docs: close Step 6 with reconciled Contract 5.3 evidence

test-fixtures/PROVENANCE.md

@@ -156,3 +156,30 @@ Verification of the regenerated artifact (raw output in
   `e.origin` as `"null"` for `file://` documents while `window.location.origin`
   is `file://`). That is the adapter's designed same-origin/self safety
   filter, not a defect; NGN attaches exhibits over `http://` only.
+
+## Accepted Contract 5.3 baseline (2026-09-15)
+
+`f163de264388f1e411cf9e54f26f72a254888afd` is the accepted Contract 5.3
+baseline, marked by the annotated tag `contract-5.3-accepted-baseline`.
+The NGN full suite passed **154/154**, and the SciFi Observation surface smoke
+suite passed **24/24**. The final live eight-point NGN verification also passed,
+including pane geometry, synchronized presentation state, lifecycle handling,
+console-only heavy subsystems, standalone attachment, and the inert orphan
+waiting state.
+
+This baseline adds two fixture-local integration corrections after the earlier
+source-to-fixture resync: `css/style.css` clears the console overlay's centered
+16:9 geometry when Observation is embedded in an NGN pane, and `js/app.js`
+presents an inert waiting state after an owner-attachment timeout. They do not
+create a second authority or alter the upstream exhibit's contract behavior.
+
+The console's existing 16:9-lock checkbox behavior is pre-existing and
+unrelated to these corrections. It remains console presentation behavior; the
+embedded-surface override is intentionally limited to keeping that behavior
+from affecting NGN pane geometry.
+
+Step 6.7 and Step 6.8 are complete and accepted, and Step 6.5 state synchronization
+is satisfied by existing implementation and later evidence. Non-blocking operator
+checks and the unreproduced session renegotiation observation are tracked
+separately. Step 6 is closed at Step 6.10 (see
+`docs/reference/XZBT-NGN-Step6.10-Closure-Report.md`).