v0.5.0

Three features had a measured call rate of zero because they were instructions
to call something rather than events. Detecting that they were idle would have
been the wrong fix. They are now events.

Added

• castra-trace.py, a PostToolUse hook that records open loops from tool use
  itself. Editing a code file records "changed, never observed running"; a command
  that actually runs that file clears it. The hook is both the only author and the
  only reader of the file, so there is no step that someone has to remember.
  Documentation and config edits are excluded — a gate that fires on things nobody
  needs to verify is a gate people learn to ignore.

Changed

• The pack no longer tells the model to invoke the risk classifier. A PreToolUse
  hook already classifies every command and the verdict arrives as a tool result.
• CLAUDE.md no longer asks the model to write open loops or to call the guard.
• castra-posture.py honours CASTRA_HOME, which the installer already honoured.
  Without it a check could read a different pack than the one it asserts against.

Design rule this release establishes

A capability that depends on the model choosing to invoke it is not a control.
Bind it to an event, and derive its input from something that always exists — the
tool call, the transcript — never from a file another party is supposed to fill in.