Count only mutating tools as evidence of work

The previous fix challenged a completion claim made before any tool
call, but treated every tool as work — so a model that ran one
list_dir and then declared the milestone done was believed, and CI
caught the same empty milestone again.

Reading a file or listing a directory is the model orienting itself.
Only write_file and run_command now count, so a completion claim must
be backed by something that changed or verified the tree.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

nisse-dev/src/nisse_dev/executor.py

@@ -30,8 +30,13 @@ plain-text summary and no tool call — that ends the milestone."""
 DEFAULT_MAX_TURNS = 24
 DEFAULT_FAILURE_LIMIT = 2
 
+# Tools that change or verify something. Reading a file or listing a
+# directory is the model looking around, not doing the work, so neither
+# counts as evidence that a milestone was carried out.
+MUTATING_TOOLS = frozenset({"write_file", "run_command"})
+
 # A turn with no tool call means "the plan is done". Believing that before
-# any tool has been called would record an empty milestone as a success, so
+# any real work has happened would record an empty milestone as a success, so
 # the claim is challenged once first.
 _NUDGE = (
     "\n\nYou have not made any change yet, so the plan cannot be complete. "
@@ -105,7 +110,8 @@ class LLMExecutor:
                 )
 
             for call in calls:
-                did_work = True
+                if call.tool in MUTATING_TOOLS:
+                    did_work = True
                 outcome = self._workspace.dispatch(call.tool, call.arguments)
                 self._store.append_event(
                     ToolResult(