feat(agent): implement /clear command

packages/agent/src/acp-extensions.ts

@@ -69,6 +69,10 @@ export const POSTHOG_NOTIFICATIONS = {
   /** Marks a boundary for log compaction */
   COMPACT_BOUNDARY: "_posthog/compact_boundary",
 
+  /** Conversation history was cleared via /clear. Carries the fresh SDK
+   * session id; rehydration treats the entry as a conversation boundary. */
+  CONVERSATION_CLEARED: "_posthog/conversation_cleared",
+
   /** Token usage update for a session turn */
   USAGE_UPDATE: "_posthog/usage_update",
 

packages/agent/src/adapters/base-acp-agent.ts

@@ -72,7 +72,7 @@ export abstract class BaseAcpAgent implements Agent {
   protected abstract interrupt(): Promise<void>;
 
   async cancel(params: CancelNotification): Promise<void> {
-    if (this.sessionId !== params.sessionId) {
+    if (!this.hasSession(params.sessionId)) {
       throw new Error("Session ID mismatch");
     }
     this.session.cancelled = true;
@@ -100,6 +100,8 @@ export abstract class BaseAcpAgent implements Agent {
     }
   }
 
+  /** Adapters may widen this to accept alternate ids for the live session
+   *  (e.g. the Claude adapter's post-/clear SDK session id). */
   hasSession(sessionId: string): boolean {
     return this.sessionId === sessionId;
   }
@@ -108,7 +110,7 @@ export abstract class BaseAcpAgent implements Agent {
     sessionId: string,
     notification: SessionNotification,
   ): void {
-    if (this.sessionId === sessionId) {
+    if (this.hasSession(sessionId)) {
       this.session.notificationHistory.push(notification);
     }
   }

packages/agent/src/adapters/claude/UPSTREAM.md

@@ -365,7 +365,11 @@ Fork of `@anthropic-ai/claude-agent-acp`. Upstream repo: https://github.com/anth
 - **Model alias version match** (#702, e1e1c69): Refuse cross-version alias matches in `resolveModelPreference`
   so `claude-opus-4-6` doesn't get copied onto the `opus` alias when it resolves to 4.7.
 - **Hide /clear** (#705, cfce130): `/clear` removed from advertised commands; clients should use
-  `session/new` for the same effect.
+  `session/new` for the same effect. Superseded: PostHog Code now implements `/clear` itself in
+  `clearConversation` (prompt() intercepts it and swaps in a fresh SDK session; a
+  `_posthog/conversation_cleared` log marker bounds rehydration), still never forwarding it to the SDK.
+  A build that predates this marker skips it as an unrecognized notification and keeps rendering
+  pre-clear history on rehydration, so the history-drop only renders correctly on builds that ship it.
 - **No-op ping events** (#698, 694221a): `streamEventToAcpNotifications` no-ops `ping` keep-alive events
   instead of falling through to `unreachable` and spamming stderr.