perf(inventory): cap concurrent forwards so flush bursts can't starve telemetry

Root cause of the player-count flapping: the plugin's debounced inventory
flush, combined with a fleet-wide relog wave (auto-update) phase-aligning the
60s flush timers, produced a synchronized burst of inventory forwards every
cycle. The burst flooded the single event loop + httpx pool (errors in
_do_handle_inventory_delta even though inventory-service was idle), periodically
starving telemetry ingest (cliff 116→5 rows/10s) so characters aged out of the
30s window and the count flapped.

- Global asyncio.Semaphore(8) around inventory forwarding: a burst can never
  monopolize the loop; telemetry always gets through.
- Tighten the shared httpx client (max_connections=10, keepalive=5, 5s timeout)
  so a stale/slow connection can't hold a slot.

Pairs with the plugin-side flush-timer jitter (2–5 min, re-rolled per tick) that
de-synchronizes the fleet at the source.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

main.py

@@ -2560,6 +2560,14 @@ _inventory_delta_tasks: set[asyncio.Task] = set()
 # while deltas for DIFFERENT characters still run concurrently.
 _inventory_char_locks: Dict[str, asyncio.Lock] = {}
 
+# Global cap on concurrent inventory forwards. The plugin debounces inventory
+# updates into a periodic per-character flush; if many characters' flush timers
+# align (e.g. after a fleet-wide auto-update relog wave) the forwards arrive as
+# a synchronized burst. Without a cap that burst floods the single event loop
+# and httpx pool, starving telemetry processing → the player count flaps.
+# This bounds how many forwards run at once so telemetry always gets the loop.
+_inventory_forward_sem = asyncio.Semaphore(8)
+
 
 def _get_inventory_char_lock(char_name: str) -> asyncio.Lock:
     lock = _inventory_char_locks.get(char_name)
@@ -2592,39 +2600,47 @@ async def _do_handle_inventory_delta(data: dict):
         char_name = data.get("character_name", "unknown")
         global _inventory_http_client
         if _inventory_http_client is None:
-            _inventory_http_client = httpx.AsyncClient(timeout=10.0)
+            # Bounded pool + short timeout: a stale/slow connection to
+            # inventory-service can't tie up a forward slot for long.
+            _inventory_http_client = httpx.AsyncClient(
+                timeout=httpx.Timeout(5.0, connect=2.0),
+                limits=httpx.Limits(max_connections=10, max_keepalive_connections=5),
+            )
         client = _inventory_http_client
 
-        if action == "remove":
-            item_id = data.get("item_id")
-            if item_id is not None:
-                resp = await client.delete(
-                    f"{INVENTORY_SERVICE_URL}/inventory/{char_name}/item/{item_id}"
-                )
-                if resp.status_code >= 400:
-                    logger.warning(
-                        f"Inventory service returned {resp.status_code} for delta remove item_id={item_id}"
+        # Cap concurrent forwards (see _inventory_forward_sem) so a synchronized
+        # flush burst can't monopolize the loop and starve telemetry.
+        async with _inventory_forward_sem:
+            if action == "remove":
+                item_id = data.get("item_id")
+                if item_id is not None:
+                    resp = await client.delete(
+                        f"{INVENTORY_SERVICE_URL}/inventory/{char_name}/item/{item_id}"
                     )
-        elif action in ("add", "update"):
-            item = data.get("item")
-            if item:
-                resp = await client.post(
-                    f"{INVENTORY_SERVICE_URL}/inventory/{char_name}/item",
-                    json=item,
-                )
-                if resp.status_code < 400:
-                    enriched_item = resp.json().get("item")
-                    if enriched_item:
-                        data = {
-                            "type": "inventory_delta",
-                            "action": action,
-                            "character_name": char_name,
-                            "item": enriched_item,
-                        }
-                else:
-                    logger.warning(
-                        f"Inventory service returned {resp.status_code} for delta {action}"
+                    if resp.status_code >= 400:
+                        logger.warning(
+                            f"Inventory service returned {resp.status_code} for delta remove item_id={item_id}"
+                        )
+            elif action in ("add", "update"):
+                item = data.get("item")
+                if item:
+                    resp = await client.post(
+                        f"{INVENTORY_SERVICE_URL}/inventory/{char_name}/item",
+                        json=item,
                     )
+                    if resp.status_code < 400:
+                        enriched_item = resp.json().get("item")
+                        if enriched_item:
+                            data = {
+                                "type": "inventory_delta",
+                                "action": action,
+                                "character_name": char_name,
+                                "item": enriched_item,
+                            }
+                    else:
+                        logger.warning(
+                            f"Inventory service returned {resp.status_code} for delta {action}"
+                        )
 
         # Broadcast delta to all browser clients
         await _broadcast_to_browser_clients(data)