diff --git a/.changeset/await-ai-diagnostics.md b/.changeset/await-ai-diagnostics.md
new file mode 100644
index 00000000000..7412e185a95
--- /dev/null
+++ b/.changeset/await-ai-diagnostics.md
@@ -0,0 +1,5 @@
+---
+"@hashintel/petrinaut": patch
+---
+
+Describe a clean net-code diagnostic check without claiming the whole model compiles.
diff --git a/.changeset/snapshot-language-diagnostics.md b/.changeset/snapshot-language-diagnostics.md
new file mode 100644
index 00000000000..2674a469523
--- /dev/null
+++ b/.changeset/snapshot-language-diagnostics.md
@@ -0,0 +1,5 @@
+---
+"@hashintel/petrinaut-core": patch
+---
+
+Describe snapshot validation and its TypeScript and HIR diagnostics in the AI tool.
diff --git a/apps/brunch-agent/test/compiler-feedback.integration.ts b/apps/brunch-agent/test/compiler-feedback.integration.ts
index a1eb83d57ee..2db5b938b37 100644
--- a/apps/brunch-agent/test/compiler-feedback.integration.ts
+++ b/apps/brunch-agent/test/compiler-feedback.integration.ts
@@ -34,8 +34,7 @@ import { openBrowserFixture } from "./browser-fixture.ts";
 import { browserResultFrom } from "./browser-result.ts";
 import { nativeSchemaProvider } from "./native-schema-provider.ts";
 
-const cleanCompilation =
-  "No errors detected in your model – everything compiles!";
+const cleanCompilation = "No errors or warnings found in net function code.";
 const output = mkdtempSync(join(tmpdir(), "m7c-compiler-feedback-"));
 const save = (name: string, value: unknown) =>
   writeFileSync(join(output, `${name}.json`), JSON.stringify(value, null, 2));
diff --git a/apps/brunch-agent/test/integration/compiler-feedback.test.ts b/apps/brunch-agent/test/integration/compiler-feedback.test.ts
index bd28ce147ad..2ea0e6a5e1b 100644
--- a/apps/brunch-agent/test/integration/compiler-feedback.test.ts
+++ b/apps/brunch-agent/test/integration/compiler-feedback.test.ts
@@ -37,7 +37,7 @@ test.skipIf(!enabled)(
     expect(summary.mode).toBe("batched-construction");
     expect(summary.dirtyCompilation).toContain("definitelyNotDefined");
     expect(summary.cleanCompilation).toBe(
-      "No errors detected in your model – everything compiles!",
+      "No errors or warnings found in net function code.",
     );
     expect(summary.repairHash).toMatch(/^[a-f0-9]{64}$/u);
     expect(summary.layoutHash).toMatch(/^[a-f0-9]{64}$/u);
diff --git a/apps/brunch-agent/test/root-creation.integration.ts b/apps/brunch-agent/test/root-creation.integration.ts
index 6ed43ad1d61..f12e4d74afa 100644
--- a/apps/brunch-agent/test/root-creation.integration.ts
+++ b/apps/brunch-agent/test/root-creation.integration.ts
@@ -301,7 +301,7 @@ try {
       save("compilation", result);
       assert.equal(
         result.output,
-        "No errors detected in your model – everything compiles!",
+        "No errors or warnings found in net function code.",
       );
       return text("Native creation and canonical check completed.");
     }),
@@ -504,7 +504,7 @@ try {
     requests: contexts.length,
     applied: records.length,
     schemaClasses: observedNodeMutationNames,
-    compilation: "No errors detected in your model – everything compiles!",
+    compilation: "No errors or warnings found in net function code.",
     scope:
       "Same-session synthetic creation/correction only; reopen assertion follows.",
   });
diff --git a/apps/brunch-agent/test/typed-state.integration.ts b/apps/brunch-agent/test/typed-state.integration.ts
index ccabbba7ab1..74a659b1701 100644
--- a/apps/brunch-agent/test/typed-state.integration.ts
+++ b/apps/brunch-agent/test/typed-state.integration.ts
@@ -631,7 +631,7 @@ try {
       compilations.push(result);
       assert.equal(
         result.output,
-        "No errors detected in your model – everything compiles!",
+        "No errors or warnings found in net function code.",
         "Final corrected net must report clean canonical diagnostics; no scenario execution follows",
       );
       return text(
diff --git a/libs/@hashintel/petrinaut-core/src/ai.ts b/libs/@hashintel/petrinaut-core/src/ai.ts
index 5d2c9afdac5..867ba5871c9 100644
--- a/libs/@hashintel/petrinaut-core/src/ai.ts
+++ b/libs/@hashintel/petrinaut-core/src/ai.ts
@@ -141,7 +141,7 @@ const getLatestNetDefinitionToolInputSchema = z
 const getNetCompilationErrorsToolInputSchema = z
   .strictObject({})
   .describe(
-    "Get the current TypeScript diagnostics for the Petrinaut net code. Use this after the net to check whether the model compiles.",
+    "Validate the current Petrinaut net snapshot and return its TypeScript and HIR diagnostics.",
   );
 
 export const setNetTitleToolInputSchema = z
diff --git a/libs/@hashintel/petrinaut-core/src/lsp/language-client.test.ts b/libs/@hashintel/petrinaut-core/src/lsp/language-client.test.ts
index 0e70656d2f8..e90e6c9bfbf 100644
--- a/libs/@hashintel/petrinaut-core/src/lsp/language-client.test.ts
+++ b/libs/@hashintel/petrinaut-core/src/lsp/language-client.test.ts
@@ -102,6 +102,55 @@ describe("createLanguageClient diagnostics", () => {
     ]);
   });
 
+  it("correlates snapshot responses without waiting for diagnostic changes", async () => {
+    const { transport, publish, respond, sent } = createFakeTransport();
+    const client = createLanguageClient({ transport });
+    const definition = {
+      places: [],
+      transitions: [],
+      parameters: [],
+      types: [],
+      differentialEquations: [],
+    };
+    const first = client.requestDiagnostics(definition);
+    const second = client.requestDiagnostics(definition);
+    publish([
+      {
+        uri: "inmemory://session",
+        diagnostics: [diagnostic("unrelated session")],
+      },
+    ]);
+    respond(1, []);
+    respond(0, [
+      { uri: "inmemory://net", diagnostics: [diagnostic("net error")] },
+    ]);
+
+    expect((await first).byUri.get("inmemory://net")?.[0]?.message).toBe(
+      "net error",
+    );
+    expect((await second).errorCount).toBe(0);
+    expect(client.diagnostics.get().byUri.has("inmemory://session")).toBe(true);
+    expect(sent).toContainEqual({
+      jsonrpc: "2.0",
+      id: 0,
+      method: "sdcpn/diagnostics",
+      params: { sdcpn: definition, extensions: undefined },
+    });
+  });
+
+  it("rejects a snapshot request when the worker is disposed", async () => {
+    const { transport } = createFakeTransport();
+    const client = createLanguageClient({ transport });
+    const response = client.requestDiagnostics({
+      places: [],
+      transitions: [],
+      parameters: [],
+      types: [],
+      differentialEquations: [],
+    });
+    client.dispose();
+    await expect(response).rejects.toThrow();
+  });
   it("notifies subscribers only when a publish changed a diagnostic", () => {
     const { transport, publish } = createFakeTransport();
     const client = createLanguageClient({ transport });
diff --git a/libs/@hashintel/petrinaut/docs/ai-assistant.md b/libs/@hashintel/petrinaut/docs/ai-assistant.md
index e97d66f9125..b828d8223ff 100644
--- a/libs/@hashintel/petrinaut/docs/ai-assistant.md
+++ b/libs/@hashintel/petrinaut/docs/ai-assistant.md
@@ -179,7 +179,11 @@ The composer stays open in all of these cases, so you can still ask questions, r
 
 ## Diagnostics integration
 
-When the assistant edits code surfaces (lambdas, kernels, dynamics, visualizers, metric/scenario code), it sees the resulting TypeScript diagnostics on the next turn and can iteratively fix them. You don't have to relay errors manually -- the post-edit re-check happens automatically. The same diagnostics also appear in the bottom **Diagnostics** tab as usual; the assistant just sees them in addition.
+The assistant can request a fresh TypeScript check of the current net and
+use the returned errors to revise its code. An unchanged set of errors still
+counts as a completed check. If checking fails, the assistant receives an
+error. The bottom **Diagnostics** tab continues to show diagnostics for the
+code you are editing.
 
 ## Host configuration
 
diff --git a/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/SimulateView/experiments/create-experiment-drawer.test.tsx b/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/SimulateView/experiments/create-experiment-drawer.test.tsx
index 917380f4c19..8af63912bdf 100644
--- a/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/SimulateView/experiments/create-experiment-drawer.test.tsx
+++ b/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/SimulateView/experiments/create-experiment-drawer.test.tsx
@@ -149,10 +149,12 @@ vi.mock("@hashintel/ds-components", async (importOriginal) => {
  */
 function makeLanguageClient(): LanguageClientContextValue {
   return {
+    requestDiagnostics: vi.fn(() =>
+      Promise.resolve({ byUri: new Map(), total: 0, errorCount: 0 }),
+    ),
     diagnosticsByUri: new Map(),
     totalDiagnosticsCount: 0,
     errorDiagnosticsCount: 0,
-    requestDiagnostics: vi.fn(),
     notifyDocumentChanged: vi.fn(),
     requestCompletion: vi.fn(() =>
       Promise.resolve({ isIncomplete: false, items: [] }),
diff --git a/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/SimulateView/metrics/create-metric-drawer.test.tsx b/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/SimulateView/metrics/create-metric-drawer.test.tsx
index 4dc1535c624..c6924fd78a0 100644
--- a/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/SimulateView/metrics/create-metric-drawer.test.tsx
+++ b/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/SimulateView/metrics/create-metric-drawer.test.tsx
@@ -30,10 +30,12 @@ vi.mock("@hashintel/ds-components", () => {
 
 function makeLanguageClientValue(): LanguageClientContextValue {
   return {
+    requestDiagnostics: vi.fn(() =>
+      Promise.resolve({ byUri: new Map(), total: 0, errorCount: 0 }),
+    ),
     diagnosticsByUri: new Map(),
     totalDiagnosticsCount: 0,
     errorDiagnosticsCount: 0,
-    requestDiagnostics: vi.fn(),
     notifyDocumentChanged: vi.fn(),
     requestCompletion: vi.fn(() =>
       Promise.resolve({ isIncomplete: false, items: [] }),
diff --git a/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/ai-assistant-panel.test.tsx b/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/ai-assistant-panel.test.tsx
index 388e52a173d..81cd533b4bf 100644
--- a/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/ai-assistant-panel.test.tsx
+++ b/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/ai-assistant-panel.test.tsx
@@ -5279,7 +5279,7 @@ describe("AiAssistantPanel host interactive tools", () => {
     expect(diagnosticsOutputs).toHaveLength(2);
     expect(
       diagnosticsOutputs.every((output) =>
-        output.includes("everything compiles"),
+        output.includes("No errors or warnings found in net function code."),
       ),
     ).toBe(true);
     expect(
diff --git a/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/ai-assistant-panel/format-diagnostics-for-ai.test.ts b/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/ai-assistant-panel/format-diagnostics-for-ai.test.ts
index 45e72d55820..c8e2a24b72d 100644
--- a/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/ai-assistant-panel/format-diagnostics-for-ai.test.ts
+++ b/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/ai-assistant-panel/format-diagnostics-for-ai.test.ts
@@ -50,13 +50,13 @@ const diagnostic = (
 });
 
 describe("formatDiagnosticsForAi", () => {
-  test("reports an empty diagnostics state", () => {
+  test("reports that no errors or warnings were found in net function code", () => {
     expect(
       formatDiagnosticsForAi({
         definition,
         diagnosticsByUri: new Map(),
       }),
-    ).toBe("No errors detected in your model – everything compiles!");
+    ).toBe("No errors or warnings found in net function code.");
   });
 
   test("formats transition and differential-equation diagnostics", () => {
diff --git a/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/ai-assistant-panel/format-diagnostics-for-ai.ts b/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/ai-assistant-panel/format-diagnostics-for-ai.ts
index ca313681623..0ddaa881f4f 100644
--- a/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/ai-assistant-panel/format-diagnostics-for-ai.ts
+++ b/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/ai-assistant-panel/format-diagnostics-for-ai.ts
@@ -62,7 +62,7 @@ export const formatDiagnosticsForAi = ({
   );
 
   if (diagnostics.length === 0) {
-    return "No errors detected in your model – everything compiles!";
+    return "No errors or warnings found in net function code.";
   }
 
   const shownDiagnostics = diagnostics.slice(0, maxDiagnostics);
diff --git a/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/ai-assistant-panel/read-current-diagnostics.test.ts b/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/ai-assistant-panel/read-current-diagnostics.test.ts
index 3075b189e70..825d3579a94 100644
--- a/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/ai-assistant-panel/read-current-diagnostics.test.ts
+++ b/libs/@hashintel/petrinaut/src/ui/views/Editor/panels/ai-assistant-panel/read-current-diagnostics.test.ts
@@ -30,7 +30,7 @@ describe("readCurrentDiagnostics", () => {
     try {
       await expect(
         readCurrentDiagnostics(instance, request),
-      ).resolves.toContain("everything compiles");
+      ).resolves.toContain("No errors or warnings found in net function code.");
       instance.mutations.addParameter({
         id: "rate",
         name: "Rate",
@@ -40,7 +40,7 @@ describe("readCurrentDiagnostics", () => {
       });
       await expect(
         readCurrentDiagnostics(instance, request),
-      ).resolves.toContain("everything compiles");
+      ).resolves.toContain("No errors or warnings found in net function code.");
       expect(
         request.mock.calls.map(([definition]) => definition.parameters.length),
       ).toEqual([0, 1]);
@@ -69,7 +69,9 @@ describe("readCurrentDiagnostics", () => {
       });
       result.resolve({ byUri: new Map(), total: 0, errorCount: 0 });
       await expect(read).resolves.toMatch(/changed.*check again/iu);
-      await expect(read).resolves.not.toMatch(/everything compiles/iu);
+      await expect(read).resolves.not.toContain(
+        "No errors or warnings found in net function code.",
+      );
     } finally {
       instance.dispose();
     }
diff --git a/libs/@hashintel/petrinaut/vite.config.ts b/libs/@hashintel/petrinaut/vite.config.ts
index e8cd7b777c3..3d8a969a454 100644
--- a/libs/@hashintel/petrinaut/vite.config.ts
+++ b/libs/@hashintel/petrinaut/vite.config.ts
@@ -8,8 +8,8 @@ const externalDependencies = [
   "@hashintel/ds-components",
   "@hashintel/ds-helpers",
   /^@hashintel\/petrinaut-core(\/.*)?$/,
-  "react",
-  "react-dom",
+  /^react(\/.*)?$/,
+  /^react-dom(\/.*)?$/,
   "@xyflow/react",
   "@babel/standalone",
   // Pure-CJS dep pulled in transitively by @tanstack/react-form →
diff --git a/libs/@local/petrinaut-arch-docs/content/ai/snapshot-diagnostics.mdx b/libs/@local/petrinaut-arch-docs/content/ai/snapshot-diagnostics.mdx
new file mode 100644
index 00000000000..454a64091e5
--- /dev/null
+++ b/libs/@local/petrinaut-arch-docs/content/ai/snapshot-diagnostics.mdx
@@ -0,0 +1,35 @@
+---
+title: Snapshot diagnostics
+description: Check a captured net through a correlated language-worker request.
+attachTo: core.lsp
+sidebar_order: 20
+---
+
+`LanguageClient.requestDiagnostics(sdcpn, extensions)` returns TypeScript and HIR
+diagnostics for the supplied net snapshot. Callers receive a response even
+when the diagnostics match the previous check.
+
+![Snapshot diagnostics flow](@diagrams/snapshot-diagnostics.svg)
+
+The [language worker](layer:core.lsp.worker) checks the snapshot separately
+from temporary editor sessions. Its response carries the request ID, so an
+editor diagnostic update cannot complete another caller's check. Worker
+errors and language-client disposal reject pending requests.
+
+The [React language provider](layer:react.lsp) exposes this method to the AI's
+`getNetCompilationErrors` tool. The tool captures the current net and formats
+the returned diagnostics. The editor continues to receive its own diagnostic
+updates. See [compiling user code](doc:simulation/user-code) for the distinction
+between TypeScript diagnostics and simulation compilation.
+
+:::danger[Important: worker timeout]
+Requests have no timeout. An unresponsive worker can leave a check pending
+until the language client is disposed.
+Tracked in [FE-1665](https://linear.app/hash/issue/FE-1665).
+:::
+
+:::danger[Important: instance API]
+AI diagnostics still use the React language provider. Exposing this capability
+through `PetrinautInstance` requires a headless diagnostics contract.
+Tracked separately in [FE-754](https://linear.app/hash/issue/FE-754).
+:::
diff --git a/libs/@local/petrinaut-arch-docs/content/diagrams/snapshot-diagnostics.d2 b/libs/@local/petrinaut-arch-docs/content/diagrams/snapshot-diagnostics.d2
new file mode 100644
index 00000000000..c810504f6ba
--- /dev/null
+++ b/libs/@local/petrinaut-arch-docs/content/diagrams/snapshot-diagnostics.d2
@@ -0,0 +1,10 @@
+direction: down
+vars: {d2-config: {theme-id: 0}}
+client: "Language client"
+worker: "Language worker"
+snapshot: "Check supplied snapshot"
+reply: "Resolve matching request"
+client -> worker: "snapshot + ID"
+worker -> snapshot
+snapshot -> reply: "diagnostics + ID"
+reply -> client: "result / error"