diff --git a/sessions/0015/SESSION-0015.0-TRANSCRIPT-2026-06-10T22-37--INPROGRESS.md b/sessions/0015/SESSION-0015.0-TRANSCRIPT-2026-06-10T22-37--INPROGRESS.md
new file mode 100644
index 0000000..acb4040
--- /dev/null
+++ b/sessions/0015/SESSION-0015.0-TRANSCRIPT-2026-06-10T22-37--INPROGRESS.md
@@ -0,0 +1,23 @@
+# Session 0015.0 — Transcript
+
+> App: vscode-cowriting-plugin
+> Start: 2026-06-10T22-37 (PST)
+> Type: planning-and-executing
+> Status: **PLACEHOLDER — claimed at session start; finalized at session end.**
+>
+> This file reserves session ID 0015 for vscode-cowriting-plugin. The driver replaces this
+> body with the full transcript and renames the file to its final
+> SESSION-0015.0-TRANSCRIPT-2026-06-10T22-37--<end>.md form at session end.
+
+## Launch prompt
+
+```
+Implement Feature #14 (F5 cross-rung format + round-trip) per the graduated spec vscode-cowriting-plugin-content/specs/coauthoring-cross-rung-format.md — plan just-in-time from its §7.2 slices, then execute; done = contract + schema published, unit + host E2E green (round-trip, merge, fail-safe, unknown-field preservation all exercised).
+
+```
+
+## Deferred decisions
+
+_Autonomous-mode low-confidence calls the driver made and would have
+liked operator input on. Appended as the session runs; surfaced at
+finalize. Empty if none._
diff --git a/sessions/sessions.json b/sessions/sessions.json
index d64ca93..d301b04 100644
--- a/sessions/sessions.json
+++ b/sessions/sessions.json
@@ -40,5 +40,8 @@
   },
   "0014": {
     "title": ""
+  },
+  "0015": {
+    "title": ""
   }
 }