fleetd #439: pin the caller at the fleet_list call site, not just the gate

Review of PR #462 found M2: the coordinatorVisibleTo gate (then an inline
principal(exchange).isPrimary() check) could survive a mutation that
replaced the argument with a literal true at the one production call
site, because every existing test drove listFleet directly and supplied
the boolean itself -- nothing exercised the handler's own call.

- Name the decision: FleetMcp.coordinatorVisibleTo(Principal), a small
  package-private predicate next to denyFor/recordPrimarySingleton. The
  fleet_list handler now calls coordinatorVisibleTo(principal(exchange))
  instead of inlining .isPrimary().
- Pin the predicate's role table in FleetMcpAuthzTest
  (onlyThePrimaryMaySeeTheCoordinatorRow), covering primary/worker/
  architect and, newly, anonymous.
- Add a source-reading detector at the boundary
  (theFleetListHandlerActuallyConsultsCoordinatorVisibleTo), same idiom as
  toolsTheServerRegisters/everyRegisteredToolHasItsHandlerActionPinned: it
  reads FleetMcp.java, isolates the listHandler block, asserts (as a
  control) that the block actually contains a listFleet( call, then
  asserts the call's trailing boolean argument is exactly
  coordinatorVisibleTo(principal(exchange)) -- not a literal true/false.

Both mutations from the review were reproduced and killed by these tests,
then reverted; see the PR body for the full break-and-restore transcript.

fleetd/src/main/java/dev/ltms/fleet/mcp/FleetMcp.java

@@ -426,7 +426,8 @@ public final class FleetMcp {
                     return listFleet(workers, sessions, messages, capacity, healthCoverage, quarantine, outage,
                             leadSeats, callers == null ? Map.of() : callers.leads(),
                             callerTerminal(exchange),
-                            new CoordinationSource(leadChannel, peers));
+                            new CoordinationSource(leadChannel, peers),
+                            coordinatorVisibleTo(principal(exchange)));
                 };
         BiFunction<McpSyncServerExchange, McpSchema.CallToolRequest, McpSchema.CallToolResult> stopHandler =
                 (exchange, req) -> {
@@ -579,6 +580,20 @@ public final class FleetMcp {
         }
     }
 
+    /**
+     * fleetd #439: only the primary may read {@code fleet_list}'s {@code coordinator} row —
+     * lead-to-lead coordination state (coord-ids, mailbox facts, held-message previews), never the
+     * roster. Split out of the {@code fleet_list} handler, same reason as {@link #denyFor} and
+     * {@link #recordPrimarySingleton}: the decision must be unit-testable without fabricating an
+     * SDK {@code McpSyncServerExchange}, and the handler must call this named predicate rather than
+     * inlining the check, so a future edit cannot silently pass a literal instead of asking who
+     * called ({@code FleetMcpAuthzTest.theFleetListHandlerActuallyConsultsCoordinatorVisibleTo}
+     * reads the source and asserts the handler calls this method by name, not a literal).
+     */
+    static boolean coordinatorVisibleTo(Principal caller) {
+        return caller.isPrimary();
+    }
+
     /** The worker identity resolved from this call's connection, or {@code null} if the primary. */
     private static String callerTerminal(McpSyncServerExchange exchange) {
         Object v = exchange.transportContext().get(CALLER_TERMINAL);
@@ -1344,12 +1359,44 @@ public final class FleetMcp {
                 LeadSeatSource.none(), leads, selfTerm, coordination);
     }
 
-    /** As above, plus fleetd #176 lead-seat facts (see {@link LeadSeatSource}). */
+    /**
+     * As above, plus fleetd #176 lead-seat facts (see {@link LeadSeatSource}).
+     *
+     * <p>Assumes the caller is the primary — every wrapper overload above delegates here without
+     * carrying a caller identity, which is exactly right for them: they exist for call sites (and
+     * unit tests) that have no {@link Principal} to hand over, and this preserves their pre-#439
+     * behavior unchanged. The one call site that has a real caller ({@code fleet_list}'s MCP
+     * handler) uses {@link #listFleet(PeerLauncher, SessionManager, MessageService, CapacitySource,
+     * HealthCoverageSource, QuarantineSource, OutageSource, LeadSeatSource, Map, String,
+     * CoordinationSource, boolean)} instead, so it can pass the true answer.
+     */
     static McpSchema.CallToolResult listFleet(PeerLauncher workers, SessionManager sessions, MessageService messages,
                                                CapacitySource capacity, HealthCoverageSource healthCoverage,
                                                QuarantineSource quarantine, OutageSource outage,
                                                LeadSeatSource leadSeats, Map<String, String> leads, String selfTerm,
                                                CoordinationSource coordination) {
+        return listFleet(workers, sessions, messages, capacity, healthCoverage, quarantine, outage,
+                leadSeats, leads, selfTerm, coordination, true);
+    }
+
+    /**
+     * As above, gated by the caller's role (fleetd #439). The {@code coordinator} row is
+     * lead-to-lead coordination state — coordination between orchestrators, not roster
+     * observation — so it is assembled and included only when {@code callerIsPrimary} is
+     * {@code true}. A worker or an architect gets a result with the {@code coordinator} key
+     * <strong>absent</strong>, never an empty or redacted one, and never pays the cost of
+     * {@link #coordinatorView} probing peer mailboxes for a row it will not receive.
+     *
+     * @param callerIsPrimary whether the {@code fleet_list} caller is the primary; only the MCP
+     *                        handler computes this from the real connection (see
+     *                        {@code Principal#isPrimary()}) — every other overload passes
+     *                        {@code true}
+     */
+    static McpSchema.CallToolResult listFleet(PeerLauncher workers, SessionManager sessions, MessageService messages,
+                                               CapacitySource capacity, HealthCoverageSource healthCoverage,
+                                               QuarantineSource quarantine, OutageSource outage,
+                                               LeadSeatSource leadSeats, Map<String, String> leads, String selfTerm,
+                                               CoordinationSource coordination, boolean callerIsPrimary) {
         try {
             Map<String, Agent> live = workers.list().stream()
                     .map(Agent.class::cast)
@@ -1371,9 +1418,14 @@ public final class FleetMcp {
             Map<String, Object> result = new LinkedHashMap<>();
             result.put("leads", leadRows); result.put("members", out);
             result.put("healthCoverage", healthCoverage.value().get());
-            Map<String, Object> coordinatorRow = coordinatorView(coordination);
-            if (coordinatorRow != null) {
-                result.put("coordinator", coordinatorRow);
+            // fleetd #439: coordinator/coordinatorView is lead-to-lead coordination state and must
+            // never reach a worker or an architect -- gate BEFORE assembling it, not after, so the
+            // key is absent rather than present-and-empty.
+            if (callerIsPrimary) {
+                Map<String, Object> coordinatorRow = coordinatorView(coordination);
+                if (coordinatorRow != null) {
+                    result.put("coordinator", coordinatorRow);
+                }
             }
             if (capacity.available()) result.put("capacity", profiles.stream()
                     .map(profile -> capacityView(profile, capacity.liveCount(), capacity.maxLoad(), roster, messages,

fleetd/src/main/java/dev/ltms/fleet/peer/PeerLauncher.java

@@ -168,6 +168,23 @@ public interface PeerLauncher {
      * answer for a launcher with no role-pool concept of its own (e.g. a single {@code
      * HerdrPeerLauncher} adapter, which is never reached this way in production: {@code
      * CompositePeerLauncher} always fronts it and resolves roles itself).
+     *
+     * <p>fleetd #453: this default is deliberately <em>not</em> abstract — unlike {@link
+     * #spawn(SpawnRequest, PlacementDecision)} (fleetd #450), there is no live defect in inheriting
+     * it today, and the only current single-adapter implementer ({@code HerdrPeerLauncher}) is
+     * correct to do so. But it stays correct only as long as that holds: <strong>if a launcher ever
+     * routes more than one profile per role, it MUST override this method</strong>, or every role
+     * silently resolves to {@link #defaultProfile()} with no error and no log line. {@code
+     * HerdrPeerLauncher.spawn(SpawnRequest, PlacementDecision)} — the override in {@code
+     * dev.ltms.fleet.member}, not the declaration below — names this method and {@link #place}
+     * explicitly as "unoverridden here" for exactly this reason. Read it before adding role-pool
+     * routing to any {@code HerdrPeerLauncher} subclass.
+     *
+     * <p>Who is forced to read which paragraph, because it is not symmetric. A new class that
+     * implements this interface directly must write a body for {@link #spawn(SpawnRequest,
+     * PlacementDecision)}, which is abstract here, so it lands on this javadoc. A subclass of
+     * {@code HerdrPeerLauncher} does not: that class already implements the method, and the
+     * subclass inherits the body. So for a subclass this paragraph is advice, not a gate.
      */
     default String defaultProfileFor(MemberRole role) {
         return defaultProfile();
@@ -228,6 +245,13 @@ public interface PeerLauncher {
      * placement condition — the right answer for a launcher with no pool or placement-policy
      * concept of its own, matching {@link #defaultProfileFor}'s own default.
      *
+     * <p>fleetd #453: same reasoning as {@link #defaultProfileFor}'s own #453 note — this default
+     * is deliberately not abstract (no live defect today, correct for the sole single-adapter
+     * implementer), but <strong>a launcher that ever routes more than one profile per role MUST
+     * override this method too</strong>, or placement silently ignores {@code role} for it. See
+     * {@code HerdrPeerLauncher.spawn(SpawnRequest, PlacementDecision)}'s javadoc, which names this
+     * method as "unoverridden here" and why that is correct only for a single-profile adapter.
+     *
      * @throws RuntimeException (implementation-specific, typically a placement exception) if no
      *                          candidate in {@code role}'s pool is currently placeable
      */

fleetd/src/test/java/dev/ltms/fleet/herdr/AgentControlContractTest.java

@@ -25,13 +25,23 @@ import static org.junit.jupiter.api.Assumptions.assumeTrue;
  * So this polls for a real signal instead of guessing a sleep length.
  *
  * <p><strong>What was measured, and what was not.</strong> Polling fixes it: 5 standalone runs
- * green. The load-bearing half is {@link #waitForText}. With {@link #SHELL_READY_TIMEOUT_MS}
- * set to 0 — so input is typed at once, with no settle wait at all — the test still passed 3 of
- * 3. So the proven cause is the 800ms READ deadline being too short, not the 1000ms write delay.
- * Note the direction, because it matters: typing at 0ms works where typing at 1000ms failed. The
- * earlier explanation for this test — that input typed before the prompt is swallowed by the
- * shell's startup — is therefore NOT supported by any measurement here. Please do not repeat it
- * as the reason; if it were true, 0ms would be worse than 1000ms, and it is better.
+ * green. The load-bearing half is {@link #waitForText}, and one cell proves it. Keep the old
+ * 1000ms write sleep and change only the read — the 800ms fixed sleep becomes a 5s poll — and
+ * the test goes from 0 of 3 passing to 3 of 3. Removing the write wait instead
+ * ({@link #SHELL_READY_TIMEOUT_MS} set to 0, so input is typed at once) also passes 3 of 3. So
+ * the cause is the 800ms READ deadline, not the 1000ms write delay. The old version fails every
+ * time, not sometimes, so "race" is the wrong word for it. The earlier explanation — that input
+ * typed before the prompt is swallowed by the shell's startup — is not supported by anything
+ * measured here. Please do not repeat it: if it were true, typing at 0ms would be worse than
+ * typing at 1000ms, and it is not.
+ *
+ * <p><strong>Where this was measured.</strong> A 12-core macOS host, load average 2.6 to 5.9,
+ * on commit 20c1094. The same four cells were also run under load and gave the same answer, but
+ * that run is not clean evidence: the load average climbed from 7 to 50 while the cells ran, and
+ * the old version ran last, at the top of that climb. Above about load 20 everything here is
+ * slow for reasons that have nothing to do with this seam. So read the claim as "measured near
+ * idle on a 12-core host", and nothing stronger. If this test fails on a smaller or busier
+ * machine, raise {@link #OUTPUT_TIMEOUT_MS} before you suspect the seam.
  *
  * <p>{@link #waitUntilSettled} is kept as cheap insurance against that swallow case, not because
  * anyone showed it was needed. If you want to delete it, the honest test is whether you can make

fleetd/src/test/java/dev/ltms/fleet/mcp/FleetMcpAuthzTest.java

@@ -187,6 +187,71 @@ class FleetMcpAuthzTest {
                 "no CallerResolver supplied ⇒ authorization not enforced (legacy behaviour)");
     }
 
+    // --- fleetd #439: who may see fleet_list's coordinator row ----------------------------------
+
+    /**
+     * fleetd #439: {@link FleetMcp#coordinatorVisibleTo} is the whole policy decision for
+     * {@code fleet_list}'s {@code coordinator} row — lead-to-lead coordination state, not roster
+     * observation. Only the primary may see it; a worker, an architect, and (the case the previous
+     * pass of this ticket did not cover) an anonymous caller must all be refused.
+     */
+    @Test
+    void onlyThePrimaryMaySeeTheCoordinatorRow() {
+        assertTrue(FleetMcp.coordinatorVisibleTo(PRIMARY), "the primary must see its own coordination state");
+        assertFalse(FleetMcp.coordinatorVisibleTo(WORKER_A), "a worker must not see lead-to-lead coordination state");
+        assertFalse(FleetMcp.coordinatorVisibleTo(ARCH_DESIGN),
+                "an architect holds READ today, but that must not extend to coordinator");
+        assertFalse(FleetMcp.coordinatorVisibleTo(ANON), "authenticated as nothing must not see it either");
+    }
+
+    /**
+     * fleetd #439 / PR #462 review finding M2: the predicate above can be perfectly correct while
+     * the one production call site (the {@code fleet_list} MCP handler) never actually asks it —
+     * a literal {@code true} compiles, and the whole suite stayed green under that mutation because
+     * every existing test drives {@link FleetMcp#listFleet} directly and supplies the boolean
+     * itself. This test reads {@code FleetMcp.java}'s own source (same idiom as {@link
+     * #toolsTheServerRegisters()} / {@link #everyRegisteredToolHasItsHandlerActionPinned()}) and
+     * asserts the handler's call passes {@code coordinatorVisibleTo(principal(exchange))} — not a
+     * literal {@code true} or {@code false} — as {@code listFleet}'s trailing argument.
+     *
+     * <p>Anchored on argument position, not a bare substring search: {@code true} appears many
+     * times elsewhere in this file for unrelated reasons, so a plain {@code contains("true")}
+     * check would prove nothing. The pattern requires the literal text immediately before the
+     * closing {@code );} of the {@code listFleet(} call inside the handler block to be exactly
+     * {@code coordinatorVisibleTo(principal(exchange))}.
+     */
+    @Test
+    void theFleetListHandlerActuallyConsultsCoordinatorVisibleTo() throws Exception {
+        String source = Files.readString(MCP_SOURCE);
+
+        // Isolate the fleet_list handler block: from its declaration up to the next handler's
+        // declaration. A change to variable naming would break this scrape loudly (see the control
+        // assertion just below), rather than silently reporting "no violation found".
+        int start = source.indexOf("listHandler =");
+        assertTrue(start >= 0, "could not find the fleet_list handler (listHandler) in " + MCP_SOURCE
+                + " -- the scrape has stopped matching, fix the anchor before trusting this test");
+        int end = source.indexOf("stopHandler =", start);
+        assertTrue(end > start, "could not find the handler declared after listHandler to bound the scrape");
+        String handlerBlock = source.substring(start, end);
+
+        // CONTROL: the block we scraped really does contain a call to listFleet(...) -- if this
+        // fails, the anchors above moved and the assertion below would otherwise pass on nothing.
+        assertTrue(handlerBlock.contains("listFleet("),
+                "control failed: the scraped listHandler block contains no listFleet( call at all -- "
+                        + "the anchors have drifted, this test is not testing what it claims to");
+
+        Pattern trailingArg = Pattern.compile(
+                "listFleet\\([^;]*?,\\s*(coordinatorVisibleTo\\(principal\\(exchange\\)\\)|true|false)\\s*\\)\\s*;",
+                Pattern.DOTALL);
+        Matcher m = trailingArg.matcher(handlerBlock);
+        assertTrue(m.find(), "could not locate listFleet(...)'s trailing boolean argument in the "
+                + "listHandler block -- the call shape changed, update this test's anchor: " + handlerBlock);
+        String trailing = m.group(1);
+        assertEquals("coordinatorVisibleTo(principal(exchange))", trailing,
+                "the fleet_list handler must ask coordinatorVisibleTo(principal(exchange)) who is "
+                        + "calling, not pass a literal boolean -- found: " + trailing);
+    }
+
     // --- which action each tool hands the gate (fleetd #272) ------------------------------------
 
     /**

fleetd/src/test/java/dev/ltms/fleet/mcp/FleetMcpTest.java

@@ -676,6 +676,95 @@ class FleetMcpTest {
                 "an ordinary fleet's output must be unchanged by this feature");
     }
 
+    /**
+     * fleetd #439: a worker calling {@code fleet_list} must get a result with the {@code
+     * coordinator} key <strong>absent</strong> -- not an empty object, not a redacted one -- even
+     * though lead coordination is fully configured and would otherwise report a row. This drives
+     * the same {@code callerIsPrimary} value the MCP handler computes ({@code
+     * Principal.worker(...).isPrimary()}), so it pins the real production boolean, not a literal.
+     */
+    @Test
+    void listOmitsTheCoordinatorKeyEntirelyForAWorkerEvenWhenLeadCoordinationIsOn() {
+        FakeHerdr h = new FakeHerdr();
+        SessionManager sessions = new SessionManager(workerService(h, "http://gx00.gw:8000", Set.of("gx00.gw")));
+        FakeLeadChannel channel = new FakeLeadChannel("mac-opus")
+                .withMailbox("mac-opus", LeadChannel.MailboxState.exists("mac-opus", 0, 1));
+        boolean callerIsPrimary = Principal.worker("term_a", 1).isPrimary();
+
+        McpSchema.CallToolResult res = FleetMcp.listFleet(
+                workerService(h, "http://gx00.gw:8000", Set.of("gx00.gw")), sessions, null,
+                FleetMcp.CapacitySource.none(), new FleetMcp.HealthCoverageSource(() -> "off"),
+                FleetMcp.QuarantineSource.none(), FleetMcp.OutageSource.none(), FleetMcp.LeadSeatSource.none(),
+                Map.of(), "", new FleetMcp.CoordinationSource(channel, List.of()), callerIsPrimary);
+
+        String out = textOf(res);
+        assertFalse(out.contains("\"coordinator\""), "a worker must never see the coordinator key at all: " + out);
+        assertFalse(out.contains("mac-opus"), "no fragment of the coordinator row may leak either: " + out);
+        assertTrue(out.contains("\"leads\""), "the rest of the result must still be present: " + out);
+        assertTrue(out.contains("\"members\""), out);
+        assertTrue(out.contains("\"healthCoverage\""), out);
+    }
+
+    /**
+     * fleetd #439 acceptance criterion 2: an architect gets exactly the same treatment as a worker.
+     * This is a real, executed test (not just reasoning by analogy) -- it drives the actual
+     * {@code Principal.architect(...).isPrimary()} value the production handler would compute for
+     * an architect caller, through the same gate a worker's call goes through.
+     */
+    @Test
+    void listOmitsTheCoordinatorKeyEntirelyForAnArchitectToo() {
+        FakeHerdr h = new FakeHerdr();
+        SessionManager sessions = new SessionManager(workerService(h, "http://gx00.gw:8000", Set.of("gx00.gw")));
+        FakeLeadChannel channel = new FakeLeadChannel("mac-opus")
+                .withMailbox("mac-opus", LeadChannel.MailboxState.exists("mac-opus", 0, 1));
+        boolean callerIsPrimary = Principal.architect("lead-designer", "term_design", 400).isPrimary();
+
+        McpSchema.CallToolResult res = FleetMcp.listFleet(
+                workerService(h, "http://gx00.gw:8000", Set.of("gx00.gw")), sessions, null,
+                FleetMcp.CapacitySource.none(), new FleetMcp.HealthCoverageSource(() -> "off"),
+                FleetMcp.QuarantineSource.none(), FleetMcp.OutageSource.none(), FleetMcp.LeadSeatSource.none(),
+                Map.of(), "", new FleetMcp.CoordinationSource(channel, List.of()), callerIsPrimary);
+
+        String out = textOf(res);
+        assertFalse(out.contains("\"coordinator\""), "an architect must never see the coordinator key either: " + out);
+    }
+
+    /**
+     * fleetd #439 acceptance criterion 3: the primary's {@code fleet_list} is byte-for-byte
+     * unchanged by this fix. Proven by comparing the new gated overload (with {@code
+     * callerIsPrimary=true}, exactly what the MCP handler passes for the primary) against the
+     * pre-#439 overload that always assembled the row -- if the gate changed anything for a
+     * primary caller, these two strings would differ.
+     */
+    @Test
+    void listIsByteForByteUnchangedForThePrimaryCaller() {
+        FakeHerdr h = new FakeHerdr();
+        SessionManager sessions = new SessionManager(workerService(h, "http://gx00.gw:8000", Set.of("gx00.gw")));
+        FakeLeadChannel channel = new FakeLeadChannel("mac-opus")
+                .withMailbox("mac-opus", LeadChannel.MailboxState.exists("mac-opus", 0, 1));
+
+        String preExisting = textOf(FleetMcp.listFleet(
+                workerService(h, "http://gx00.gw:8000", Set.of("gx00.gw")), sessions, null,
+                FleetMcp.CapacitySource.none(), new FleetMcp.HealthCoverageSource(() -> "off"),
+                FleetMcp.QuarantineSource.none(), Map.of(), "",
+                new FleetMcp.CoordinationSource(channel, List.of())));
+        String gatedAsPrimary = textOf(FleetMcp.listFleet(
+                workerService(h, "http://gx00.gw:8000", Set.of("gx00.gw")), sessions, null,
+                FleetMcp.CapacitySource.none(), new FleetMcp.HealthCoverageSource(() -> "off"),
+                FleetMcp.QuarantineSource.none(), FleetMcp.OutageSource.none(), FleetMcp.LeadSeatSource.none(),
+                Map.of(), "", new FleetMcp.CoordinationSource(channel, List.of()), true));
+
+        assertEquals(preExisting, gatedAsPrimary,
+                "a primary caller must see byte-for-byte the same result as before this fix");
+        assertTrue(gatedAsPrimary.contains("\"coordinator\""), gatedAsPrimary);
+        assertTrue(gatedAsPrimary.contains("\"selfId\":\"mac-opus\""), gatedAsPrimary);
+        assertTrue(gatedAsPrimary.contains("\"mailbox\""), gatedAsPrimary);
+        assertTrue(gatedAsPrimary.contains("\"heldCount\""), gatedAsPrimary);
+        assertTrue(gatedAsPrimary.contains("\"heldDurable\""), gatedAsPrimary);
+        assertTrue(gatedAsPrimary.contains("\"held\""), gatedAsPrimary);
+        assertTrue(gatedAsPrimary.contains("\"peers\""), gatedAsPrimary);
+    }
+
     @Test
     void listReportsHeldMessagesWithATruncatedPreviewNeverTheFullBody() {
         FakeHerdr h = new FakeHerdr();