From 1da08c3242b531e0f987fff10ab05786a9061c81 Mon Sep 17 00:00:00 2001
From: Rhys Sullivan <39114868+RhysSullivan@users.noreply.github.com>
Date: Sat, 29 Aug 2026 00:24:47 -0700
Subject: [PATCH] Annotate session init spans with catalog size counts

---
 apps/cloud/src/mcp/session-durable-object.ts  | 27 ++++++++++++++++++-
 .../src/mcp/agent-session-durable-object.ts   | 21 ++++++++++++++-
 2 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/apps/cloud/src/mcp/session-durable-object.ts b/apps/cloud/src/mcp/session-durable-object.ts
index 6b9963eb8..f6746ccf7 100644
--- a/apps/cloud/src/mcp/session-durable-object.ts
+++ b/apps/cloud/src/mcp/session-durable-object.ts
@@ -43,7 +43,11 @@ import {
   type McpExecutionOwnerRoute,
 } from "@executor-js/cloudflare/mcp/execution-owner-directory";
 import { mcpSessionStub } from "@executor-js/cloudflare/mcp/session-stub";
-import { buildExecuteDescription, type ResumeResponse } from "@executor-js/execution";
+import {
+  buildExecuteDescription,
+  parseIntegrationInventory,
+  type ResumeResponse,
+} from "@executor-js/execution";
 import { acquireBuildSlot, type BuildSlotHandle } from "./session-build-semaphore";
 
 // The DO meters executions just like the HTTP `/api/*` plane: it builds its
@@ -182,6 +186,16 @@ const smokeRenderArtifactAfterQuickJsPreload: typeof smokeRenderArtifact = async
 // ---------------------------------------------------------------------------
 
 export class McpSessionDOSqlite extends McpAgentSessionDOBase<Env, CloudSessionDbHandle> {
+  // Set once per `buildMcpServer` call, read back by `sessionFootprintAttributes`
+  // so the counts land on the base's `McpSessionDO.init` span alongside
+  // `mcp.isolate.*` residency — see the comment at the `parseIntegrationInventory`
+  // call site below for why this is free to compute.
+  private lastSessionFootprint: Record<string, number> = {};
+
+  protected override sessionFootprintAttributes(): Record<string, number> {
+    return this.lastSessionFootprint;
+  }
+
   protected override sessionTimeoutMs(): number {
     return positiveMilliseconds(env.MCP_SESSION_TIMEOUT_MS) ?? super.sessionTimeoutMs();
   }
@@ -327,6 +341,17 @@ export class McpSessionDOSqlite extends McpAgentSessionDOBase<Env, CloudSessionD
       const description = yield* buildExecuteDescription(executor).pipe(
         Effect.withSpan("mcp.execute.description.build"),
       );
+      // Cheap size proxy for the session's footprint: `parseIntegrationInventory`
+      // is a regex walk over the description string already built above, the
+      // same trick `createExecutorMcpServer` uses to derive its per-integration
+      // search tools without a second `connections.list()` — no new query, no
+      // catalog serialization. This is a *count* of distinct connected
+      // integrations, not raw connections (several connections can share one
+      // integration) and is capped at the description's 50-item inventory
+      // limit, same as what the model itself sees.
+      self.lastSessionFootprint = {
+        "mcp.session.integration_count": parseIntegrationInventory(description).length,
+      };
       const sessionElicitationMode = sessionMeta.elicitationMode ?? "model";
       const mcpServer = yield* createExecutorMcpServer({
         engine,
diff --git a/packages/hosts/cloudflare/src/mcp/agent-session-durable-object.ts b/packages/hosts/cloudflare/src/mcp/agent-session-durable-object.ts
index 4afc54651..c582cf7e2 100644
--- a/packages/hosts/cloudflare/src/mcp/agent-session-durable-object.ts
+++ b/packages/hosts/cloudflare/src/mcp/agent-session-durable-object.ts
@@ -290,6 +290,20 @@ export abstract class McpAgentSessionDOBase<
     dbHandle: TDbHandle,
   ): Effect.Effect<BuiltMcpServer>;
 
+  /**
+   * Cheap, count-only proxies for what the runtime `buildMcpServer` just built
+   * holds — e.g. connected-integration counts — attributed alongside
+   * `residencyAttributes()` on the same `McpSessionDO.init` span so per-session
+   * memory footprint is queryable next to isolate residency without a
+   * cross-span join. Empty by default: a host that has nothing free to read
+   * (or nothing beyond what `buildMcpServer` already returns) need not
+   * override this. MUST stay O(1)/O(count) over already-materialized state —
+   * never trigger a new query or serialize a catalog to compute these.
+   */
+  protected sessionFootprintAttributes(): Record<string, number> {
+    return {};
+  }
+
   protected withTelemetry<A, E>(
     effect: Effect.Effect<A, E>,
     _incoming?: IncomingTraceHeaders,
@@ -1001,7 +1015,12 @@ export abstract class McpAgentSessionDOBase<
       // The gauge on the way up. Paired with the same attributes on
       // `mcp.session.idle_runtime_dispose`, this is what shows whether idle
       // sessions are actually giving their runtimes back in production.
-      yield* Effect.annotateCurrentSpan(residencyAttributes());
+      // `sessionFootprintAttributes()` rides the same span so a heavy session
+      // can be attributed to what it holds, not just counted.
+      yield* Effect.annotateCurrentSpan({
+        ...residencyAttributes(),
+        ...self.sessionFootprintAttributes(),
+      });
       // Last statement, and pure bookkeeping: the runtime above is already
       // installed and serving. Losing the timestamp/alarm write to a platform
       // reset must not undo any of it — the in-memory clock is already set and