A crowd you can find, and a phone 65px too narrow

Two reports against 1.6.0 and 1.7.0, both correct.

The crowd worked end to end and was, in practice, not there: the picker was
behind the ⋯ menu of a chat that already existed, and the switch was a card on
the Agents page, which made it read as an agent-chat feature. The picker is now
a button in the composer toolbar on both screens that include it, and on the
new-chat screen the choice rides along with the first message, so a chat can
start as a crowd instead of having to be converted into one. The instance
switch has its own page.

The width bug was the suggestion cards, exactly as reported. `.suggestions`
rendered 455px inside a 366px column, and the tree's standing rule applied on
its own made it worse -- 428px to 455px. A grid item carries `min-width: auto`,
which is a min-content floor, and a floor beats `width: 100%`; the floor is
measured while the percentage is indefinite, so `min(100%, …)` alone sends the
track to a card's max-content. Both halves now go on all four auto-fit grids,
and a test refuses either alone.

It survived four releases of narrow-width checking because the harness never
rendered that screen: `TestClient(app)` runs no lifespan outside a `with` block,
so the startup-seeded cards were missing from every shot ever taken of it. And
its overflow check skipped anything inside a scroller -- right for a table in
its own scroller, blind to the scroller itself, which `overflow-y: auto` makes
scroll sideways too. Both fixed; it now names the box and the child to blame.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/test_narrow_grids.py

@@ -0,0 +1,85 @@
+"""A grid that reflows can still overflow a phone, and twice it has.
+
+`repeat(auto-fit, minmax(13rem, 1fr))` puts two 208px cards side by side on a
+390px screen: `auto-fit` decides how many columns fit, and a track whose minimum
+is a fixed length never gives that minimum up. The tree's standing rule is to
+write `minmax(min(100%, 13rem), 1fr)` instead, so the *track* yields rather than
+the viewport.
+
+Half of the rule is not the rule. `.suggestions` had `width: 100%` and got the
+`min(100%, …)` track, and still rendered 455px wide inside a 366px column -- it
+is a grid item, so it carries `min-width: auto`, which for a grid item means a
+min-content floor, and a floor beats `width`. Worse, the floor is measured while
+the percentage is indefinite, so the track falls back to a card's max-content:
+adding `min(100%, …)` on its own moved the overflow from 428px to 455px.
+
+So both halves are asserted here, on every auto-fit grid in the stylesheets. A
+stylesheet cannot see whether a given grid is a flex item on some page today or
+becomes one next week, and `min-width: 0` costs nothing where it is not needed.
+
+Found on a phone, on the one screen the screenshot harness had never actually
+rendered -- `scripts/shoot.py` builds its client without a lifespan, so the
+suggestion cards were absent from every shot ever taken of the new-chat screen.
+That is fixed there; this file is the cheap half that runs in the suite.
+"""
+
+from __future__ import annotations
+
+import re
+from pathlib import Path
+
+import lembas
+
+CSS = Path(lembas.__file__).parent / "web/static/css"
+
+# `[^{}]*` cannot cross a brace, so an `@media` prelude never matches and the
+# rules nested inside it do.
+RULE = re.compile(r"([^{}]*)\{([^{}]*)\}")
+COMMENT = re.compile(r"/\*.*?\*/", re.S)
+
+
+def _auto_grids() -> list[tuple[str, str, dict[str, str]]]:
+    found = []
+    for path in sorted(CSS.glob("*.css")):
+        text = COMMENT.sub("", path.read_text(encoding="utf-8"))
+        for prelude, body in RULE.findall(text):
+            if "auto-fit" not in body and "auto-fill" not in body:
+                continue
+            declarations = {
+                part.partition(":")[0].strip(): part.partition(":")[2].strip()
+                for part in body.split(";")
+                if ":" in part
+            }
+            found.append((path.name, prelude.strip(), declarations))
+    return found
+
+
+def test_the_stylesheets_still_have_auto_fit_grids_to_check():
+    # Otherwise the two tests below pass by finding nothing, which is how a
+    # coverage test quietly stops covering anything.
+    assert len(_auto_grids()) >= 4
+
+
+def test_every_auto_fit_track_can_give_up_its_minimum():
+    offenders = [
+        f"{name} {selector}"
+        for name, selector, declarations in _auto_grids()
+        for value in [declarations.get("grid-template-columns", "")]
+        if "minmax(" in value and "min(100%" not in value
+    ]
+    assert not offenders, (
+        "an auto-fit track with a fixed minimum overflows a phone; write "
+        f"minmax(min(100%, X), 1fr): {offenders}"
+    )
+
+
+def test_every_auto_fit_grid_drops_its_automatic_minimum_size():
+    offenders = [
+        f"{name} {selector}"
+        for name, selector, declarations in _auto_grids()
+        if declarations.get("min-width") != "0"
+    ]
+    assert not offenders, (
+        "a grid item's `min-width: auto` is a min-content floor and beats "
+        f"`width`, so `min(100%, …)` alone does not save it: {offenders}"
+    )