fix(discord): bound component labels by UTF-16 units

plugins/platforms/discord/adapter.py

@@ -52,6 +52,9 @@ def __init__(self, id: int) -> None:  # noqa: A002 - matches discord API
 # every slash command — not just the overflow ones. We keep the desired set
 # at or below this limit at registration time.
 _DISCORD_MAX_APP_COMMANDS = 100
+_DISCORD_SELECT_FIELD_LIMIT = 100
+_DISCORD_BUTTON_LABEL_LIMIT = 80
+_DISCORD_ELLIPSIS = "\u2026"
 _DISCORD_NONCONVERSATIONAL_METADATA_KEYS = frozenset({
     "non_conversational",
     "non_conversational_history",
@@ -117,11 +120,18 @@ def __init__(self, id: int) -> None:  # noqa: A002 - matches discord API
     cache_document_from_bytes,
     SUPPORTED_DOCUMENT_TYPES,
     _TEXT_INJECT_EXTENSIONS,
+    _prefix_within_utf16_limit,
+    utf16_len,
     validate_inbound_media_size,
 )
 from tools.url_safety import is_safe_url
 
 
+def _truncate_discord_component_text(text: str, limit: int) -> str:
+    """Return text within Discord's UTF-16 component field budget."""
+    return _prefix_within_utf16_limit(str(text or ""), max(0, limit))
+
+
 async def _wait_for_ready_or_bot_exit(
     ready_event: asyncio.Event,
     bot_task: asyncio.Task,
@@ -6293,7 +6303,10 @@ def _build_provider_select(self):
                 desc = "current" if p.get("is_current") else None
                 options.append(
                     discord.SelectOption(
-                        label=label[:100],
+                        label=_truncate_discord_component_text(
+                            label,
+                            _DISCORD_SELECT_FIELD_LIMIT,
+                        ),
                         value=p["slug"],
                         description=desc,
                     )
@@ -6330,8 +6343,14 @@ def _build_model_select(self, provider_slug: str):
                 short = model_id.split("/")[-1] if "/" in model_id else model_id
                 options.append(
                     discord.SelectOption(
-                        label=short[:100],
-                        value=model_id[:100],
+                        label=_truncate_discord_component_text(
+                            short,
+                            _DISCORD_SELECT_FIELD_LIMIT,
+                        ),
+                        value=_truncate_discord_component_text(
+                            model_id,
+                            _DISCORD_SELECT_FIELD_LIMIT,
+                        ),
                     )
                 )
             if not options:
@@ -6610,15 +6629,18 @@ def __init__(
                 #      budget (hyphen, comma, period, paren)
                 #   3. Hard cut at the budget limit (last resort)
                 prefix = f"{index + 1}. "
-                budget = 80 - len(prefix)
-                if len(choice) <= budget:
+                budget = _DISCORD_BUTTON_LABEL_LIMIT - utf16_len(prefix)
+                if utf16_len(choice) <= budget:
                     label_body = choice
                 else:
-                    truncated = choice[: budget - 1].rstrip()
+                    truncated = _prefix_within_utf16_limit(
+                        choice,
+                        max(0, budget - utf16_len(_DISCORD_ELLIPSIS)),
+                    ).rstrip()
                     cut_at = -1
                     # 1. Last space in the trailing half of the budget.
                     space = truncated.rfind(" ")
-                    if space >= budget // 2:
+                    if space >= len(truncated) // 2:
                         cut_at = space
                     # 2. Soft boundary — only if no word boundary found.
                     # Find the latest soft boundary in the trailing half
@@ -6631,11 +6653,11 @@ def __init__(
                             (truncated.rfind(s) for s in ("-", ",", ".", ")")),
                             default=-1,
                         )
-                        if latest_soft >= budget // 2:
+                        if latest_soft >= len(truncated) // 2:
                             cut_at = latest_soft + 1
                     if cut_at > 0:
                         truncated = truncated[:cut_at]
-                    label_body = truncated.rstrip() + "…"
+                    label_body = truncated.rstrip() + _DISCORD_ELLIPSIS
                 button = discord.ui.Button(
                     label=f"{prefix}{label_body}",
                     style=discord.ButtonStyle.primary,

tests/gateway/test_discord_clarify_buttons.py

@@ -30,6 +30,7 @@
     DiscordAdapter,
 )
 from gateway.config import PlatformConfig  # noqa: E402
+from gateway.platforms.base import utf16_len  # noqa: E402
 
 
 # ---------------------------------------------------------------------------
@@ -130,6 +131,19 @@ def test_truncates_long_choice_label(self):
         # Final label total <= 80 (Discord cap on button labels)
         assert len(first_label) <= 80
 
+    def test_truncates_emoji_choice_label_by_utf16_limit(self):
+        long_choice = "\U0001f600" * 80
+        view = ClarifyChoiceView(
+            choices=[long_choice],
+            clarify_id="cidEmoji",
+            allowed_user_ids=set(),
+        )
+
+        first_label = view.children[0].label
+        assert first_label.startswith("1. ")
+        assert first_label.endswith("\u2026")
+        assert utf16_len(first_label) <= 80
+
     def test_truncates_long_choice_label_breaks_on_word_boundary(self):
         # Long choice with spaces — should cut at the last whole word so the
         # trailing text stays readable on Discord mobile.

tests/gateway/test_discord_model_picker.py

@@ -11,6 +11,7 @@
 
 import pytest
 
+from gateway.platforms.base import utf16_len
 from plugins.platforms.discord.adapter import ModelPickerView
 
 
@@ -82,6 +83,58 @@ async def edit_original_response(**kwargs):
     interaction.edit_original_response.assert_awaited_once()
 
 
+def test_model_picker_provider_labels_fit_discord_utf16_limit():
+    provider_name = "Provider " + ("\U0001f600" * 80)
+
+    view = ModelPickerView(
+        providers=[
+            {
+                "slug": "emoji",
+                "name": provider_name,
+                "models": ["gpt-5-mini"],
+                "total_models": 1,
+                "is_current": False,
+            }
+        ],
+        current_model="gpt-5-mini",
+        current_provider="emoji",
+        session_key="session-1",
+        on_model_selected=AsyncMock(return_value="ok"),
+        allowed_user_ids={"123"},
+    )
+
+    provider_select = view.children[0]
+    option = provider_select.options[0]
+    assert utf16_len(option.label) <= 100
+
+
+def test_model_picker_model_labels_and_values_fit_discord_utf16_limit():
+    model_id = "emoji/" + ("\U0001f600" * 80)
+
+    view = ModelPickerView(
+        providers=[
+            {
+                "slug": "emoji",
+                "name": "Emoji",
+                "models": [model_id],
+                "total_models": 1,
+                "is_current": False,
+            }
+        ],
+        current_model="gpt-5-mini",
+        current_provider="emoji",
+        session_key="session-1",
+        on_model_selected=AsyncMock(return_value="ok"),
+        allowed_user_ids={"123"},
+    )
+
+    view._build_model_select("emoji")
+    model_select = view.children[0]
+    option = model_select.options[0]
+    assert utf16_len(option.label) <= 100
+    assert utf16_len(option.value) <= 100
+
+
 @pytest.mark.asyncio
 async def test_expensive_model_requires_confirmation(monkeypatch):
     events: list[object] = []