Enable sequence.concurrent: true in vite.config.ts so the non-PTY suite runs
concurrently like the PTY suite. Stress-verified stable (8/8 at maxForks=4);
the suite drops from ~13s to ~4-5s.
Three test patterns were incompatible with concurrency; handled per cause:
- Inline snapshots (background-color, borders): the module-level `expect`
loses snapshot test context under concurrency. Fixed in place by using the
context-local `expect` (async ({ expect }) => ...), so they stay concurrent.
- Process-global state (throttle/animation-scheduler use fake timers; leak
asserts on process exit/SIGINT listener counts and live yoga nodes): a
concurrent sibling clobbers the shared global mid-test. These genuinely
require serial execution, so they move to *.sequential.test.* files with
it.sequential / describe.sequential and a header explaining why.
`vp run ready` passes.
Yunfei He
ee6004b8be