fix(scanner): constrain generic cache marker evidence

CHANGELOG.md

@@ -16,6 +16,8 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/). cargo-r
 
 ### Fixed
 
+- Require the conventional `target` directory name before accepting generic `CACHEDIR.TAG` evidence. Custom Cargo output directories remain supported through Cargo configuration or `.rustc_info.json`.
+
 - The scheduler service never pruned its own state, so plans, reports, and run logs grew unbounded — on a large workspace a plan snapshot reaches hundreds of megabytes, so a 5-minute trigger wrote gigabytes per hour. The service now prunes at startup (clearing any existing backlog) and after every cycle; terminal `apply` prunes the reports directory it writes to.
 
 ### Changed

src/scanner/targets.rs

@@ -124,7 +124,9 @@ pub(crate) fn classify_target_candidate_with_overrides(
         ));
     }
 
-    if path.join(CACHEDIR_TAG).is_file() {
+    if path.file_name().is_some_and(|name| name == TARGET_DIR_NAME)
+        && path.join(CACHEDIR_TAG).is_file()
+    {
         return Ok(TargetCandidate::candidate(
             path.to_path_buf(),
             TargetCandidateKind::CargoTargetDir,

tests/scanner_foundation.rs

@@ -483,3 +483,19 @@ impl Drop for TestTemp {
         let _ = fs::remove_dir_all(&self.path);
     }
 }
+
+#[test]
+fn generic_cache_marker_does_not_make_a_non_target_directory_a_cargo_target()
+-> Result<(), Box<dyn Error>> {
+    let temp = TestTemp::new("non_cargo_cache")?;
+    let cache = temp.path().join("python-cache");
+    fs::create_dir(&cache)?;
+    fs::write(
+        cache.join("CACHEDIR.TAG"),
+        "Signature: 8a477f597d28d172789f06886806bc55\n",
+    )?;
+    let candidate = classify_target_candidate(&cache, None, None, &ScannerOptions::default())?;
+    assert!(candidate.evidence.is_none());
+    assert!(candidate.skip_reason.is_some());
+    Ok(())
+}

tests/scanner_recursive.rs

@@ -329,3 +329,26 @@ fn test_lock() -> Result<std::sync::MutexGuard<'static, ()>, Box<dyn Error>> {
         .lock()
         .map_err(|_| std::io::Error::other("env lock poisoned").into())
 }
+
+#[test]
+fn recursive_scan_preserves_non_cargo_cache_contents() -> Result<(), Box<dyn Error>> {
+    let _test_guard = test_lock()?;
+    let temp = TestTemp::new("recursive_non_cargo_cache")?;
+    let cache = temp.path().join("python-cache");
+    let valuable = cache.join("release/deps/valuable.txt");
+    fs::create_dir_all(valuable.parent().expect("parent"))?;
+    fs::write(
+        cache.join("CACHEDIR.TAG"),
+        "Signature: 8a477f597d28d172789f06886806bc55\n",
+    )?;
+    fs::write(&valuable, "user data")?;
+    let plan = cargo_reclaim::build_plan_from_roots(
+        [temp.path()],
+        cargo_reclaim::PolicyKind::Balanced,
+        &ScannerOptions::default(),
+        &cargo_reclaim::InventoryOptions::default(),
+    )?;
+    assert_eq!(plan.totals.delete_candidate_count, 0);
+    assert_eq!(fs::read_to_string(valuable)?, "user data");
+    Ok(())
+}