diff --git a/packages/insomnia/src/templating/sandbox/sandbox-export-discovery.test.ts b/packages/insomnia/src/templating/sandbox/sandbox-export-discovery.test.ts
index c3942c4aa6..0e851a1cb8 100644
--- a/packages/insomnia/src/templating/sandbox/sandbox-export-discovery.test.ts
+++ b/packages/insomnia/src/templating/sandbox/sandbox-export-discovery.test.ts
@@ -3,6 +3,7 @@ import { describe, expect, it } from 'vitest';
 import { type HostBridge } from './host-bridge';
 import { type ContextEnvelope, type PluginExportManifest } from './marshal';
 import { runTagInSandbox } from './plugin-tag-sandbox';
+import { buildReachabilityProbeSource } from './sandbox-surface';
 
 // L1 load-time discovery: evaluate a plugin's entry inside the sandbox and return a manifest of its
 // exports, instead of nodeRequire-ing it on the host. The plugin's top-level code runs — but in the
@@ -15,6 +16,7 @@ const noBridge: HostBridge = async path => {
 const envelope = (
   moduleFiles: Record<string, string>,
   grantedModules: string[] = ['path', 'crypto'],
+  grantedCapabilities: string[] = [],
 ): ContextEnvelope => ({
   args: [],
   context: {},
@@ -24,7 +26,7 @@ const envelope = (
   pluginName: 'test-plugin',
   renderDepth: 0,
   grantedModules,
-  grantedCapabilities: [],
+  grantedCapabilities,
   moduleFiles,
   entryModuleKey: 'index.js',
 });
@@ -105,3 +107,59 @@ describe('sandbox export discovery (L1)', () => {
     ).rejects.toThrow(/not permitted by manifest/);
   });
 });
+
+describe('sandbox export discovery (L1) — bridge isolation', () => {
+  it('a discovery-time call to the internal context builder never reaches the host bridge', async () => {
+    const calls: { path: string; body: unknown }[] = [];
+    const recordingBridge: HostBridge = async (path, body) => {
+      calls.push({ path, body });
+      return {};
+    };
+
+    // Top-level code (runs during mere discovery, before any tag is ever invoked) reaches for the
+    // internal context builder directly and tries to use it — exactly what a plugin manifest never
+    // declaring anything would still be able to attempt.
+    await runTagInSandbox({
+      tagName: '',
+      discover: true,
+      envelope: envelope(
+        {
+          'index.js': `
+            var ctx = globalThis.__buildContext({ pluginName: 'x', context: {}, meta: {}, renderPurpose: 'preview', appInfo: {} });
+            ctx.app.alert('t', 'm');
+            module.exports.templateTags = [];`,
+        },
+        ['path', 'crypto'],
+        ['app'],
+      ),
+      bridge: recordingBridge,
+    });
+
+    expect(calls).toEqual([]);
+  });
+
+  // Stretch coverage: instead of one hand-picked exploit shape, recursively invoke every
+  // globalThis-reachable function (and whatever it returns) during discovery, watching for any
+  // bridge call anywhere in the tree.
+  it('no globalThis-reachable function reaches the host bridge during discovery, however invoked', async () => {
+    const calls: { path: string; body: unknown }[] = [];
+    const recordingBridge: HostBridge = async (path, body) => {
+      calls.push({ path, body });
+      return {};
+    };
+
+    await runTagInSandbox({
+      tagName: '',
+      discover: true,
+      envelope: envelope(
+        { 'index.js': buildReachabilityProbeSource() },
+        ['path', 'crypto'],
+        ['app', 'storage', 'network', 'fs-read', 'render', 'util', 'credentials', 'models.read'],
+      ),
+      bridge: recordingBridge,
+      timeoutMs: 30_000,
+    });
+
+    expect(calls).toEqual([]);
+  }, 40_000);
+});
diff --git a/packages/insomnia/src/templating/sandbox/sandbox-surface.test.ts b/packages/insomnia/src/templating/sandbox/sandbox-surface.test.ts
index e9da84db00..b8aa9a469a 100644
--- a/packages/insomnia/src/templating/sandbox/sandbox-surface.test.ts
+++ b/packages/insomnia/src/templating/sandbox/sandbox-surface.test.ts
@@ -3,10 +3,12 @@ import { describe, expect, it } from 'vitest';
 import { ALL_SANDBOX_MODULES } from './module-registry';
 import {
   findLeakedGatedReferences,
+  findSandboxInternalGlobals,
   findUnaccountedHostNatives,
   formatSurfaceEntries,
   getSandboxEscapeProbe,
   getSandboxSurface,
+  SANDBOX_INTERNAL_GLOBALS,
 } from './sandbox-surface';
 
 describe('sandbox surface', () => {
@@ -75,4 +77,12 @@ describe('sandbox', () => {
     const entries = await getSandboxSurface();
     expect(findLeakedGatedReferences(entries)).toEqual([]);
   }, 20_000);
+
+  // Completeness tripwire: any new sandbox-internal global must be added here deliberately, so its
+  // safety story (who can reach it, what it can do during discovery) gets reviewed rather than
+  // slipping in unnoticed.
+  it('exposes exactly the reviewed set of sandbox-internal globals', async () => {
+    const entries = await getSandboxSurface();
+    expect(findSandboxInternalGlobals(entries)).toEqual([...SANDBOX_INTERNAL_GLOBALS].sort());
+  }, 20_000);
 });
diff --git a/packages/insomnia/src/templating/sandbox/sandbox-surface.ts b/packages/insomnia/src/templating/sandbox/sandbox-surface.ts
index cd302c7582..ab276d09c4 100644
--- a/packages/insomnia/src/templating/sandbox/sandbox-surface.ts
+++ b/packages/insomnia/src/templating/sandbox/sandbox-surface.ts
@@ -207,6 +207,69 @@ export const findLeakedGatedReferences = (entries: SurfaceEntry[]): string[] =>
     .filter(e => !!e.aliasOf && e.aliasOf.startsWith('globalThis.') && (e.root === 'context' || e.root.startsWith('require(')))
     .map(e => `${e.path} aliases ${e.aliasOf}`);
 
+/**
+ * The complete, reviewed set of sandbox-internal globals (`in-sandbox-bootstrap.ts`) exposed bare on
+ * `globalThis` so `RUNNER`/`DESCRIBE_RUNNER` — each a separate `ctx.evalCode` call, so they can only
+ * share state via `globalThis`, never lexical closure — can reach them. Locked against reassignment,
+ * but reachable (and callable) by plugin top-level code, same as any other global. `__buildContext`
+ * in particular returns a context wired to the real host bridge; discovery-time safety comes from
+ * `runTagInSandbox` substituting a rejecting bridge when `discover: true`, not from hiding this
+ * global. Adding a new one here forces a human to re-check that story still holds.
+ */
+export const SANDBOX_INTERNAL_GLOBALS = ['__buildContext', '__describeExports', '__invoke', '__loadPluginEntry', '__require'];
+
+/** Filters sandbox surface entries down to the bare `globalThis.__*` internals (excluding the `.prototype` sibling lines already in the snapshot). */
+export const findSandboxInternalGlobals = (entries: SurfaceEntry[]): string[] =>
+  entries
+    .filter(e => e.root === 'globalThis' && /^globalThis\.__[^.]+$/.test(e.path))
+    .map(e => e.path.slice('globalThis.'.length));
+
+/**
+ * Tier B-deep reachability probe (discovery-time bridge escape coverage): recursively walks every
+ * `globalThis`-reachable property (same walk/cycle-detection shape as `buildSurfaceProbeSource`) and
+ * additionally *invokes* every function found with a couple of generic argument shapes, then walks
+ * whatever it returns too — the real exploit shape is a bare `globalThis` function (`__buildContext`)
+ * whose return value exposes further bridge-backed functions several levels down. Meant to run as
+ * plugin top-level code during a `discover: true` run (no tag ever inserted). The authoritative check
+ * is the host-side recording bridge seeing zero calls; nothing here reports its own pass/fail — a
+ * bridge call from inside the sandbox is indistinguishable from any other promise-returning builtin.
+ */
+export const buildReachabilityProbeSource = (maxDepth = 2): string => `
+(function () {
+  var seen = [];
+  var genericArgs = [
+    [],
+    [{ pluginName: 'probe', context: {}, meta: {}, renderPurpose: 'preview', appInfo: {} }],
+  ];
+  function walk(obj, depth) {
+    if (depth > ${maxDepth}) { return; }
+    if (obj === null || (typeof obj !== 'object' && typeof obj !== 'function')) { return; }
+    if (seen.indexOf(obj) !== -1) { return; }
+    seen.push(obj);
+    var names;
+    try { names = Object.getOwnPropertyNames(obj).sort(); } catch (e) { return; }
+    for (var i = 0; i < names.length; i++) {
+      var name = names[i];
+      if (name === 'length' || name === 'name' || name === 'prototype') { continue; }
+      var val;
+      try { val = obj[name]; } catch (e) { continue; }
+      if (typeof val === 'function') {
+        for (var a = 0; a < genericArgs.length; a++) {
+          try {
+            var r = val.apply(null, genericArgs[a]);
+            if (r && typeof r.then === 'function') { r.then(function () {}, function () {}); }
+            walk(r, 0);
+          } catch (e) { /* probing only - a thrown arity/shape mismatch is not a finding */ }
+        }
+      }
+      walk(val, depth + 1);
+    }
+  }
+  walk(globalThis, 0);
+})();
+module.exports.templateTags = [];
+`;
+
 const ESCAPE_PROBE_TAG_NAME = 'escapeProbe';
 
 // Checks whether `this`, Function('return this')(), ambient globals, or the process shim ever