From cc2e7b7eee4fb0944968d1d1233ef7d1174263b8 Mon Sep 17 00:00:00 2001
From: BFlat <bombayapirat@gmail.com>
Date: Mon, 2 Nov 2026 15:29:06 +0700
Subject: [PATCH] Comparing two runs tells a deleted file from a created one
 (#340)

`runtime_captures_compare` compared the filesystem dimension by the set of changed paths only. A run that deleted a watched file and a run that created the same file both "changed" that path, so they matched, and the comparison said the two runs were the same.

Each path is now compared together with how it changed (created, deleted or modified). Two deletions of the same file still match, and different paths still differ.

**Verified:** a new test of the filesystem comparison covering deleted vs created (changed), deleted vs deleted (unchanged), different paths (changed), and an `unchanged` effect against none (unchanged). The engine's process-tool tests, clippy and fmt pass.

Fixes #300
---
 crates/engine/src/tools/process_tools.rs | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/crates/engine/src/tools/process_tools.rs b/crates/engine/src/tools/process_tools.rs
index 8792b373..07b4e995 100644
--- a/crates/engine/src/tools/process_tools.rs
+++ b/crates/engine/src/tools/process_tools.rs
@@ -569,8 +569,8 @@ fn dispatched(v: &Value) -> usize {
 fn compare_filesystem(l: &Value, r: &Value) -> Dimension {
     let both_observed = l.pointer("/filesystem").is_some_and(Value::is_object) && r.pointer("/filesystem").is_some_and(Value::is_object);
     if both_observed {
-        let lc = changed_paths(l);
-        let rc = changed_paths(r);
+        let lc = changes(l);
+        let rc = changes(r);
         let status = if lc == rc { "unchanged" } else { "changed" };
         Dimension { dimension: "filesystem", status, detail: json!({"left_changes": lc.len(), "right_changes": rc.len()}) }
     } else {
@@ -578,13 +578,14 @@ fn compare_filesystem(l: &Value, r: &Value) -> Dimension {
     }
 }
 
-fn changed_paths(v: &Value) -> std::collections::BTreeSet<String> {
+/// Each changed path with how it changed: deleting a file and creating it are different runs (#300).
+fn changes(v: &Value) -> std::collections::BTreeSet<(String, String)> {
     v.pointer("/filesystem/effects")
         .and_then(Value::as_array)
         .map(|a| {
             a.iter()
-                .filter(|e| matches!(e.get("change").and_then(Value::as_str), Some("created") | Some("deleted") | Some("modified")))
-                .filter_map(|e| e.get("path").and_then(Value::as_str).map(String::from))
+                .filter_map(|e| Some((e.get("path")?.as_str()?.to_string(), e.get("change")?.as_str()?.to_string())))
+                .filter(|(_, c)| matches!(c.as_str(), "created" | "deleted" | "modified"))
                 .collect()
         })
         .unwrap_or_default()
@@ -599,6 +600,18 @@ mod tests {
         e.call(id, p, CallOptions::new(Caller::Cli).with_consent(Consent::Granted)).map(|o| o.to_json())
     }
 
+    /// #300: one run deleting a file and the other creating it matched, as only paths were compared.
+    #[test]
+    fn deleting_and_creating_a_file_differ() {
+        let run = |effects: Value| json!({"filesystem": {"effects": effects}});
+        let fx = |change: &str, path: &str| json!([{"path": path, "change": change}]);
+        let status = |l: Value, r: Value| super::compare_filesystem(&run(l), &run(r)).status;
+        assert_eq!(status(fx("deleted", "/w/a"), fx("created", "/w/a")), "changed");
+        assert_eq!(status(fx("deleted", "/w/a"), fx("deleted", "/w/a")), "unchanged");
+        assert_eq!(status(fx("deleted", "/w/a"), fx("deleted", "/w/b")), "changed");
+        assert_eq!(status(fx("unchanged", "/w/a"), json!([])), "unchanged");
+    }
+
     #[test]
     fn capture_needs_consent() {
         let e = Engine::new(crate::testing::session());