fleetd #669 Unit C: add the COLLABORATOR role and its authorization row

Adds Role.COLLABORATOR, Principal.collaborator(), and the Authz.permits grant:
READ/METRICS open, REPLY/ASK via ownership, SEND limited to a configured lead
or collaborator via a new classifier parameter, everything else denied.
isSpawnedMember() stays WORKER || ARCHITECT. fleet_whoami reports role and
collaborator name with no leader key.

Per a same-day ticket correction, the existing 3-argument Authz.permits is
kept (fail-closed default via the new NO_KNOWN_LEAD_OR_COLLABORATOR
classifier) rather than deleted, so the 47 pre-existing call sites in
AuthzTest/CallerResolverTest are untouched; both production gates
(FleetMcp#denyFor, FleetApp#allow via the new permitsFor seam) call the
4-argument form explicitly with the shared constant.

Mutation-verified: removing the classifier conjunct from the SEND arm kills
exactly 3 tests (AuthzTest, FleetMcpAuthzTest, FleetAppAuthTest), one per
gate, no cascade.

Full mvn clean install at this commit: 1974 tests, 0 failures (baseline at
f0ff252 was 1964; +10 are the new collaborator-matrix tests). Independently
counted from target/surefire-reports/*.xml after rm -rf: 173 report files,
aggregate tests=1974 failures=0 errors=0.

fleetd/fleetd.example.yaml

@@ -669,6 +669,15 @@ fleet:
   #     kind: opencode
   #     model: openai/gpt-5.6-terra
 
+  # A collaborator tab, keyed by name (fleetd #669). This block is parsed and validated today;
+  # nothing yet recognises or addresses the tab it names. Recognise-only, like a profile-less
+  # `leaders:` entry above: there is no `profile:`, no `instances:` and no `kind:`. `tab:` is
+  # REQUIRED and is the only field identity depends on, matched case-insensitively — the same
+  # GET-THE-VALUE-RIGHT warning above the `leaders:` block applies here too.
+  # collaborators:
+  #   reviewer-alex:
+  #     tab: "collab: alex"
+
   # architects:
   #   architect-1:
   #     profile: opus                # a strong model, on the operator's subscription

fleetd/src/main/java/dev/ltms/fleet/auth/Authz.java

@@ -1,5 +1,7 @@
 package dev.ltms.fleet.auth;
 
+import java.util.function.Predicate;
+
 /**
  * The authorization table (CB-505), stated once and enforced on both entry paths.
  *
@@ -60,58 +62,92 @@ public final class Authz {
     }
 
     /**
-     * Whether {@code caller} may perform {@code action} against {@code targetSession}.
-     *
-     * @param targetSession the session id in the request path; only consulted for the worker-scoped
-     *                      actions ({@code REPLY}, {@code ASK}), ignored otherwise, may be
-     *                      {@code null}
+     * Stands in for the terminal-to-tab registry a collaborator's {@code SEND} is checked
+     * against, until one exists: answers no for every target, so a collaborator reaches nothing
+     * today. Both production gates ({@code FleetMcp#denyFor}, {@code FleetApp#allow}) pass this
+     * exact instance, so the classifier is defined once and replacing it is a one-line change in
+     * each.
+     */
+    public static final Predicate<String> NO_KNOWN_LEAD_OR_COLLABORATOR = target -> false;
+
+    /**
+     * Convenience form for a caller with no classifier to supply. Fails closed: a collaborator's
+     * {@code SEND} is refused, as if no terminal were a configured lead or collaborator — the
+     * same decision {@link #NO_KNOWN_LEAD_OR_COLLABORATOR} gives explicitly. Every other action's
+     * result is identical to the four-argument form's, since none of them consult the classifier.
      */
     public static boolean permits(Principal caller, Action action, String targetSession) {
+        return permits(caller, action, targetSession, NO_KNOWN_LEAD_OR_COLLABORATOR);
+    }
+
+    /**
+     * Whether {@code caller} may perform {@code action} against {@code targetSession}.
+     *
+     * @param targetSession           the session id in the request path; only consulted for the
+     *                                worker-scoped actions ({@code REPLY}, {@code ASK}) and for a
+     *                                collaborator's {@code SEND}, ignored otherwise, may be
+     *                                {@code null}
+     * @param knownLeadOrCollaborator whether a terminal is a configured lead or collaborator —
+     *                                consulted only for a collaborator's {@code SEND}, to confine
+     *                                it to another named peer and never a spawned member's
+     *                                terminal
+     */
+    public static boolean permits(Principal caller, Action action, String targetSession,
+                                   Predicate<String> knownLeadOrCollaborator) {
         if (caller == null || caller.isAnonymous()) {
             return false; // authenticated as nothing ⇒ authorized for nothing
         }
         return switch (action) {
-            // Fleet lifecycle is the primary's alone — spawn, stop, drain. An architect
-            // deliberately does NOT get these (CB-548), so it cannot tear down or stand up workers
-            // even though it coordinates them; and a worker driving any of these would be a worker
-            // escalating into the orchestrator role.
+            // Fleet lifecycle is the primary's alone — spawn, stop, drain. An architect and a
+            // collaborator deliberately do NOT get these, so neither can tear down or stand up
+            // workers even though one of them coordinates them; and a worker driving any of these
+            // would be a worker escalating into the orchestrator role.
             case SPAWN, STOP, DRAIN, HANDOVER -> caller.isPrimary();
 
-            // Delivering a turn to a local session is open to the primary and the architect: an
-            // architect delegates to workers (that is the role's point) but still has no lifecycle
-            // rights. A worker is excluded — sending would be it escalating.
-            case SEND -> caller.isPrimary() || caller.isArchitect();
+            // Delivering a turn to a local session is open to the primary, the architect, and a
+            // collaborator whose target is itself a configured lead or collaborator: the architect
+            // delegates to workers (that is the role's point); a collaborator may reach only
+            // another named peer, never a spawned member's terminal. A worker is excluded —
+            // sending would be it escalating.
+            case SEND -> caller.isPrimary() || caller.isArchitect()
+                    || (caller.isCollaborator() && knownLeadOrCollaborator.test(targetSession));
 
-            // Same grant as SEND. Resolving a worker's blocked question is part of delegating to
-            // it, not a separate capability.
+            // Resolving a worker's blocked question is part of delegating to it, open to the same
+            // two roles that may stand up that delegation in the first place. Not a collaborator:
+            // resuming another session's turn is lifecycle-adjacent, not peer messaging.
             case ANSWER -> caller.isPrimary() || caller.isArchitect();
 
-            // Same grant as SEND. This leaves the daemon over the coordination broker rather than
-            // addressing a local session, but the caller who may do one may do the other.
+            // Leaves the daemon over the coordination broker rather than addressing a local
+            // session, open to the same two roles as ANSWER. Not a collaborator: it is a
+            // local-tab peer with no cross-host route.
             case COORD_SEND -> caller.isPrimary() || caller.isArchitect();
 
             // The load-bearing rule: a caller acts only as the pane it occupies. CB-532 widened who
             // that can be — a lead answering another lead is replying for its OWN terminal, which
             // this already permits — while the rule itself is unchanged, and is what stops anyone
-            // forging a reply for a rendezvous someone else is waiting on. An architect's own pane
-            // passes through the same check, so it can answer a funnel that delegated to it. An
-            // unnamed primary (token/loopback, no pane) owns nothing and is still excluded.
+            // forging a reply for a rendezvous someone else is waiting on. An architect's or a
+            // collaborator's own pane passes through the same check, so each can answer a funnel
+            // that delegated to it. An unnamed primary (token/loopback, no pane) owns nothing and
+            // is still excluded.
             case REPLY, ASK -> caller.ownsSession(targetSession);
 
             // READ is roster, profile, and identity observation — fleet_list, fleet_profiles, and
             // fleet_whoami — and carries no secrets: no ticket reply, no pending question, and no
             // other session's turn state. Those live under TASK_READ. METRICS is the separate
-            // Prometheus scrape. Both stay open to every authenticated role.
-            case READ, METRICS -> caller.isPrimary() || caller.isWorker() || caller.isArchitect();
+            // Prometheus scrape. Both are open to every authenticated role, including a
+            // collaborator.
+            case READ, METRICS -> caller.isPrimary() || caller.isWorker() || caller.isArchitect()
+                    || caller.isCollaborator();
 
-            // Ticket polling and session status, open to every authenticated role the same as READ.
-            // Unlike READ, a holder may poll a ticket it did not create, or read another session's
-            // pending question and the turnId that answers it.
+            // Ticket polling and session status, open to every role READ is open to except a
+            // collaborator: ticket ids are a sequential counter with no owner check, so a holder
+            // could walk every ticket and read another session's delegation reply.
             case TASK_READ -> caller.isPrimary() || caller.isWorker() || caller.isArchitect();
 
             // fleetd #421: reading held lead-to-lead mail is the primary's alone. An architect
             // holds READ today (CB-548), so "not primary" must mean not-architect here too — this
-            // is coordination between leads, not observation of the roster.
+            // is coordination between leads, not observation of the roster. The same reasoning
+            // excludes a collaborator.
             case COORD_READ -> caller.isPrimary();
         };
     }

fleetd/src/main/java/dev/ltms/fleet/auth/Principal.java

@@ -11,7 +11,9 @@ package dev.ltms.fleet.auth;
  * @param pid      the connecting process id, or {@code -1} when not resolvable (audit context)
  * @param name     for a lead resolved from the CB-530 {@code leaders:} registry, which lead it is;
  *                 for an architect resolved from the CB-548 {@code architects:} registry, which
- *                 slot it occupies; {@code null} for every other caller, including an unnamed primary
+ *                 slot it occupies; for a collaborator resolved from the {@code collaborators:}
+ *                 registry, which collaborator it is; {@code null} for every other caller,
+ *                 including an unnamed primary
  */
 public record Principal(Role role, String terminal, long pid, String name) {
 
@@ -73,6 +75,19 @@ public record Principal(Role role, String terminal, long pid, String name) {
         return new Principal(Role.ARCHITECT, terminal, pid, slotName);
     }
 
+    /**
+     * A collaborator: a human-opened tab recognised by its exact label in the
+     * {@code collaborators:} registry.
+     *
+     * <p>Carries {@link Role#COLLABORATOR}. {@code name} is reporting only — it lets
+     * {@code fleet_whoami} say which collaborator is asking. Identity is the {@code terminal}:
+     * like a worker's it comes from the connection, so {@code ownsSession} works exactly as it
+     * does for a worker — a collaborator acts as its own pane and no other.
+     */
+    public static Principal collaborator(String name, String terminal, long pid) {
+        return new Principal(Role.COLLABORATOR, terminal, pid, name);
+    }
+
     public boolean isPrimary() {
         return role == Role.PRIMARY;
     }
@@ -81,6 +96,10 @@ public record Principal(Role role, String terminal, long pid, String name) {
         return role == Role.ARCHITECT;
     }
 
+    public boolean isCollaborator() {
+        return role == Role.COLLABORATOR;
+    }
+
     public boolean isWorker() {
         return role == Role.WORKER;
     }
@@ -120,6 +139,7 @@ public record Principal(Role role, String terminal, long pid, String name) {
         return switch (role) {
             case WORKER -> "worker:" + terminal;
             case ARCHITECT -> "architect:" + name;
+            case COLLABORATOR -> "collaborator:" + name;
             case PRIMARY -> name == null ? "primary" : "leader:" + name;
             case ANONYMOUS -> "anonymous";
         };

fleetd/src/main/java/dev/ltms/fleet/auth/Role.java

@@ -34,6 +34,17 @@ public enum Role {
      */
     ARCHITECT,
 
+    /**
+     * A config-declared, human-opened tab recognised by its exact label (the {@code
+     * fleet.collaborators.<name>.tab} registry). Never spawned — identity comes from the
+     * connection, never a request argument, exactly like {@link #WORKER} and {@link #ARCHITECT}.
+     * May {@code SEND} only to a configured lead or collaborator, {@code REPLY}/{@code ASK} only
+     * as its own pane, and {@code READ}/{@code METRICS}; may not {@code SPAWN}/{@code STOP}/
+     * {@code DRAIN}/{@code HANDOVER}, poll a ticket ({@code TASK_READ}), or reach the
+     * coordination broker ({@code COORD_SEND}/{@code COORD_READ}).
+     */
+    COLLABORATOR,
+
     /** Authenticated as nothing. Authorized for nothing but {@code /healthz}. */
     ANONYMOUS
 }

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

@@ -1176,6 +1176,25 @@ public record FleetConfig(
         }
     }
 
+    /**
+     * A tab fleetd recognises as a collaborator, keyed by name (fleetd #669).
+     *
+     * <p>Recognise-only: there is no {@code profile}, no {@code instances} and no {@code kind}.
+     * Nothing here ever launches a pane.
+     *
+     * <p>{@code tabPrefix} is absent. Identity is matched on the exact {@code tab} alone.
+     *
+     * @param tab the exact tab label hosting this collaborator, matched case-insensitively; the
+     *            only field identity depends on. Required — an entry with no {@code tab} can
+     *            never be discovered.
+     */
+    @JsonIgnoreProperties(ignoreUnknown = true)
+    public record Collaborator(String tab) {
+        public Collaborator {
+            tab = (tab == null || tab.isBlank()) ? null : tab.strip();
+        }
+    }
+
     /**
      * One entry of a {@code fleet:} role pool — a role paired with the backend it runs on.
      *
@@ -1213,15 +1232,18 @@ public record FleetConfig(
      * is exactly compatible with that. The pool is also what replaced {@code defaultProfile:} — an
      * unqualified spawn names a role, and the role's pool supplies the candidates.
      *
-     * @param leaders     panes that orchestrate rather than are orchestrated, keyed by lead name
-     * @param architects  profiles the {@code architect} role may run on
-     * @param developers  profiles the {@code dev} role may run on
-     * @param hunters     profiles the {@code hunter} role may run on
-     * @param reviewers   profiles the {@code reviewer} role may run on
-     * @param charters    optional launch-charter text keyed by singular role wire name
-     * @param tabLabel    template for a member tab's label; {@code {role}}, {@code {profile}},
-     *                    {@code {model}} and {@code {n}} (a per role+profile counter) are
-     *                    substituted. Default {@link #DEFAULT_TAB_LABEL}
+     * @param leaders       panes that orchestrate rather than are orchestrated, keyed by lead name
+     * @param architects    profiles the {@code architect} role may run on
+     * @param developers    profiles the {@code dev} role may run on
+     * @param hunters       profiles the {@code hunter} role may run on
+     * @param reviewers     profiles the {@code reviewer} role may run on
+     * @param charters      optional launch-charter text keyed by singular role wire name
+     * @param tabLabel      template for a member tab's label; {@code {role}}, {@code {profile}},
+     *                      {@code {model}} and {@code {n}} (a per role+profile counter) are
+     *                      substituted. Default {@link #DEFAULT_TAB_LABEL}
+     * @param collaborators tabs fleetd recognises as collaborators (fleetd #669), keyed by name.
+     *                      Recognise-only, exactly like a {@code profile}-less {@link Leader}:
+     *                      nothing here is ever auto-launched.
      */
     @JsonIgnoreProperties(ignoreUnknown = true)
     public record Fleet(Map<String, Leader> leaders,
@@ -1230,7 +1252,8 @@ public record FleetConfig(
                         Map<String, Slot> hunters,
                         Map<String, Slot> reviewers,
                         Map<String, String> charters,
-                        String tabLabel) {
+                        String tabLabel,
+                        Map<String, Collaborator> collaborators) {
 
         /**
          * Role first, so the tab bar identifies the member's fleet role.
@@ -1245,26 +1268,30 @@ public record FleetConfig(
             reviewers = unmodifiableOrEmpty(reviewers);
             charters = unmodifiableOrEmpty(charters);
             tabLabel = (tabLabel == null || tabLabel.isBlank()) ? DEFAULT_TAB_LABEL : tabLabel;
+            collaborators = unmodifiableOrEmpty(collaborators);
         }
 
         /**
-         * A fleet with no configured launch charters — the shape every deployment had before
-         * CB-566, and what most tests want.
+         * A fleet with no configured launch charters and no collaborators — the shape every
+         * deployment had before CB-566, and what most tests want.
          *
          * <p>Kept deliberately, even though an overload that drops a new field is normally the
          * shape to avoid. It is safe here because nothing <em>reads</em> a charter through a
          * constructor: the launcher reads {@code fleet.charters()} from the live config. Jackson
          * binds the canonical constructor, so this one cannot swallow an operator's YAML.
+         * {@code collaborators} is dropped the same way and for the same reason: no caller of
+         * this overload has ever needed to set it, so it defaults to empty here exactly as the
+         * canonical constructor would default an absent YAML key.
          */
         public Fleet(Map<String, Leader> leaders, Map<String, Slot> architects,
                      Map<String, Slot> developers, Map<String, Slot> reviewers,
                      Map<String, String> charters, String tabLabel) {
-            this(leaders, architects, developers, null, reviewers, charters, tabLabel);
+            this(leaders, architects, developers, null, reviewers, charters, tabLabel, null);
         }
 
         public Fleet(Map<String, Leader> leaders, Map<String, Slot> architects,
                      Map<String, Slot> developers, Map<String, Slot> reviewers, String tabLabel) {
-            this(leaders, architects, developers, null, reviewers, null, tabLabel);
+            this(leaders, architects, developers, null, reviewers, null, tabLabel, null);
         }
 
         /**
@@ -1910,7 +1937,7 @@ public record FleetConfig(
 
     /** The {@code fleet:} child blocks whose direct children are slot names. */
     private static final Set<String> FLEET_POOL_KEYS =
-            Set.of("leaders", "architects", "developers", "hunters", "reviewers");
+            Set.of("leaders", "architects", "developers", "hunters", "reviewers", "collaborators");
 
     /**
      * Reject a {@code fleet:} role pool whose slot names repeat (CB-548, re-homed by CB-557).
@@ -1920,7 +1947,7 @@ public record FleetConfig(
      * daemon would never know. Jackson's YAML parser does not fail on duplicate mapping keys by
      * default, so duplicates are caught here, at parse time, before the map is built.
      *
-     * <p>Only the five pools <em>directly under the top-level {@code fleet:}</em> are considered,
+     * <p>Only the six pools <em>directly under the top-level {@code fleet:}</em> are considered,
      * and only their direct child keys (the slot names). A nested field elsewhere, even one also
      * named {@code developers:}, is ignored, so parsing of the rest of the config is unaffected.
      *
@@ -2679,17 +2706,21 @@ public record FleetConfig(
     }
 
     /**
-     * Reject a member tab-label template that could render as a configured lead tab or match a
-     * lead-tab naming convention, and reject two {@code fleet.leaders} entries that share one exact
-     * tab.
+     * Reject a member tab-label template that could render as a configured lead or collaborator
+     * tab or match a lead-tab naming convention, and reject two {@code fleet.leaders} or
+     * {@code fleet.collaborators} entries — across either registry — that share one exact tab.
+     *
+     * <p>{@code fleet.collaborators} has no {@code tabPrefix}: identity is matched on the exact
+     * {@code tab} alone, so only the exact-render check applies there, not the prefix check.
      *
      * @throws IllegalStateException when the fleet template or a profile {@code tabLabel} override
-     *                               can render as a configured lead tab or match a lead-tab prefix,
-     *                               or when two {@code fleet.leaders} entries carry the same exact
-     *                               {@code tab} (case-insensitively)
+     *                               can render as a configured lead or collaborator tab or match a
+     *                               lead-tab prefix, or when two entries — of either registry, or
+     *                               one of each — carry the same exact {@code tab}
+     *                               (case-insensitively)
      */
     public void validateLeadTabPrefixes() {
-        if (fleet == null || fleet.leaders().isEmpty()) {
+        if (fleet == null) {
             return;
         }
         List<String> bad = new ArrayList<>();
@@ -2722,11 +2753,32 @@ public record FleetConfig(
                         }
                     });
         });
+        fleet.collaborators().forEach((collabName, collaborator) -> {
+            if (collaborator == null) {
+                return;
+            }
+            String tab = collaborator.tab();
+            if (templateCanRenderAs(fleet.tabLabel(), tab)) {
+                bad.add("fleet.tabLabel=\"" + fleet.tabLabel() + "\" can render as the tab of "
+                        + "collaborator '" + collabName + "' (\"" + tab + "\")");
+            }
+            profiles().entrySet().stream()
+                    .map(Map.Entry::getKey)
+                    .sorted()
+                    .forEach(p -> {
+                        String label = profiles().get(p).tabLabel();
+                        if (templateCanRenderAs(label, tab)) {
+                            bad.add("profile '" + p + "' overrides tabLabel with \"" + label
+                                    + "\", which can render as the tab of collaborator '"
+                                    + collabName + "' (\"" + tab + "\")");
+                        }
+                    });
+        });
         if (!bad.isEmpty()) {
             throw new IllegalStateException("refusing to start: " + String.join("; ", bad)
-                    + ". Every member labelled that way would be read back as a lead and granted "
-                    + "spawn/stop/send on the whole fleet. Change one of the two so member tabs "
-                    + "and lead tabs cannot be confused.");
+                    + ". Every member labelled that way would be read back as a lead or "
+                    + "collaborator and granted that identity's authority. Change one of the two "
+                    + "so member tabs cannot be confused with a lead's or collaborator's tab.");
         }
 
         List<String> collisions = new ArrayList<>();
@@ -2749,13 +2801,49 @@ public record FleetConfig(
                 }
             }
         }
+        List<String> collabNames = fleet.collaborators().keySet().stream().sorted().toList();
+        for (int i = 0; i < collabNames.size(); i++) {
+            String nameA = collabNames.get(i);
+            Collaborator a = fleet.collaborators().get(nameA);
+            if (a == null || a.tab() == null || a.tab().isBlank()) {
+                continue;
+            }
+            for (int j = i + 1; j < collabNames.size(); j++) {
+                String nameB = collabNames.get(j);
+                Collaborator b = fleet.collaborators().get(nameB);
+                if (b == null || b.tab() == null || b.tab().isBlank()) {
+                    continue;
+                }
+                if (a.tab().equalsIgnoreCase(b.tab())) {
+                    collisions.add("collaborator '" + nameA + "' and collaborator '" + nameB
+                            + "' both use tab \"" + a.tab() + "\"");
+                }
+            }
+        }
+        for (String leadName : leadNames) {
+            Leader lead = fleet.leaders().get(leadName);
+            if (lead == null || lead.tab() == null || lead.tab().isBlank()) {
+                continue;
+            }
+            for (String collabName : collabNames) {
+                Collaborator collaborator = fleet.collaborators().get(collabName);
+                if (collaborator == null || collaborator.tab() == null
+                        || collaborator.tab().isBlank()) {
+                    continue;
+                }
+                if (lead.tab().equalsIgnoreCase(collaborator.tab())) {
+                    collisions.add("lead '" + leadName + "' and collaborator '" + collabName
+                            + "' both use tab \"" + lead.tab() + "\"");
+                }
+            }
+        }
         if (collisions.isEmpty()) {
             return;
         }
         throw new IllegalStateException("refusing to start: " + String.join("; ", collisions)
-                + ". Tab identity is matched exactly, so only one of two leads sharing a tab can "
-                + "ever be found — the other is silently unreachable. Give each lead its own "
-                + "exact tab.");
+                + ". Tab identity is matched exactly, so only one of two entries sharing a tab can "
+                + "ever be found — the other is silently unreachable. Give each lead and "
+                + "collaborator its own exact tab.");
     }
 
     private static boolean templateCanRenderAs(String template, String tab) {
@@ -2785,25 +2873,28 @@ public record FleetConfig(
 
     /**
      * Reject a profile that places its members by {@code "pane"} while any {@code fleet.leaders}
-     * entry names a {@code tab}. A pane-placed member lands inside the focused tab rather than its
-     * own, so it can land inside a lead's own labelled tab. {@link
-     * dev.ltms.fleet.herdr.LeadTabScanner} identifies a lead purely by that tab's label — it does
-     * not exclude the member space — so a member that ends up there would be read back as the lead
-     * and granted spawn/stop/send on the whole fleet.
+     * or {@code fleet.collaborators} entry names a {@code tab}. A pane-placed member lands inside
+     * the focused tab rather than its own, so it can land inside a lead's or collaborator's own
+     * labelled tab. {@link dev.ltms.fleet.herdr.LeadTabScanner} identifies a lead or collaborator
+     * purely by that tab's label — it does not exclude the member space — so a member that ends up
+     * there would be read back as that lead or collaborator and granted that identity's authority.
      *
-     * <p>Only a leader with a non-blank {@code tab} is in scope: one with no {@code tab} feeds
+     * <p>Only an entry with a non-blank {@code tab} is in scope: one with no {@code tab} feeds
      * nothing into {@link dev.ltms.fleet.herdr.LeadTabScanner}, so it creates no hazard here.
      *
      * @throws IllegalStateException when any {@code profiles:} entry is pane-placed while any
-     *                               {@code fleet.leaders} entry names a non-blank {@code tab}
+     *                               {@code fleet.leaders} or {@code fleet.collaborators} entry
+     *                               names a non-blank {@code tab}
      */
     public void validatePanePlacementAgainstLeadTabs() {
-        if (fleet == null || fleet.leaders().isEmpty()) {
+        if (fleet == null) {
             return;
         }
         boolean anyLeaderHasTab = fleet.leaders().values().stream()
                 .anyMatch(leader -> leader != null && leader.tab() != null && !leader.tab().isBlank());
-        if (!anyLeaderHasTab) {
+        boolean anyCollaboratorHasTab = fleet.collaborators().values().stream()
+                .anyMatch(c -> c != null && c.tab() != null && !c.tab().isBlank());
+        if (!anyLeaderHasTab && !anyCollaboratorHasTab) {
             return;
         }
         List<String> bad = new ArrayList<>();
@@ -2816,10 +2907,11 @@ public record FleetConfig(
             return;
         }
         throw new IllegalStateException("refusing to start: profile(s) " + bad
-                + " use placement: pane while fleet.leaders names a tab. A pane-placed member can "
-                + "land inside a lead's labelled tab and be read back as the lead, granted "
-                + "spawn/stop/send on the whole fleet. Set placement: tab for each named profile, "
-                + "or remove the tab from every fleet.leaders entry.");
+                + " use placement: pane while fleet.leaders or fleet.collaborators names a tab. A "
+                + "pane-placed member can land inside that labelled tab and be read back as the "
+                + "lead or collaborator, granted that identity's authority. Set placement: tab for "
+                + "each named profile, or remove the tab from every fleet.leaders and "
+                + "fleet.collaborators entry.");
     }
 
     /**
@@ -2926,8 +3018,14 @@ public record FleetConfig(
      * so duplicates are unrepresentable by construction once loaded — and {@link #load(Path)}
      * already rejects a duplicated slot name at parse time, before the map collapses.
      *
-     * @throws IllegalStateException when a slot names no profile or an unknown one, or when a lead
-     *                               can be neither found nor created, naming the offending entry
+     * <p>Also rejects a {@code fleet.collaborators} entry with no (or a blank) {@code tab}. A
+     * {@code profile}-less lead is still useful recognise-only — {@code tab} is the only field
+     * that matters to it either way. A collaborator carries no other field at all, so a blank
+     * {@code tab} leaves nothing for the entry to mean.
+     *
+     * @throws IllegalStateException when a slot names no profile or an unknown one, when a lead
+     *                               can be neither found nor created, or when a collaborator names
+     *                               no tab, naming the offending entry
      */
     public void validateMembers() {
         if (fleet == null) {
@@ -2965,6 +3063,16 @@ public record FleetConfig(
                         + "auto-launched, labelled) purely by its tab, so every entry must name one.");
             }
         });
+        fleet.collaborators().forEach((name, collaborator) -> {
+            if (collaborator == null) {
+                return;
+            }
+            if (collaborator.tab() == null || collaborator.tab().isBlank()) {
+                bad.add("fleet.collaborators." + name + " has no tab: — a collaborator is "
+                        + "recognised purely by its tab, and carries no other field, so every "
+                        + "entry must name one.");
+            }
+        });
         if (!bad.isEmpty()) {
             throw new IllegalStateException("refusing to start: " + String.join(" ", bad));
         }

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

@@ -689,7 +689,7 @@ public final class FleetMcp {
         if (!authorizationEnforced) {
             return null; // AuthorizationMode.UNENFORCED: authorization not enforced (fleetd #518)
         }
-        if (Authz.permits(caller, action, target)) {
+        if (Authz.permits(caller, action, target, Authz.NO_KNOWN_LEAD_OR_COLLABORATOR)) {
             if (action != Authz.Action.READ && action != Authz.Action.TASK_READ) {
                 AuditLog.allowed(caller, action, target); // reads would drown the trail
             }
@@ -1309,6 +1309,18 @@ public final class FleetMcp {
             }
             return text(json(m));
         }
+        if (caller.isCollaborator()) {
+            // A collaborator's name is its slot in the collaborators: registry; sessionId is its
+            // pane so a peer knows where to reach it. No leader key: a collaborator is not a
+            // primary for authorization, unlike a lead.
+            if (caller.name() != null) {
+                m.put("collaborator", caller.name());
+            }
+            if (caller.terminal() != null) {
+                m.put("sessionId", caller.terminal());
+            }
+            return text(json(m));
+        }
         if (!caller.isWorker()) {
             // CB-530: which lead, once more than one pane is configured as one. `role` deliberately
             // still reads "primary" — the fallback ladder in CLAUDE.md keys on it, and a lead IS a

fleetd/src/main/java/dev/ltms/fleet/rest/FleetApp.java

@@ -83,6 +83,18 @@ public final class FleetApp {
         };
     }
 
+    /**
+     * The second gate for {@code POST /sessions/{id}/message}: checked only when {@code turnId}
+     * is present and non-blank, against {@link Authz.Action#ANSWER}. A request with no {@code
+     * turnId} passes this gate unconditionally, without consulting {@code permit} at all, having
+     * already cleared the coarse {@link Authz.Action#SEND} grant checked ahead of it.
+     *
+     * @param permit reports whether the caller holds the named grant
+     */
+    static boolean answerGatePasses(String turnId, Predicate<Authz.Action> permit) {
+        return turnId == null || turnId.isBlank() || permit.test(Authz.Action.ANSWER);
+    }
+
     /** Default blocking window for a message; kept under typical HTTP idle timeouts. */
     private static final long DEFAULT_MESSAGE_TIMEOUT_MS = 25_000;
     private static final long MAX_MESSAGE_TIMEOUT_MS = 120_000;
@@ -254,6 +266,17 @@ public final class FleetApp {
         return app;
     }
 
+    /**
+     * The authorization decision behind {@link #allow}, taking the caller directly rather than
+     * pulling it from a servlet {@link Context} — unit-testable without fabricating a live
+     * request, the same reason {@code FleetMcp#denyFor} is split from {@code FleetMcp#deny}. The
+     * classifier is the same shared instance {@link #allow} would use, so a test calling this
+     * exercises the real production gate, not a test-supplied stand-in.
+     */
+    static boolean permitsFor(Principal caller, Authz.Action action, String target) {
+        return Authz.permits(caller, action, target, Authz.NO_KNOWN_LEAD_OR_COLLABORATOR);
+    }
+
     /**
      * Gate a handler on the CB-505 authorization table. Returns {@code true} when the request may
      * proceed; otherwise writes the error response and returns {@code false}.
@@ -267,7 +290,7 @@ public final class FleetApp {
             return true; // legacy: authorization not enforced
         }
         Principal caller = ctx.attribute(CALLER);
-        if (Authz.permits(caller, action, target)) {
+        if (permitsFor(caller, action, target)) {
             if (action != Authz.Action.READ && action != Authz.Action.METRICS
                     && action != Authz.Action.TASK_READ) {
                 AuditLog.allowed(caller, action, target); // reads would drown the trail
@@ -625,27 +648,31 @@ public final class FleetApp {
      *
      * <p>Two call shapes share this route, exactly as {@code fleet_send} does over MCP (see
      * {@code FleetMcp#sendAction}): a plain delivery to {@code id}, and -- when the body carries
-     * {@code turnId} -- resolving a worker's blocked question. The body is parsed before the
-     * authorization check so the right one of {@link Authz.Action#SEND}/{@link Authz.Action#ANSWER}
-     * reaches the gate; a body that fails to parse is treated as the plain shape for that check
-     * alone, and is rejected afterward exactly as before.
+     * {@code turnId} -- resolving a worker's blocked question. The coarse {@link
+     * Authz.Action#SEND} grant is checked first, before the body is read at all; only once that
+     * passes is the body parsed, and a present {@code turnId} is then checked again against
+     * {@link Authz.Action#ANSWER}. A body that fails to parse is rejected with 400 and reaches
+     * neither {@code messages.answer} nor {@code messages.send}.
      */
     private void sendMessage(Context ctx) {
         String id = ctx.pathParam("id");
+        if (!allow(ctx, routeAction("POST /sessions/{id}/message"), id)) {
+            return;
+        }
         JsonNode body;
         try {
             body = mapper.readTree(ctx.body());
         } catch (Exception e) {
             body = null;
         }
-        String turnId = body == null ? null : body.path("turnId").asText(null);
-        if (!allow(ctx, routeAction("POST /sessions/{id}/message", turnId), id)) {
-            return;
-        }
         if (body == null) {
             ctx.status(400).json(Map.of("error", "bad_request", "detail", "body must be JSON"));
             return;
         }
+        String turnId = body.path("turnId").asText(null);
+        if (!answerGatePasses(turnId, action -> allow(ctx, action, id))) {
+            return;
+        }
         String content = body.path("content").asText("");
         long timeout = body.path("timeoutMs").asLong(DEFAULT_MESSAGE_TIMEOUT_MS);
         boolean wait = body.path("wait").asBoolean(true); // default: block for the reply (CB-104)

fleetd/src/test/java/dev/ltms/fleet/auth/AuthzTest.java

@@ -14,6 +14,7 @@ class AuthzTest {
     private static final Principal ANON = Principal.anonymous();
     private static final Principal ARCH_DESIGN = Principal.architect("lead-designer", "term_design", 400);
     private static final Principal ARCH_OTHER = Principal.architect("reviewer", "term_review", 500);
+    private static final Principal COLLABORATOR = Principal.collaborator("ops", "term_collab", 600);
 
     @Test
     void anonymousIsAuthorizedForNothing() {
@@ -166,4 +167,87 @@ class AuthzTest {
         assertFalse(Authz.isUnauthenticated(WORKER_A));
         assertFalse(Authz.isUnauthenticated(PRIMARY));
     }
+
+    // ── the collaborator matrix ─────────────────────────────────────────────────────────────────
+
+    /**
+     * {@code SEND} for a collaborator is the one grant that is conditional rather than fixed:
+     * flipping only the classifier's answer for the target flips only this outcome.
+     */
+    @Test
+    void aCollaboratorMaySendOnlyWhenTheClassifierAcceptsTheTarget() {
+        assertTrue(Authz.permits(COLLABORATOR, SEND, "term_lead", target -> true),
+                "the classifier accepting the target must grant SEND");
+        assertFalse(Authz.permits(COLLABORATOR, SEND, "term_lead", target -> false),
+                "the classifier refusing the target must deny SEND");
+        assertFalse(Authz.permits(COLLABORATOR, SEND, "term_lead"),
+                "the real production classifier recognises no terminal yet, so SEND is refused today");
+    }
+
+    /**
+     * Control for the test above: every other action's result for a collaborator does not move
+     * when the classifier does. Only {@code SEND} is wired to it.
+     */
+    @Test
+    void theClassifierMovesOnlySendForACollaborator() {
+        for (Authz.Action a : Authz.Action.values()) {
+            if (a == SEND) {
+                continue;
+            }
+            assertEquals(
+                    Authz.permits(COLLABORATOR, a, "term_lead"),
+                    Authz.permits(COLLABORATOR, a, "term_lead", target -> true),
+                    a + " must not depend on the classifier at all");
+        }
+    }
+
+    @Test
+    void aCollaboratorMayReadAndScrapeMetrics() {
+        assertTrue(Authz.permits(COLLABORATOR, READ, null));
+        assertTrue(Authz.permits(COLLABORATOR, METRICS, null));
+    }
+
+    @Test
+    void aCollaboratorMayReplyAndAskOnlyAsItsOwnPane() {
+        assertTrue(Authz.permits(COLLABORATOR, REPLY, "term_collab"),
+                "its own pane is its own");
+        assertTrue(Authz.permits(COLLABORATOR, ASK, "term_collab"));
+
+        assertFalse(Authz.permits(COLLABORATOR, REPLY, "term_design"),
+                "a collaborator must not reply on another pane");
+        assertFalse(Authz.permits(COLLABORATOR, REPLY, null),
+                "an absent target must not pass the own-session rule");
+    }
+
+    /**
+     * Every action denied to a collaborator, asserted denied even when the classifier would
+     * accept any target — proving none of these is actually gated on the classifier at all.
+     */
+    @Test
+    void aCollaboratorIsDeniedLifecycleCoordinationAndTicketPolling() {
+        for (Authz.Action a : new Authz.Action[]{SPAWN, STOP, DRAIN, HANDOVER, ANSWER, COORD_SEND,
+                COORD_READ, TASK_READ}) {
+            assertFalse(Authz.permits(COLLABORATOR, a, "term_lead", target -> true),
+                    "a collaborator must not " + a + " even when the classifier accepts every target");
+        }
+    }
+
+    @Test
+    void aCollaboratorIsNotCountedAsPrimaryWorkerOrArchitect() {
+        assertFalse(COLLABORATOR.isPrimary());
+        assertFalse(COLLABORATOR.isWorker());
+        assertFalse(COLLABORATOR.isArchitect());
+        assertTrue(COLLABORATOR.isCollaborator());
+    }
+
+    /**
+     * A collaborator is never spawned, so it must not be enrolled in the presence map as an
+     * available member. Control: both a worker and an architect — which ARE spawned — still are.
+     */
+    @Test
+    void isSpawnedMemberIsFalseForACollaboratorButTrueForAWorkerAndAnArchitect() {
+        assertFalse(COLLABORATOR.isSpawnedMember());
+        assertTrue(WORKER_A.isSpawnedMember());
+        assertTrue(ARCH_DESIGN.isSpawnedMember());
+    }
 }

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

@@ -1000,6 +1000,273 @@ class FleetConfigTest {
                 "no primary.terminal pin ⇒ nothing registered, even with fleet.leaders configured");
     }
 
+    // ── fleetd #669: the collaborators registry ────────────────────────────────────────────────
+
+    /**
+     * {@code Fleet} is {@code @JsonIgnoreProperties(ignoreUnknown = true)}, so a config naming
+     * {@code fleet.collaborators.<name>.tab} loads with no exception whether or not the key is
+     * ever read into the object model. Asserting only "no exception" would pass both before and
+     * after the real fix, so this asserts the parsed value is actually reachable from the loaded
+     * {@code FleetConfig} — the one thing a vacuous "no exception" test cannot tell apart.
+     */
+    @Test
+    void collaboratorsBlockIsActuallyParsedNotSilentlyDropped(@TempDir Path dir) throws Exception {
+        Path f = dir.resolve("collaborators.yaml");
+        Files.writeString(f, """
+                bind:
+                  port: 8080
+                fleet:
+                  collaborators:
+                    reviewer-alex:
+                      tab: "collab: alex"
+                """);
+
+        FleetConfig cfg = FleetConfig.load(f);
+        assertEquals("collab: alex", cfg.fleet().collaborators().get("reviewer-alex").tab());
+    }
+
+    /** A collaborator carries no field other than {@code tab}, so a blank one is meaningless. */
+    @Test
+    void aCollaboratorWithNoTabRefusesToStart(@TempDir Path dir) throws Exception {
+        Path f = dir.resolve("useless-collaborator.yaml");
+        Files.writeString(f, """
+                bind:
+                  port: 8080
+                fleet:
+                  collaborators:
+                    ghost: {}
+                """);
+        FleetConfig cfg = FleetConfig.load(f);
+
+        IllegalStateException e = assertThrows(IllegalStateException.class, cfg::validateMembers);
+        assertTrue(e.getMessage().contains("ghost"), "the message must name the useless entry");
+        assertTrue(e.getMessage().contains("tab:"), "the message must say what is missing");
+    }
+
+    /** Control for {@link #aCollaboratorWithNoTabRefusesToStart}: a named tab loads cleanly. */
+    @Test
+    void aCollaboratorWithATabIsAllowed(@TempDir Path dir) throws Exception {
+        Path f = dir.resolve("named-collaborator.yaml");
+        Files.writeString(f, """
+                bind:
+                  port: 8080
+                fleet:
+                  collaborators:
+                    reviewer-alex:
+                      tab: "collab: alex"
+                """);
+        FleetConfig cfg = FleetConfig.load(f);
+
+        assertDoesNotThrow(cfg::validateMembers);
+    }
+
+    /**
+     * fleetd #669: the fleet-wide {@code tabLabel} template can render as a collaborator tab, the
+     * same hazard {@link #aFleetTabLabelTemplateThatCanRenderAsALeadTabRefusesToStart} covers on
+     * the lead side. Drives the fleet-wide branch directly, with no profile override involved.
+     */
+    @Test
+    void aFleetTabLabelTemplateThatCanRenderAsACollaboratorTabRefusesToStart(@TempDir Path dir)
+            throws Exception {
+        Path f = dir.resolve("collide-template-collaborator.yaml");
+        Files.writeString(f, """
+                bind:
+                  port: 8080
+                fleet:
+                  tabLabel: "al{profile}"
+                  collaborators:
+                    alex:
+                      tab: "alpha"
+                """);
+        FleetConfig cfg = FleetConfig.load(f);
+
+        IllegalStateException e =
+                assertThrows(IllegalStateException.class, cfg::validateLeadTabPrefixes);
+        assertTrue(e.getMessage().contains("fleet.tabLabel"));
+        assertTrue(e.getMessage().contains("alex"), "the message must name the offending collaborator");
+    }
+
+    /**
+     * fleetd #669: a member tabLabel that can render as a configured collaborator tab is the same
+     * hazard as the lead case above — a member labelled that way is read back as the collaborator.
+     */
+    @Test
+    void aProfileTabLabelOverrideMatchingACollaboratorTabRefusesToStart(@TempDir Path dir)
+            throws Exception {
+        Path f = dir.resolve("collide-collaborator.yaml");
+        Files.writeString(f, """
+                bind:
+                  port: 8080
+                profiles:
+                  gx10:
+                    tabLabel: "collab-tab"
+                fleet:
+                  collaborators:
+                    alex:
+                      tab: "collab-tab"
+                """);
+        FleetConfig cfg = FleetConfig.load(f);
+
+        IllegalStateException e =
+                assertThrows(IllegalStateException.class, cfg::validateLeadTabPrefixes);
+        assertTrue(e.getMessage().contains("gx10"), "the message must name the offending profile");
+        assertTrue(e.getMessage().contains("collab-tab"), "the message must name the offending label");
+    }
+
+    /** Control: a profile tabLabel that cannot render as the collaborator tab is allowed. */
+    @Test
+    void aProfileTabLabelThatCannotRenderAsACollaboratorTabIsAllowed(@TempDir Path dir)
+            throws Exception {
+        Path f = dir.resolve("ok-collaborator.yaml");
+        Files.writeString(f, """
+                bind:
+                  port: 8080
+                profiles:
+                  gx10:
+                    tabLabel: "worker-{profile}"
+                fleet:
+                  collaborators:
+                    alex:
+                      tab: "collab-tab"
+                """);
+        FleetConfig cfg = FleetConfig.load(f);
+
+        assertDoesNotThrow(cfg::validateLeadTabPrefixes);
+    }
+
+    /** fleetd #669: identity is matched on a collaborator's exact tab, so two sharing one are unreachable. */
+    @Test
+    void twoCollaboratorsSharingTheSameExactTabRefusesToStart(@TempDir Path dir) throws Exception {
+        Path f = dir.resolve("shared-collaborator-tab.yaml");
+        Files.writeString(f, """
+                bind:
+                  port: 8080
+                fleet:
+                  collaborators:
+                    alex:
+                      tab: "shared tab"
+                    sam:
+                      tab: "Shared Tab"
+                """);
+        FleetConfig cfg = FleetConfig.load(f);
+
+        IllegalStateException e =
+                assertThrows(IllegalStateException.class, cfg::validateLeadTabPrefixes);
+        assertTrue(e.getMessage().contains("alex"), "the message must name one offending collaborator");
+        assertTrue(e.getMessage().contains("sam"), "the message must name the other offending collaborator");
+    }
+
+    /** Control for {@link #twoCollaboratorsSharingTheSameExactTabRefusesToStart}: distinct tabs load cleanly. */
+    @Test
+    void twoCollaboratorsWithDistinctExactTabsAreAllowed(@TempDir Path dir) throws Exception {
+        Path f = dir.resolve("distinct-collaborator-tabs.yaml");
+        Files.writeString(f, """
+                bind:
+                  port: 8080
+                fleet:
+                  collaborators:
+                    alex:
+                      tab: "alex tab"
+                    sam:
+                      tab: "sam tab"
+                """);
+        FleetConfig cfg = FleetConfig.load(f);
+
+        assertDoesNotThrow(cfg::validateLeadTabPrefixes);
+    }
+
+    /**
+     * fleetd #669: a collaborator tab equal to a lead tab crosses a privilege boundary — the worst
+     * of the three new collisions, since only one of the two identities is ever found.
+     */
+    @Test
+    void aCollaboratorTabEqualToALeadTabRefusesToStart(@TempDir Path dir) throws Exception {
+        Path f = dir.resolve("lead-collaborator-collision.yaml");
+        Files.writeString(f, """
+                bind:
+                  port: 8080
+                fleet:
+                  leaders:
+                    opus:
+                      tab: "shared tab"
+                  collaborators:
+                    alex:
+                      tab: "Shared Tab"
+                """);
+        FleetConfig cfg = FleetConfig.load(f);
+
+        IllegalStateException e =
+                assertThrows(IllegalStateException.class, cfg::validateLeadTabPrefixes);
+        assertTrue(e.getMessage().contains("opus"), "the message must name the offending lead");
+        assertTrue(e.getMessage().contains("alex"), "the message must name the offending collaborator");
+    }
+
+    /** Control for {@link #aCollaboratorTabEqualToALeadTabRefusesToStart}: distinct tabs load cleanly. */
+    @Test
+    void aLeadAndACollaboratorWithDistinctTabsAreAllowed(@TempDir Path dir) throws Exception {
+        Path f = dir.resolve("lead-collaborator-ok.yaml");
+        Files.writeString(f, """
+                bind:
+                  port: 8080
+                fleet:
+                  leaders:
+                    opus:
+                      tab: "lead tab"
+                  collaborators:
+                    alex:
+                      tab: "collab tab"
+                """);
+        FleetConfig cfg = FleetConfig.load(f);
+
+        assertDoesNotThrow(cfg::validateLeadTabPrefixes);
+    }
+
+    /**
+     * fleetd #669: a pane-placed member can land in a collaborator's labelled tab exactly as it
+     * can land in a lead's — {@code validatePanePlacementAgainstLeadTabs()} must fire even when
+     * {@code fleet.leaders} is empty, which is the early-return the brief flagged as the bug.
+     */
+    @Test
+    void aPanePlacedProfileWithACollaboratorTabRefusesToStartEvenWithNoLeaders(@TempDir Path dir)
+            throws Exception {
+        Path f = dir.resolve("pane-hazard-collaborator.yaml");
+        Files.writeString(f, """
+                bind:
+                  port: 8080
+                profiles:
+                  gx10:
+                    placement: pane
+                fleet:
+                  collaborators:
+                    alex:
+                      tab: "collab: alex"
+                """);
+        FleetConfig cfg = FleetConfig.load(f);
+
+        IllegalStateException e = assertThrows(IllegalStateException.class,
+                cfg::validatePanePlacementAgainstLeadTabs);
+        assertTrue(e.getMessage().contains("gx10"), "the message must name the offending profile");
+    }
+
+    /** Control: a pane-placed profile with no lead or collaborator tab configured is allowed. */
+    @Test
+    void aPanePlacedProfileWithNoLeaderOrCollaboratorTabIsAllowed(@TempDir Path dir) throws Exception {
+        Path f = dir.resolve("pane-no-tab-at-all.yaml");
+        Files.writeString(f, """
+                bind:
+                  port: 8080
+                profiles:
+                  gx10:
+                    placement: pane
+                fleet:
+                  collaborators:
+                    alex: {}
+                """);
+
+        assertDoesNotThrow(() -> FleetConfig.load(f).validatePanePlacementAgainstLeadTabs(),
+                "a collaborator with no tab feeds nothing into the scanner, so pane placement is safe");
+    }
+
     // ── CB-548: the architects registry ────────────────────────────────────────────────────────
 
     @Test
@@ -1272,6 +1539,60 @@ class FleetConfigTest {
         assertEquals(Set.of("sonnet"), cfg.fleet().pool(MemberRole.REVIEWER).keySet());
     }
 
+    /**
+     * A duplicated name in {@code fleet.collaborators} is refused at parse time, like any other
+     * {@code fleet:} pool. See {@link #duplicateSlotNamesInOnePoolAreRejectedAtParseTime}.
+     */
+    @Test
+    void duplicateCollaboratorNamesAreRejectedAtParseTime(@TempDir Path dir) throws Exception {
+        Path f = dir.resolve("collaborator-dup.yaml");
+        Files.writeString(f, """
+                bind:
+                  port: 8080
+                fleet:
+                  collaborators:
+                    alex:
+                      tab: "collab: alex"
+                    alex:
+                      tab: "collab: alex, second"
+                """);
+
+        IllegalStateException e =
+                assertThrows(IllegalStateException.class, () -> FleetConfig.load(f));
+        assertTrue(e.getMessage().contains("alex"),
+                "the refusal names the duplicated entry, was: " + e.getMessage());
+        assertTrue(e.getMessage().contains("fleet.collaborators"),
+                "the refusal names the pool the duplicate is in, was: " + e.getMessage());
+    }
+
+    /**
+     * Control for {@link #duplicateCollaboratorNamesAreRejectedAtParseTime}: the same name reused
+     * across the collaborators registry and a member role pool is the role × profile matrix doing
+     * its job in the other pool, not a mistake — only a repeat within one pool loses an entry.
+     */
+    @Test
+    void theSameNameInCollaboratorsAndAnotherPoolIsNotADuplicate(@TempDir Path dir) throws Exception {
+        Path f = dir.resolve("collaborator-cross-pool.yaml");
+        Files.writeString(f, """
+                bind:
+                  port: 8080
+                profiles:
+                  sonnet:
+                    baseUrl: http://gx10.gw:8000
+                fleet:
+                  architects:
+                    alex:
+                      profile: sonnet
+                  collaborators:
+                    alex:
+                      tab: "collab: alex"
+                """);
+
+        FleetConfig cfg = assertDoesNotThrow(() -> FleetConfig.load(f));
+        assertEquals(Set.of("alex"), cfg.fleet().pool(MemberRole.ARCHITECT).keySet());
+        assertEquals(Set.of("alex"), cfg.fleet().collaborators().keySet());
+    }
+
     @Test
     void duplicateKeysOutsideTheFleetPoolsAreUnaffected(@TempDir Path dir) throws Exception {
         // The duplicate check is scoped to the fleet pools — a duplicate elsewhere is not this

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

@@ -97,6 +97,7 @@ class FleetMcpAuthzTest {
     private static final Principal WORKER_A = Principal.worker("term_a", 200);
     private static final Principal ANON = Principal.anonymous();
     private static final Principal ARCH_DESIGN = Principal.architect("lead-designer", "term_design", 400);
+    private static final Principal COLLABORATOR = Principal.collaborator("ops", "term_collab", 600);
 
     // --- the table, enforced on THIS path too ---------------------------------------------------
 
@@ -226,6 +227,19 @@ class FleetMcpAuthzTest {
                 "the caller IS authenticated — it is just not the right role");
     }
 
+    /**
+     * {@code denyFor} passes the real production classifier, not a test-supplied one — no
+     * terminal is recognised as a configured lead or collaborator, so a collaborator's SEND is
+     * refused over MCP.
+     */
+    @Test
+    void aCollaboratorMayNotSendOverMcpWithTheRealProductionClassifier() {
+        FleetMcp m = mcp(true);
+        McpSchema.CallToolResult denied = m.denyFor(COLLABORATOR, Authz.Action.SEND, "term_lead");
+        assertNotNull(denied, "no terminal is recognised as a lead or collaborator yet");
+        assertTrue(denied.isError());
+    }
+
     @Test
     void theLegacyConstructorLeavesTheGateOpen() {
         // The 22 pre-existing FleetMcpTest cases rely on no authorization being enforced.

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

@@ -1837,6 +1837,32 @@ class FleetMcpTest {
         assertTrue(out.contains("\"sessionId\":\"term_design\""), out);
     }
 
+    /**
+     * A collaborator reports its own role and name, never the {@code leader} key a lead gets —
+     * {@code role} already reads {@code "collaborator"}, so a {@code leader} key alongside it
+     * would be self-contradicting. Control: the same call shape fed a named lead must still carry
+     * {@code leader}, so this is not passing because the key stopped being emitted for everyone.
+     */
+    @Test
+    void whoamiReportsACollaboratorWithNoLeaderKeyButALeadStillGetsOne() {
+        FakeHerdr h = new FakeHerdr();
+        SessionManager sessions = sessionManager(h, "http://gx00.gw:8000", Set.of("gx00.gw"));
+
+        McpSchema.CallToolResult collabRes = FleetMcp.whoami(
+                Principal.collaborator("ops", "term_collab", 700), sessions);
+        assertNotEquals(Boolean.TRUE, collabRes.isError());
+        String collabOut = textOf(collabRes);
+        assertTrue(collabOut.contains("\"role\":\"collaborator\""), collabOut);
+        assertTrue(collabOut.contains("\"collaborator\":\"ops\""), collabOut);
+        assertTrue(collabOut.contains("\"sessionId\":\"term_collab\""), collabOut);
+        assertFalse(collabOut.contains("leader"), collabOut);
+
+        McpSchema.CallToolResult leadRes = FleetMcp.whoami(
+                Principal.leader("opus", "term_lead", 100), sessions);
+        String leadOut = textOf(leadRes);
+        assertTrue(leadOut.contains("\"leader\":\"opus\""), leadOut);
+    }
+
     /**
      * CB-548: an architect SEND delegates as its own pane (recording the per-target delegation) but
      * must NEVER become the legacy singleton "primary" fallback — the per-target map does not cure

fleetd/src/test/java/dev/ltms/fleet/rest/FleetAppAuthTest.java

@@ -1,8 +1,12 @@
 package dev.ltms.fleet.rest;
 
+import ch.qos.logback.classic.Level;
+import ch.qos.logback.classic.spi.ILoggingEvent;
+import com.fasterxml.jackson.databind.ObjectMapper;
 import dev.ltms.fleet.auth.CallerResolver;
 import dev.ltms.fleet.auth.Authz;
 import dev.ltms.fleet.auth.MemberRegistry;
+import dev.ltms.fleet.auth.Principal;
 import dev.ltms.fleet.config.FleetConfig;
 import dev.ltms.fleet.guard.SubscriptionGuard;
 import dev.ltms.fleet.herdr.AgentControl;
@@ -18,6 +22,7 @@ import dev.ltms.fleet.msg.Rendezvous;
 import dev.ltms.fleet.session.FakeWorktrees;
 import dev.ltms.fleet.session.SessionManager;
 import dev.ltms.fleet.member.ClaudeCodeLauncher;
+import dev.ltms.fleet.testing.CapturedLog;
 import io.javalin.Javalin;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.Test;
@@ -28,10 +33,13 @@ import java.net.http.HttpRequest;
 import java.net.http.HttpResponse;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.util.ArrayList;
 import java.util.LinkedHashSet;
+import java.util.List;
 import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
+import java.util.function.Predicate;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 import java.util.stream.Collectors;
@@ -144,6 +152,38 @@ class FleetAppAuthTest {
         assertEquals(Authz.Action.ANSWER, FleetApp.routeAction("POST /sessions/{id}/message", "turn-1"));
     }
 
+    /**
+     * fleetd #689: {@code answerGatePasses} is the second, conditional gate behind {@code
+     * sendMessage}'s coarse {@link Authz.Action#SEND} check. With the {@code ANSWER} grant denied,
+     * a {@code turnId}-bearing request is refused while a plain one still passes — and the denied
+     * permit is queried only for the {@code turnId} case, never for the plain one, which is what
+     * proves this is a genuinely separate, conditional check rather than the {@code SEND} check
+     * renamed or an unconditional call whose result is ignored. Flipping only the {@code ANSWER}
+     * grant to allowed then flips only the {@code turnId} shape's outcome.
+     */
+    @Test
+    void answerGatePassesOnlyWhenTurnIdAbsentOrAnswerGranted() {
+        List<Authz.Action> queried = new ArrayList<>();
+        Predicate<Authz.Action> denyAnswer = action -> {
+            queried.add(action);
+            return false;
+        };
+
+        assertFalse(FleetApp.answerGatePasses("turn-1", denyAnswer),
+                "ANSWER denied ⇒ the turnId shape is refused");
+        assertEquals(List.of(Authz.Action.ANSWER), queried,
+                "the ANSWER grant, specifically, must be the one consulted");
+
+        queried.clear();
+        assertTrue(FleetApp.answerGatePasses(null, denyAnswer),
+                "no turnId ⇒ the plain shape passes even though ANSWER is denied");
+        assertTrue(FleetApp.answerGatePasses("  ", denyAnswer), "a blank turnId is treated as absent");
+        assertEquals(List.of(), queried, "the plain shape must never consult the permit at all");
+
+        assertTrue(FleetApp.answerGatePasses("turn-1", action -> true),
+                "flipping only the ANSWER grant to allowed flips only the turnId shape's outcome");
+    }
+
     private static Set<String> routesTheServerRegisters() {
         try {
             String source = Files.readString(REST_SOURCE).lines()
@@ -163,6 +203,18 @@ class FleetAppAuthTest {
         }
     }
 
+    /**
+     * {@code permitsFor} is the exact decision {@link FleetApp#allow} makes, passing the real
+     * production classifier rather than a test-supplied one — no terminal is recognised as a
+     * configured lead or collaborator, so a collaborator's SEND is refused through the REST gate.
+     */
+    @Test
+    void aCollaboratorMayNotSendOverRestWithTheRealProductionClassifier() {
+        Principal collaborator = Principal.collaborator("ops", "term_collab", 700);
+        assertFalse(FleetApp.permitsFor(collaborator, Authz.Action.SEND, "term_lead"),
+                "no terminal is recognised as a lead or collaborator yet");
+    }
+
     // --- loopback-trust: the caller is the primary -------------------------------------------
 
     @Test
@@ -223,6 +275,92 @@ class FleetAppAuthTest {
                 "resolving another session's blocked question would be a worker escalating too");
     }
 
+    /**
+     * fleetd #689: a caller refused the coarse {@link Authz.Action#SEND} grant is refused on
+     * {@code SEND} specifically, even on the {@code turnId}-bearing shape that otherwise raises
+     * the check to {@link Authz.Action#ANSWER} — proving {@code turnId} was never read from the
+     * body before the refusal (reading it would have changed which action is named in the 403).
+     * The same caller refused with no body at all gets the identical detail, which could not hold
+     * if the decision depended on anything read from the body. Control: a caller who IS granted
+     * reaches past the gate and the body is used normally.
+     */
+    @Test
+    void aDeniedCallerIsRefusedOnSendEvenWithATurnIdBodyAndNeverReadsTheBody() throws Exception {
+        int workerPort = start(FakeHerdr.WORKER_PID, false, null); // denied: not primary/architect
+
+        HttpResponse<String> withTurnId = send(workerPort, "POST", "/sessions/term_b/message",
+                "{\"turnId\":\"turn-1\",\"content\":\"hi\"}", null);
+        assertEquals(403, withTurnId.statusCode());
+        assertTrue(withTurnId.body().contains("may not SEND"),
+                "the SEND check must be the one that fired, not ANSWER — ANSWER would only be "
+                        + "reachable by having already read turnId out of the body");
+
+        HttpResponse<String> noBody = send(workerPort, "POST", "/sessions/term_b/message", null, null);
+        assertEquals(403, noBody.statusCode());
+        assertTrue(noBody.body().contains("may not SEND"),
+                "refused identically with no body at all — the refusal cannot depend on body content");
+
+        // Control: a primary IS granted SEND, so the same turnId body is read and acted on —
+        // reaching messages.answer, which reports this unknown turnId as a stale one.
+        int primaryPort = start(999_999, false, null);
+        HttpResponse<String> granted = send(primaryPort, "POST", "/sessions/term_b/message",
+                "{\"turnId\":\"turn-1\",\"content\":\"hi\"}", null);
+        assertEquals(409, granted.statusCode());
+        assertTrue(granted.body().contains("stale_turn"), "a granted caller's body IS read and acted on");
+    }
+
+    /**
+     * fleetd #689 (ticket comment 18353): the only place {@code sendMessage}'s call to {@code
+     * answerGatePasses} is observable is the audit trail — {@code allow()} logs an {@code
+     * "allowed"} entry for every granted action except {@code READ}/{@code METRICS}/{@code
+     * TASK_READ}, and {@code ANSWER} is none of those. A granted {@code turnId} request must
+     * therefore log both a {@code SEND} and an {@code ANSWER} entry; a granted plain request must
+     * log {@code SEND} alone. A unit test of the extracted helper pins the helper; this pins the
+     * call site — deleting the {@code answerGatePasses} call from {@code sendMessage} leaves the
+     * helper's own test green but turns this one red.
+     */
+    @Test
+    void aGrantedTurnIdRequestAuditsBothSendAndAnswerButAPlainRequestAuditsSendAlone() throws Exception {
+        int port = start(999_999, false, null); // primary: granted both SEND and ANSWER
+        ObjectMapper mapper = new ObjectMapper();
+
+        try (CapturedLog audit = CapturedLog.at("audit", Level.INFO)) {
+            send(port, "POST", "/sessions/term_b/message",
+                    "{\"turnId\":\"turn-1\",\"content\":\"hi\"}", null);
+
+            List<String> allowed = allowedActions(audit, mapper);
+            assertTrue(allowed.contains("SEND"),
+                    "a turnId request must still clear the coarse SEND grant first");
+            assertTrue(allowed.contains("ANSWER"),
+                    "a turnId request must ALSO clear the ANSWER grant — this is the call site itself");
+        }
+
+        try (CapturedLog audit = CapturedLog.at("audit", Level.INFO)) {
+            send(port, "POST", "/sessions/term_b/message",
+                    "{\"content\":\"hi\",\"timeoutMs\":50}", null);
+
+            List<String> allowed = allowedActions(audit, mapper);
+            assertEquals(List.of("SEND"), allowed,
+                    "a plain request must log SEND and nothing else — ANSWER is conditional on "
+                            + "turnId, not something every request happens to log");
+        }
+    }
+
+    private static List<String> allowedActions(CapturedLog audit, ObjectMapper mapper) {
+        return audit.events().stream()
+                .map(ILoggingEvent::getFormattedMessage)
+                .map(line -> {
+                    try {
+                        return mapper.readTree(line);
+                    } catch (Exception e) {
+                        throw new AssertionError("audit line is not valid JSON: " + line, e);
+                    }
+                })
+                .filter(n -> "allowed".equals(n.path("outcome").asText()))
+                .map(n -> n.path("action").asText())
+                .toList();
+    }
+
     // --- token mode ---------------------------------------------------------------------------
 
     @Test

fleetd/src/test/java/dev/ltms/fleet/rest/FleetAppTest.java

@@ -675,6 +675,26 @@ class FleetAppTest {
         assertEquals(400, postMessage(port, "{}").statusCode());
     }
 
+    /**
+     * fleetd #689: a body that fails to parse is rejected with 400 before {@code turnId} is ever
+     * read from it, so it reaches neither {@code messages.answer} (which needs a {@code turnId})
+     * nor {@code messages.send} — confirmed here for {@code send} by the fake agent's idle status,
+     * which would otherwise make an immediate {@code agent.prompt} delivery observable.
+     */
+    @Test
+    void malformedBodyReturns400AndNeverReachesSendOrAnswer() throws Exception {
+        FakeHerdr herdr = new FakeHerdr().agentStatus("idle"); // idle ⇒ send would deliver right away if reached
+        int port = start(herdr, "http://gx00.gw:8000", Set.of("gx00.gw"));
+
+        HttpResponse<String> res = postMessage(port, "not json at all");
+        assertEquals(400, res.statusCode());
+        JsonNode err = mapper.readTree(res.body());
+        assertEquals("bad_request", err.get("error").asText());
+        assertEquals("body must be JSON", err.get("detail").asText());
+        assertFalse(herdr.called("agent.prompt"),
+                "a malformed body must never reach messages.send's delivery");
+    }
+
     @Test
     void sessionStatusReportsLiveAgentStatus() throws Exception {
         FakeHerdr herdr = new FakeHerdr().agentStatus("blocked");

scripts/config-edit.sh

@@ -213,6 +213,17 @@ map_masked_lines() {
   done < "$file"
 }
 
+# Masks every `scheme://user:pass@host` userinfo on one line of text, replacing just that
+# userinfo with `<redacted>` and leaving the rest of the line untouched, byte for byte. The
+# pattern stops at the first `/`, whitespace, or `@` reached after `://` — a URI's userinfo
+# component cannot contain any of those three characters — so a URI with no userinfo, followed
+# later on the same line by an unrelated `@`, never matches. The `g` flag matters: a line can
+# carry more than one URI. Shared by every caller that prints a line which may hold a
+# credentialed URI, so the bound lives in exactly one place.
+mask_url_userinfo() {
+  printf '%s\n' "$1" | sed -E 's#://[^@/[:space:]]*@#://<redacted>@#g'
+}
+
 redact() {
   local old_file="$1" new_file="$2"
   local line prefix content indent lead key old_line=0 new_line=0 in_hunk=0
@@ -270,7 +281,7 @@ redact() {
         continue
       fi
     fi
-    printf '%s\n' "$line" | sed -E 's#://[^@]*@#://<redacted>@#g'
+    mask_url_userinfo "$line"
   done
   [ "$saved_nocasematch" = 1 ] || shopt -u nocasematch
 }
@@ -583,7 +594,7 @@ install_candidate() {
 # Masks basic-auth userinfo (scheme://user:pass@host) in a daemon verdict line before it reaches
 # the terminal.
 mask_verdict_userinfo() {
-  printf '%s\n' "$1" | sed -E 's#://[^@/[:space:]]*@#://<redacted>@#g'
+  mask_url_userinfo "$1"
 }
 
 # Prints the literal command the operator (or a test) can run to restore the backup by hand — the

scripts/test-config-edit.sh

@@ -233,6 +233,66 @@ test_redaction_holds() {
   assert_contains "weight" "$RUN_OUTPUT" "a diff must have been demonstrably printed at all"
 }
 
+# redact()'s key-name filter only inspects the KEY, so a diff line whose key does not match
+# TOKEN|SECRET|PASSWORD|PASSWD|PASSPHRASE|CREDENTIAL|URI|_KEY still reaches the final userinfo
+# sed even when its VALUE holds a credentialed URI. "note" is not a sensitive key name, so this
+# line must fall all the way through to that sed, not the earlier whole-value branch. The
+# trailing prose on both sides of the userinfo is a positive control: it proves the line reached
+# the userinfo sed (which touches only the userinfo) rather than the earlier branch (which would
+# have replaced the whole value with a bare "<redacted>" and dropped the prose).
+test_diff_line_userinfo_is_masked_with_positive_control() {
+  local dir
+  dir="$(new_fixture)"
+
+  start_run "$dir" 5 --set '.profiles.sonnet.note=see amqp://alice:wonderland@rabbit.local:5672/vhost for details'
+  sleep 1
+  printf 'config reloaded\n' >> "$dir/fleetd.out"
+  collect_run "$dir"
+
+  assert_equals 0 "$RUN_RC" "diff-userinfo-case reload exit code"
+  assert_not_contains "alice:wonderland" "$RUN_OUTPUT" "the userinfo must never reach the output"
+  assert_contains "amqp://<redacted>@rabbit.local:5672/vhost" "$RUN_OUTPUT" \
+    "the userinfo must be MASKED, not deleted — the rest of the value must survive"
+  assert_contains "note:" "$RUN_OUTPUT" "the key name must still reach the output"
+  assert_contains "see " "$RUN_OUTPUT" "prose BEFORE the userinfo must still reach the output"
+  assert_contains "for details" "$RUN_OUTPUT" "prose AFTER the userinfo must still reach the output"
+}
+
+# A diff line can hold a URL with no userinfo, followed later on the same line by an unrelated @
+# (free text in a string value, for example an email address). The line must pass through the
+# userinfo sed byte for byte: the match must stop at the end of the URL and must not treat the
+# later @ as a second userinfo delimiter.
+test_diff_line_uri_without_userinfo_survives_a_later_at_sign() {
+  local dir
+  dir="$(new_fixture)"
+
+  start_run "$dir" 5 --set '.profiles.sonnet.note2=see https://docs.local/guide and mail ops@example.com'
+  sleep 1
+  printf 'config reloaded\n' >> "$dir/fleetd.out"
+  collect_run "$dir"
+
+  assert_equals 0 "$RUN_RC" "diff-no-userinfo-with-later-at-sign reload exit code"
+  assert_contains "note2: see https://docs.local/guide and mail ops@example.com" "$RUN_OUTPUT" \
+    "a URL with no userinfo plus a later @ on the same line must pass through byte for byte"
+}
+
+# Two credentialed URIs on one diff line must both be masked — the g flag matters.
+test_diff_line_masks_multiple_userinfo_with_g_flag() {
+  local dir
+  dir="$(new_fixture)"
+
+  start_run "$dir" 5 --set '.profiles.sonnet.note3=amqp://u1:p1@host1/vhost1 and amqp://u2:p2@host2/vhost2'
+  sleep 1
+  printf 'config reloaded\n' >> "$dir/fleetd.out"
+  collect_run "$dir"
+
+  assert_equals 0 "$RUN_RC" "diff-two-userinfo-on-one-line reload exit code"
+  assert_not_contains "u1:p1" "$RUN_OUTPUT" "the first userinfo must never reach the output"
+  assert_not_contains "u2:p2" "$RUN_OUTPUT" "the second userinfo must never reach the output"
+  assert_contains "amqp://<redacted>@host1/vhost1" "$RUN_OUTPUT" "the first URI must be masked"
+  assert_contains "amqp://<redacted>@host2/vhost2" "$RUN_OUTPUT" "the second URI must be masked"
+}
+
 # ------------------------------------------------------- acceptance criterion 9: forgotten value
 # `--set .a.b=` is a plausible typo (the value simply forgotten), and it must be refused outright
 # rather than silently nulling the field — a null numeric field falls back to its default, which
@@ -753,6 +813,12 @@ echo "== acceptance criterion 6: the marker works =="
 test_marker_skips_lines_before_it
 echo "== acceptance criterion 7 (+13: redaction is proven to have run) =="
 test_redaction_holds
+echo "== fleetd #692: a diff line's userinfo is masked, rest of the value survives =="
+test_diff_line_userinfo_is_masked_with_positive_control
+echo "== fleetd #692: a diff line's URI with no userinfo survives a later @ in the line =="
+test_diff_line_uri_without_userinfo_survives_a_later_at_sign
+echo "== fleetd #692: two userinfo URIs on one diff line are both masked =="
+test_diff_line_masks_multiple_userinfo_with_g_flag
 echo "== acceptance criterion 9: a forgotten value refuses and installs nothing =="
 test_forgotten_value_refuses_and_installs_nothing
 echo "== acceptance criterion 10: an explicit clear writes a bare null =="