fleetd #361 review round 2: pin isMissingQueue's false branch

The reviewer's mutation (isMissingQueue always returns true) restored
the exact overstatement fleetd #361 exists to fix -- every declare
failure reading as a confirmed absence -- and still left mvn clean
install green (1389/1389), because no test drove a non-404 shape
through inspect(). The false branch was the whole discriminator
between MailboxState.absent() and MailboxState.unknown(), unpinned.

Widened LeadMailbox.isMissingQueue from private to package-private and
added LeadMailboxIsMissingQueueTest: five hermetic tests (no broker)
covering the true case and all three false shapes isMissingQueue's own
javadoc lists -- a different reply code, a ShutdownSignalException
whose reason isn't a Channel.Close, and an IOException with no such
cause at all (plus an IOException wrapping an unrelated exception
type). Re-ran the reviewer's exact mutation locally: 4 of 5 new tests
went red with the expected assertion messages; reverted, and mvn clean
install is green again at 1394/1394 (1389 + 5 new).

Also added a one-line javadoc note on LeadMailbox.inspect being honest
about which of its two RuntimeException catches is proven by a test
(the createChannel() one, end-to-end against a real broker) and which
stays purely defensive (the declare-site one, for a connection-drops-
mid-call race no test drives on purpose).

fleetd/fleetd.example.yaml

@@ -821,10 +821,17 @@ guard:
 #              across every daemon sharing this vhost.
 #   prefetch → consumer basicQos, capping how many unacked messages the mailbox holds in-heap.
 #              Default 32 when omitted.
+#   peers    → fleetd #361: the coord-ids of the OTHER daemons on this vhost, declared by the
+#              operator (the daemon never guesses). fleet_list reports each one's live reachability
+#              (a passive queue check, never a presence protocol) alongside this daemon's own
+#              mailbox state. Omit, or leave empty, for a daemon with no known peers yet — an
+#              undeclared peer can still reach you and be reached by fleet_send, it just will not
+#              show up as a row in fleet_list.
 # coordinator:
 #   uriEnv: LEAD_COORD_URI
 #   selfId: mac-opus
 #   prefetch: 32
+#   peers: [fleet01-lead]
 
 # Active push-to-primary (CB-307 Stage 3). When a worker reply lands with no open fleet_send,
 # the ReplyPushLoop injects a *drain nudge* (never the payload) into the primary's own herdr

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

@@ -652,7 +652,12 @@ public final class Fleetd {
                 quarantineSource,
                 leadMailbox,
                 outageSource,
-                new FleetMcp.LeadSeatSource(leadSeatLookup(() -> config.get().profiles(), leaders, leads)));
+                new FleetMcp.LeadSeatSource(leadSeatLookup(() -> config.get().profiles(), leaders, leads)),
+                // fleetd #361: the operator-declared peers this daemon's fleet_list should try to
+                // reach. Read from the SAME snapshot leadMailbox itself opened from (cfg.coordinator()),
+                // not the live config.get() — coordinator wiring is already boot-time-fixed (see
+                // leadMailbox above), so peers follows the same rule rather than half hot-reloading.
+                cfg.coordinator() == null ? List.of() : cfg.coordinator().peers());
 
         // CB-637: the receive half. Only constructed when a lead mailbox actually opened — with no
         // coordinator (or an unreachable one) there is nothing to deliver, so no scheduler is

fleetd/src/main/java/dev/ltms/fleet/config/FleetConfig.java

@@ -888,12 +888,18 @@ public record FleetConfig(
      *                 {@code null} ⇒ kept as {@code null} (no self id configured).
      * @param prefetch the consumer's {@code basicQos} prefetch count. {@code null}/non-positive ⇒
      *                 {@link LeadMailbox#DEFAULT_PREFETCH}.
+     * @param peers    fleetd #361: the coord-ids the operator declares as this daemon's peers — the
+     *                 daemon never guesses who else exists. {@code fleet_list} reports each one's
+     *                 live reachability. Blank entries are dropped; {@code null} ⇒ an empty list, so
+     *                 a config written before this field existed still parses unchanged.
      */
     @JsonIgnoreProperties(ignoreUnknown = true)
-    public record Coordinator(String uri, String uriEnv, String selfId, Integer prefetch) {
+    public record Coordinator(String uri, String uriEnv, String selfId, Integer prefetch, List<String> peers) {
 
         public Coordinator {
             selfId = (selfId == null || selfId.isBlank()) ? null : selfId;
+            peers = peers == null ? List.of()
+                    : peers.stream().filter(p -> p != null && !p.isBlank()).toList();
         }
 
         /** True when a {@code uriEnv} is configured by name, whether or not its variable resolves. */

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

@@ -44,6 +44,7 @@ import java.util.Objects;
 import java.util.Set;
 import java.util.UUID;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.TimeUnit;
 import java.util.function.BiFunction;
 import java.util.function.Function;
 import java.util.function.LongSupplier;
@@ -101,6 +102,8 @@ public final class FleetMcp {
     private final LeadSeatSource leadSeats;
     /** CB-637: this daemon's lead-to-lead channel; {@code null} when no coordinator is configured. */
     private final LeadChannel leadChannel;
+    /** fleetd #361: {@code coordinator.peers} — see {@link CoordinationSource}. Empty when unset. */
+    private final List<String> peers;
 
     /** Capacity facts used by {@code fleet_list}; production must supply the placement live count. */
     public record CapacitySource(Function<String, Integer> liveCount, Function<String, Integer> maxLoad,
@@ -164,6 +167,32 @@ public final class FleetMcp {
         public static LeadSeatSource none() { return new LeadSeatSource(_ -> 0); }
     }
 
+    /**
+     * fleetd #361: peer-visibility facts for {@code fleet_list}'s {@code coordinator} row — this
+     * daemon's own {@link LeadChannel} (for its self mailbox state and held messages) plus the
+     * coord-ids the operator has declared as peers ({@code coordinator.peers}). Bundled as its own
+     * Source, the same idiom as {@link OutageSource}/{@link QuarantineSource}/{@link LeadSeatSource},
+     * so {@code listFleet}'s already-long overload chain gains exactly one new required parameter
+     * instead of a further bare positional argument.
+     *
+     * <p>Every mailbox look this triggers goes through {@link LeadChannel#inspect}, which is
+     * specified to run on its own disposable channel — never the channel {@link LeadChannel#publish}
+     * or the consume loop depends on — so a peer that happens to be down, or the coordination broker
+     * itself being unreachable, can never take {@code fleet_send}/{@code LeadCoordLoop}'s own path
+     * down with it. See {@code FleetMcp.probe} for the additional timeout bound on top of that.
+     *
+     * @param leadChannel this daemon's own channel, or {@code null} when no coordinator is configured
+     * @param peers       the coord-ids declared under {@code coordinator.peers}, or empty
+     */
+    public record CoordinationSource(LeadChannel leadChannel, List<String> peers) {
+        public CoordinationSource {
+            peers = peers == null ? List.of() : List.copyOf(peers);
+        }
+
+        /** Inert source — no coordinator row is ever reported. */
+        public static CoordinationSource none() { return new CoordinationSource(null, List.of()); }
+    }
+
     /**
      * @param callers resolves each call's {@link Principal}; {@code null} disables authorization.
      *                This surface needs its own enforcement: {@code /mcp} is a raw servlet on
@@ -211,19 +240,34 @@ public final class FleetMcp {
     }
 
     /**
-     * As above, with fleetd #176 lead-seat facts (see {@link LeadSeatSource}). This is what
-     * {@code Fleetd.main} actually wires up.
-     *
-     * @param leadSeats required — pass {@link LeadSeatSource#none()} for a caller that does not want
-     *                  the feature, never a defaulting overload (the same rule {@code quarantine} and
-     *                  {@code outage} follow).
+     * As above, with fleetd #176 lead-seat facts (see {@link LeadSeatSource}).
      */
     public FleetMcp(MessageService messages, PeerLauncher workers, SessionManager sessions,
                      ConnectionIdentity identity, MemberPresence presence, PrimaryRegistry primaryRegistry,
                       CallerResolver callers, Metrics metrics, CapacitySource capacity, HealthCoverageSource healthCoverage,
                       QuarantineSource quarantine, LeadChannel leadChannel, OutageSource outage,
                       LeadSeatSource leadSeats) {
+        this(messages, workers, sessions, identity, presence, primaryRegistry, callers, metrics, capacity,
+                healthCoverage, quarantine, leadChannel, outage, leadSeats, List.of());
+    }
+
+    /**
+     * As above, with fleetd #361 {@code coordinator.peers} (see {@link CoordinationSource}). This is
+     * what {@code Fleetd.main} actually wires up.
+     *
+     * @param leadSeats required — pass {@link LeadSeatSource#none()} for a caller that does not want
+     *                  the feature, never a defaulting overload (the same rule {@code quarantine} and
+     *                  {@code outage} follow).
+     * @param peers     the coord-ids declared under {@code coordinator.peers}; empty when unset or
+     *                  when {@code leadChannel} is {@code null}.
+     */
+    public FleetMcp(MessageService messages, PeerLauncher workers, SessionManager sessions,
+                     ConnectionIdentity identity, MemberPresence presence, PrimaryRegistry primaryRegistry,
+                      CallerResolver callers, Metrics metrics, CapacitySource capacity, HealthCoverageSource healthCoverage,
+                      QuarantineSource quarantine, LeadChannel leadChannel, OutageSource outage,
+                      LeadSeatSource leadSeats, List<String> peers) {
         this.leadChannel = leadChannel;
+        this.peers = peers == null ? List.of() : List.copyOf(peers);
         this.capacity = capacity;
         this.quarantine = Objects.requireNonNull(quarantine, "quarantine");
         this.outage = Objects.requireNonNull(outage, "outage");
@@ -361,7 +405,7 @@ public final class FleetMcp {
                     return listFleet(workers, sessions, messages, capacity, healthCoverage, quarantine, outage,
                             leadSeats, callers == null ? Map.of() : callers.leads(),
                             callerTerminal(exchange),
-                            leadChannel == null ? null : leadChannel.selfCoordId());
+                            new CoordinationSource(leadChannel, peers));
                 };
         BiFunction<McpSyncServerExchange, McpSchema.CallToolRequest, McpSchema.CallToolResult> stopHandler =
                 (exchange, req) -> {
@@ -697,6 +741,15 @@ public final class FleetMcp {
      * turned into a tool error naming the coord-id. It is never allowed to escape as a crash: an
      * unreachable peer is an ordinary outcome of addressing a fleet you do not control.
      *
+     * <p><strong>fleetd #361: the success text is honest about what "durably confirmed" does and
+     * does not mean.</strong> The broker's publisher confirm proves the message is durably queued —
+     * it says nothing about whether the peer's pane has, or ever will, receive it. After a
+     * successful publish this looks at the target mailbox's consumer count (via
+     * {@link LeadChannel#inspect}, bounded and never allowed to fail the call — see {@link #probe})
+     * and appends a warning when it is zero: that is the observable form of "nobody is reading this
+     * right now". A zero-consumer publish is still reported as a SUCCESS, never an error — the
+     * message is safely queued and will be read once a daemon owning that coord-id connects.
+     *
      * @param leadChannel this daemon's channel, or {@code null} when no coordinator is configured
      */
     static McpSchema.CallToolResult sendToLead(LeadChannel leadChannel, String coordId, String content,
@@ -724,7 +777,16 @@ public final class FleetMcp {
                     + ". Check that a daemon is running with coordinator.selfId=\"" + coordId
                     + "\" and is connected to the same coordination broker.");
         }
-        return text("delivered to peer lead " + coordId + " (msgId " + msg.msgId() + ")");
+        String result = "published to peer lead \"" + coordId + "\"'s mailbox and durably confirmed "
+                + "by the broker (msgId " + msg.msgId() + ").";
+        LeadChannel.MailboxState state = probe(leadChannel, coordId);
+        if (state.exists() && state.consumers() == 0) {
+            result += " Warning: that mailbox currently has NO consumers attached — nobody is reading "
+                    + "it right now. The message is safely queued and will be delivered once a daemon "
+                    + "with coordinator.selfId=\"" + coordId + "\" is running and connected; until then "
+                    + "it will not reach that lead's pane.";
+        }
+        return text(result);
     }
 
     /**
@@ -1110,7 +1172,8 @@ public final class FleetMcp {
     static McpSchema.CallToolResult listFleet(PeerLauncher workers, SessionManager sessions, MessageService messages,
                                                CapacitySource capacity, HealthCoverageSource healthCoverage,
                                                QuarantineSource quarantine, Map<String, String> leads, String selfTerm) {
-        return listFleet(workers, sessions, messages, capacity, healthCoverage, quarantine, leads, selfTerm, null);
+        return listFleet(workers, sessions, messages, capacity, healthCoverage, quarantine, leads, selfTerm,
+                CoordinationSource.none());
     }
 
     /** As above, plus fleetd #201 Unit 5 cool-off facts (see {@link OutageSource}). */
@@ -1119,33 +1182,33 @@ public final class FleetMcp {
                                                QuarantineSource quarantine, OutageSource outage,
                                                Map<String, String> leads, String selfTerm) {
         return listFleet(workers, sessions, messages, capacity, healthCoverage, quarantine, outage,
-                LeadSeatSource.none(), leads, selfTerm, null);
+                LeadSeatSource.none(), leads, selfTerm, CoordinationSource.none());
     }
 
     /**
-     * As above, additionally reporting this daemon's own lead coordination id (CB-637) when one is
-     * configured and its channel opened. There is no peer-discovery surface yet — a lead addresses a
-     * peer by a coord-id it was told — so this row exists to answer the one question the operator
-     * cannot answer any other way: what is MY coord-id, the one a peer must use to reach me. It is
-     * omitted entirely when no coordinator is configured, so an ordinary fleet's output is unchanged.
+     * As above, additionally reporting this daemon's own lead coordination state (CB-637, fleetd
+     * #361) when a coordinator is configured and its channel opened — see {@link #coordinatorView}
+     * for the shape. Omitted entirely when no coordinator is configured, so an ordinary fleet's
+     * output is unchanged.
      *
-     * @param selfCoordId this daemon's coord-id, or {@code null} when lead coordination is off
+     * @param coordination this daemon's lead channel plus its declared peers, or
+     *                      {@link CoordinationSource#none()} when lead coordination is off
      */
     static McpSchema.CallToolResult listFleet(PeerLauncher workers, SessionManager sessions, MessageService messages,
                                                CapacitySource capacity, HealthCoverageSource healthCoverage,
                                                QuarantineSource quarantine, Map<String, String> leads, String selfTerm,
-                                               String selfCoordId) {
+                                               CoordinationSource coordination) {
         return listFleet(workers, sessions, messages, capacity, healthCoverage, quarantine, OutageSource.none(),
-                LeadSeatSource.none(), leads, selfTerm, selfCoordId);
+                LeadSeatSource.none(), leads, selfTerm, coordination);
     }
 
     /** As above, plus fleetd #201 Unit 5 cool-off facts (see {@link OutageSource}). */
     static McpSchema.CallToolResult listFleet(PeerLauncher workers, SessionManager sessions, MessageService messages,
                                                CapacitySource capacity, HealthCoverageSource healthCoverage,
                                                QuarantineSource quarantine, OutageSource outage,
-                                               Map<String, String> leads, String selfTerm, String selfCoordId) {
+                                               Map<String, String> leads, String selfTerm, CoordinationSource coordination) {
         return listFleet(workers, sessions, messages, capacity, healthCoverage, quarantine, outage,
-                LeadSeatSource.none(), leads, selfTerm, selfCoordId);
+                LeadSeatSource.none(), leads, selfTerm, coordination);
     }
 
     /** As above, plus fleetd #176 lead-seat facts (see {@link LeadSeatSource}). */
@@ -1153,7 +1216,7 @@ public final class FleetMcp {
                                                CapacitySource capacity, HealthCoverageSource healthCoverage,
                                                QuarantineSource quarantine, OutageSource outage,
                                                LeadSeatSource leadSeats, Map<String, String> leads, String selfTerm,
-                                               String selfCoordId) {
+                                               CoordinationSource coordination) {
         try {
             Map<String, Agent> live = workers.list().stream()
                     .map(Agent.class::cast)
@@ -1175,8 +1238,9 @@ public final class FleetMcp {
             Map<String, Object> result = new LinkedHashMap<>();
             result.put("leads", leadRows); result.put("members", out);
             result.put("healthCoverage", healthCoverage.value().get());
-            if (selfCoordId != null && !selfCoordId.isBlank()) {
-                result.put("coordinator", Map.of("selfId", selfCoordId, "configured", true));
+            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,
@@ -1187,6 +1251,140 @@ public final class FleetMcp {
         }
     }
 
+    /**
+     * fleetd #361: the {@code coordinator} row — this daemon's own coord-id and mailbox state, the
+     * messages currently held for it, and the live reachability of every operator-declared peer.
+     * {@code null} (the row is then omitted entirely) when lead coordination is off, so an ordinary
+     * fleet's {@code fleet_list} output is byte-identical to before this feature existed.
+     *
+     * <p>Every peer/self mailbox look goes through {@link #probe}, which bounds each
+     * {@link LeadChannel#inspect} call to {@link #PEER_PROBE_TIMEOUT_MS} and never lets it throw —
+     * a coordination broker that is down or slow degrades this row toward "unreachable"/"unknown"
+     * counts, it can never make {@code fleet_list} itself slow or fail. {@code held} comes from
+     * {@link LeadChannel#peek}, a pure in-memory read with no broker round trip, so it is never
+     * subject to that bound.
+     */
+    private static Map<String, Object> coordinatorView(CoordinationSource coordination) {
+        LeadChannel channel = coordination.leadChannel();
+        if (channel == null) {
+            return null;
+        }
+        String selfId = channel.selfCoordId();
+        Map<String, Object> row = new LinkedHashMap<>();
+        row.put("selfId", selfId);
+        row.put("configured", true);
+        row.put("mailbox", mailboxView(probe(channel, selfId)));
+        row.put("held", channel.peek().stream().map(FleetMcp::heldView).toList());
+        row.put("peers", coordination.peers().stream().map(p -> peerView(channel, p)).toList());
+        return row;
+    }
+
+    /**
+     * fleetd #361: render a {@link LeadChannel.MailboxState} without ever presenting an unmeasured
+     * fact as a measured one. {@code status} is the tri-state itself — {@code "exists"},
+     * {@code "absent"} (the broker positively confirmed no such queue), or {@code "unknown"} (the
+     * probe could not determine either way: down, unreachable, or timed out). {@code pending}/
+     * {@code consumers} are included ONLY when {@code status == "exists"} — a reader must never see
+     * them default to {@code 0} for a mailbox this call never actually measured. This is the fix for
+     * the review finding that a collapsed {@code absent()} rendered a self-probe timeout as
+     * "pending: 0, consumers: 0", indistinguishable from an actually-empty, actually-unread mailbox.
+     */
+    private static Map<String, Object> mailboxView(LeadChannel.MailboxState state) {
+        Map<String, Object> row = new LinkedHashMap<>();
+        row.put("status", state.exists() ? "exists" : state.known() ? "absent" : "unknown");
+        if (state.exists()) {
+            row.put("pending", state.pending());
+            row.put("consumers", state.consumers());
+        }
+        return row;
+    }
+
+    /** One held-for-me message: enough to identify it and see roughly what it says, never the whole body. */
+    private static Map<String, Object> heldView(LeadMessage m) {
+        Map<String, Object> row = new LinkedHashMap<>();
+        row.put("msgId", m.msgId());
+        row.put("from", m.from());
+        row.put("preview", preview(m.content()));
+        return row;
+    }
+
+    /** Cap a held message's content to a short preview — {@code fleet_list} must never dump a full body. */
+    private static final int HELD_PREVIEW_MAX_CHARS = 80;
+
+    private static String preview(String content) {
+        if (content == null) {
+            return "";
+        }
+        return content.length() <= HELD_PREVIEW_MAX_CHARS
+                ? content
+                : content.substring(0, HELD_PREVIEW_MAX_CHARS) + "…";
+    }
+
+    /**
+     * One declared peer's row: its coord-id, then the same tri-state {@link #mailboxView} shape.
+     * Deliberately no boolean "reachable" field — that collapsed "confirmed gone" and "could not
+     * check" into the same {@code false}, which is exactly the review finding this row now avoids:
+     * an operator reading {@code status} can tell "fleet01 is down" (a {@code coordinator.selfId}
+     * nobody has ever run) apart from "my own broker is slow or unreachable right now".
+     */
+    private static Map<String, Object> peerView(LeadChannel channel, String coordId) {
+        Map<String, Object> row = new LinkedHashMap<>();
+        row.put("coordId", coordId);
+        row.putAll(mailboxView(probe(channel, coordId)));
+        return row;
+    }
+
+    /**
+     * fleetd #361: how long {@code fleet_list} waits on any single {@link LeadChannel#inspect} call
+     * before giving up on it — see {@link #probe}.
+     */
+    private static final long PEER_PROBE_TIMEOUT_MS = 1_500L;
+
+    /**
+     * Dedicated pool for {@link LeadChannel#inspect} calls so a slow one blocks only its own virtual
+     * thread, never the MCP request thread calling {@code fleet_list}. Not a <em>bounded</em> pool —
+     * {@code newThreadPerTaskExecutor} starts a fresh virtual thread per call with no cap on how many
+     * run at once; virtual threads make that cheap, not bounded. What actually keeps a hung probe
+     * from accumulating forever is the {@link Future#cancel} in {@link #probe}, not a pool limit.
+     */
+    private static final java.util.concurrent.ExecutorService PEER_PROBE_POOL =
+            java.util.concurrent.Executors.newThreadPerTaskExecutor(Thread.ofVirtual().name("fleet-peer-probe-", 0).factory());
+
+    /**
+     * fleetd #361: {@link LeadChannel#inspect}, bounded to {@link #PEER_PROBE_TIMEOUT_MS} and never
+     * allowed to throw or hang the caller — a coordination broker that is unreachable or slow
+     * degrades to {@link LeadChannel.MailboxState#unknown} (never {@code absent}: a timeout proves
+     * nothing about whether the mailbox exists) rather than making {@code fleet_list} slow or
+     * failing it. {@code inspect} itself is already specified to never throw, but this is the seam
+     * that also survives an implementation that does, or one that blocks indefinitely on a dead
+     * connection.
+     *
+     * <p><strong>A timeout cancels the orphaned task</strong> rather than abandoning it. Before this,
+     * {@code get(timeout)} on a hung {@code inspect} left the submitted task running forever on its
+     * own virtual thread, holding the AMQP channel it had already opened — against a broker that
+     * hangs rather than fails fast, every {@code fleet_list} call would orphan one more channel until
+     * the connection's channel-max (2047 by default) was exhausted, which would break {@link
+     * LeadChannel#publish} too. {@link Future#cancel(boolean) cancel(true)} interrupts the orphaned
+     * task's thread; {@link LeadMailbox#inspect} has no interruptible wait of its own to catch that,
+     * but the underlying AMQP RPC continuation does block on one, so the interrupt reaches it and the
+     * task's {@code finally} still closes the probe channel it opened rather than leaking it forever.
+     */
+    private static LeadChannel.MailboxState probe(LeadChannel channel, String coordId) {
+        return probe(channel, coordId, PEER_PROBE_TIMEOUT_MS);
+    }
+
+    /** As {@link #probe(LeadChannel, String)}, with an explicit timeout — a seam for tests. */
+    static LeadChannel.MailboxState probe(LeadChannel channel, String coordId, long timeoutMs) {
+        java.util.concurrent.Future<LeadChannel.MailboxState> future =
+                PEER_PROBE_POOL.submit(() -> channel.inspect(coordId));
+        try {
+            return future.get(timeoutMs, TimeUnit.MILLISECONDS);
+        } catch (Exception e) {
+            future.cancel(true); // best-effort: don't leave a hung probe (and its channel) running forever
+            return LeadChannel.MailboxState.unknown(coordId);
+        }
+    }
+
     /**
      * Capacity is advisory only. {@code reclaimable} says there is no bridge work, not that fleetd
      * may stop the member: the bridge has capacity facts but no work list, and choosing work needs
@@ -1377,8 +1575,12 @@ public final class FleetMcp {
                                 + "routes your answer back into the same turn (omit for a normal delegation)"),
                         "coordId", stringProp("A peer LEAD's coordination id — delivers content to that "
                                 + "lead's durable mailbox on the shared coordination broker, which works "
-                                + "across hosts. Mutually exclusive with sessionId and turnId. Your own "
-                                + "coordId is reported by fleet_list.")),
+                                + "across hosts. Mutually exclusive with sessionId and turnId. Success means "
+                                + "the message is durably queued and confirmed by the broker, with a warning "
+                                + "if that mailbox has no consumers attached right now (queued, but nobody is "
+                                + "reading it yet) — it does not mean the peer's pane has seen it. Your own "
+                                + "coordId, this daemon's mailbox state, and every coordinator.peers entry's "
+                                + "live reachability are reported by fleet_list's coordinator row.")),
                         List.of("content")));
     }
 
@@ -1486,7 +1688,13 @@ public final class FleetMcp {
                         + "for a quarantined profile's credential (see fleet_profiles), whatever its "
                         + "maxLoad/live — with credentialId and quarantinedForSeconds naming the "
                         + "quarantine, so 'free: 0, busy' can be told apart from 'free: 0, refusing "
-                        + "for N seconds'.",
+                        + "for N seconds'. When lead-to-lead coordination is configured, a 'coordinator' "
+                        + "object reports this daemon's own coord-id ('selfId') and mailbox state "
+                        + "('mailbox': pending/consumers), the messages currently held for it ('held': "
+                        + "msgId/from/preview, never the full body), and one row per coordinator.peers "
+                        + "coord-id ('peers': coordId/reachable, plus pending/consumers when reachable) — "
+                        + "this is peer DISCOVERY for cross-host leads, distinct from the local 'leads' "
+                        + "array above. It is omitted entirely when no coordinator is configured.",
                 objectSchema(Map.of(), List.of()));
     }
 

fleetd/src/main/java/dev/ltms/fleet/msg/LeadChannel.java

@@ -4,8 +4,8 @@ import java.util.List;
 
 /**
  * The lead-to-lead message channel this daemon speaks, as its callers need it — one lead's own
- * mailbox: publish to a peer's coord-id, look at what has arrived for me, and ack what I have
- * delivered.
+ * mailbox: publish to a peer's coord-id, look at what has arrived for me, ack what I have
+ * delivered, and (fleetd #361) inspect any coord-id's mailbox from the outside without owning it.
  *
  * <p>Extracted from {@link LeadMailbox} purely as a seam. {@code LeadMailbox} is the one production
  * implementation and owns a live AMQP connection, so a test that wanted to exercise the routing in
@@ -37,4 +37,78 @@ public interface LeadChannel {
 
     /** This daemon's own lead coordination id — the mailbox it owns, and the {@code from} it sends as. */
     String selfCoordId();
+
+    /**
+     * A non-destructive look at {@code coordId}'s mailbox — does it exist, how many messages are
+     * waiting on it, and how many consumers are attached — without owning, consuming, or otherwise
+     * changing it. {@code consumers == 0} on an existing mailbox is the observable form of "nobody
+     * is reading this right now": a publish to it will sit queued rather than reach a pane.
+     *
+     * <p><strong>Never throws</strong> — this is a best-effort fact-finding call, not an operation a
+     * caller must handle failing. But it must never turn "I could not check" into a false negative:
+     * {@link MailboxState#absent(String)} means the broker positively confirmed there is no such
+     * queue, and {@link MailboxState#unknown(String)} — a distinct value — means the look could not
+     * be completed at all (broker unreachable, timed out, connection closed). A caller that
+     * collapses those two into one, as fleetd #361 initially did, cannot tell "that peer is down"
+     * from "I could not check", and a reader of {@code pending}/{@code consumers} cannot tell a
+     * measured zero from a zero standing in for "not measured".
+     *
+     * <p><strong>Must never share fate with {@link #publish} or {@link #peek}/{@link #ack}.</strong>
+     * fleetd #361: in AMQP 0-9-1 a passive queue declare of a queue that does not exist closes the
+     * channel it was declared on with a 404. An implementation backed by a real broker connection
+     * must inspect on a channel it can afford to lose — never the channel {@link #publish} or the
+     * consume loop depends on — so that looking at a peer that happens to be down can never break
+     * this daemon's own send or receive path.
+     */
+    MailboxState inspect(String coordId);
+
+    /**
+     * The result of {@link #inspect}. {@code presence} tells apart three states a caller must not
+     * conflate: a confirmed-existing mailbox ({@link Presence#EXISTS}, the only case where
+     * {@code pending}/{@code consumers} are measured facts), a confirmed-absent one
+     * ({@link Presence#ABSENT} — the broker positively said "no such queue"), and one this call
+     * simply could not determine ({@link Presence#UNKNOWN} — broker unreachable, timed out,
+     * connection closed). {@code pending}/{@code consumers} are always {@code 0} and meaningless
+     * outside {@link Presence#EXISTS}; a renderer must gate on {@link #exists()} (or {@code
+     * presence} directly), never present them as measured otherwise.
+     *
+     * @param coordId   the coord-id inspected
+     * @param presence  whether the mailbox is confirmed to exist, confirmed absent, or unknown
+     * @param pending   messages ready for delivery but not yet in a consumer's hands (0 unless EXISTS)
+     * @param consumers how many consumers are attached (0 unless EXISTS)
+     */
+    record MailboxState(String coordId, Presence presence, int pending, int consumers) {
+
+        /** Whether {@link #inspect} was able to reach a definite answer, of either kind. */
+        public enum Presence { EXISTS, ABSENT, UNKNOWN }
+
+        /** {@code true} only when the broker confirmed this exact queue is currently declared. */
+        public boolean exists() {
+            return presence == Presence.EXISTS;
+        }
+
+        /**
+         * {@code true} when {@link #inspect} reached a definite answer (exists or confirmed
+         * absent); {@code false} when it could not determine either way. A caller must never treat
+         * {@code !known()} the same as a confirmed absence — the mailbox may well exist.
+         */
+        public boolean known() {
+            return presence != Presence.UNKNOWN;
+        }
+
+        /** The broker confirmed this queue exists, with these measured counts. */
+        public static MailboxState exists(String coordId, int pending, int consumers) {
+            return new MailboxState(coordId, Presence.EXISTS, pending, consumers);
+        }
+
+        /** The broker positively confirmed there is no such queue (e.g. a 404 on passive declare). */
+        public static MailboxState absent(String coordId) {
+            return new MailboxState(coordId, Presence.ABSENT, 0, 0);
+        }
+
+        /** The look could not be completed — broker unreachable, timed out, or connection closed. */
+        public static MailboxState unknown(String coordId) {
+            return new MailboxState(coordId, Presence.UNKNOWN, 0, 0);
+        }
+    }
 }

fleetd/src/main/java/dev/ltms/fleet/msg/LeadMailbox.java

@@ -10,6 +10,7 @@ import com.rabbitmq.client.DeliverCallback;
 import com.rabbitmq.client.Recoverable;
 import com.rabbitmq.client.RecoveryListener;
 import com.rabbitmq.client.Return;
+import com.rabbitmq.client.ShutdownSignalException;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -259,6 +260,89 @@ public final class LeadMailbox implements LeadChannel, AutoCloseable {
         }
     }
 
+    /**
+     * fleetd #361: look at {@code coordId}'s mailbox on a fresh, immediately-closed throwaway
+     * channel — never {@link #channel} (consume/ack) or {@link #publishChannel} (publish). A
+     * passive queue declare of a queue that does not exist closes the channel it was declared on
+     * with a 404; using a disposable probe channel means that closure can never touch either
+     * long-lived channel this instance depends on for {@link #publish} or the consume loop.
+     *
+     * <p>Classifies failures rather than collapsing them, both measured against a real broker in
+     * {@code LeadMailboxTest} rather than assumed from the AMQP 0-9-1 spec text:
+     * <ul>
+     *   <li>a genuine 404 — an {@link IOException} wrapping a {@link ShutdownSignalException} whose
+     *       {@link AMQP.Channel.Close#getReplyCode()} is {@code 404} — reports
+     *       {@link MailboxState#absent}; every other declare failure reports
+     *       {@link MailboxState#unknown} instead of quietly becoming the same "absent" value;
+     *   <li>{@code catch (RuntimeException e)} on both attempts matters as much as the checked
+     *       catches: a connection that is already closed makes {@link Connection#createChannel()}
+     *       throw {@link com.rabbitmq.client.AlreadyClosedException} (a {@link RuntimeException},
+     *       not an {@link IOException}) — an {@code inspect} that only caught {@code IOException}
+     *       would let that escape, breaking the "never throws" contract this method promises.
+     * </ul>
+     *
+     * <p><strong>Honesty about which catch is measured and which is defensive:</strong> the
+     * {@code createChannel()} catch above is exercised end-to-end against a real broker by
+     * {@code LeadMailboxTest.inspectReportsUnknownRatherThanThrowingWhenTheConnectionIsAlreadyClosed}.
+     * The second {@code catch (RuntimeException e)}, around the passive declare itself — for the
+     * narrower race where the connection drops <em>between</em> {@code createChannel()} succeeding
+     * and the declare landing — has no such test; reaching it needs a connection that dies at that
+     * exact instant, which is not a scenario this suite drives on purpose. It stays purely
+     * defensive: correct by the same reasoning as the first catch, but unproven the way the first
+     * one is proven.
+     */
+    @Override
+    public MailboxState inspect(String coordId) {
+        String queue = queueName(coordId);
+        Channel probe;
+        try {
+            probe = connection.createChannel();
+        } catch (IOException | RuntimeException e) {
+            log.debug("lead mailbox inspect: cannot open a probe channel for {}: {}", coordId, e.toString());
+            return MailboxState.unknown(coordId);
+        }
+        try {
+            AMQP.Queue.DeclareOk declared = probe.queueDeclarePassive(queue);
+            return MailboxState.exists(coordId, declared.getMessageCount(), declared.getConsumerCount());
+        } catch (IOException e) {
+            // The broker (or the client library) has already closed `probe` for us either way; only
+            // a confirmed 404 means "no such queue" — anything else (a different declare failure) is
+            // "could not determine", never silently reported as the same value as a genuine absence.
+            return isMissingQueue(e) ? MailboxState.absent(coordId) : MailboxState.unknown(coordId);
+        } catch (RuntimeException e) {
+            // E.g. the connection dropped between createChannel() and the declare landing.
+            log.debug("lead mailbox inspect: declare failed unexpectedly for {}: {}", coordId, e.toString());
+            return MailboxState.unknown(coordId);
+        } finally {
+            try {
+                if (probe.isOpen()) {
+                    probe.close();
+                }
+            } catch (Exception e) {
+                log.debug("lead mailbox inspect: probe channel close for {}: {}", coordId, e.toString());
+            }
+        }
+    }
+
+    /**
+     * {@code true} only for the specific shape a missing-queue passive declare actually produces —
+     * measured against a real broker, not assumed from the spec text (see {@code
+     * LeadMailboxTest.passiveDeclareOfAMissingQueueThrowsAnIOExceptionWrappingA404ShutdownSignal}):
+     * an {@link IOException} whose cause is a {@link ShutdownSignalException} carrying an
+     * {@link AMQP.Channel.Close} reason with {@code replyCode == 404}. Any other shape (a different
+     * reply code, a {@code ShutdownSignalException} cause whose reason is not a
+     * {@code Channel.Close}, or no cause at all) is a declare failure of some other kind and must
+     * not be read as "confirmed absent" — pinned hermetically, with no broker needed, by
+     * {@code LeadMailboxIsMissingQueueTest} for exactly those three false shapes. Package-private
+     * (not {@code private}) so that test can call it directly.
+     */
+    static boolean isMissingQueue(IOException e) {
+        if (!(e.getCause() instanceof ShutdownSignalException sse)) {
+            return false;
+        }
+        return sse.getReason() instanceof AMQP.Channel.Close close && close.getReplyCode() == AMQP.NOT_FOUND;
+    }
+
     /** Convenience: {@link #peek} the current snapshot, then {@link #ack} every message in it. */
     public List<LeadMessage> drain() {
         List<LeadMessage> snapshot = peek();

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

@@ -80,7 +80,7 @@ class FleetdLeadMailboxSelectionTest {
     @Test
     void opensTheMailboxWhenAUriAndSelfIdAreConfigured() {
         var opener = new RecordingOpener();
-        var coordinator = new FleetConfig.Coordinator(RESOLVED_URI, null, "mac-opus", null);
+        var coordinator = new FleetConfig.Coordinator(RESOLVED_URI, null, "mac-opus", null, null);
 
         Fleetd.openLeadMailbox(coordinator, Map.of(), opener);
 
@@ -94,7 +94,7 @@ class FleetdLeadMailboxSelectionTest {
     void honoursUriEnvOverALiteralUri() {
         var opener = new RecordingOpener();
         var coordinator = new FleetConfig.Coordinator("amqp://stale:stale@old:5672/x", "COORD_URI",
-                "mac-opus", 8);
+                "mac-opus", 8, null);
 
         Fleetd.openLeadMailbox(coordinator, Map.of("COORD_URI", RESOLVED_URI), opener);
 
@@ -105,7 +105,7 @@ class FleetdLeadMailboxSelectionTest {
     @Test
     void turnsOffWhenUriEnvDoesNotResolve() {
         var opener = new RecordingOpener();
-        var coordinator = new FleetConfig.Coordinator(null, "COORD_URI", "mac-opus", null);
+        var coordinator = new FleetConfig.Coordinator(null, "COORD_URI", "mac-opus", null, null);
 
         assertNull(Fleetd.openLeadMailbox(coordinator, Map.of(), opener));
 
@@ -116,7 +116,7 @@ class FleetdLeadMailboxSelectionTest {
     void warnsAndStaysOffWhenSelfIdIsMissing() {
         var appender = captureFleetdLogs();
         var opener = new RecordingOpener();
-        var coordinator = new FleetConfig.Coordinator(RESOLVED_URI, null, null, null);
+        var coordinator = new FleetConfig.Coordinator(RESOLVED_URI, null, null, null, null);
 
         assertNull(Fleetd.openLeadMailbox(coordinator, Map.of(), opener));
 
@@ -131,7 +131,7 @@ class FleetdLeadMailboxSelectionTest {
         var appender = captureFleetdLogs();
         var opener = new RecordingOpener();
         opener.unreachable = true;
-        var coordinator = new FleetConfig.Coordinator(RESOLVED_URI, null, "mac-opus", null);
+        var coordinator = new FleetConfig.Coordinator(RESOLVED_URI, null, "mac-opus", null, null);
 
         assertNull(Fleetd.openLeadMailbox(coordinator, Map.of(), opener),
                 "a down coordination broker turns the feature off; it must never take the daemon down");

fleetd/src/test/java/dev/ltms/fleet/config/ConfigRefTopLevelReportingCoverageTest.java

@@ -104,7 +104,7 @@ class ConfigRefTopLevelReportingCoverageTest {
         v.put("configReload", new FleetConfig.ConfigReload(true, 10));
         v.put("quarantineCooldownSeconds", 1800);
         v.put("memberCredentials", null);
-        v.put("coordinator", new FleetConfig.Coordinator("amqp://coord-a", null, "self-a", 1));
+        v.put("coordinator", new FleetConfig.Coordinator("amqp://coord-a", null, "self-a", 1, null));
         v.put("worktreeGroup", "group-a");
         v.put("memberLoginShell", null);
         assertNamesMatchComponents(v);
@@ -144,7 +144,7 @@ class ConfigRefTopLevelReportingCoverageTest {
         v.put("configReload", new FleetConfig.ConfigReload(false, 20));
         v.put("quarantineCooldownSeconds", 3600);
         v.put("memberCredentials", null);
-        v.put("coordinator", new FleetConfig.Coordinator("amqp://coord-b", null, "self-b", 2));
+        v.put("coordinator", new FleetConfig.Coordinator("amqp://coord-b", null, "self-b", 2, null));
         v.put("worktreeGroup", "group-b");
         v.put("memberLoginShell", null);
         assertNamesMatchComponents(v);

fleetd/src/test/java/dev/ltms/fleet/config/FleetConfigTest.java

@@ -1189,7 +1189,7 @@ class FleetConfigTest {
     @Test
     void coordinatorEffectiveUriHonorsUriEnv() {
         FleetConfig.Coordinator withEnv = new FleetConfig.Coordinator(
-                "amqp://stale-clear-text@127.0.0.1:5672/coord", "LEAD_COORD_URI", "fleet01-lead", null);
+                "amqp://stale-clear-text@127.0.0.1:5672/coord", "LEAD_COORD_URI", "fleet01-lead", null, null);
 
         assertEquals("amqp://from-env@127.0.0.1:5672/coord",
                 withEnv.effectiveUri(Map.of("LEAD_COORD_URI", "amqp://from-env@127.0.0.1:5672/coord")),
@@ -1200,12 +1200,61 @@ class FleetConfigTest {
                 "a blank uriEnv variable must not fall back to the literal uri");
 
         FleetConfig.Coordinator noEnv = new FleetConfig.Coordinator(
-                "amqp://guest:guest@127.0.0.1:5672/coord", null, null, null);
+                "amqp://guest:guest@127.0.0.1:5672/coord", null, null, null, null);
         assertEquals("amqp://guest:guest@127.0.0.1:5672/coord", noEnv.effectiveUri(Map.of()),
                 "the literal uri is used when no uriEnv is configured");
         assertEquals(LeadMailbox.DEFAULT_PREFETCH, noEnv.prefetchOrDefault());
     }
 
+    /**
+     * fleetd #361: the live block ships as just {@code uriEnv} + {@code selfId} (see
+     * {@code Fleetd.example.yaml} / the operator's real {@code fleetd.yaml}, gitignored). That exact
+     * shape, with no {@code peers:} key at all, must keep parsing unchanged after this field is added.
+     */
+    @Test
+    void coordinatorBlockWithNoPeersKeyStillParses(@TempDir Path dir) throws Exception {
+        Path f = dir.resolve("coordinator-no-peers.yaml");
+        Files.writeString(f, """
+                bind:
+                  port: 8080
+                coordinator:
+                  uriEnv: COORD_AMQP_URI
+                  selfId: mac
+                """);
+
+        FleetConfig cfg = FleetConfig.load(f);
+        assertNotNull(cfg.coordinator());
+        assertEquals("mac", cfg.coordinator().selfId());
+        assertEquals(List.of(), cfg.coordinator().peers(), "no peers: key means no configured peers, never null");
+    }
+
+    @Test
+    void coordinatorPeersParsesAndDropsBlankEntries(@TempDir Path dir) throws Exception {
+        Path f = dir.resolve("coordinator-peers.yaml");
+        Files.writeString(f, """
+                bind:
+                  port: 8080
+                coordinator:
+                  selfId: mac
+                  uri: amqp://guest:guest@127.0.0.1:5672/coord
+                  peers:
+                    - fleet01
+                    - ""
+                    - fleet02
+                """);
+
+        FleetConfig cfg = FleetConfig.load(f);
+        assertEquals(List.of("fleet01", "fleet02"), cfg.coordinator().peers(),
+                "a blank peer entry must be dropped, never kept as an empty coord-id");
+    }
+
+    @Test
+    void coordinatorPeersDefaultsToEmptyWhenConstructedWithNull() {
+        FleetConfig.Coordinator c = new FleetConfig.Coordinator(
+                "amqp://guest:guest@127.0.0.1:5672/coord", null, "mac", null, null);
+        assertEquals(List.of(), c.peers(), "a null peers list must default to empty, never NPE downstream");
+    }
+
     @Test
     void absentWorktreeGroupLeavesItNull(@TempDir Path dir) throws Exception {
         Path f = dir.resolve("no-worktree-group.yaml");

fleetd/src/test/java/dev/ltms/fleet/config/FleetConfigWithDefaultsPreservesEveryComponentTest.java

@@ -92,7 +92,7 @@ class FleetConfigWithDefaultsPreservesEveryComponentTest {
         v.put("memberCredentials", new FleetConfig.MemberCredentials(
                 FleetConfig.MemberCredentials.POLICY_DENY_BY_DEFAULT,
                 List.of("git"), List.of("git", "ssh"), null));
-        v.put("coordinator", new FleetConfig.Coordinator("amqp://coord-guard", null, "self-guard", 3));
+        v.put("coordinator", new FleetConfig.Coordinator("amqp://coord-guard", null, "self-guard", 3, null));
         v.put("worktreeGroup", "group-guard");
         v.put("memberLoginShell", "/bin/zsh");
         assertNamesMatchComponents(v);

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

@@ -1,6 +1,7 @@
 package dev.ltms.fleet.mcp;
 
 import dev.ltms.fleet.msg.FakeLeadChannel;
+import dev.ltms.fleet.msg.LeadChannel;
 import dev.ltms.fleet.msg.LeadMessage;
 import io.modelcontextprotocol.spec.McpSchema;
 import org.junit.jupiter.api.Test;
@@ -93,4 +94,56 @@ class FleetMcpLeadCoordTest {
         assertTrue(FleetMcp.sendToLead(channel, PEER, "   ", null, null).isError());
         assertEquals(0, channel.published().size());
     }
+
+    /**
+     * fleetd #361: "delivered" overstated what publish actually proves — the broker's confirm means
+     * durably queued, not read. A zero-consumer target is the observable form of "this will not
+     * reach a pane right now", so the (still-successful) result must say so.
+     */
+    @Test
+    void warnsWhenThePeerMailboxHasNoConsumersButStillReportsSuccess() {
+        var channel = new FakeLeadChannel(SELF)
+                .withMailbox(PEER, LeadChannel.MailboxState.exists(PEER, 0, 0));
+
+        McpSchema.CallToolResult res = FleetMcp.sendToLead(channel, PEER, "hi", null, null);
+
+        assertFalse(res.isError(), "a zero-consumer mailbox is still a successful, durably-queued publish");
+        String out = textOf(res);
+        assertTrue(out.contains("durably confirmed"), out);
+        assertTrue(out.toLowerCase().contains("no consumers"), () -> "must warn nobody is reading it: " + out);
+    }
+
+    @Test
+    void staysQuietAboutConsumersWhenThePeerMailboxHasOne() {
+        var channel = new FakeLeadChannel(SELF)
+                .withMailbox(PEER, LeadChannel.MailboxState.exists(PEER, 0, 1));
+
+        McpSchema.CallToolResult res = FleetMcp.sendToLead(channel, PEER, "hi", null, null);
+
+        assertFalse(res.isError());
+        String out = textOf(res);
+        assertTrue(out.contains("durably confirmed"), out);
+        assertFalse(out.toLowerCase().contains("no consumers"), () -> "a consumer IS attached: " + out);
+    }
+
+    /**
+     * fleetd #361 review finding 1: an unmeasured fact must never render as a definite one. When
+     * the post-publish probe could not determine the mailbox's consumer count at all (broker slow,
+     * unreachable, or the probe timed out — {@link LeadChannel.MailboxState#unknown}), the result
+     * must stay just as quiet as the has-a-consumer case — never assert "no consumers" for a mailbox
+     * this call never actually measured.
+     */
+    @Test
+    void staysQuietAboutConsumersWhenThePeerMailboxStateIsUnknown() {
+        var channel = new FakeLeadChannel(SELF)
+                .withMailbox(PEER, LeadChannel.MailboxState.unknown(PEER));
+
+        McpSchema.CallToolResult res = FleetMcp.sendToLead(channel, PEER, "hi", null, null);
+
+        assertFalse(res.isError(), "an unresolved post-publish probe must never turn a durably-confirmed publish into an error");
+        String out = textOf(res);
+        assertTrue(out.contains("durably confirmed"), out);
+        assertFalse(out.toLowerCase().contains("no consumers"),
+                () -> "an unmeasured fact must never be reported as a definite zero-consumer mailbox: " + out);
+    }
 }

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

@@ -10,6 +10,9 @@ import dev.ltms.fleet.herdr.FakeHerdr;
 import dev.ltms.fleet.herdr.PaneLocator;
 import dev.ltms.fleet.herdr.WorkspaceControl;
 import dev.ltms.fleet.inject.Injector;
+import dev.ltms.fleet.msg.FakeLeadChannel;
+import dev.ltms.fleet.msg.LeadChannel;
+import dev.ltms.fleet.msg.LeadMessage;
 import dev.ltms.fleet.msg.MessageService;
 import dev.ltms.fleet.msg.Rendezvous;
 import dev.ltms.fleet.session.FakeWorktrees;
@@ -34,7 +37,9 @@ import java.util.Map;
 import java.util.EnumSet;
 import java.util.Set;
 import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Function;
 
 import static org.junit.jupiter.api.Assertions.*;
@@ -576,17 +581,48 @@ class FleetMcpTest {
     void listReportsThisDaemonsOwnCoordIdWhenLeadCoordinationIsOn() {
         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));
 
         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(), Map.of(), "", "mac-opus");
+                FleetMcp.QuarantineSource.none(), Map.of(), "",
+                new FleetMcp.CoordinationSource(channel, List.of()));
 
         String out = textOf(res);
-        // There is no peer-discovery surface yet, so this row answers the one question an operator
-        // cannot answer any other way: which coord-id a peer must use to reach ME.
+        // fleetd #361: reports both which coord-id a peer must use to reach ME, and this daemon's
+        // own mailbox state (a self-diagnosis: is my own consumer actually attached?).
         assertTrue(out.contains("\"coordinator\""), out);
         assertTrue(out.contains("\"selfId\":\"mac-opus\""), out);
+        assertTrue(out.contains("\"mailbox\":{\"status\":\"exists\",\"pending\":0,\"consumers\":1}"), out);
+        assertTrue(out.contains("\"held\":[]"), out);
+        assertTrue(out.contains("\"peers\":[]"), out);
+    }
+
+    /**
+     * fleetd #361 review finding 1: a self-probe that could not complete (broker unreachable, timed
+     * out) must never render the same as a measured "0 pending, 0 consumers" — that was exactly the
+     * bug: a reader could not tell "my mailbox is empty and idle" from "I could not check", and the
+     * second one is the far more alarming state.
+     */
+    @Test
+    void listReportsAnUnresolvedSelfProbeAsUnknownNeverAsAMeasuredZero() {
+        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.unknown("mac-opus"));
+
+        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(), Map.of(), "",
+                new FleetMcp.CoordinationSource(channel, List.of()));
+
+        String out = textOf(res);
+        assertTrue(out.contains("\"mailbox\":{\"status\":\"unknown\"}"), out);
+        assertFalse(out.contains("\"pending\""), "an unresolved probe must never carry a pending count at all: " + out);
+        assertFalse(out.contains("\"consumers\""), "an unresolved probe must never carry a consumers count at all: " + out);
     }
 
     @Test
@@ -601,6 +637,110 @@ class FleetMcpTest {
                 "an ordinary fleet's output must be unchanged by this feature");
     }
 
+    @Test
+    void listReportsHeldMessagesWithATruncatedPreviewNeverTheFullBody() {
+        FakeHerdr h = new FakeHerdr();
+        SessionManager sessions = new SessionManager(workerService(h, "http://gx00.gw:8000", Set.of("gx00.gw")));
+        String longContent = "x".repeat(200);
+        FakeLeadChannel channel = new FakeLeadChannel("mac-opus")
+                .hold(new LeadMessage("m1", "fleet01-lead", "mac-opus", longContent));
+
+        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(), Map.of(), "",
+                new FleetMcp.CoordinationSource(channel, List.of()));
+
+        String out = textOf(res);
+        assertTrue(out.contains("\"msgId\":\"m1\""), out);
+        assertTrue(out.contains("\"from\":\"fleet01-lead\""), out);
+        assertFalse(out.contains(longContent), "fleet_list must never dump a held message's full body: " + out);
+        assertTrue(out.contains("x".repeat(80) + "…"), "expected an 80-char preview with an ellipsis: " + out);
+    }
+
+    @Test
+    void listReportsEachDeclaredPeersLiveReachability() {
+        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("fleet01-lead", LeadChannel.MailboxState.exists("fleet01-lead", 2, 1))
+                .withMailbox("fleet03-lead", LeadChannel.MailboxState.unknown("fleet03-lead"));
+        // "fleet02-lead" is declared as a peer but never configured on the fake — inspect() falls
+        // back to MailboxState.absent, exactly as a real down (never-run) peer would report.
+        // "fleet03-lead" IS configured, as unknown — a broker that could not be reached in time,
+        // which review finding 1 says must render distinctly from "fleet02-lead"'s confirmed absence.
+
+        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(), Map.of(), "",
+                new FleetMcp.CoordinationSource(channel, List.of("fleet01-lead", "fleet02-lead", "fleet03-lead")));
+
+        String out = textOf(res);
+        assertTrue(out.contains("\"coordId\":\"fleet01-lead\",\"status\":\"exists\",\"pending\":2,\"consumers\":1"), out);
+        assertTrue(out.contains("\"coordId\":\"fleet02-lead\",\"status\":\"absent\""), out);
+        assertTrue(out.contains("\"coordId\":\"fleet03-lead\",\"status\":\"unknown\""), out);
+        assertFalse(out.contains("\"coordId\":\"fleet02-lead\",\"status\":\"absent\",\"pending\""),
+                "pending/consumers must be omitted, not faked as zero, for a confirmed-absent peer: " + out);
+        assertFalse(out.contains("\"coordId\":\"fleet03-lead\",\"status\":\"unknown\",\"pending\""),
+                "pending/consumers must be omitted, not faked as zero, for an unresolved peer probe: " + out);
+    }
+
+    /**
+     * fleetd #361 review finding 2: {@code get(timeout)} alone times out the CALLER but leaves the
+     * submitted {@link LeadChannel#inspect} task running forever on its own virtual thread — against
+     * a hung (not down) broker every probe would orphan one more thread holding an AMQP channel
+     * until the connection's channel-max is exhausted, which would break {@code publish} too. This
+     * proves {@link FleetMcp#probe(LeadChannel, String, long)} does not merely give up on a slow
+     * task: it interrupts it, so the task does not go on running unbounded after the caller has
+     * already moved on. No hung broker needed — a {@link LeadChannel} fake that blocks until
+     * interrupted is enough to observe the same mechanism.
+     */
+    @Test
+    void aTimedOutProbeInterruptsTheOrphanedTaskRatherThanAbandoningIt() throws Exception {
+        CountDownLatch started = new CountDownLatch(1);
+        AtomicBoolean wasInterrupted = new AtomicBoolean(false);
+        LeadChannel hangs = new LeadChannel() {
+            @Override
+            public void publish(String toCoordId, LeadMessage m) { }
+
+            @Override
+            public List<LeadMessage> peek() { return List.of(); }
+
+            @Override
+            public void ack(String msgId) { }
+
+            @Override
+            public String selfCoordId() { return "mac-opus"; }
+
+            @Override
+            public MailboxState inspect(String coordId) {
+                started.countDown();
+                try {
+                    Thread.sleep(60_000);
+                } catch (InterruptedException e) {
+                    wasInterrupted.set(true);
+                    Thread.currentThread().interrupt();
+                }
+                return MailboxState.unknown(coordId);
+            }
+        };
+
+        LeadChannel.MailboxState result = FleetMcp.probe(hangs, "fleet01-lead", 100L);
+
+        assertFalse(result.exists(), "a timed-out probe must never claim the mailbox exists");
+        assertFalse(result.known(), "a timed-out probe proves nothing either way — it must report unknown");
+        assertTrue(started.await(2, TimeUnit.SECONDS), "the probe task must actually have started");
+        // The interrupt is delivered asynchronously to the orphaned task's own thread — poll briefly
+        // rather than assume it has already landed the instant probe() returns.
+        long deadline = System.nanoTime() + TimeUnit.SECONDS.toNanos(2);
+        while (!wasInterrupted.get() && System.nanoTime() < deadline) {
+            Thread.sleep(20);
+        }
+        assertTrue(wasInterrupted.get(),
+                "probe() must cancel the orphaned task (interrupt it) instead of leaving it to run forever");
+    }
+
     @Test
     void capacityUsesThePlacementLiveCount() {
         FakeHerdr h = new FakeHerdr();
@@ -911,7 +1051,8 @@ class FleetMcpTest {
         String out = textOf(FleetMcp.listFleet(workerService(h, "http://gx00.gw:8000", Set.of("gx00.gw")),
                 sessions, null, new FleetMcp.CapacitySource(profile -> 2, profile -> 3,
                 () -> Set.of("sonnet"), () -> 0), new FleetMcp.HealthCoverageSource(() -> "off"),
-                FleetMcp.QuarantineSource.none(), FleetMcp.OutageSource.none(), leadSeats, Map.of(), "", null));
+                FleetMcp.QuarantineSource.none(), FleetMcp.OutageSource.none(), leadSeats, Map.of(), "",
+                FleetMcp.CoordinationSource.none()));
 
         assertTrue(out.contains("\"maxLoad\":3"), "maxLoad itself must be left untouched: " + out);
         assertTrue(out.contains("\"live\":2"), out);
@@ -934,7 +1075,8 @@ class FleetMcpTest {
         String out = textOf(FleetMcp.listFleet(workerService(h, "http://gx00.gw:8000", Set.of("gx00.gw")),
                 sessions, null, new FleetMcp.CapacitySource(profile -> 0, profile -> 3,
                 () -> Set.of("sonnet"), () -> 0), new FleetMcp.HealthCoverageSource(() -> "off"),
-                FleetMcp.QuarantineSource.none(), FleetMcp.OutageSource.none(), leadSeats, Map.of(), "", null));
+                FleetMcp.QuarantineSource.none(), FleetMcp.OutageSource.none(), leadSeats, Map.of(), "",
+                FleetMcp.CoordinationSource.none()));
 
         assertTrue(out.contains("\"live\":0"), out);
         assertTrue(out.contains("\"free\":3"), "the real gate never subtracts the lead's seat: " + out);
@@ -988,7 +1130,7 @@ class FleetMcpTest {
         String out = textOf(FleetMcp.listFleet(composite, sm, null,
                 new FleetMcp.CapacitySource(liveCount, p -> profiles.get(p).maxLoad(), profiles::keySet, () -> 0),
                 new FleetMcp.HealthCoverageSource(() -> "off"), FleetMcp.QuarantineSource.none(),
-                FleetMcp.OutageSource.none(), leadSeats, Map.of(), "", null));
+                FleetMcp.OutageSource.none(), leadSeats, Map.of(), "", FleetMcp.CoordinationSource.none()));
         int reportedFree = extractInt(out, "free");
 
         for (int i = 0; i < reportedFree; i++) {
@@ -1017,7 +1159,7 @@ class FleetMcpTest {
                 sessions, null, new FleetMcp.CapacitySource(profile -> 0, profile -> 2,
                 () -> Set.of("terra"), () -> 0), new FleetMcp.HealthCoverageSource(() -> "off"),
                 FleetMcp.QuarantineSource.none(), FleetMcp.OutageSource.none(), FleetMcp.LeadSeatSource.none(),
-                Map.of(), "", null));
+                Map.of(), "", FleetMcp.CoordinationSource.none()));
 
         assertTrue(out.contains("\"free\":2"), out);
         assertFalse(out.contains("leadSeats"), "no lead shares this profile's credential: " + out);

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

@@ -146,7 +146,7 @@ class MemberEnvAllowListTest {
         return new FleetConfig(null, null, null, Map.of(), null, null, null, null, null,
                 new FleetConfig.Broker(null, brokerUriEnv, null), null, null, null, null, null,
                 null, null, null, null,
-                new FleetConfig.Coordinator(null, coordinatorUriEnv, null, null)).withDefaults();
+                new FleetConfig.Coordinator(null, coordinatorUriEnv, null, null, null)).withDefaults();
     }
 
     /** {@code LC_*} categories are infrastructure by prefix; everything else needs an exact match. */

fleetd/src/test/java/dev/ltms/fleet/msg/FakeLeadChannel.java

@@ -3,6 +3,8 @@ package dev.ltms.fleet.msg;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 /**
  * Hermetic stand-in for {@link LeadChannel}: an in-memory mailbox that records what was published
@@ -24,11 +26,19 @@ public final class FakeLeadChannel implements LeadChannel {
     private final List<String> acked = Collections.synchronizedList(new ArrayList<>());
     /** When set, every {@link #publish} throws it — the unroutable/nacked/timed-out peer. */
     private volatile IllegalStateException publishFailure;
+    /** Canned {@link #inspect} results by coord-id — absent for any coord-id not configured here. */
+    private final Map<String, MailboxState> mailboxes = new ConcurrentHashMap<>();
 
     public FakeLeadChannel(String selfCoordId) {
         this.selfCoordId = selfCoordId;
     }
 
+    /** Make {@link #inspect(String)} return {@code state} for {@code coordId} instead of "absent". */
+    public FakeLeadChannel withMailbox(String coordId, MailboxState state) {
+        mailboxes.put(coordId, state);
+        return this;
+    }
+
     /** Make every publish fail as an unreachable peer would. */
     public FakeLeadChannel failPublishWith(String message) {
         this.publishFailure = new IllegalStateException(message);
@@ -65,6 +75,11 @@ public final class FakeLeadChannel implements LeadChannel {
         return selfCoordId;
     }
 
+    @Override
+    public MailboxState inspect(String coordId) {
+        return mailboxes.getOrDefault(coordId, MailboxState.absent(coordId));
+    }
+
     public List<LeadMessage> published() {
         return List.copyOf(published);
     }

fleetd/src/test/java/dev/ltms/fleet/msg/LeadMailboxIsMissingQueueTest.java

@@ -0,0 +1,77 @@
+package dev.ltms.fleet.msg;
+
+import com.rabbitmq.client.ShutdownSignalException;
+import com.rabbitmq.client.impl.AMQImpl;
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * fleetd #361 review round 2: a mutation that made {@link LeadMailbox#isMissingQueue} return
+ * {@code true} unconditionally still left {@code mvn clean install} green — 1389 tests, 0
+ * failures — because nothing exercised its false branch. That branch is the whole discriminator
+ * between {@link LeadChannel.MailboxState#absent} and {@link LeadChannel.MailboxState#unknown};
+ * without a test pinning it, a future refactor that widens it back to "always true" (restoring the
+ * exact overstatement fleetd #361 exists to fix) would pass this suite.
+ *
+ * <p>Hermetic — no broker needed, per the review's own suggestion. {@code isMissingQueue} takes a
+ * plain {@link IOException}, so every input here is constructed directly rather than provoked from
+ * a live connection. The real 404 shape itself is still pinned against a real broker, in
+ * {@code LeadMailboxTest.passiveDeclareOfAMissingQueueThrowsAnIOExceptionWrappingA404ShutdownSignal}
+ * — this class covers the three false shapes {@link LeadMailbox#isMissingQueue}'s own javadoc
+ * lists, so both directions of the discriminator are proven somewhere.
+ */
+class LeadMailboxIsMissingQueueTest {
+
+    @Test
+    void aConfirmedMissingQueueIsRecognized() {
+        ShutdownSignalException sse = new ShutdownSignalException(true, false,
+                new AMQImpl.Channel.Close(404, "NOT_FOUND - no queue 'lead.x.inbox' in vhost '/'", 50, 10), null);
+        IOException e = new IOException("channel error", sse);
+
+        assertTrue(LeadMailbox.isMissingQueue(e), "a genuine 404 Channel.Close must be recognized as a missing queue");
+    }
+
+    @Test
+    void aDifferentReplyCodeIsNotAMissingQueue() {
+        // E.g. 403 ACCESS_REFUSED — the queue may well exist; this call was simply refused.
+        ShutdownSignalException sse = new ShutdownSignalException(true, false,
+                new AMQImpl.Channel.Close(403, "ACCESS_REFUSED", 50, 10), null);
+        IOException e = new IOException("channel error", sse);
+
+        assertFalse(LeadMailbox.isMissingQueue(e),
+                "a non-404 reply code must never be read as a confirmed absence — the mailbox's real state is unknown");
+    }
+
+    @Test
+    void aShutdownSignalWhoseReasonIsNotAChannelCloseIsNotAMissingQueue() {
+        // A Connection.Close (a whole different broker-level shutdown) is still a ShutdownSignalException,
+        // but its reason is not a Channel.Close at all — must not be misread as "no such queue".
+        ShutdownSignalException sse = new ShutdownSignalException(true, false,
+                new AMQImpl.Connection.Close(404, "coincidentally 404, but this is a CONNECTION close", 10, 50), null);
+        IOException e = new IOException("connection error", sse);
+
+        assertFalse(LeadMailbox.isMissingQueue(e),
+                "a ShutdownSignalException whose reason is not a Channel.Close must never be read as a missing queue,"
+                        + " even if its reply code happens to be 404");
+    }
+
+    @Test
+    void anIOExceptionWithNoCauseAtAllIsNotAMissingQueue() {
+        IOException e = new IOException("some other declare failure, no cause attached");
+
+        assertFalse(LeadMailbox.isMissingQueue(e),
+                "an IOException with no ShutdownSignalException cause must never be read as a confirmed absence");
+    }
+
+    @Test
+    void anIOExceptionWithAnUnrelatedCauseIsNotAMissingQueue() {
+        IOException e = new IOException("wrapped something else entirely", new RuntimeException("boom"));
+
+        assertFalse(LeadMailbox.isMissingQueue(e),
+                "a cause that isn't even a ShutdownSignalException must never be read as a confirmed absence");
+    }
+}

fleetd/src/test/java/dev/ltms/fleet/msg/LeadMailboxTest.java

@@ -1,5 +1,9 @@
 package dev.ltms.fleet.msg;
 
+import com.rabbitmq.client.AMQP;
+import com.rabbitmq.client.Channel;
+import com.rabbitmq.client.Connection;
+import com.rabbitmq.client.ShutdownSignalException;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.Tag;
 import org.junit.jupiter.api.Test;
@@ -7,11 +11,14 @@ import org.testcontainers.containers.RabbitMQContainer;
 import org.testcontainers.junit.jupiter.Testcontainers;
 import org.testcontainers.utility.DockerImageName;
 
+import java.io.IOException;
 import java.util.List;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicLong;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
@@ -159,6 +166,145 @@ class LeadMailboxTest {
         }
     }
 
+    @Test
+    void inspectReportsAnOwnedMailboxAsExistingWithItsOwnConsumer() throws Exception {
+        // A LeadMailbox declares AND consumes its own queue the moment open() returns (see own()),
+        // so inspecting a coord-id this same process owns must always find exactly one consumer.
+        String self = coordId("lead-inspect-self");
+        try (LeadMailbox mailbox = LeadMailbox.open(uri(), self)) {
+            LeadChannel.MailboxState state = mailbox.inspect(self);
+            assertEquals(self, state.coordId());
+            assertTrue(state.exists(), "this daemon owns and has declared this exact queue");
+            assertEquals(0, state.pending(), "nothing has been published to it yet");
+            assertEquals(1, state.consumers(), "the mailbox's own constructor already attached a consumer");
+        }
+    }
+
+    @Test
+    void inspectReportsAMissingMailboxAsAbsentRatherThanThrowing() throws Exception {
+        String nobody = coordId("lead-inspect-nobody");
+        try (LeadMailbox mailbox = LeadMailbox.open(uri(), coordId("lead-inspect-caller"))) {
+            LeadChannel.MailboxState state = mailbox.inspect(nobody);
+            assertEquals(LeadChannel.MailboxState.absent(nobody), state,
+                    "a queue nobody has ever declared must report absent, never throw");
+            assertTrue(state.known(), "a confirmed 404 IS a definite answer — this is not the unknown case");
+        }
+    }
+
+    /**
+     * fleetd #361 review finding 3: {@code inspect} is specified to never throw, but the original
+     * implementation caught only {@link IOException} — and {@link Connection#createChannel()} on an
+     * already-closed connection throws {@link com.rabbitmq.client.AlreadyClosedException}, an
+     * unchecked {@link RuntimeException} (pinned by {@code
+     * createChannelOnAnAlreadyClosedConnectionThrowsAnUncheckedException} above). This drives that
+     * exact scenario through the real {@link LeadMailbox#inspect} — not the raw client call — and
+     * checks both halves of finding 1 and finding 3 at once: no exception escapes, and the result is
+     * {@code UNKNOWN} rather than the wrong-but-plausible-looking {@code ABSENT}.
+     */
+    @Test
+    void inspectReportsUnknownRatherThanThrowingWhenTheConnectionIsAlreadyClosed() throws Exception {
+        LeadMailbox mailbox = LeadMailbox.open(uri(), coordId("lead-inspect-dead-connection"));
+        mailbox.close(); // tears down the connection `inspect` will try to open a probe channel on
+
+        LeadChannel.MailboxState state = mailbox.inspect(coordId("lead-inspect-irrelevant-target"));
+
+        assertFalse(state.exists());
+        assertFalse(state.known(), "a dead connection proves nothing about the target mailbox — it must be unknown, not absent");
+        assertEquals(LeadChannel.MailboxState.Presence.UNKNOWN, state.presence());
+    }
+
+    @Test
+    void inspectReportsPendingMessagesAndZeroConsumersWhenNobodyIsReadingAnymore() throws Exception {
+        // Publish into a mailbox this test owns, then never consume from it, to prove `pending` and
+        // `consumers` really come off the broker rather than off this process's own in-memory state.
+        String to = coordId("lead-inspect-pending");
+        String observerId = coordId("lead-inspect-observer");
+        try (LeadMailbox owner = LeadMailbox.open(uri(), to);
+             LeadMailbox observer = LeadMailbox.open(uri(), observerId)) {
+            owner.publish(to, new LeadMessage("m1", "lead-from", to, "sitting in the queue"));
+            awaitPeek(owner); // make sure the broker has actually enqueued it before inspecting
+        } // `owner` closes here: its consumer disconnects, but the durable, unacked message stays queued.
+
+        try (LeadMailbox observer = LeadMailbox.open(uri(), coordId("lead-inspect-observer-2"))) {
+            // The broker requeues `owner`'s unacked delivery asynchronously once its connection drops,
+            // so poll rather than assume the very first passive declare already sees the settled state.
+            LeadChannel.MailboxState state = awaitInspect(observer, to, s -> s.consumers() == 0);
+            assertTrue(state.exists());
+            assertEquals(0, state.consumers(), "the only owner just closed — nobody is reading this anymore");
+            assertEquals(1, state.pending(), "the unacked message must be requeued, never dropped");
+        }
+    }
+
+    /**
+     * fleetd #361's central invariant, proved rather than assumed: a passive queue declare of a
+     * missing queue closes ITS channel with a 404 in AMQP 0-9-1. {@link LeadMailbox#inspect} is
+     * specified to run on its own disposable channel for exactly this reason — this test is the one
+     * that actually exercises the failure mode and shows {@link LeadMailbox#publish} on the SAME
+     * instance is unaffected by it.
+     */
+    @Test
+    void inspectingAMissingMailboxNeverBreaksPublishOnTheSameInstance() throws Exception {
+        String self = coordId("lead-invariant-self");
+        try (LeadMailbox mailbox = LeadMailbox.open(uri(), self)) {
+            // Miss on a queue that has never existed — this is exactly the 404-closes-the-channel case.
+            LeadChannel.MailboxState missed = mailbox.inspect(coordId("lead-invariant-nobody-home"));
+            assertFalse(missed.exists());
+            assertTrue(missed.known(), "a genuine 404 on a queue that never existed is a confirmed fact, not an unknown");
+
+            // publish() must still work on THIS SAME instance: if inspect() had reused `publishChannel`
+            // (or `channel`), the broker's 404 would have closed it out from underneath publish().
+            LeadMessage sent = new LeadMessage("after-miss", "lead-from", self, "still alive");
+            mailbox.publish(self, sent);
+            List<LeadMessage> got = awaitPeek(mailbox);
+            assertEquals(1, got.size(), "publish must still reach this mailbox's own queue after a missed inspect");
+            assertEquals("after-miss", got.getFirst().msgId());
+
+            // And a second inspect() — of a mailbox that DOES exist this time — must also still work,
+            // proving the miss did not wedge inspect() itself either.
+            LeadChannel.MailboxState self2 = mailbox.inspect(self);
+            assertTrue(self2.exists());
+        }
+    }
+
+    /**
+     * Pins the exact exception shape {@link LeadMailbox#inspect} relies on to tell a genuine 404
+     * (mailbox confirmed absent) apart from everything else (mailbox state unknown) — measured
+     * against a real broker rather than assumed from the AMQP 0-9-1 spec text. If this ever fails,
+     * the classification in {@code inspect} is reading the wrong shape and must be revisited.
+     */
+    @Test
+    void passiveDeclareOfAMissingQueueThrowsAnIOExceptionWrappingA404ShutdownSignal() throws Exception {
+        try (Connection conn = LeadMailbox.connectionFactory(uri()).newConnection()) {
+            Channel probe = conn.createChannel();
+            String missing = LeadMailbox.queueName(coordId("lead-404-shape"));
+            IOException thrown = assertThrows(IOException.class, () -> probe.queueDeclarePassive(missing));
+            assertInstanceOf(ShutdownSignalException.class, thrown.getCause(),
+                    () -> "expected the IOException to wrap a ShutdownSignalException, got: " + thrown);
+            ShutdownSignalException sse = (ShutdownSignalException) thrown.getCause();
+            assertInstanceOf(AMQP.Channel.Close.class, sse.getReason(),
+                    () -> "expected a Channel.Close reason: " + sse);
+            AMQP.Channel.Close close = (AMQP.Channel.Close) sse.getReason();
+            assertEquals(404, close.getReplyCode(), () -> "expected AMQP NOT_FOUND (404): " + close);
+            assertFalse(probe.isOpen(), "the 404 must have closed the channel the declare ran on");
+        }
+    }
+
+    /**
+     * The other half of the same measurement: calling {@code createChannel()} on an
+     * already-closed connection — the shape {@link LeadMailbox#inspect} hits when the broker
+     * connection itself is gone — throws {@link com.rabbitmq.client.AlreadyClosedException}, an
+     * unchecked {@link RuntimeException}, not an {@link IOException}. An {@code inspect} that only
+     * caught {@code IOException} here would let this escape instead of reporting "unknown".
+     */
+    @Test
+    void createChannelOnAnAlreadyClosedConnectionThrowsAnUncheckedException() throws Exception {
+        Connection conn = LeadMailbox.connectionFactory(uri()).newConnection();
+        conn.close();
+        RuntimeException thrown = assertThrows(RuntimeException.class, conn::createChannel);
+        assertInstanceOf(com.rabbitmq.client.AlreadyClosedException.class, thrown,
+                () -> "expected AlreadyClosedException, got: " + thrown);
+    }
+
     /** Poll peek until at least one message is held, or ~10s elapse (broker delivery is async). */
     @SuppressWarnings("BusyWait")
     private static List<LeadMessage> awaitPeek(LeadMailbox inbox) throws InterruptedException {
@@ -170,4 +316,18 @@ class LeadMailboxTest {
         }
         return msgs;
     }
+
+    /** Poll inspect(coordId) until it satisfies {@code done}, or ~10s elapse (broker state settles async). */
+    @SuppressWarnings("BusyWait")
+    private static LeadChannel.MailboxState awaitInspect(
+            LeadMailbox observer, String coordId, java.util.function.Predicate<LeadChannel.MailboxState> done)
+            throws InterruptedException {
+        long deadline = System.nanoTime() + TimeUnit.SECONDS.toNanos(10);
+        LeadChannel.MailboxState state = observer.inspect(coordId);
+        while (!done.test(state) && System.nanoTime() < deadline) {
+            Thread.sleep(50);
+            state = observer.inspect(coordId);
+        }
+        return state;
+    }
 }