fleetd #296: close panes on failed spawn

fleetd/src/main/java/dev/ltms/fleet/member/HerdrPeerLauncher.java

@@ -697,7 +697,20 @@ public abstract class HerdrPeerLauncher implements PeerLauncher {
         if (paneId == null) {
             throw new IllegalStateException("pane.split returned no pane — cannot start a peer");
         }
-        Agent peer = startUniquelyNamed(cfg, argv, paneId).agent();
+        Agent peer;
+        try {
+            peer = startUniquelyNamed(cfg, argv, paneId).agent();
+        } catch (RuntimeException e) {
+            // The peer never started — don't leave the pane we just created orphaned.
+            // Best-effort cleanup; never let it mask the real spawn failure.
+            try {
+                stop(paneId);
+            } catch (RuntimeException cleanup) {
+                log.warn("failed to close orphaned pane {} after spawn error: {}",
+                        paneId, cleanup.getMessage());
+            }
+            throw e;
+        }
         log.info("{} started pane={} terminal={}", namePrefix, peer.paneId(), peer.terminalId());
         return peer;
     }
@@ -996,7 +1009,8 @@ public abstract class HerdrPeerLauncher implements PeerLauncher {
      * that gap: it stops waiting immediately (never burns the rest of the timeout), runs the same
      * teardown the timeout path below runs, and throws with a message that says the backend exited
      * rather than that the pane was slow. Any other {@link HerdrException} still propagates
-     * unchanged — this gate does not know how to recover from it.
+     * unchanged — this gate does not interpret or recover from it, but it still closes the pane
+     * it opened before handing the exception to its caller.
      */
     private void waitUntilInjectableOrThrow(String paneId) {
         long start = nowMillis.getAsLong();
@@ -1010,7 +1024,15 @@ public abstract class HerdrPeerLauncher implements PeerLauncher {
                 if (isAlreadyGone(e)) {
                     failFastOnGoneBackend(paneId, e, nowMillis.getAsLong() - start);
                 }
-                throw e; // any other herdr failure is not ours to interpret — let it propagate
+                // This gate must not interpret an unrelated herdr error, but the caller does not
+                // receive paneId when spawn throws. Close the pane here before propagating e unchanged.
+                try {
+                    stop(paneId);
+                } catch (RuntimeException cleanup) {
+                    log.warn("failed to close orphaned pane {} after readiness-gate error: {}",
+                            paneId, cleanup.getMessage());
+                }
+                throw e;
             }
             lastStatus = sample.status();
             if (lastStatus.injectable() || refinedInjectable(paneId, sample)) {

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

@@ -40,6 +40,7 @@ public final class FakeHerdr implements HerdrClient {
     private final Map<String, List<String>> extraTabs = new LinkedHashMap<>();
     private int agentNameTakenFor = 0;
     private int agentPaneBusyFor = 0;
+    private String agentStartErrorCode = null;
     private int workerTabPaneCount = 1;
     private String paneCloseErrorCode = null;
     private final Map<String, String> paneCloseErrorCodeFor = new ConcurrentHashMap<>();
@@ -84,6 +85,12 @@ public final class FakeHerdr implements HerdrClient {
         return this;
     }
 
+    /** Make every {@code agent.start} call fail with this herdr error code. */
+    public FakeHerdr agentStartFailsWith(String code) {
+        this.agentStartErrorCode = code;
+        return this;
+    }
+
     /** Make the worker tab (w9:t2) report this many panes in {@code tab.list} (default 1). */
     public FakeHerdr withWorkerTabPaneCount(int n) {
         this.workerTabPaneCount = n;
@@ -311,6 +318,10 @@ public final class FakeHerdr implements HerdrClient {
                                             + required + "`", "invalid_request", null);
                         }
                     }
+                    if (agentStartErrorCode != null) {
+                        throw new HerdrException("herdr error [" + agentStartErrorCode + "]: agent.start failed",
+                                agentStartErrorCode, null);
+                    }
                     long starts = calls.stream().filter(c -> c.method().equals("agent.start")).count();
                     if (starts <= agentPaneBusyFor) {
                         throw new HerdrException(

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

@@ -1165,7 +1165,8 @@ class ClaudeCodeLauncherTest {
     @Test
     void spawnLetsAnUnrelatedHerdrErrorPropagateUnchanged() {
         // Fix 1 must only special-case a "*_not_found" answer. Any other herdr failure keeps
-        // propagating as-is — this gate does not know how to recover from it.
+        // propagating as-is — this gate does not know how to recover from it. The pane still needs
+        // closing because spawn throws before it can return the pane id to a caller that could stop it.
         FakeHerdr herdr = new FakeHerdr();
         herdr.agentStatus("unknown");
         herdr.agentGetFailsWithAfter(0, "internal_error");
@@ -1182,8 +1183,27 @@ class ClaudeCodeLauncherTest {
                 () -> svc.spawn(new SpawnRequest(null, null, null)));
 
         assertEquals("internal_error", ex.code());
-        assertEquals(0, paneCloseCount(herdr, "w9:pRoot_1"),
-                "an error this gate does not recognize is not this gate's teardown to run");
+        assertEquals(1, paneCloseCount(herdr, "w9:pRoot_1"),
+                "the unchanged error leaves spawn without a pane id, so this gate closes its orphaned pane");
+    }
+
+    @Test
+    void panePlacementClosesTheSplitPaneWhenAgentStartFails() {
+        FakeHerdr herdr = new FakeHerdr().agentStartFailsWith("internal_error");
+        FleetConfig.Profile cfg = new FleetConfig.Profile(
+                "ltms-local", "http://gx00.gw:8000", "coder", null, "FLEETD_WORKER_TOKEN",
+                List.of("claude"), "pane", "fleetd-workers", "w #{n}", null, null, null);
+        ClaudeCodeLauncher svc = new ClaudeCodeLauncher(
+                new AgentControl(herdr), new WorkspaceControl(herdr),
+                new SubscriptionGuard(Set.of("gx00.gw")), Map.of(cfg.profile(), cfg), cfg.profile(), _ -> null);
+
+        dev.ltms.fleet.herdr.HerdrException ex = assertThrows(
+                dev.ltms.fleet.herdr.HerdrException.class,
+                () -> svc.spawn(new SpawnRequest(null, null, null)));
+
+        assertEquals("internal_error", ex.code(), "agent.start failure propagates unchanged");
+        assertEquals(1, paneCloseCount(herdr, "w1:pSplit"),
+                "the pane split for a peer that never starts is closed instead of left orphaned");
     }
 
     // --- fleetd #176 fix 2: corroborated UNKNOWN refinement --------------------------------------