feat(webui): support image uploads in composer and message bubbles

tests/agent/test_session_manager_history.py

@@ -217,3 +217,55 @@ def test_window_cuts_mid_tool_group():
     # leaving orphan tool results for split_a at the front.
     history = session.get_history(max_messages=6)
     _assert_no_orphans(history)
+
+
+# --- Image breadcrumbs: media kwarg is synthesized into content for replay ---
+
+
+def test_get_history_synthesizes_image_breadcrumb_from_media_kwarg():
+    """Persisted user turns carry image paths as a ``media`` kwarg; LLM
+    replay must still see an ``[image: path]`` breadcrumb so the assistant's
+    follow-up reply has a referent instead of trailing an empty user row."""
+    session = Session(key="test:media")
+    session.messages.append(
+        {"role": "user", "content": "look", "media": ["/m/a.png", "/m/b.png"]}
+    )
+    session.messages.append({"role": "assistant", "content": "nice"})
+
+    history = session.get_history(max_messages=500)
+
+    assert history == [
+        {"role": "user", "content": "look\n[image: /m/a.png]\n[image: /m/b.png]"},
+        {"role": "assistant", "content": "nice"},
+    ]
+
+
+def test_get_history_synthesizes_breadcrumb_for_image_only_turn():
+    """Turns with no text but attached images must not replay as empty
+    strings — the LLM would otherwise see a bare user turn followed by an
+    unexplained assistant answer."""
+    session = Session(key="test:image-only")
+    session.messages.append({"role": "user", "content": "", "media": ["/m/pic.png"]})
+    session.messages.append({"role": "assistant", "content": "I see a cat"})
+
+    history = session.get_history(max_messages=500)
+
+    assert history[0] == {"role": "user", "content": "[image: /m/pic.png]"}
+
+
+def test_get_history_ignores_media_kwarg_on_non_user_rows():
+    """``media`` only ever appears on user entries in practice, but the
+    synthesizer must be defensive: assistants / tools with list content
+    don't get the breadcrumb pasted on top."""
+    session = Session(key="test:defensive")
+    session.messages.append(
+        {
+            "role": "assistant",
+            "content": [{"type": "text", "text": "structured"}],
+            "media": ["/m/x.png"],  # nonsense but shouldn't crash
+        }
+    )
+    history = session.get_history(max_messages=500)
+    # List content is passed through verbatim — the synthesizer only
+    # rewrites plain-string content.
+    assert history[0]["content"] == [{"type": "text", "text": "structured"}]