fix(discord): preserve channel session keys via channel_id fallbacks (#17622)

* fix(discord): preserve channel session keys via channel_id fallbacks

* docs(changelog): add discord session continuity note

* Tests: cover discord channel_id fallback

---------

Co-authored-by: Shadow <hi@shadowing.dev>

src/logging/diagnostic-session-state.ts

@@ -56,10 +56,20 @@ function resolveSessionKey({ sessionKey, sessionId }: SessionRef) {
   return sessionKey ?? sessionId ?? "unknown";
 }
 
+function findStateBySessionId(sessionId: string): SessionState | undefined {
+  for (const state of diagnosticSessionStates.values()) {
+    if (state.sessionId === sessionId) {
+      return state;
+    }
+  }
+  return undefined;
+}
+
 export function getDiagnosticSessionState(ref: SessionRef): SessionState {
   pruneDiagnosticSessionStates();
   const key = resolveSessionKey(ref);
-  const existing = diagnosticSessionStates.get(key);
+  const existing =
+    diagnosticSessionStates.get(key) ?? (ref.sessionId && findStateBySessionId(ref.sessionId));
   if (existing) {
     if (ref.sessionId) {
       existing.sessionId = ref.sessionId;

src/logging/diagnostic.test.ts

@@ -34,6 +34,18 @@ describe("diagnostic session state pruning", () => {
 
     expect(getDiagnosticSessionStateCountForTest()).toBe(2000);
   });
+
+  it("reuses keyed session state when later looked up by sessionId", () => {
+    const keyed = getDiagnosticSessionState({
+      sessionId: "s1",
+      sessionKey: "agent:main:discord:channel:c1",
+    });
+    const bySessionId = getDiagnosticSessionState({ sessionId: "s1" });
+
+    expect(bySessionId).toBe(keyed);
+    expect(bySessionId.sessionKey).toBe("agent:main:discord:channel:c1");
+    expect(getDiagnosticSessionStateCountForTest()).toBe(1);
+  });
 });
 
 describe("logger import side effects", () => {