Merge CB-564: give every silent failure path a voice

The bridge cannot classify what it never emits. Fleet-health monitoring —
detect a wedged member, decide, escalate — is blocked on that, so this is the
foundation rather than the feature.

A survey of Injector, CompletionResolver, StatusPoller, SessionManager,
SessionReaper and MessageService found six conditions that ended a member's
usefulness while saying nothing useful:

  * Injector.drop()             — worker gone, queue cleared: SILENT
  * CompletionResolver.fail()   — "via turn-stall fallback" at DEBUG, no reason
  * SessionManager.onFailed()   — "session marked failed" at DEBUG, no stage
  * SessionManager.reapIdle()   — indistinguishable from any other release
  * SessionManager.acquire()    — spawn failure rethrown with no log at all
  * MessageService.abandon()    — failed a caller's request at DEBUG

The first two are the exact phrases that misled the CB-560 diagnosis: both name
a symptom and neither names a cause. They are now WARN and carry the reason,
the stage, and the counts.

Conditions already loud were left alone, and so were two by-design timeouts in
MessageService — an async model exists precisely for those, and promoting them
would turn healthy operation into noise.

Behaviour is unchanged: every edit is a log statement.

Merge note: the recycle test deleted by CB-565 conflicted with a test added
here. Resolved by keeping the new onTurnFailed assertion and dropping the
recycle test, which tests a method that no longer exists.

bridged/src/main/java/dev/ltms/bridged/inject/CompletionResolver.java

@@ -214,7 +214,7 @@ public final class CompletionResolver implements TurnListener {
         }
         if (rendezvous.resolveFailure(waiter, reason)) {
             inFlight.remove(target, turn);
-            log.debug("failed send to {} via turn-stall fallback", target);
+            log.warn("failing send to {} via turn-stall fallback: {}", target, reason);
         }
     }
 

bridged/src/main/java/dev/ltms/bridged/inject/Injector.java

@@ -402,6 +402,10 @@ public final class Injector {
             t.awaitingPostTurnPickup = false;
             t.postTurnObserved = false;
         }
+        log.warn("{} is gone, dropping its queue: {} message(s) failed{}; cause: {}", target,
+                pending.size(),
+                hadDeliveredTurn ? " (including one turn already in flight whose completion was never confirmed)" : "",
+                cause.getMessage());
         forget.accept(target); // the worker is gone — clear its readiness/presence too (CB-114)
         for (Pending p : pending) {
             p.delivered().completeExceptionally(cause);

bridged/src/main/java/dev/ltms/bridged/msg/MessageService.java

@@ -277,7 +277,7 @@ public final class MessageService {
         }
         boolean failed = rendezvous.resolveFailure(waiter, reason);
         if (failed) {
-            log.debug("abandoned send to {}: {}", target, reason);
+            log.warn("abandoning the blocked send to {}: {}", target, reason);
         }
         return failed;
     }

bridged/src/main/java/dev/ltms/bridged/session/SessionManager.java

@@ -140,7 +140,13 @@ public final class SessionManager implements TurnListener {
             // to pick the profile out of that role's pool and to label the tab; a role kept only on
             // the MemberSession is recorded after the spawn it was supposed to steer.
             SpawnRequest req = new SpawnRequest(profile, requestedCwd, callerCwd, null, null, memberRole);
-            PeerHandle handle = launcher.spawn(req);
+            PeerHandle handle;
+            try {
+                handle = launcher.spawn(req);
+            } catch (RuntimeException e) {
+                log.warn("spawn failed for profile={} role={}: {}", profile, memberRole, e.getMessage());
+                throw e;
+            }
             String resolvedProfile = resolveProfile(handle, profile);
             String cwd = launcher.effectiveCwd(new SpawnRequest(resolvedProfile, requestedCwd, callerCwd));
             long now = nowNanos.getAsLong();
@@ -312,6 +318,8 @@ public final class SessionManager implements TurnListener {
             worktrees.overlayParity(repoRoot, path, launcher.parityOverlay(preResolvedProfile));
             handle = launcher.spawn(new SpawnRequest(profile, path, callerCwd, null, null, memberRole));
         } catch (RuntimeException e) {
+            log.warn("spawn failed for profile={} role={} branch={} path={}: {}",
+                    preResolvedProfile, memberRole, branch, path, e.getMessage());
             if (path != null) {
                 try {
                     worktrees.remove(repoRoot, path);
@@ -484,8 +492,10 @@ public final class SessionManager implements TurnListener {
         MemberSession current = findByTerminal(target);
         if (current == null) return;
         if (current.state() == MemberSession.State.RELEASED) return;
+        MemberSession.State priorState = current.state();
         if (replace(current, current.withState(MemberSession.State.FAILED))) {
-            log.debug("session marked failed terminal={} pane={}", target, current.paneId());
+            log.warn("member terminal={} pane={} can no longer be delegated to: its turn never resolved "
+                    + "(was {} when it failed)", target, current.paneId(), priorState);
         }
     }
 
@@ -501,7 +511,11 @@ public final class SessionManager implements TurnListener {
             if (s.state() != MemberSession.State.READY && s.state() != MemberSession.State.DONE) {
                 continue;
             }
-            if (now - s.lastActivityAtNanos() > idleTtlNanos) {
+            long idleNanos = now - s.lastActivityAtNanos();
+            if (idleNanos > idleTtlNanos) {
+                log.debug("reaping idle session terminal={} pane={}: idle {}s exceeds the {}s ttl",
+                        s.terminalId(), s.paneId(), TimeUnit.NANOSECONDS.toSeconds(idleNanos),
+                        TimeUnit.NANOSECONDS.toSeconds(idleTtlNanos));
                 release(s.paneId());
                 reaped++;
             }