diff --git a/alembic/versions/20260529_0036_ain303_outcome_source.py b/alembic/versions/20260529_0036_ain303_outcome_source.py
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+++ b/alembic/versions/20260529_0036_ain303_outcome_source.py
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+"""AIN-303 · routing_outcomes.source — synthetic/shadow tagging (INVARIANT 1).
+
+Revision ID: 20260529_0036
+Revises: 20260529_0035
+Create Date: 2026-05-29
+
+The synthetic cold-start loop writes outcomes that must NEVER feed a prod
+routing-policy promotion. This adds a `source` discriminator so the wall is
+enforceable in SQL: prod-policy refits filter `source = 'prod'`; the synthetic
+warmup loop tags its rows `source = 'synthetic'` (and shadow-replay rows
+`'shadow'`). Existing rows are real traffic → backfilled to 'prod'.
+
+Additive: NOT NULL with server_default 'prod' (existing 147 rows become 'prod'),
+a CHECK constraint pinning the vocabulary, and an index for the source-filtered
+corpus reads. No scoring/auth/candidate-set change (Disc #12 intact).
+"""
+
+from __future__ import annotations
+
+import sqlalchemy as sa
+
+from alembic import op
+
+revision = "20260529_0036"
+down_revision = "20260529_0035"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "routing_outcomes",
+        sa.Column("source", sa.Text(), nullable=False, server_default="prod"),
+    )
+    op.create_check_constraint(
+        "ck_routing_outcomes_source",
+        "routing_outcomes",
+        "source IN ('prod','synthetic','shadow')",
+    )
+    op.create_index(
+        "ix_routing_outcomes_source",
+        "routing_outcomes",
+        ["source"],
+    )
+
+
+def downgrade() -> None:
+    op.drop_index("ix_routing_outcomes_source", table_name="routing_outcomes")
+    op.drop_constraint("ck_routing_outcomes_source", "routing_outcomes", type_="check")
+    op.drop_column("routing_outcomes", "source")