fix(mcp): recover truncated prepared proposals

tests/api/test_mcp_contribution.py

@@ -252,6 +252,38 @@ def test_mcp_source_to_citation_vertical_slice(tmp_path: Path) -> None:
                     assert prepared_proposal.payload_digest == proposal_payload_digest(
                         prepared_proposal
                     )
+                    truncated_evaluation = await mcp.call_tool(
+                        "proposal_evaluate",
+                        {"proposal_json": prepared_payload["proposal_json"][:-1]},
+                    )
+                    assert not truncated_evaluation.is_error, truncated_evaluation.content
+                    truncated_evaluation_payload = json.loads(
+                        _text_payload(truncated_evaluation)
+                    )
+                    assert truncated_evaluation_payload["proposal_id"] == (
+                        prepared_proposal.proposal_id
+                    )
+                    assert truncated_evaluation_payload["input_repaired"] is True
+                    malformed_prepare = await mcp.call_tool(
+                        "proposal_prepare", {"proposal_json": '{"schema_version":'}
+                    )
+                    assert not malformed_prepare.is_error, malformed_prepare.content
+                    malformed_prepare_payload = json.loads(_text_payload(malformed_prepare))
+                    assert malformed_prepare_payload["status"] == "invalid"
+                    assert malformed_prepare_payload["issues"][0]["code"] == (
+                        "invalid_proposal_draft"
+                    )
+                    malformed_evaluation = await mcp.call_tool(
+                        "proposal_evaluate", {"proposal_json": '{"schema_version":'}
+                    )
+                    assert not malformed_evaluation.is_error, malformed_evaluation.content
+                    malformed_evaluation_payload = json.loads(
+                        _text_payload(malformed_evaluation)
+                    )
+                    assert malformed_evaluation_payload["status"] == "invalid"
+                    assert malformed_evaluation_payload["findings"][0]["code"] == (
+                        "PROPOSAL_JSON_INVALID"
+                    )
                     invalid_draft = json.loads(json.dumps(draft))
                     invalid_evidence = invalid_draft["operations"][1]["node"]["claims"][0][
                         "evidence"
@@ -928,12 +960,13 @@ def test_mcp_source_to_citation_vertical_slice(tmp_path: Path) -> None:
 
                     submitted = await mcp.call_tool(
                         "proposal_submit",
-                        {"proposal_json": candidate.model_dump_json()},
+                        {"proposal_json": candidate.model_dump_json()[:-1]},
                     )
                     assert not submitted.is_error, submitted.content
                     outcome = json.loads(_text_payload(submitted))
                     assert outcome["status"] == "accepted"
                     assert outcome["validation_status"] == "eligible"
+                    assert outcome["input_repaired"] is True
                     assert outcome["receipt"] is not None
                     accepted_head = repository.head()
                     retried = await mcp.call_tool(