry of format handlers — extend for Phase 2
 FORMAT_HANDLERS: dict[str, ExtractHandler] = {
     "txt": _extract_txt,
+    "md": _extract_txt,
     "paste": _extract_paste,
     "docx": _extract_docx,
 }

backend/app/models/plan_limits.py

@@ -23,7 +23,7 @@ class PlanLimits(Base):
     kb_accelerator_enabled: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False, server_default=text("false"))
     kb_max_lifetime_conversions: Mapped[int | None] = mapped_column(Integer, nullable=True)
     kb_batch_max_size: Mapped[int | None] = mapped_column(Integer, nullable=True)
-    kb_allowed_formats: Mapped[list] = mapped_column(JSONB, nullable=False, default=lambda: ["txt", "paste"], server_default=text("'[\"txt\",\"paste\"]'::jsonb"))
+    kb_allowed_formats: Mapped[list] = mapped_column(JSONB, nullable=False, default=lambda: ["txt", "paste", "md"], server_default=text("'[\"txt\",\"paste\",\"md\"]'::jsonb"))
     kb_detailed_analysis: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False, server_default=text("false"))
     kb_conversational_refinement: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False, server_default=text("false"))
     kb_step_library_matching: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False, server_default=text("false"))