A durable `user/message` event lacking a non-empty string `data.id` passes
the runtime append unchecked but makes the harness refuse the whole session
at its next load (`... lacks an identified message`, issue #51). The archived
wrap-up notice carried a rebuild signature (role-first key order, `id` and
`summary` stripped) that no shipped harness producer emits, so the strip
happens upstream of the append, outside both audited codebases.
Guard the durability boundary from the plugin side: a prepended
`agent/pre-step` listener runs last in the waterfall and mints a `dshctx-`
prefixed id for any decision message that would persist unidentified,
leaving everything else — including the decision's reference identity —
verbatim, and failing open on hostile entries. The seam is pinned per
baseline (the event dispatch, the user/message append that consumes it,
and the prepend option) in the real-code matrix.
bowenliang123
ba074e078e