The scanner read 2581 files and reported zero. The defect was on line 403.

On 2026-09-04 I pointed a scanner at langchain-ai/langchain . Shallow clone of the default branch, HEAD 79cab2d , read only. It walked 2581 files and printed zero sites. Its own control had passed immediately before the run, with two positive fixtures seen and four negative fixtures clean, so the zero was a measurement rather than a crash. Then I opened one file by hand. libs/langchain_v1/langchain/agents/middleware/human_in_the_loop.py , line 403: def _should_interrupt ( self , tool_call , config , state , runtime ) -> bool : """ Return False if the `when` predicate rejects this tool call, True otherwise. """ when = config . get ( " when " ) if when is None : return True ... return when ( req ) when is supplied by the caller. It is declared NotRequired[Callable[[ToolCallRequest], bool]] on line 195 and documented as returning True to interrupt or False to auto-approve. Its result is handed back unchanged. A predicate that falls off a branch returns None , and the caller on line 436 reads: if not self . _should_interrupt ( tool_call , config , state , runtime ): continue None is falsy. The interrupt is skipped and the tool call proceeds with nobody looking at it. The annotation says bool ; nothing at runtime makes that true. Why the machine stayed quiet I took the failure apart instead of guessing at it. Three causes, each sufficient on its own: Vocabulary. 22 lines in that file matched the approval vocabulary the scanner looks for. Not one of them put line 403 inside its window. The nearest match was 26 lines away and sat in a comment. This project calls the decision interrupt , not approval. Window. The -> bool annotation is on line 378. The return is on 403. That is 25 lines apart, and the window was 12. Signals. Widened to 55 lines, the three behaviour signals still matched nothing on that line. The file walk was innocent. The file is .py , 18256 bytes, and no skip rule matched it. It was read. What I got wrong The window of 12 lines had no measurement behind it