D-50 behavior 4: opening a renderable .md in the editor now auto-reveals the
context-panel reader, which mirrors the buffer read-only and re-renders as the
user types — rather than a one-shot disk read.
The extension reveals the tab on editor.opened (renderable only — D-50 behavior
5 leaves non-.md files alone). The viewer owns the mirror: on mount it picks up
the active buffer (editor.read, no id), enters mirror mode on editor.opened /
active-changed for a renderable file, re-reads the in-memory buffer on
editor.edited, and drops the mirror (with its edit affordance back) on a disk
load or a switch to a non-renderable buffer.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>