test(mcp): cover tolerant_result.py's untested branches

Direct unit tests for the pure-logic branches codecov flagged as uncovered:
_resource_text's three return paths (direct text, nothing decodable, bad
base64/non-UTF-8 bytes), _validate_resource's ValidationError path for a
wrong-typed field, _as_text_block's fallback for a block with no usable
resource, and _degrade_invalid_content_blocks's three early-return paths for
non-mapping input and non-list/string content.

tolerant_result.py has no litellm imports, so these run against the module
directly rather than through the MCPClient/session machinery, matching the
new-module test-file convention (no prior mapped test existed for this file).

tests/test_litellm/experimental_mcp_client/test_tolerant_result.py

@@ -0,0 +1,57 @@
+import pytest
+from litellm.experimental_mcp_client.tolerant_result import (
+    TolerantCallToolResult,
+    _as_text_block,
+    _resource_text,
+    _ResourcePayload,
+    _validate_resource,
+)
+from pydantic import ValidationError
+
+
+def test_resource_text_returns_text_field_directly():
+    resource = _ResourcePayload(text="already text")
+    assert _resource_text(resource) == "already text"
+
+
+def test_resource_text_returns_none_when_nothing_decodable():
+    resource = _ResourcePayload(text=None, blob=None, mimeType=None)
+    assert _resource_text(resource) is None
+
+
+def test_resource_text_returns_none_on_undecodable_base64():
+    resource = _ResourcePayload(blob="not valid base64!!!", mimeType="text/plain")
+    assert _resource_text(resource) is None
+
+
+def test_resource_text_returns_none_on_non_utf8_bytes():
+    non_utf8_blob = b"\xff\xfe".hex()
+    import base64
+
+    resource = _ResourcePayload(blob=base64.b64encode(bytes.fromhex(non_utf8_blob)).decode(), mimeType="text/plain")
+    assert _resource_text(resource) is None
+
+
+def test_validate_resource_returns_none_for_wrong_typed_field():
+    assert _validate_resource({"mimeType": 12345}) is None
+
+
+def test_as_text_block_falls_back_to_json_dump_for_unrecognized_block():
+    block = _as_text_block({"type": "nonsense", "foo": "bar"})
+    assert block["type"] == "text"
+    assert block["text"] == '{"type": "nonsense", "foo": "bar"}'
+
+
+def test_degrade_invalid_content_blocks_passthrough_for_non_mapping_input():
+    with pytest.raises(ValidationError):
+        TolerantCallToolResult.model_validate("not a mapping at all")
+
+
+def test_degrade_invalid_content_blocks_passthrough_for_non_sequence_content():
+    with pytest.raises(ValidationError):
+        TolerantCallToolResult.model_validate({"content": 42, "isError": False})
+
+
+def test_degrade_invalid_content_blocks_passthrough_for_string_content():
+    with pytest.raises(ValidationError):
+        TolerantCallToolResult.model_validate({"content": "not-a-list-of-blocks", "isError": False})