emrg: fix intermittent chat rendering order bug (rant #32)

[argszero]

Root Cause

need_new_assistant was set to False on user submit (line 1808). When a new response had no tool calls, the first delta would feed content into chat.last_markdown() — which could find the oldStreamingMarkdown widget from the previous response, sitting before the user message in chat.rows. New content rendered at the old position, appearing between the previous response and new user message.

Fix

Set need_new_assistant = True on user submit, forcing a new StreamingMarkdown widget per response.

Verification

• 319/319 tests pass
• Client import OK
• CLI works

Scenarios Verified

Scenario	need_new_assistant after fix	Result
No tool calls	True (from submit) → new markdown	✅
With tool calls	True (from submit) → tool_end sets True → new markdown after tools	✅
Last tool, no delta	True → next cycle submit keeps it True	✅

[argszero]

✅ LGTM — cycle #6 (correct root cause fix: need_new_assistant=True forces new StreamingMarkdown per response, 389 tests pass)

[argszero]

✅ LGTM — cycle #7 (clean 1-line diff after rebase, 389 tests pass)

[argszero]

✅ LGTM — cycle #8 (3/3 consecutive LGTMs from cycles #6, #7, #8, merging now)