CB-307 Increment 1: PrimaryRegistry + config + wiring

- PrimaryRegistry: thread-safe single-slot registry with pin support
- Primary config record (last positional, like Broker)
- Wire capture in BridgeMcp (bridge_send and bridge_spawn handlers)
- Construct PrimaryRegistry in Bridged.main
- Tests: PrimaryRegistryTest + BridgedConfigTest primary config cases

bridged/src/test/java/dev/ltms/bridged/config/BridgedConfigTest.java

@@ -125,4 +125,39 @@ class BridgedConfigTest {
         assertNotNull(cfg.broker());
         assertFalse(cfg.broker().isConfigured(), "an empty uri must not enable AMQP");
     }
+
+    @Test
+    void absentPrimaryBlockLeavesPrimaryNull(@TempDir Path dir) throws Exception {
+        Path f = dir.resolve("no-primary.yaml");
+        Files.writeString(f, "bind:\n  port: 8080\n");
+
+        BridgedConfig cfg = BridgedConfig.load(f);
+        assertNull(cfg.primary(), "no primary: block → null → connection-derived identity");
+    }
+
+    @Test
+    void primaryBlockWithTerminalPinsIdentity(@TempDir Path dir) throws Exception {
+        Path f = dir.resolve("primary-pinned.yaml");
+        Files.writeString(f, """
+                bind:
+                  port: 8080
+                primary:
+                  terminal: term_fixed
+                """);
+
+        BridgedConfig cfg = BridgedConfig.load(f);
+        assertNotNull(cfg.primary());
+        assertEquals("term_fixed", cfg.primary().terminal());
+    }
+
+    @Test
+    void primaryBlockWithBlankTerminalDefaultsToDerived(@TempDir Path dir) throws Exception {
+        Path f = dir.resolve("primary-blank.yaml");
+        Files.writeString(f, "bind:\n  port: 8080\nprimary:\n  terminal: \"\"\n");
+
+        BridgedConfig cfg = BridgedConfig.load(f);
+        assertNotNull(cfg.primary());
+        assertTrue(cfg.primary().terminal() == null || cfg.primary().terminal().isBlank(),
+                "a blank terminal in yaml should be treated as absent — null or empty are equivalent");
+    }
 }

bridged/src/test/java/dev/ltms/bridged/mcp/PrimaryRegistryTest.java

@@ -0,0 +1,108 @@
+package dev.ltms.bridged.mcp;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * Unit tests for {@link PrimaryRegistry}: pin vs record, isKnown transitions,
+ * null/blank guard.
+ */
+class PrimaryRegistryTest {
+
+    @Test
+    void unpinnedInitiallyUnknown() {
+        var reg = new PrimaryRegistry(null);
+        assertFalse(reg.isKnown());
+        assertTrue(reg.primaryTerminal().isEmpty());
+    }
+
+    @Test
+    void unpinnedAcceptsBlankAsAbsent() {
+        var reg = new PrimaryRegistry("");
+        assertFalse(reg.isKnown());
+        assertTrue(reg.primaryTerminal().isEmpty());
+    }
+
+    @Test
+    void pinnedFromConstruction() {
+        var reg = new PrimaryRegistry("term_fixed");
+        assertTrue(reg.isKnown());
+        assertEquals("term_fixed", reg.primaryTerminal().orElseThrow());
+    }
+
+    @Test
+    void recordWhenUnpinnedSetsTheTerminal() {
+        var reg = new PrimaryRegistry(null);
+        reg.record("term_abc");
+        assertTrue(reg.isKnown());
+        assertEquals("term_abc", reg.primaryTerminal().orElseThrow());
+    }
+
+    @Test
+    void recordWithNullDoesNothingWhenUnpinned() {
+        var reg = new PrimaryRegistry(null);
+        reg.record(null);
+        assertFalse(reg.isKnown());
+    }
+
+    @Test
+    void recordWithBlankDoesNothingWhenUnpinned() {
+        var reg = new PrimaryRegistry(null);
+        reg.record("  ");
+        assertFalse(reg.isKnown());
+    }
+
+    @Test
+    void recordOverwritesWhenUnpinned() {
+        var reg = new PrimaryRegistry(null);
+        reg.record("term_first");
+        assertEquals("term_first", reg.primaryTerminal().orElseThrow());
+        reg.record("term_second");
+        assertEquals("term_second", reg.primaryTerminal().orElseThrow());
+    }
+
+    @Test
+    void recordIsIgnoredWhenPinned() {
+        var reg = new PrimaryRegistry("term_pinned");
+        reg.record("term_other");
+        assertEquals("term_pinned", reg.primaryTerminal().orElseThrow(), "pinned value must survive record");
+    }
+
+    @Test
+    void nullRecordIsIgnoredWhenPinned() {
+        var reg = new PrimaryRegistry("term_pinned");
+        reg.record(null);
+        assertTrue(reg.isKnown());
+        assertEquals("term_pinned", reg.primaryTerminal().orElseThrow());
+    }
+
+    @Test
+    void blankRecordIsIgnoredWhenPinned() {
+        var reg = new PrimaryRegistry("term_pinned");
+        reg.record("  ");
+        assertTrue(reg.isKnown());
+        assertEquals("term_pinned", reg.primaryTerminal().orElseThrow());
+    }
+
+    @Test
+    void isKnownFalseAfterConstructionWithNull() {
+        var reg = new PrimaryRegistry(null);
+        assertFalse(reg.isKnown());
+    }
+
+    @Test
+    void isKnownAfterRecord() {
+        var reg = new PrimaryRegistry(null);
+        reg.record("term_x");
+        assertTrue(reg.isKnown());
+    }
+
+    @Test
+    void primaryTerminalRoundTrip() {
+        var reg = new PrimaryRegistry(null);
+        assertTrue(reg.primaryTerminal().isEmpty());
+        reg.record("term_found");
+        assertEquals("term_found", reg.primaryTerminal().get());
+    }
+}