dsh-ptc-discipline: Hard Goals and Pending Gates in PTC Mode

This article introduces the DSH agent preset `dsh-ptc-discipline` maintained by yuan-source-666. It implements hard gates using `ctx.tools.guard()` built upon the PTC mode: tool calls are rejected when there is no active goal, a non-empty todo list, and at least one item in progress; exemptions are granted to guided tools, `run_code` itself, and non-root agents; it fails open if a service is missing. The article covers installation commands, configuration options, typical usage, 10 unit test scenarios, DSH 0.2.2+ compatibility, and notes regarding the plan mode.