fix: stop invalid message ref assignment on exhaustion

Author: gmnstr

lib/message-ids.ts

@@ -136,14 +136,17 @@ export function assignMessageRefs(state: SessionState, messages: WithParts[]): n
         }
 
         const existingRef = state.messageIds.byRawId.get(rawMessageId)
-        if (existingRef) {
+        if (existingRef !== undefined) {
             if (state.messageIds.byRef.get(existingRef) !== rawMessageId) {
                 state.messageIds.byRef.set(existingRef, rawMessageId)
             }
             continue
         }
 
         const ref = allocateNextMessageRef(state)
+        if (!ref) {
+            break
+        }
         state.messageIds.byRawId.set(rawMessageId, ref)
         state.messageIds.byRef.set(ref, rawMessageId)
         assigned++

tests/message-ids.test.ts

@@ -87,3 +87,42 @@ test("checkSession resets message id aliases after native compaction", async ()
     assert.equal(state.messageIds.byRef.get("m0002"), "msg-user-follow-up")
     assert.equal(state.messageIds.nextRef, 3)
 })
+
+test("assignMessageRefs stops cleanly when alias capacity is exhausted", () => {
+    const sessionID = `ses_message_ids_exhausted_${Date.now()}`
+    const state = createSessionState()
+    state.messageIds.nextRef = 10000
+
+    const messages: WithParts[] = [
+        {
+            info: {
+                id: "msg-a",
+                role: "assistant",
+                sessionID,
+                agent: "assistant",
+                time: { created: 1 },
+            } as WithParts["info"],
+            parts: [textPart("msg-a", sessionID, "msg-a-part", "A")],
+        },
+        {
+            info: {
+                id: "msg-b",
+                role: "assistant",
+                sessionID,
+                agent: "assistant",
+                time: { created: 2 },
+            } as WithParts["info"],
+            parts: [textPart("msg-b", sessionID, "msg-b-part", "B")],
+        },
+    ]
+
+    const firstAssigned = assignMessageRefs(state, messages)
+    const secondAssigned = assignMessageRefs(state, messages)
+
+    assert.equal(firstAssigned, 0)
+    assert.equal(secondAssigned, 0)
+    assert.equal(state.messageIds.byRawId.size, 0)
+    assert.equal(state.messageIds.byRef.size, 0)
+    assert.equal(state.messageIds.byRawId.get("msg-a"), undefined)
+    assert.equal(state.messageIds.byRawId.get("msg-b"), undefined)
+})