fix(rules): anchor system var tmp paths

CHANGELOG.md

@@ -8,6 +8,7 @@ All notable changes to Diskern are documented here. The format follows
 
 ### Fixed
 
+- The system temp rule no longer reaches user and project `var/tmp` directories
 - A relative scan root no longer hides every finding a root-anchored rule
   would have made. `diskern scan tmp` from `/var` reported nothing to
   clean; roots are resolved to absolute paths before the walk

crates/diskern-core/rules/base.json

@@ -87,7 +87,7 @@
     },
     {
       "id": "temp-dirs",
-      "patterns": ["/tmp/**", "**/var/tmp/**", "**/appdata/local/temp/**"],
+      "patterns": ["/tmp/**", "/var/tmp/**", "/private/var/tmp/**", "**/appdata/local/temp/**"],
       "category": "temp_file",
       "verdict": "review",
       "description": "Temporary files. Usually safe once no program is using them."

crates/diskern-core/src/rules.rs

@@ -334,8 +334,11 @@ mod tests {
     fn rules_do_not_reach_outside_the_paths_they_name() {
         let db = RulesDb::embedded();
         for path in [
-            "/home/user/tmp/tax-return.pdf",     // not /tmp
-            "/home/user/var/log/notes.txt",      // not /var/log
+            "/home/user/tmp/tax-return.pdf", // not /tmp
+            "/home/user/var/log/notes.txt",  // not /var/log
+            "/home/user/var/tmp/notes.txt",  // not /var/tmp
+            "/home/user/project/var/tmp/session.dat",
+            "/opt/homebrew/var/tmp/formula.lock",
             "/home/user/Downloads/holiday.dmgx", // not a .dmg
             "/home/user/mytmp/scratch.bin",
         ] {
@@ -351,6 +354,7 @@ mod tests {
         for (path, expected) in [
             ("/tmp/build-9a2f/out.o", Category::TempFile),
             ("/var/tmp/systemd-private/x", Category::TempFile),
+            ("/private/var/tmp/com.apple.launchd/x", Category::TempFile),
             (
                 "C:\\Users\\x\\AppData\\Local\\Temp\\a.tmp",
                 Category::TempFile,

docs/RULES.md

@@ -48,9 +48,10 @@ evidence (e.g. recently-accessed files), never less.
   - a pattern that starts with `/` is anchored at the filesystem root
 
 That anchoring is what keeps a rule inside the directory it names.
-`/tmp/**` is the root's scratch directory; it does not reach
-`/home/user/tmp/tax-return.pdf`. `**/node_modules/**` still matches at
-any depth, because that is what the rule means.
+`/tmp/**` and `/var/tmp/**` are root scratch directories; they do not reach
+`/home/user/tmp/tax-return.pdf` or a project's `var/tmp`. macOS's corresponding
+system path is `/private/var/tmp/**`. `**/node_modules/**` still matches at any
+depth, because that is what the rule means.
 
 Write patterns to end in `/**` when the rule is about a directory, and
 as `**/*.ext` when it is about an extension. A directory pattern without