Detect missed trailing whitespace in concatenated messages

Rule request

Thesis

Sometimes, a plaintext message is split by a few separate string literals with concatenation. And sometimes a whitespace is missed. For example:

message = "An error occurred."  # <- would have a whitespace at the end.
message += "Try to call for help."
print(message)
# An error occurred.Try to call for help.

Reasoning

For human-facing messages, it is a typo.

Implementation

The challenge is to make an effective heuristic to detect when it is a plain message and when it is something else (for machines). Please, share your examples. Do you have string concatenation for something else rather than for human-facing messages?

Examples I have in mind:

• SQL queries. For them, prefer multiline strings instead of concatenation, SQL databases are pretty fine with newlines in queries.
• URLs. I'd say, it's better just not to split them (see #1182)

Start by reviewing the proposed examples and deciding how to distinguish human-facing messages from SQL, URLs, and other machine-oriented concatenations. Define the heuristic and its edge cases, then add coverage showing that missed whitespace is reported without flagging valid concatenation; no implementation files or tests are named in the issue.