A freshly created shell session rendered blank until a tab-switch. selectSession()
fetches the terminal buffer, but for a just-started shell that fetch resolves before
the PTY emits its prompt, so the buffer is empty; the prompt then arrives as a live
SSE event queued during the load and _finishBufferLoad() discarded it. The discard is
correct for an established session (its fetched buffer already contains that output),
but harmful when the load painted nothing.
_finishBufferLoad(owner, { flushQueued }) now REPLAYS the queued events through
batchTerminalWrite (after _isLoadingBuffer is cleared, so they write through, not
re-queue) instead of discarding. selectSession passes flushQueued only in the empty
branch (no fresh buffer + no cache), so the established-session de-dup path is
unchanged. TDD: test/terminal-buffer-flush.test.ts exercises the real begin/finish
mixin (vm-harness, no jsdom).
