feat: Gen 5 improvements — stream subscription check + auto-subscribe

Adds two improvements from pi Zulip extension lessons:

1. _ensure_stream_subscriptions() — checks at connect time if the bot
   is subscribed to the primary stream and general-chat; auto-subscribes
   if missing. Without this, bots with 0 subscriptions can't receive
   stream events (DMs only).

2. selftest check #9 — verifies stream subscriptions and reports
   count + names. Catches the 'zero subscriptions' failure mode that
   was a major debugging bottleneck in the pi extension.

plugins/platforms/zulip/adapter.py

@@ -302,6 +302,9 @@ class ZulipAdapter(BasePlatformAdapter):
             # Gen 2: Try to resolve @all-bots user ID dynamically
             await self._resolve_all_bots_user_id()
 
+            # Gen 5: Ensure bot is subscribed to primary stream
+            await self._ensure_stream_subscriptions()
+
             self._mark_connected()
             logger.info(
                 "[%s] Connected to %s as %s (queue=%s, bot_id=%s, all_bots_id=%s)",
@@ -681,6 +684,64 @@ class ZulipAdapter(BasePlatformAdapter):
     # Gen 2: Dynamic @all-bots resolution
     # ------------------------------------------------------------------
 
+    async def _ensure_stream_subscriptions(self) -> None:
+        """Ensure the bot is subscribed to the primary streams.
+
+        Checks current subscriptions and subscribes to the configured primary
+        stream (and general-chat) if missing. Without subscription, the bot
+        receives DMs but no stream events — @mentions in streams are invisible.
+
+        This is a Gen 5 improvement based on lessons from the pi Zulip extension,
+        where the bot had zero stream subscriptions and couldn't receive
+        @mentions in stream topics.
+        """
+        try:
+            # Check current subscriptions
+            resp, _ = await self._api_call(
+                "GET", "/api/v1/users/me/subscriptions",
+            )
+            if not resp:
+                return
+
+            subscribed = resp.get("subscriptions", [])
+            subscribed_names = [s.get("name", "") for s in subscribed if isinstance(s, dict)]
+
+            # Streams the bot should be subscribed to
+            required_streams = [self._stream, "general chat"]
+            missing = [s for s in required_streams if s not in subscribed_names]
+
+            if not missing:
+                logger.info(
+                    "[%s] Stream subscriptions OK: %s",
+                    self.name, ", ".join(subscribed_names),
+                )
+                return
+
+            # Subscribe to missing streams
+            import json as _json
+            payload = {"subscriptions": _json.dumps(
+                [{"name": s} for s in missing]
+            )}
+            sub_resp, _ = await self._api_call(
+                "POST", "/api/v1/users/me/subscriptions",
+                data=payload,
+            )
+            if sub_resp and sub_resp.get("result") == "success":
+                subscribed_str = ", ".join(missing)
+                logger.info(
+                    "[%s] Subscribed to: %s", self.name, subscribed_str,
+                )
+                self._health_stats["subscriptions_fixed"] = (
+                    self._health_stats.get("subscriptions_fixed", 0) + 1
+                )
+            else:
+                logger.warning(
+                    "[%s] Failed to subscribe to %s",
+                    self.name, ", ".join(missing),
+                )
+        except Exception as e:
+            logger.warning("[%s] Subscription check failed: %s", self.name, e)
+
     async def _resolve_all_bots_user_id(self) -> None:
         """Try to resolve the @all-bots user ID from the Zulip server.
 
@@ -1100,6 +1161,35 @@ class ZulipAdapter(BasePlatformAdapter):
             "detail": f"@all-bots user_id: {self._all_bots_user_id}",
         }
 
+        # 9. Stream subscriptions (verifies bot is subscribed to at least one stream)
+        try:
+            from urllib.parse import urlencode
+            import json as _json
+            key_str = f"{self._email}:{self._api_key}"
+            auth_b64 = base64.b64encode(key_str.encode()).decode()
+            resp, _ = await self._api_call(
+                "GET", "/api/v1/users/me/subscriptions",
+            )
+            if resp and "subscriptions" in resp:
+                stream_count = len(resp["subscriptions"])
+                stream_names = [s.get("name", "?") for s in resp["subscriptions"]][:5]
+                checks["stream_subscriptions"] = {
+                    "status": stream_count > 0,
+                    "detail": f"{stream_count} stream(s): {', '.join(stream_names)}"
+                    if stream_count > 0
+                    else "No stream subscriptions — bot will not receive stream events",
+                }
+            else:
+                checks["stream_subscriptions"] = {
+                    "status": False,
+                    "detail": "Failed to check subscriptions",
+                }
+        except Exception as sub_err:
+            checks["stream_subscriptions"] = {
+                "status": False,
+                "detail": f"Subscription check failed: {sub_err}",
+            }
+
         # Overall verdict
         critical = ["connected", "queue_registered", "http_client", "poll_loop"]
         passed = sum(1 for c in checks.values() if c["status"])