diff --git a/runner/harness/meta.py b/runner/harness/meta.py
index 947af37..19fd451 100644
--- a/runner/harness/meta.py
+++ b/runner/harness/meta.py
@@ -132,6 +132,17 @@ KEYS: tuple[Key, ...] = (
         "Callable `(ctx)` invoked after UPGRADE_EXTRA_ENV env_set but before `abra secret generate --all` in the upgrade path. Use to pre-insert secrets that `generate --all` would produce with wrong format (e.g. when the .env.sample spec is commented out).",
         hook_params=("ctx",),
     ),
+    Key(
+        "UPGRADE_BASE_FLOOR",
+        "str",
+        None,
+        "Declared STRUCTURAL breaking boundary for the upgrade tier (phase basefloor): the first "
+        "post-break published version tag. Bases strictly below it are excluded from resolution "
+        "(canonical / step-back / no-canonical fallback) because an in-place upgrade across the "
+        "boundary is not supported upstream (e.g. a db-family change). When no ≥-floor predecessor "
+        "exists the tier records a DECLARED skip. NOT a static base pin (§2.G stays removed) — "
+        "resolution remains dynamic above the floor.",
+    ),
     # (CHAOS_BASE_DEPLOY, OIDC_AT_INSTALL and SKIP_GENERIC were deleted in restructure P2:
     # compose.ccci.yml is first-class + auto-chaos; install-time deps wiring is the only mode;
     # the generic floor is suppressible only via the dev-only CCCI_SKIP_GENERIC* env form.)