docs(cli): record the fork gap the design turned up

Runtime new-tab dropped purposes until 5873374; the design depends on it, so
the dependency is written down rather than assumed. Also notes the single-line
KDL terminator trap, which cost a debugging round.

1 files changed, 16 insertions, 0 deletions

diff --git a/docs/cli-design.md b/docs/cli-design.md
index 00650fd..f5d4168 100644
--- a/docs/cli-design.md
+++ b/docs/cli-design.md
@@ -152,6 +152,22 @@ Absorbing `pir` into `sl0ppi agent --resume` (D10) removes the `python3`
 dependency. `fzf` then becomes either a declared external dependency or an
 internal picker.
 
+## Fork changes this design required
+
+Designing against the fork turned up one real gap, found by integration-testing
+rather than reading:
+
+- **purposes were dropped by runtime `new-tab`** (`sl0p: carry pane and tab
+  purposes over the wire`). `TiledPaneLayout`/`FloatingPaneLayout` had no
+  protobuf `purpose` field, so a layout sent as an Action lost every purpose it
+  declared. Session-creation layouts kept theirs, which is why the feature
+  looked fine until an orchestrator tried to add a tab. Both protobuf schemas
+  now carry it, sanitised on ingest.
+
+Also worth recording, because it costs an afternoon otherwise: **KDL nodes on a
+single line need `;` terminators**. `tab x { pane }` fails to parse; the
+generator emits multi-line KDL, which sidesteps it entirely.
+
 ## MVP scope
 
 1. discovery + slug + `list-tabs --json` diff (the idempotency core)