#384: write shared scrub receipts

fleetd/src/main/java/dev/ltms/fleet/member/EnvAllowListScrub.java

@@ -105,9 +105,9 @@ public final class EnvAllowListScrub {
             reapOrphans(parentDir);
             Path dir = Files.createTempDirectory(parentDir, DIR_PREFIX);
             dir.toFile().deleteOnExit();
-            // The report is written by zsh, after these hooks are registered, so register its path
-            // too — otherwise the directory is non-empty at JVM exit and cannot be removed at all.
-            dir.resolve(REPORT_FILE).toFile().deleteOnExit();
+            // zsh truncates this pre-created receipt after these hooks are registered. Register its
+            // path too — otherwise the directory is non-empty at JVM exit and cannot be removed.
+            Files.createFile(dir.resolve(REPORT_FILE)).toFile().deleteOnExit();
             write(dir, SCRUB_FILE, scrubScript(allowedNames));
             write(dir, ".zshenv", homeSourcingFile(".zshenv"));
             write(dir, ".zprofile", homeSourcingFile(".zprofile"));
@@ -147,12 +147,11 @@ public final class EnvAllowListScrub {
      * into it: owner keeps full access, {@code group} gets traverse+read on the directory ({@code
      * rwxr-x---}, so a member process — a login shell reading it via {@code ZDOTDIR}, or another
      * process simply opening a file under it — running under that group can find and read the
-     * files) and read-only on each file ({@code rw-r-----}) — deliberately no group WRITE anywhere,
-     * since a member never needs to add or change what fleetd generated. (For the ZDOTDIR scrub
-     * specifically, this also means the scrub script's own report write inside the pane fails
-     * closed rather than open — see {@code scrub.zsh}'s trailing {@code 2>/dev/null} — which {@link
-     * dev.ltms.fleet.member.HerdrPeerLauncher#releaseZdotdir} already treats as "cannot be
-     * confirmed to have run" rather than success.)
+      * files) and read-only on each file ({@code rw-r-----}), except the pre-created ZDOTDIR
+      * {@code scrub-report.txt}. That receipt gets group write ({@code rw-rw----}), so
+      * {@code scrub.zsh} can truncate and write it without granting group write on the directory.
+      * If its optional permission change fails, the member cannot write a receipt and the launcher
+      * keeps its existing WARN rather than failing the spawn.
      *
      * <p>Package-private and named generically on purpose: fleetd #213 built this for the ZDOTDIR
      * scrub directory, and fleetd #219 reuses it verbatim for {@link
@@ -167,7 +166,15 @@ public final class EnvAllowListScrub {
             setGroupAndPermissions(dir, principal, "rwxr-x---");
             try (Stream<Path> entries = Files.list(dir)) {
                 for (Path file : entries.toList()) {
-                    setGroupAndPermissions(file, principal, "rw-r-----");
+                    if (REPORT_FILE.equals(file.getFileName().toString())) {
+                        try {
+                            setGroupAndPermissions(file, principal, "rw-rw----");
+                        } catch (IOException | UnsupportedOperationException ignored) {
+                            // The receipt is optional. Its absence keeps the existing WARN path.
+                        }
+                    } else {
+                        setGroupAndPermissions(file, principal, "rw-r-----");
+                    }
                 }
             }
         } catch (IOException e) {

fleetd/src/test/java/dev/ltms/fleet/member/EnvAllowListScrubTest.java

@@ -108,6 +108,31 @@ class EnvAllowListScrubTest {
                 "allowed N of M with N <= M — the denominator is always reported");
     }
 
+    /** A group-shared ZDOTDIR still lets the member truncate and write its pre-created receipt. */
+    @Test
+    void groupSharedScrubWritesAndReadsItsReport(@TempDir Path tmp) throws Exception {
+        assumeTrue(Files.isExecutable(ZSH), "/bin/zsh not present — nothing to prove here");
+        Set<String> allowed = MemberEnvAllowList.derive(List.of());
+        Path zdotdir = EnvAllowListScrub.generate(tmp, allowed, currentUserGroup());
+
+        Map<String, String> cleanParent = Map.of(
+                "HOME", System.getProperty("user.home"),
+                "PATH", "/usr/bin:/bin",
+                "SHELL", "/bin/zsh");
+        exportedNamesFromCleanParent(cleanParent, zdotdir);
+
+        EnvAllowListScrub.ScrubReport report = EnvAllowListScrub.readReport(zdotdir);
+        assertNotNull(report, "a group-shared completed login shell must leave a report behind");
+        assertTrue(report.allowed() >= 0 && report.total() >= report.allowed(),
+                "allowed N of M with N <= M — the denominator is always reported");
+        assertEquals("rw-rw----", java.nio.file.attribute.PosixFilePermissions.toString(
+                        Files.getPosixFilePermissions(zdotdir.resolve(EnvAllowListScrub.REPORT_FILE))),
+                "the pre-created receipt must be group-writable");
+        assertEquals("rwxr-x---", java.nio.file.attribute.PosixFilePermissions.toString(
+                        Files.getPosixFilePermissions(zdotdir)),
+                "group sharing must not make the ZDOTDIR directory group-writable");
+    }
+
     /** Report parsing is lenient: absent file → null (no measurement), not an exception. */
     @Test
     void readReportReturnsNullForADirectoryWithoutOne(@TempDir Path dir) {