# Direct scenario editing — bounded implementation plan

Status: implementation in the isolated `codex/scenario-direct` checkout, based on
ab661f2. Native acceptance is pending the root's Windows/Linux trials. This does
not complete the release or the separate process/chain gesture work.

## Decisions

Extend the existing `behavior::Scene`; retain its derived lifeline columns and
ordered occurrence rows. No model/schema/layout records are added. Lifeline and
occurrence UUIDs remain distinct from represented work and global exchanges.

Select mode selects headers, stems, messages and occurrence boxes. A selected
occurrence has a reorder handle; dragging it chooses a visible slot in its same
parent sequence. It never reparents or changes lifeline columns. A Message tool
uses the existing MessageStyle, with Call + correlated reply initially selected.
Click-click or drag between represented lifelines captures a highlighted explicit
insertion slot `(parent, before occurrence or append)` and opens the existing
typed draft with those endpoints. Existing exchanges/calls are filtered against
the complete candidate at that slot and shown through search plus 24-item pages.
No compatible exchange produces an actionable retained draft, not a new global
exchange or a silently changed endpoint. Timer remains available as a local tool.

The canvas remains rendered while a bounded, independently scrollable form is
open. Values keep the existing qualified-path editor and lifecycle. Final creation
uses ordinary CreateElement plus SetSteps in one Batch; paired call/reply are
inserted together and undo together. Reordering uses SetSteps within the captured
parent. Existing core validation decides reply order, branch dominance, lifetime,
phase and endpoint compatibility. Failed preparation/source writes retain drafts.

Transient events capture document/scenario/revision/epoch, and the App validates
the current Behavior owner before handling them. Selection does not invalidate a
gesture within the same scenario. Escape, unfocus, context/tool change and pending
drafts cancel gestures. Ordered pointer events and captured window positions avoid
coalesced-click and changed-scroll-origin commits. No geometry is persisted.

Execution bars derive their ends from actual correlated reply positions; separate
conditional reply branches render their corresponding spans. Calls without a
visible reply use a short explicitly open activation, not a fabricated reply.

## Acceptance checks

Production-event tests cover hit priority, click-click/drag, scroll-origin changes,
Escape/unfocus/stale contexts and exactly one result per gesture. Planner/App tests
cover middle/operand insertion, paired identities, complete SetSteps ordering,
same-parent reorder, rejected reply-before-call, unchanged global exchanges, exact
source/model Undo, draft retention and bounded exchange/call controls. Run focused
and full desktop tests, strict all-target desktop Clippy and optimized build with
the dedicated `D:/CodexBuilds/Capella2-scenario-target` target.

Root native tasks (not yet performed):
1. Draw an existing exchange again into the middle of a scenario as Call+Reply;
   enter a qualified value, select both occurrences, Undo/Redo, save/reopen.
2. Insert inside an ALT/LOOP operand, reorder within it, reject a reply before its
   call, and inspect correlated execution bars and preserved occurrence identities.
3. Cancel drawing after scrolling/layout change, retry, retain typed values while
   navigation is blocked, and open/return from a referenced scenario. Verify at
   1440x900 and 1100x700 on Windows and Linux before scoped acceptance.