diff --git a/src/permission/reactor-authorize.ts b/src/permission/reactor-authorize.ts
index f1e5666e6..3f44afdd8 100644
--- a/src/permission/reactor-authorize.ts
+++ b/src/permission/reactor-authorize.ts
@@ -14,7 +14,10 @@
 import { getLogger } from "@intx/log";
 
 import { LOG_NAMESPACE_ROOT } from "../branding.js";
-import { ToolCall, type ToolCall as ToolCallType } from "@intx/types/runtime";
+import {
+  ToolCall,
+  type ToolCall as ToolCallType,
+} from "@intx/types/runtime-core";
 import { type } from "arktype";
 
 import type { AuthzCallResult } from "@intx/inference";
diff --git a/src/session/optimized-context-store.ts b/src/session/optimized-context-store.ts
index 265dca56a..13af98b76 100644
--- a/src/session/optimized-context-store.ts
+++ b/src/session/optimized-context-store.ts
@@ -13,7 +13,7 @@ import {
   TokenUsage,
   type ConversationTurn,
   type PendingOperation,
-} from "@intx/types/runtime";
+} from "@intx/types/runtime-core";
 import { getLogger } from "@intx/log";
 import {
   createSegmentedJSONLWriter,
diff --git a/src/session/pending-approval-record.ts b/src/session/pending-approval-record.ts
index 021b6ea8b..4a90632c0 100644
--- a/src/session/pending-approval-record.ts
+++ b/src/session/pending-approval-record.ts
@@ -3,7 +3,7 @@ import {
   ApprovalSnapshot,
   type PendingOperation,
   ToolCall,
-} from "@intx/types/runtime";
+} from "@intx/types/runtime-core";
 
 /**
  * A pending operation as it rests in session state (metadata.json, or a turn
diff --git a/src/session/runtime-core-import.test.ts b/src/session/runtime-core-import.test.ts
new file mode 100644
index 000000000..c6d195782
--- /dev/null
+++ b/src/session/runtime-core-import.test.ts
@@ -0,0 +1,64 @@
+// Loading the @intx/types/runtime barrel evaluates inference-events.ts and
+// builds the InferenceEvent union. Session modules that need runtime values
+// import @intx/types/runtime-core so that boot does not pay for the union.
+
+import { expect, test } from "bun:test";
+import { spawnSync } from "node:child_process";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+
+const repoRoot = path.resolve(
+  path.dirname(fileURLToPath(import.meta.url)),
+  "../..",
+);
+
+const probe = `
+import { mock } from "bun:test";
+mock.module("@intx/types/inference-events", () => {
+  throw new Error("evaluated-inference-events");
+});
+const specifier = process.env.PROBE_SPECIFIER;
+if (specifier === undefined || specifier.length === 0) {
+  throw new Error("missing PROBE_SPECIFIER");
+}
+for (const target of specifier.split(",")) {
+  await import(target);
+}
+`;
+
+function importUnderProbe(specifier: string): {
+  status: number | null;
+  stderr: string;
+} {
+  const result = spawnSync("bun", ["-e", probe], {
+    cwd: repoRoot,
+    encoding: "utf8",
+    env: { ...process.env, PROBE_SPECIFIER: specifier },
+  });
+  return {
+    status: result.status,
+    stderr: result.stderr,
+  };
+}
+
+const sessionBootModules = [
+  "./src/session/optimized-context-store.ts",
+  "./src/session/pending-approval-record.ts",
+  "./src/session/summarizer.ts",
+].join(",");
+
+test("the runtime barrel evaluates the inference event union", () => {
+  const result = importUnderProbe("@intx/types/runtime");
+  expect(result.status).not.toBe(0);
+  expect(result.stderr).toContain("evaluated-inference-events");
+});
+
+test(
+  "session value imports do not evaluate the inference event union",
+  () => {
+    const result = importUnderProbe(sessionBootModules);
+    expect(result.stderr).not.toContain("evaluated-inference-events");
+    expect(result.status).toBe(0);
+  },
+  { timeout: 60_000 },
+);
diff --git a/src/session/summarizer.ts b/src/session/summarizer.ts
index af0d35df1..a9f1c7a29 100644
--- a/src/session/summarizer.ts
+++ b/src/session/summarizer.ts
@@ -14,7 +14,7 @@ import {
   type ConversationTurn,
   type InferenceSource,
   type RetryPolicy,
-} from "@intx/types/runtime";
+} from "@intx/types/runtime-core";
 import { LOG_NAMESPACE_ROOT } from "../branding.js";
 import { NOOP_TELEMETRY, type Telemetry } from "../telemetry/index.js";
 import {