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/tests/test_executor.py

@@ -161,11 +161,14 @@ def test_a_success_resets_the_failure_count(store: StateStore, ws: Workspace) ->
 def test_failed_reads_do_not_count_toward_escalation(
     store: StateStore, ws: Workspace
 ) -> None:
+    # Two failed reads in a row must not trip the failure limit: looking for
+    # a file that is not there is the model orienting itself, not failing.
     client = ScriptedClient(
         [
             [call("read_file", path="missing-a.txt")],
             [call("read_file", path="missing-b.txt")],
-            [AssistantText(text="looked around, done", model="m")],
+            [call("write_file", path="a.py", content="x")],
+            [AssistantText(text="done", model="m")],
         ]
     )
     assert build(client, store, ws, failure_limit=2).run(milestone=1).status == (
@@ -173,6 +176,20 @@ def test_failed_reads_do_not_count_toward_escalation(
     )
 
 
+def test_reading_alone_is_not_doing_the_work(store: StateStore, ws: Workspace) -> None:
+    # Exploration is not evidence a milestone was carried out, so a
+    # completion claim backed only by reads is still challenged.
+    client = ScriptedClient(
+        [
+            [call("list_dir", path=".")],
+            [AssistantText(text="looks done to me", model="m")],
+            [AssistantText(text="really, done", model="m")],
+        ]
+    )
+    outcome = build(client, store, ws).run(milestone=1)
+    assert outcome.status == "escalate"
+
+
 def test_turn_cap_is_enforced(store: StateStore, ws: Workspace) -> None:
     forever = [[call("list_dir", path=".")] for _ in range(50)]
     client = ScriptedClient(forever)