A directory chip that stopped eating the row

The project directory showed its whole path, which on anything real filled the
chip's 16rem basis and pushed the Manual/Edit/Auto/Plan select off the end of
the composer. It shows the directory's own name now, with the full path in the
tooltip -- the leading directories are the part nobody reads, since what you
check before sending is that you are in `myproject` rather than `myproject-old`.

The hidden field still submits the whole path. Shortening a label must never
shorten a value, and there is a test on the row rather than on the markup for
exactly that.

Three CSS rules hold the row together, and none of them is visible from the
markup. `.composer__agent` needed `min-width: 0`: a flex item will not shrink
below its content without it, so the group refused to give and the *last* child
was what fell off -- which is why the mode select was the thing being cut rather
than the path that was too long. `.composer__dir` is capped, being the only
child here whose content is unbounded; a connection name and a mode are both
short and known. And the mode select is `flex: none`, because it is read and
changed constantly and should never be the thing that scrolls out of reach.

`baseName` driven under node against ten paths, trailing slashes and `/`
included. The topbar's copy of the same path was already capped and truncating,
so it is left alone.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/test_agent_mode.py

@@ -316,3 +316,59 @@ def test_an_unknown_mode_on_the_row_refreshes_to_manual(client: TestClient, db,
     db.commit()
     agent_session.refresh(db, agent)
     assert agent.mode == policy.MODE_MANUAL
+
+
+# --- The directory chip on the new-chat screen ------------------------------------
+def test_the_directory_is_a_hidden_field_carrying_the_whole_path(
+    client: TestClient, db, registered
+):
+    """The button shows the directory's own name so it stops eating the row, and
+    the mode select beside it stops being cut. What is *submitted* has to stay
+    the full path -- shortening a label must never shorten a value."""
+    _agent_chat(db)  # gives us an enabled feature and a profile to pick
+
+    page = client.get("/chat").text
+    assert 'name="project_dir"' in page
+    assert "data-dir-value" in page
+    assert "data-dir-label" in page
+    # The hidden field is what the form posts; the button is decoration beside
+    # it. If the name ever moved onto the button, the label would become the
+    # value and the shortening would reach the server.
+    field = control_named(page, "project_dir")
+    assert field.get("type") == "hidden"
+    assert "data-dir-value" in field
+
+
+def test_starting_a_chat_stores_the_full_path(client: TestClient, db, registered):
+    """The behaviour behind the markup above, asserted on the row."""
+    from lembas.db.models import Chat as ChatRow
+
+    chat = _agent_chat(db)
+    deep = "/srv/projects/a-rather-long-project-name/services/worker"
+
+    client.post(
+        "/api/chats/start",
+        data={
+            "content": "Hello",
+            "kind": "agent",
+            "ssh_profile_id": chat.ssh_profile_id,
+            "project_dir": deep,
+        },
+    )
+    started = db.scalars(select(ChatRow).where(ChatRow.project_dir != "")).all()
+    assert deep in [c.project_dir for c in started]
+
+
+def test_the_composer_row_cannot_be_pushed_apart_by_a_path():
+    """Three rules that have to hold together, and none of which is visible from
+    the markup: the group may shrink, the directory is capped, and the mode
+    never shrinks. The mode select was what fell off the end of the row."""
+    from pathlib import Path
+
+    import lembas
+
+    css = (Path(lembas.__file__).parent / "web/static/css/chat.css").read_text(encoding="utf-8")
+    agent = css[css.index(".composer__agent {") : css.index(".composer__dir {")]
+    assert "min-width: 0" in agent, "the group cannot shrink below its content"
+    assert "max-width" in css[css.index(".composer__dir {") : css.index(".composer__dir-path")]
+    assert 'select[name="agent_mode"] { flex: none; }' in css