feat(chat): the edit and delete UI

[bmc08gt]

Last of four stacked PRs adding edit and delete to chat messages. Stacked on #714 — this diff is against it.

Everything a person touches: the context menu that offers the actions, the composer that performs an edit, and the keyboard behaviour around both.

Contents

Context menu built from capabilities. The menu lists what the message allows, resolved upstream in #713, so adding a group permission later changes the resolution rather than this call site.

Composer takeover. An edit swaps the bar's controls instead of adding a banner above it, so entering and leaving an edit does not shift the transcript. Cancel replaces Send Cash in the leading slot; the submit button stays up for the whole edit with its glyph crossfading arrow to checkmark. Confirming an unchanged edit exits without a request. The cancel button needs an explicit content shape — the glyph is its only drawn content, so taps landing on the glass around it missed the button while the interactive platter lit up, leaving the edit open.

Keyboard handoff around the context menu. UIKit hides the keyboard for a context menu's whole lifetime but leaves the composer first responder, and lays the menu out in the space the keyboard vacated — so a long press left a caret with no keyboard, and a press near the bottom of the transcript put the bubble behind the keyboard once the menu landed. Three points fix it:

• Freeze the transcript inset when the menu is configured, before anything moves, so the keyboard's space stays reserved and the transcript does not reflow under the lifted preview.
• Resign at willDisplayContextMenu rather than at the long-press threshold, so the keyboard animates away alongside the menu. The resign stays outside the animator's block — the composer bar rides the keyboard's own notifications, and folding it in strands the bar at its keyboard-up position.
• Re-take the responder as willEndContextMenuInteraction fires rather than in its completion; waiting for the menu to finish left a beat of empty composer before the keyboard moved.

Actions then follow the keyboard they need: edit focuses the composer, delete keeps it down so it does not rise behind the confirmation dialog. Delete asks "Delete message?" over "This can't be undone", and its destructive action names the scope — "Delete For Everyone" — because WhatsApp's sheet offers that beside "Delete for me" and we have no delete-for-me to distinguish it from.

Blur behind the menu, held through the edit. UIKit only dims the content behind a context menu, so every other bubble stays legible under the platter; WhatsApp blurs it. MessageBackdrop fades a .systemUltraThinMaterialDark view over the navigation controller's view, which the menu's own container sits above, so the platter and the lifted bubble stay sharp.

Choosing Edit claims that same blur from the menu action itself, before the dismissal would fade it, and drops it below the composer bar — so the transcript never flashes back to legible between the two states, and the field stays sharp. The edited message is floated above the blur as a detached snapshot, re-framed on scroll and layout: a UIVisualEffectView renders its backdrop through a private layer that ignores layer.mask, so cutting a hole for the real bubble does not render. Tapping the blur ends the edit, as tapping outside the message does in WhatsApp.

.maestro/login.yaml signs in through the flipcash://login deep link so simulator runs can reach a conversation without hand-driving onboarding; the access key is passed at run time, not stored.

Reply is scoped to a separate plan and is not built here.