Pattern: Hook and Halt Semantics Are the New Silent-Failure Surface in Agent Harnesses

Claude Code Changelog·high signal

Across v2.1.212 and v2.1.214, four separate fixes address guardrails that reported blocking but didn't: `continue:false` halts dropped when a tool failed or completed mid-stream, hook infrastructure errors misreported as user rejections, exit-code-2 hooks not blocking when their stdout JSON failed validation, and (in v2.1.211) an 'ask' decision being overridable. The pattern is that harnesses reliably surface the happy path of a hook and silently degrade its failure path. Treat any hook you use as a safety control as untested until you've verified it blocks under a malformed payload, a mid-stream tool failure, and a non-zero infrastructure error.