fleetd #131: enforce package boundaries with an ArchUnit cycle test

Adds PackageCyclesTest, which fails the build on any new cycle between
the top-level dev.ltms.fleet.* packages. Today's five real cycles are
recorded as narrow, explicit exceptions (ignoreDependency per named
pair, both directions), each commented with the ticket step (or a note
that it needs its own) that removes it. No package moves in this PR.

archunit-junit5 1.5.0 (current stable, newer than an earlier 1.4.1
draft). Main code only (DO_NOT_INCLUDE_TESTS) and importPackages(...)
instead of a working-directory-relative target/classes path.

fleetd/fleetd.example.yaml

@@ -686,6 +686,19 @@ guard:
 #            confidentiality boundary. A real boundary needs a different OS user or OS-level
 #            confinement, such as a container or VM. That is the open question in fleetd #184.
 #
+#            Still do not set this to "allow" casually. SSH_AUTH_SOCK is a live handle to YOUR
+#            ssh-agent, so a member holding it can sign with EVERY key the agent holds. It sits in
+#            no secret file and looks like no credential, which is why it slipped past three
+#            earlier tickets (gitea #110). Blocking it does not contain a member, but allowing it
+#            hands one a signing capability for no gain — the block costs nothing, so keep it.
+#
+#            Both halves of this are measured, not argued. 2026-08-28: a member with
+#            SSH_AUTH_SOCK blanked pushed to the forge over SSH successfully, because `ssh -G`
+#            resolves an IdentityFile outside ~/.ssh that is readable and has no passphrase. An
+#            earlier version of this comment claimed blocking the socket BREAKS git over SSH. It
+#            does not. That claim came from looking only in ~/.ssh, which holds nothing but four
+#            `Include` lines — looking in one place and concluding about the whole host.
+#
 # HOT-RELOADABLE the same way `fleet:` is (CB-559): read fresh on every spawn, so editing this list
 # and reloading config (or restarting) changes what the NEXT spawn inherits; already-running members
 # are unaffected either way.

fleetd/pom.xml

@@ -29,6 +29,7 @@
         <commons-compress.version>1.27.1</commons-compress.version>
         <commons-lang3.version>3.18.0</commons-lang3.version>
         <sqlite-jdbc.version>3.53.4.0</sqlite-jdbc.version>
+        <archunit.version>1.5.0</archunit.version>
     </properties>
 
     <!--
@@ -176,6 +177,14 @@
             <version>${testcontainers.version}</version>
             <scope>test</scope>
         </dependency>
+
+        <!-- fleetd #131: package-boundary and cycle enforcement (PackageCyclesTest). -->
+        <dependency>
+            <groupId>com.tngtech.archunit</groupId>
+            <artifactId>archunit-junit5</artifactId>
+            <version>${archunit.version}</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>

fleetd/src/main/java/dev/ltms/fleet/Fleetd.java

@@ -121,6 +121,7 @@ public final class Fleetd {
         // else can fail on a silently-empty one. A daemon started without a login shell (launchd)
         // boots fine either way — this is the only thing that says so out loud.
         reportRequiredSecrets(cfg);
+        reportMemberTrustModel(cfg);
         // CB-596: an absent (or empty) memberCredentials: block blocks NOTHING — no credential
         // name is hardcoded any more to fall back on. Say so loudly, the same way a missing
         // secret is reported above, so upgrading past this commit never silently drops CB-592's
@@ -1136,6 +1137,24 @@ public final class Fleetd {
         });
     }
 
+    /**
+     * fleetd #184: state the member trust model at startup. Environment controls and worktrees do
+     * not make a sandbox when fleetd and its members use the same OS user. A separate herdr may
+     * provide that boundary, but fleetd cannot inspect the uid at the other end of its socket.
+     */
+    static void reportMemberTrustModel(FleetConfig cfg) {
+        if (cfg.memberHerdrSocket() != null && !cfg.memberHerdrSocket().isBlank()) {
+            log.info("member trust model: members are routed to a separate herdr through "
+                    + "memberHerdrSocket. fleetd cannot see that herdr's uid, so confirm it runs "
+                    + "as a different OS user before treating it as a boundary.");
+            return;
+        }
+        log.info("member trust model: members run as the same OS user as fleetd, not in a sandbox. "
+                + "A member can read any file this user can read, including SSH keys and credential "
+                + "stores, whatever memberCredentials says. To add a real boundary, route members to "
+                + "a second herdr under a different OS user with memberHerdrSocket.");
+    }
+
     /**
      * CB-596: {@code known:} empty (block absent entirely, or present but empty) means {@link
      * FleetConfig.MemberCredentials#blockedSet()} is empty too — every member pane inherits the

fleetd/src/test/java/dev/ltms/fleet/MemberTrustModelReportTest.java

@@ -0,0 +1,73 @@
+package dev.ltms.fleet;
+
+import ch.qos.logback.classic.Logger;
+import ch.qos.logback.classic.spi.ILoggingEvent;
+import ch.qos.logback.core.read.ListAppender;
+import dev.ltms.fleet.config.FleetConfig;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+import org.slf4j.LoggerFactory;
+
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ * fleetd #184: startup must state whether members share fleetd's OS user or use a separate herdr.
+ */
+class MemberTrustModelReportTest {
+
+    private static FleetConfig load(Path dir, String yaml) throws Exception {
+        Path f = dir.resolve("fleetd.yaml");
+        Files.writeString(f, yaml);
+        return FleetConfig.load(f);
+    }
+
+    private static ListAppender<ILoggingEvent> attach() {
+        Logger logger = (Logger) LoggerFactory.getLogger(Fleetd.class);
+        ListAppender<ILoggingEvent> appender = new ListAppender<>();
+        appender.start();
+        logger.addAppender(appender);
+        return appender;
+    }
+
+    private static void detach(ListAppender<ILoggingEvent> appender) {
+        ((Logger) LoggerFactory.getLogger(Fleetd.class)).detachAppender(appender);
+    }
+
+    private static String report(FleetConfig cfg) {
+        Logger logger = (Logger) LoggerFactory.getLogger(Fleetd.class);
+        ch.qos.logback.classic.Level original = logger.getLevel();
+        logger.setLevel(ch.qos.logback.classic.Level.INFO);
+        ListAppender<ILoggingEvent> appender = attach();
+        try {
+            Fleetd.reportMemberTrustModel(cfg);
+        } finally {
+            detach(appender);
+            logger.setLevel(original);
+        }
+        return appender.list.getFirst().getFormattedMessage();
+    }
+
+    @Test
+    void unsetMemberHerdrSocketStatesThatMembersAreNotSandboxed(@TempDir Path dir) throws Exception {
+        FleetConfig cfg = load(dir, "bind:\n  host: 127.0.0.1\n  port: 8765\n");
+
+        assertEquals("member trust model: members run as the same OS user as fleetd, not in a sandbox. "
+                        + "A member can read any file this user can read, including SSH keys and credential "
+                        + "stores, whatever memberCredentials says. To add a real boundary, route members to "
+                        + "a second herdr under a different OS user with memberHerdrSocket.",
+                report(cfg));
+    }
+
+    @Test
+    void configuredMemberHerdrSocketStatesThatFleetdCannotConfirmTheBoundary(@TempDir Path dir) throws Exception {
+        FleetConfig cfg = load(dir, "memberHerdrSocket: /tmp/member-herdr.sock\n");
+
+        assertEquals("member trust model: members are routed to a separate herdr through "
+                        + "memberHerdrSocket. fleetd cannot see that herdr's uid, so confirm it runs "
+                        + "as a different OS user before treating it as a boundary.",
+                report(cfg));
+    }
+}

fleetd/src/test/java/dev/ltms/fleet/PackageCyclesTest.java

@@ -0,0 +1,96 @@
+package dev.ltms.fleet;
+
+import com.tngtech.archunit.base.DescribedPredicate;
+import com.tngtech.archunit.core.domain.JavaClass;
+import com.tngtech.archunit.core.domain.JavaClass.Predicates;
+import com.tngtech.archunit.core.importer.ClassFileImporter;
+import com.tngtech.archunit.core.importer.ImportOption;
+import com.tngtech.archunit.library.dependencies.SliceRule;
+import com.tngtech.archunit.library.dependencies.SlicesRuleDefinition;
+import org.junit.jupiter.api.Test;
+
+/**
+ * fleetd #131 (CB-627): enforce package boundaries with an ArchUnit test instead of a
+ * Maven module split.
+ *
+ * <p>This test fails the build the moment a NEW cycle appears between the top-level
+ * {@code dev.ltms.fleet.*} packages. Today's cycles are recorded below as explicit,
+ * narrow exceptions: each one ignores dependencies between exactly the two named
+ * packages, in both directions, and nothing else. A cycle through any other pair of
+ * packages -- or a brand new pair -- still fails this test.
+ *
+ * <p><b>Main code only.</b> The import excludes test classes
+ * ({@link ImportOption.Predefined#DO_NOT_INCLUDE_TESTS}). Test code legitimately wires
+ * across many packages for setup and mocking; that is not part of the shipped
+ * architecture this rule protects. Verified: importing test classes too pulls in a much
+ * larger, noisier cycle set -- {@code herdr}, {@code member}, {@code peer}, {@code
+ * config}, {@code guard} and {@code placement} all show up in cycles that disappear the
+ * moment test classes are excluded. Scanning off the classpath via {@code
+ * importPackages(...)} (not a hardcoded {@code target/classes} path) also keeps this
+ * test correct regardless of the working directory the build is invoked from.
+ *
+ * <p><b>No package moves here</b> -- ticket #131 is explicit that removing a cycle is
+ * its own, later PR. See the comment on each exception below for which ticket step
+ * removes it.
+ */
+class PackageCyclesTest {
+
+    @Test
+    void packagesAreFreeOfCycles() {
+        var classes = new ClassFileImporter()
+                .withImportOption(ImportOption.Predefined.DO_NOT_INCLUDE_TESTS)
+                .importPackages("dev.ltms.fleet");
+
+        SliceRule rule = SlicesRuleDefinition.slices()
+                .matching("dev.ltms.fleet.(*)..")
+                .should().beFreeOfCycles();
+
+        // fleetd #131 step 1: move ConnectionIdentity so authz stops depending on the
+        // MCP layer. Evidence: auth/CallerResolver.java:3 imports mcp.ConnectionIdentity;
+        // mcp/FleetMcp.java:3-7 imports auth.AuditLog, Authz, CallerResolver, Principal,
+        // Role.
+        rule = ignoreCycle(rule, "auth", "mcp");
+
+        // fleetd #131 step 2: PrimaryRegistry is used by loops in msg; move it, or put
+        // an interface between msg and mcp. Evidence: msg/ReplyPushLoop.java:5 and
+        // msg/LeadHeartbeatLoop.java:5 import mcp.PrimaryRegistry; mcp/FleetMcp.java:15-18
+        // imports msg.LeadChannel, LeadMessage, MessageService, Rendezvous.
+        rule = ignoreCycle(rule, "mcp", "msg");
+
+        // fleetd #131 -- found while implementing this test, NOT one of the ticket's
+        // original three; it names its own follow-up step before removal. Evidence:
+        // inject/CompletionResolver.java:4-5, inject/Injector.java:6 and
+        // inject/TurnListener.java:3 import msg.Rendezvous / msg.TurnToken;
+        // msg/MessageService.java:6 imports inject.Injector.
+        rule = ignoreCycle(rule, "inject", "msg");
+
+        // fleetd #131 -- same as above, its own follow-up. Evidence:
+        // metrics/FleetMetrics.java:3 imports msg.ReplyInbox; msg/MessageService.java:7-8,
+        // msg/LeadHeartbeatLoop.java:6-7 and msg/ReplyPushLoop.java:6-7 import
+        // metrics.FleetMetrics / metrics.Metrics.
+        rule = ignoreCycle(rule, "metrics", "msg");
+
+        // fleetd #131 -- same as above, its own follow-up. Evidence:
+        // session/SessionManager.java:7 imports msg.TurnToken;
+        // msg/LeadHeartbeatLoop.java:8 imports session.MemberSession.
+        rule = ignoreCycle(rule, "msg", "session");
+
+        rule.check(classes);
+    }
+
+    /**
+     * Accepts today's known cycle between two top-level packages, and nothing else.
+     * Ignoring both directions removes exactly this pair from cycle detection; every
+     * other dependency -- including any new one added later, between these same two
+     * packages or any other pair -- is still checked.
+     */
+    private static SliceRule ignoreCycle(SliceRule rule, String packageA, String packageB) {
+        return rule
+                .ignoreDependency(residesIn(packageA), residesIn(packageB))
+                .ignoreDependency(residesIn(packageB), residesIn(packageA));
+    }
+
+    private static DescribedPredicate<JavaClass> residesIn(String topLevelPackage) {
+        return Predicates.resideInAPackage("dev.ltms.fleet." + topLevelPackage + "..");
+    }
+}