CB-571: make PeerHandle.charterReceipt() abstract, fix OpenCode adapter's silent null

SessionAwareHandle wrapped the base's WorkerHandle but never overrode
charterReceipt(), so it silently inherited the interface default (null)
while the real receipt sat on its delegate. sol/terra never got a
charterSource/charterSha256 roster row.

Deletes the default so every PeerHandle must answer explicitly; the
compiler now catches this class of gap instead of a roster field
quietly going missing.

bridged/src/test/java/dev/ltms/bridged/member/CompositePeerLauncherTest.java

@@ -10,6 +10,7 @@ import dev.ltms.bridged.herdr.AgentControl;
 import dev.ltms.bridged.herdr.FakeHerdr;
 import dev.ltms.bridged.herdr.WorkspaceControl;
 import dev.ltms.bridged.peer.Capability;
+import dev.ltms.bridged.peer.CharterReceipt;
 import dev.ltms.bridged.peer.MemberRole;
 import dev.ltms.bridged.peer.PeerHandle;
 import dev.ltms.bridged.peer.PeerLauncher;
@@ -93,6 +94,7 @@ class CompositePeerLauncherTest {
                 @Override public String id() { return "pane-" + p; }
                 @Override public String terminalId() { return "term-" + p; }
                 @Override public String profile() { return p; }
+                @Override public CharterReceipt charterReceipt() { return null; }
             };
         }
 

bridged/src/test/java/dev/ltms/bridged/member/OpenCodeLauncherTest.java

@@ -7,6 +7,7 @@ import dev.ltms.bridged.herdr.AgentControl;
 import dev.ltms.bridged.herdr.FakeHerdr;
 import dev.ltms.bridged.herdr.WorkspaceControl;
 import dev.ltms.bridged.peer.Capability;
+import dev.ltms.bridged.peer.CharterReceipt;
 import dev.ltms.bridged.peer.PeerHandle;
 import dev.ltms.bridged.peer.PeerUnreachableException;
 import dev.ltms.bridged.peer.SpawnRequest;
@@ -322,6 +323,26 @@ class OpenCodeLauncherTest {
         assertFalse(herdr.called("agent.get"), "no polling when the gate is disabled");
     }
 
+    @Test
+    void handleCarriesTheRealCharterReceiptNotTheInterfaceDefault(@TempDir Path root) {
+        // The base's WorkerHandle computes a real CharterReceipt (CB-571), but the opencode adapter
+        // wraps it in SessionAwareHandle for lazy session discovery. Before this fix that decorator
+        // did not override charterReceipt(), so it silently inherited PeerHandle's `null` default
+        // and the real receipt sitting on its delegate was lost.
+        FakeHerdr herdr = new FakeHerdr();
+        BridgedConfig.Fleet fleet = new BridgedConfig.Fleet(Map.of(), Map.of(), Map.of(), Map.of(),
+                Map.of("dev", "role rule"), null);
+        PeerHandle handle = service(herdr, root,
+                opencodeCfg("google/gemini-2.5-pro", "http://127.0.0.1:8765/mcp", null), () -> fleet)
+                .spawn(new SpawnRequest(null, null, null));
+
+        assertNotNull(handle.charterReceipt(),
+                "an opencode spawn's charterReceipt() must not silently be null");
+        String composed = "role rule\n\n" + HerdrPeerLauncher.REPLY_CHARTER;
+        assertEquals(CharterReceipt.digestOf(composed), handle.charterReceipt().charterSha256(),
+                "the receipt on the wrapped handle must match the exact composed charter bytes");
+    }
+
     // --- CB-508: pinned OpenAI-compatible endpoint (e.g. a local vLLM) ---------------------------
 
     /** A profile with a baseUrl but no model provider prefix cannot be resolved — fail loudly. */