Per-tool emoji on tool cards (gateway-resolved via hermes get_tool_emoji)

tool.start gains an optional cosmetic 'emoji' field, resolved server-side
through hermes' own display layer (active-skin overrides, then the tool
registry's per-tool emoji) so icons track the user's hermes theme and
new/plugin tools get their glyph for free. Omitted for unknown tools so
the app falls back to its default wrench.

- protocol.py: tool_start(emoji=...) kwarg, payload field when set
- adapter.py: _tool_emoji() helper (lazy import, None on unknown/failure)
- frames.schema.json + docs/04: field documented
- app: ToolStartPayload.emoji -> ToolItem.emoji -> ToolCard header
- tests: frame shape, resolution/fallback, end-to-end tool.start emoji

gateway-plugin/tests/test_android.py

@@ -2285,6 +2285,67 @@ def test_parse_tool_line_or_block_verbose(plugin):
     assert name2 == "web_search" and preview2 == "x" and args2 is None
 
 
+def test_tool_start_frame_emoji_field(plugin):
+    """``tool.start`` carries the cosmetic emoji when given, omits it when
+    None (the app then falls back to its own default glyph)."""
+    pf = plugin.protocol.tool_start
+    f = pf("android:default", 3, "terminal", emoji="💻")
+    assert f.payload["emoji"] == "💻"
+    f2 = pf("android:default", 3, "terminal")
+    assert "emoji" not in f2.payload
+    f3 = pf("android:default", 3, "terminal", emoji=None)
+    assert "emoji" not in f3.payload
+
+
+def test_tool_emoji_resolves_via_hermes_display(plugin, monkeypatch):
+    """``_tool_emoji`` delegates to hermes' ``get_tool_emoji`` (skin overrides
+    -> registry) and maps unknown tools / failures to None (field omitted)."""
+    a = plugin.adapter
+    seen = {}
+
+    def fake_get_tool_emoji(name, default="⚡"):
+        seen[name] = default
+        return {"terminal": "💻", "read_file": "📖"}.get(name, default)
+
+    monkeypatch.setattr("agent.display.get_tool_emoji", fake_get_tool_emoji)
+    assert a._tool_emoji("terminal") == "💻"
+    assert a._tool_emoji("read_file") == "📖"
+    # Unknown tool: the adapter asks for an empty default and drops it.
+    assert a._tool_emoji("no_such_tool") is None
+    assert seen["no_such_tool"] == ""
+    # A display-layer failure degrades to None, never a crash.
+    def boom(name, default="⚡"):
+        raise RuntimeError("no display")
+
+    monkeypatch.setattr("agent.display.get_tool_emoji", boom)
+    assert a._tool_emoji("terminal") is None
+
+
+@pytest.mark.asyncio
+async def test_tool_start_frame_carries_emoji(plugin, adapter, ws_client, monkeypatch):
+    """A tool-progress line emits ``tool.start`` with the per-tool emoji
+    resolved from hermes' display layer."""
+    ws, _ = ws_client
+    monkeypatch.setattr(
+        "agent.display.get_tool_emoji",
+        lambda name, default="⚡": "💻" if name == "terminal" else default,
+    )
+    res = await adapter.send('android:default', '💻 terminal: "ls -la"')
+    assert res.success
+    frames = await recv_until(ws, lambda f: f.get("type") == "tool.start")
+    payload = frames[-1]["payload"]
+    assert payload["name"] == "terminal"
+    assert payload["emoji"] == "💻"
+    # Unknown tool -> field omitted (app falls back to its default glyph).
+    monkeypatch.setattr("agent.display.get_tool_emoji", lambda name, default="⚡": default)
+    res2 = await adapter.send('android:default', '🔧 patch: "x"')
+    assert res2.success
+    frames2 = await recv_until(
+        ws, lambda f: f.get("type") == "tool.start" and f["payload"]["name"] == "patch"
+    )
+    assert "emoji" not in frames2[-1]["payload"]
+
+
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