Map the .cs extension to the built-in csharp StreamLanguage from
@codemirror/legacy-modes/mode/clike (already a dependency, no new packages),
so .cs files open with syntax highlighting in the sidebar editor.
- markdown tabs open in rendered preview with a 预览/编辑 segmented toggle;
edit mode uses the CodeMirror source editor (markdown highlighting), the
preview renders the live unsaved draft, and the editor stays mounted while
previewing so edits survive the toggle.
- an empty pane shows openable-type cards (explorer / git / terminal, the
same options as the + menu, terminal dimmed at the cap) instead of the
bare 'this pane is empty' message; clicking a card opens the tab.
- the + button sits immediately right of the last tab (sticky at the
scrollport's right edge when the tab row overflows, so it stays
reachable).
- cwd resolution falls back (attached header → client summary cwd → process
cwd) across the JSON API, media route and terminal upgrade, so explorer/
git/terminal work from first paint instead of 'session ... has no working
directory' while the web client hydrates the session (refresh-only fix).
- terminal client threads the summary cwd into the WS URL and stops the
reconnect loop after three unreasoned failures, showing the close code
with a manual retry; a 1011+reason refusal already showed the reason.
- white screen: persisted state is structurally sanitized on load (malformed
shapes fall back to default) and the restored width is clamped to the
viewport; the layout margin is capped at the viewport; the client entry
wraps every lifecycle step in try/catch and pins a visible diagnostic bar
on load/mount/interception failure instead of failing silently.
- editor: textarea replaced with CodeMirror 6 — line wrapping, per-extension
syntax highlighting (js/ts/jsx/tsx, json, python, html, css, xml, yaml,
sql, java, c/c++, rust, go, php, shell, toml, nginx, dockerfile,
properties), one-dark theme, dirty dot + Ctrl/Cmd+S save kept.
- tests: +9 (cwd fallback chain over the API route, state sanitization,
language mapping); 36 pass, typecheck + build + vm materialize clean.
ymac