diff --git a/scripts/__tests__/demo-published-password-guard.test.ts b/scripts/__tests__/demo-published-password-guard.test.ts
new file mode 100644
index 000000000..e9167a684
--- /dev/null
+++ b/scripts/__tests__/demo-published-password-guard.test.ts
@@ -0,0 +1,73 @@
+import { readFileSync } from "node:fs";
+import { join } from "node:path";
+
+import { describe, expect, it } from "vitest";
+
+/**
+ * The demo password is published in the README so anyone can sign in to
+ * demo.healthlog.dev. Its Argon2id hash lives in two places that must agree:
+ *
+ *   - scripts/seed-demo.ts          writes it when a demo tenant is seeded
+ *   - scripts/migrate-demo-edge01.sh overwrites it after a migration load
+ *
+ * Public issue #805: the migration used to carry the SOURCE account's hash
+ * across instead, so once the operator rotated their own demo password the
+ * credentials the README advertises stopped working, and nothing noticed until
+ * a visitor filed a bug. These assertions make the two copies move together.
+ */
+
+const REPO_ROOT = join(__dirname, "..", "..");
+const SEED = join(REPO_ROOT, "scripts", "seed-demo.ts");
+const MIGRATE = join(REPO_ROOT, "scripts", "migrate-demo-edge01.sh");
+
+/** Every Argon2id hash literal in a file, in source order. */
+function argon2Hashes(path: string): string[] {
+  const source = readFileSync(path, "utf8");
+  return source.match(/\$argon2id\$[^"'\s]+/g) ?? [];
+}
+
+describe("published demo password", () => {
+  it("is the same hash in the seed script and the edge01 migration", () => {
+    const seeded = argon2Hashes(SEED);
+    const migrated = argon2Hashes(MIGRATE);
+
+    // An empty match set would make every assertion below vacuously true —
+    // the failure mode this repo keeps rediscovering. Demand a hit first.
+    expect(seeded.length).toBeGreaterThan(0);
+    expect(migrated.length).toBeGreaterThan(0);
+
+    // Each file states the hash exactly once, so a stray second copy (the
+    // thing that lets the two drift again) is a failure in its own right.
+    expect(new Set(seeded).size).toBe(1);
+    expect(new Set(migrated).size).toBe(1);
+
+    expect(migrated[0]).toBe(seeded[0]);
+  });
+
+  it("is written by the migration rather than carried from the source", () => {
+    const script = readFileSync(MIGRATE, "utf8");
+
+    // The overwrite must exist...
+    expect(script).toMatch(
+      /UPDATE users SET password_hash = '\$\{?PUBLIC_DEMO_PASSWORD_HASH\}?'/,
+    );
+
+    // ...and it must be proven, not merely attempted. Without the check a
+    // mangled hash would reach a visitor's login screen instead of the script.
+    expect(script).toContain(
+      "ABORT/FAIL: demo password_hash on edge01 is not the published literal",
+    );
+  });
+
+  it("keeps the overwrite off the ssh command line", () => {
+    const script = readFileSync(MIGRATE, "utf8");
+
+    // The hash carries '$argon2id', '$v', '$m', '$t', '$p'. Interpolated into
+    // a double-quoted remote command those expand to empty strings and the
+    // stored hash matches nothing. It has to travel on stdin.
+    const sshWithHashInline = new RegExp(
+      String.raw`ssh\s+"\$DST_SSH"\s+"[^"]*PUBLIC_DEMO_PASSWORD_HASH`,
+    );
+    expect(script).not.toMatch(sshWithHashInline);
+  });
+});
diff --git a/scripts/migrate-demo-edge01.README.md b/scripts/migrate-demo-edge01.README.md
index 80eac968c..35dd6cd15 100644
--- a/scripts/migrate-demo-edge01.README.md
+++ b/scripts/migrate-demo-edge01.README.md
@@ -68,7 +68,17 @@ reset to `'disconnected'`), `ai_anthropic_key_encrypted`,
 Forced flags: `telegram_enabled=false`,
 `role='ADMIN'`.
 
-**Kept:** `password_hash` (demo login works), `avatar_bytes` /
+**Overwritten:** `password_hash`. The row arrives carrying the source
+account's hash, and the load is immediately followed by an `UPDATE` that sets
+the Argon2id hash of the demo password the README publishes, then asserts the
+stored value matches it byte for byte and aborts if it does not. The source is
+the operator's own instance, so its demo password can be rotated at any time;
+carrying that hash across is what silently broke the advertised demo login in
+issue #805. The statement travels on psql's stdin, never inside the ssh command
+string, because the hash contains `$argon2id` / `$v` / `$m` / `$t` / `$p`
+segments that a remote shell would expand to nothing.
+
+**Kept:** `avatar_bytes` /
 `avatar_content_type` / `avatar_updated_at` (profile photo), and all
 display / preference / layout JSON (`thresholds_json`,
 `dashboard_widgets_json`, `insights_layout_json`, `coach_prefs_json`,
diff --git a/scripts/migrate-demo-edge01.sh b/scripts/migrate-demo-edge01.sh
index 4ecf556c3..e91c66d92 100755
--- a/scripts/migrate-demo-edge01.sh
+++ b/scripts/migrate-demo-edge01.sh
@@ -102,6 +102,23 @@ readonly SRC_DB_CONTAINER
 readonly PG_USER="healthlog"
 readonly PG_DB="healthlog"
 
+# Argon2id hash of the demo password the README publishes ("demo123demo123").
+# Not a secret: it is printed in the README so anyone can sign in to the demo,
+# and it is the same literal that scripts/seed-demo.ts writes on a fresh seed.
+# The transfer still carries the source column, but the load is followed by an
+# explicit overwrite with this literal (see "FORCE THE PUBLISHED DEMO PASSWORD"
+# below). The source is the operator's own instance and its demo password can
+# be rotated at any time; carrying it across silently invalidated the published
+# credentials once already (public issue #805). Overwriting afterwards makes the
+# documented login true by construction after every migration.
+#
+# The overwrite travels on psql's STDIN, never inside the ssh command string:
+# the hash contains '$' segments that a remote shell would expand away.
+#
+# scripts/__tests__/demo-published-password-guard.test.ts pins this literal to
+# the one in scripts/seed-demo.ts, so editing one without the other fails.
+readonly PUBLIC_DEMO_PASSWORD_HASH='$argon2id$v=19$m=65536,t=3,p=4$Kips6OxPAl0vmspO9SoKZQ$oX9gLgwHVnnENCqBloyM13ewuqmhPnw8EpLoemS3MNI'
+
 # psql invocation builders. -v ON_ERROR_STOP=1 makes any SQL error a non-zero
 # exit so `set -e` aborts the pipeline. -X skips ~/.psqlrc.
 psql_src() {
@@ -466,6 +483,38 @@ copy_table() {
 copy_table "users" "$USERS_SELECT" \
   "users WHERE id = '$DEMO_USER_ID'" "$USERS_COLS"
 
+# ----------------------------------------------------------------------------
+# FORCE THE PUBLISHED DEMO PASSWORD
+# ----------------------------------------------------------------------------
+# The row just loaded carries the SOURCE account's password_hash. The source is
+# the operator's own instance, so that hash is whatever the operator last set —
+# not necessarily the password the README publishes. Overwrite it here so the
+# documented demo login works after every migration, not just the first one.
+#
+# The statement goes in on psql's STDIN. It must NOT be interpolated into the
+# ssh command string: the Argon2id hash contains '$argon2id', '$v', '$m', '$t'
+# and '$p' segments, and a remote shell would expand each of those to an empty
+# string and store a mangled hash that no password can ever match.
+echo
+echo "## FORCE published demo password on the loaded row ..."
+printf '%s\n' \
+  "UPDATE users SET password_hash = '$PUBLIC_DEMO_PASSWORD_HASH' WHERE id = '$DEMO_USER_ID';" \
+  | ssh "$DST_SSH" "docker exec -i $DST_DB_CONTAINER \
+      psql -X -v ON_ERROR_STOP=1 -U $PG_USER -d $PG_DB"
+
+# Prove the stored hash is byte-for-byte the published one. A mangled or
+# carried-over hash fails here instead of at some visitor's login screen.
+PW_OK="$(printf '%s\n' \
+  "SELECT count(*) FROM users WHERE id = '$DEMO_USER_ID' AND password_hash = '$PUBLIC_DEMO_PASSWORD_HASH';" \
+  | ssh "$DST_SSH" "docker exec -i $DST_DB_CONTAINER \
+      psql -X -tA -v ON_ERROR_STOP=1 -U $PG_USER -d $PG_DB" | tr -d '[:space:]')"
+if [[ "$PW_OK" != "1" ]]; then
+  echo "ABORT/FAIL: demo password_hash on edge01 is not the published literal (matched rows: $PW_OK)."
+  echo "            The demo login would be broken. Fix before serving the demo."
+  exit 1
+fi
+echo "   demo password_hash matches the published literal."
+
 # 2. measurements (live rows only).
 copy_table "measurements" "$MEAS_COLS" \
   "measurements WHERE user_id = '$DEMO_USER_ID' AND deleted_at IS NULL" "$MEAS_COLS"