fix(telegram): guard unsupported attachment type with ValidationError (coderabbit)

Addresses CodeRabbit's CHANGES_REQUESTED on #119. `ATTACHMENT_UPLOADS[attachment.type]`
raised a bare `KeyError` for any `attachment.type` outside the supported set.
`Attachment.type` is a `Literal`, but Python does not enforce Literals at
runtime, so an untyped/dynamic caller can supply an out-of-set value. Guard
the lookup and raise a `ValidationError` naming the bad type and the supported
set, consistent with the other validation paths in `send_attachment`.

New `test_rejects_unsupported_attachment_type` is load-bearing — reverting the
guard makes the call raise `KeyError` (not `ValidationError`) and the test fails.

https://claude.ai/code/session_01FyMxQn2BEAzmwKS1GZczKj

Author: claude

src/chat_sdk/adapters/telegram/adapter.py

@@ -1902,6 +1902,11 @@ async def send_attachment(
         """
         import aiohttp
 
+        if attachment.type not in ATTACHMENT_UPLOADS:
+            raise ValidationError(
+                "telegram",
+                f"Unsupported attachment type: {attachment.type}. Supported types: {', '.join(ATTACHMENT_UPLOADS)}",
+            )
         upload = ATTACHMENT_UPLOADS[attachment.type]
 
         data = attachment.data

tests/test_telegram_api.py

@@ -397,6 +397,32 @@ async def test_rejects_attachment_without_data_or_url(self):
 
         adapter.telegram_fetch.assert_not_called()
 
+    @pytest.mark.asyncio
+    async def test_rejects_unsupported_attachment_type(self):
+        """An attachment.type not in ATTACHMENT_UPLOADS raises a clear ValidationError.
+
+        ``Attachment.type`` is a ``Literal``, but Python does not enforce it at
+        runtime, so an untyped/dynamic caller can supply an out-of-set value.
+        Without the guard the per-type dict lookup raises a bare ``KeyError``;
+        we surface a ``ValidationError`` naming the bad type and the supported
+        set instead. Load-bearing: reverting the guard makes this raise
+        ``KeyError`` (not ``ValidationError``) and the test fails.
+        """
+        adapter = _make_adapter()
+        _init_adapter(adapter)
+        adapter.telegram_fetch = AsyncMock(return_value=_make_telegram_message())
+
+        with pytest.raises(ValidationError, match="Unsupported attachment type: sticker"):
+            await adapter.post_message(
+                THREAD_ID,
+                PostableRaw(
+                    raw="",
+                    attachments=[Attachment(type="sticker", data=b"x")],  # type: ignore[arg-type]
+                ),
+            )
+
+        adapter.telegram_fetch.assert_not_called()
+
 
 # =============================================================================
 # Tests -- edit_message