Adds EffectKind::{ViewOnly, Model(ModelChange)} with ModelChange::{CellData,
LayoutGeometry, WholeWorkbook}, so a server can decide which effects owe
connected clients an update. All 58 effects are classified.
kind() has no default. The design offered a per-struct method; making it
required means a new effect cannot forget to classify itself, and the failure
mode here is silent — a mis-declared ViewOnly edit would simply never reach
connected clients. It paid off at once: the compiler found a 58th Effect impl
living in command/keymap.rs rather than effect.rs.
The classification was derived from what each apply() body touches and
reasoned about in Prolog, not eyeballed. That surfaced the trap: the View is
stored inside model_state.workbook, so "touches model_state" does not mean
"is a model change". Axis, page, grouping, hidden items, number format and
active view are LayoutGeometry; cursor and scroll are per-client ViewOnly;
Save, SaveAs and MarkDirty touch model_state for bookkeeping only. Classifying
by grepping for model_state would have had the projection layer broadcasting
cell updates for cursor moves.
The tests verify the declarations rather than restate them: each applies the
effect to a probe App and fingerprints the shared state it claims not to
touch, in both directions.
Cursor and scroll are the one judgement call — they write the shared,
persisted View but must not move another client's viewport. Filed as
improvise-8uz to resolve before the projection layer builds on this.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V69PGQfMJuGRmtSWpfVAqn
Edward Langley
3b1607d29b