diff --git a/deploy/postgres/goose/00042_2026-09-15-workflow-advance-outcome.sql b/deploy/postgres/goose/00042_2026-09-15-workflow-advance-outcome.sql
new file mode 100644
index 00000000..2e40546d
--- /dev/null
+++ b/deploy/postgres/goose/00042_2026-09-15-workflow-advance-outcome.sql
@@ -0,0 +1,12 @@
+-- +goose Up
+-- E1B: correlate stage-ready unique outcome to envelope event_id.
+ALTER TABLE stage_advance_requests
+    ADD COLUMN IF NOT EXISTS source_event_id TEXT NOT NULL DEFAULT '';
+
+CREATE UNIQUE INDEX IF NOT EXISTS uq_sar_source_event
+    ON stage_advance_requests (source_event_id)
+    WHERE source_event_id <> '';
+
+-- +goose Down
+DROP INDEX IF EXISTS uq_sar_source_event;
+ALTER TABLE stage_advance_requests DROP COLUMN IF EXISTS source_event_id;