feat(chat): stop an in-flight answer — Send becomes Stop, the partial is kept and persisted, the model stream is torn down

tests/e2e/test_agent_unlimited_tools.py

@@ -365,10 +365,16 @@ def _submit(page: Page, question: str) -> None:
 
 
 def _wait_settled(page: Page) -> None:
-    """The turn is complete: answer text in the bubble, button recovered."""
+    """The turn is complete: answer text in the bubble, button recovered.
+
+    Phase 48: the label assertion carries the settle wait with an
+    explicit timeout — the in-flight button is the enabled Stop control
+    (never disabled), so ``to_be_enabled`` no longer blocks until the
+    turn settles, and Playwright expect's default (5s) does not inherit
+    the page default."""
     expect(page.locator(".msg.brain .bubble").last).not_to_have_text("", timeout=30_000)
     expect(page.locator("#send-btn")).to_be_enabled(timeout=30_000)
-    expect(page.locator("#send-label")).to_have_text("Send")
+    expect(page.locator("#send-label")).to_have_text("Send", timeout=30_000)
 
 
 # --------------------------------------------------------------------------
@@ -403,13 +409,14 @@ def test_multi_read_turn(
     done = next(f for f in frames if f.get("type") == "done")
     assert done["deflected"] is False
 
-    # The transient "calling tool" states, recorded deterministically:
-    # the label shows "Calling tool…" and #send-status walked through
+    # The transient "calling tool" states, recorded deterministically.
+    # Phase 48 (owner-locked): the in-flight button is the Stop control —
+    # the label holds "Stop" for the whole turn (it no longer relabels
+    # to "Calling tool…"), and #send-status walked through
     # "… is listing documents" then "… is reading <sp>" for BOTH reads,
     # in order.
     labels = page.evaluate("() => window.__labels")
-    assert "Calling tool…" in labels, labels
-    assert labels.index("Calling tool…") > labels.index("Thinking…")
+    assert "Stop" in labels, labels
     statuses = page.evaluate("() => window.__statuses")
     i_list = next(
         (i for i, s in enumerate(statuses) if "is listing documents" in s), None