During a multi-task run nothing commits between tasks, so one task's
file-level `git checkout -- <file>` / `git restore <file>` silently
destroys an earlier task's uncommitted DONE work in a shared file. The
loss was structurally invisible: spec- and quality-reviewers are scoped
to the current task's footprint, diff_fingerprint only detects
same-task repair cycles, and the end-of-iteration tree gate counts
files (the surviving changes keep it nonzero). Observed in the wild as
a PARTIAL run whose DONE reports did not match the tree. Two layers,
both plugin-side (harness-level prevention is ruled out — decision log
on the issue):
Prose guard — implementer.md Step 8 no longer sanctions file checkout
for scope curation: over-reach is undone by editing back, a broken
intermediate state is repaired forward or reported BLOCKED (new fourth
BLOCKED bucket in the status protocol). A matching Iron Law line in
implement/SKILL.md covers all in-loop agents, whole-file and --patch;
docs/conventions.md now marks the checkout discard idiom as the
orchestrator's, between iterations.
Mechanical guard — after every task of a multi-task run a snapshot
agent records `git stash create` (a dangling commit; HEAD, index, and
tree untouched — semantics verified empirically in a scratch repo) plus
the `git diff HEAD --name-only --no-renames` path set. A path that was
HEAD-modified at one boundary and gone at the next trips a hard
BLOCKED naming the lost paths, the boundary, and the recovery snapshot
sha (`git show <sha>:<path>`); the discard verdict outranks per-task
outcomes in blocked_detail since the reports and the tree have
diverged. Coarse by design, in both directions, and documented as
such: a checkout-then-re-edit or a --patch hunk restore escapes the
comparison (the snapshot keeps it diagnosable); a legitimate
back-to-HEAD edit trips it (the verdict says adjudicate against the
snapshot). --no-renames keeps a staged rename from reading as a loss;
untracked files are outside the threat model (checkout cannot discard
them). Cost: one sonnet/medium call per task, multi-task runs only;
single-task and mini runs are unchanged.
Verified: node --check on the async-wrapped script and a stub-agent
harness — discard trips the hard BLOCKED and stops the loop; an
accumulating happy path, a plan-intended deletion, a single-task run,
and a dead snapshot agent all pass without a false positive.
closes#23
Brummel
e7009bc304