diff --git a/editors/vscode/src/compiler.cjs b/editors/vscode/src/compiler.cjs
index e8078845..689dc78e 100644
--- a/editors/vscode/src/compiler.cjs
+++ b/editors/vscode/src/compiler.cjs
@@ -1,6 +1,6 @@
 "use strict";
 // Generated by scripts/build-editor-compiler.mjs. Do not edit directly.
-// WRN editor compiler source hash: 2987e8e9d91b793818a195395e740d35d0d5c2a320ff1c3a5ae77363850c7b8e
+// WRN editor compiler source hash: 4ba6ddaf22c0a33fa1c2a108a97f077a69c0a46de9fe031c0a00e38863fab613
 // WRN editor compiler generator hash: a54ca847c758bc98d8e353ad6d70088df31de1820f6cf9d1c3462505f563e6b8
 // Generated with TypeScript: 6.0.3
 const __nodeRequire = require;
@@ -6762,7 +6762,7 @@ function parse(source) {
                         break;
                     }
                     if (lx.peek().type === "lbrace") {
-                        throw new ParseError(`"${rawMode} { … }" data blocks were removed. Declare API calls in a page-level "apis { }" block, and move mode-scoped helpers into "functions { shared function … }".`);
+                        throw new ParseError(`"${rawMode} { … }" data blocks were removed. Declare API calls in a page-level "apis { }" block, and move mode-scoped helpers into "functions { shared function … }" (at offset ${kw.pos}).`);
                     }
                     throw new ParseError(`Expected a ${rawMode} state block or hydrate assignment`);
                 }
diff --git a/editors/vscode/src/extension.bundle.cjs b/editors/vscode/src/extension.bundle.cjs
index a7f79288..75be8487 100644
--- a/editors/vscode/src/extension.bundle.cjs
+++ b/editors/vscode/src/extension.bundle.cjs
@@ -1,4 +1,4 @@
-// WRN editor extension source hash: d0ca0feee6516ae43e902e6aea0424bc5c3d05790708eb8a8c68c98162eb99bb
+// WRN editor extension source hash: 566bce98338a6a99c6c5c15017d92b3a5fd8ed376dd6abd932179a1e79c00f70
 // WRN editor extension generator hash: 456d1d614e44e5fb1f19b784176c09cf2ade9b64ef73a17934c2698150b62728
 "use strict";
 var __commonJS = (cb, mod) => () => (mod || cb((mod = { exports: {} }).exports, mod), mod.exports);
diff --git a/editors/vscode/src/language-server.cjs b/editors/vscode/src/language-server.cjs
index 18057976..9cb78f44 100644
--- a/editors/vscode/src/language-server.cjs
+++ b/editors/vscode/src/language-server.cjs
@@ -1,5 +1,5 @@
 #!/usr/bin/env node
-// WRN editor language server source hash: 2e1803dd46a175316931c0390c5af90dc35a5cd2299798014cbe46b075fee15d
+// WRN editor language server source hash: a8bac4fc444116cc73f898d51989b058370ba9cfd8413b62974a8ce2d841ab6f
 // WRN editor language server generator hash: f593a44aaf05495b789ce7a3086bee1eebb951b884d41c0e017bbcfe5f547e72
 // @bun @bun-cjs
 (function(exports, require, module, __filename, __dirname) {var __create = Object.create;
@@ -171799,7 +171799,7 @@ function parse(source) {
             break;
           }
           if (lx.peek().type === "lbrace") {
-            throw new ParseError(`"${rawMode} { … }" data blocks were removed. Declare API calls in a page-level "apis { }" block, and move mode-scoped helpers into "functions { shared function … }".`);
+            throw new ParseError(`"${rawMode} { … }" data blocks were removed. Declare API calls in a page-level "apis { }" block, and move mode-scoped helpers into "functions { shared function … }" (at offset ${kw.pos}).`);
           }
           throw new ParseError(`Expected a ${rawMode} state block or hydrate assignment`);
         }
diff --git a/packages/language-server/test/removed-construct-diagnostics.test.ts b/packages/language-server/test/removed-construct-diagnostics.test.ts
new file mode 100644
index 00000000..bbe9692c
--- /dev/null
+++ b/packages/language-server/test/removed-construct-diagnostics.test.ts
@@ -0,0 +1,120 @@
+import { expect, test } from "bun:test";
+import { documentDiagnostics } from "../src/index.ts";
+
+// documentDiagnostics is the language server's actual diagnostic entry point.
+// The plan's draft guessed a `diagnoseWrn` export that does not exist.
+
+// These two tests are the plan's original assertions, kept verbatim. They
+// already passed before this change — the message produced by the parser
+// named "apis" from the start — so on their own they are a false-green:
+// they would not catch a regression to the fix below. They stay as cheap
+// regression guards, not as the load-bearing coverage for this task.
+test("an ssr data block is flagged and names the replacement", () => {
+  const diagnostics = documentDiagnostics({
+    uri: "file:///removed-ssr.wrn",
+    text: `page P {
+  ssr { api x GET /api/x { response { return data } } }
+  view { <main>x</main> }
+}
+`,
+  });
+
+  expect(diagnostics.length).toBeGreaterThan(0);
+  expect(diagnostics[0]!.message).toContain("apis");
+});
+
+test("client state is not flagged", () => {
+  const diagnostics = documentDiagnostics({
+    uri: "file:///client-state.wrn",
+    text: `page P {
+  client state { count = 0 }
+  view { <main>x</main> }
+}
+`,
+  });
+
+  expect(diagnostics.filter((item) => item.severity === 1)).toEqual([]);
+});
+
+// --- Load-bearing tests -----------------------------------------------
+//
+// The message alone doesn't prove the diagnostic is useful: before the fix,
+// documentDiagnostics reported this error at line 0 / character 0 for every
+// input, no matter where the offending block actually was. These tests pin
+// the range to the real position of the "ssr" / "client" keyword, with the
+// block moved off line 1 so a hardcoded line number cannot pass.
+
+test("an ssr block diagnostic lands on the ssr keyword, not offset zero", () => {
+  const diagnostics = documentDiagnostics({
+    uri: "file:///removed-ssr-position.wrn",
+    text: `page P {
+  ssr { api x GET /api/x { response { return data } } }
+  view { <main>x</main> }
+}
+`,
+  });
+
+  expect(diagnostics.length).toBeGreaterThan(0);
+  // "  ssr { ... }" — the keyword starts at line 1 (0-indexed), character 2.
+  expect(diagnostics[0]!.range.start).toEqual({ line: 1, character: 2 });
+});
+
+test("a client block diagnostic lands on the client keyword when it is not on line 1", () => {
+  const diagnostics = documentDiagnostics({
+    uri: "file:///removed-client-position.wrn",
+    text: `page P {
+  view { <main>x</main> }
+  client { api x GET /api/x { response { return data } } }
+}
+`,
+  });
+
+  expect(diagnostics.length).toBeGreaterThan(0);
+  // The client block is on line 2 (0-indexed) here, preceded by "view { ... }"
+  // on line 1 — a diagnostic hardcoded to line 1 would fail this assertion.
+  expect(diagnostics[0]!.range.start).toEqual({ line: 2, character: 2 });
+});
+
+// --- Legal `client` forms stay legal ------------------------------------
+//
+// `client` is one word with several jobs. Only the `ssr { }` / `client { }`
+// data-block form was removed; these forms must never be flagged.
+
+test("client state block produces no error-severity diagnostic", () => {
+  const diagnostics = documentDiagnostics({
+    uri: "file:///client-state-2.wrn",
+    text: `page P {
+  client state { count = 0 }
+  view { <main>x</main> }
+}
+`,
+  });
+
+  expect(diagnostics.filter((item) => item.severity === 1)).toEqual([]);
+});
+
+test('runtime = "client" produces no error-severity diagnostic', () => {
+  const diagnostics = documentDiagnostics({
+    uri: "file:///runtime-client.wrn",
+    text: `page P {
+  runtime = "client"
+  view { <main>x</main> }
+}
+`,
+  });
+
+  expect(diagnostics.filter((item) => item.severity === 1)).toEqual([]);
+});
+
+test("client function inside functions { } produces no error-severity diagnostic", () => {
+  const diagnostics = documentDiagnostics({
+    uri: "file:///client-function.wrn",
+    text: `page P {
+  functions { client function go() { console.log(1) } }
+  view { <main>x</main> }
+}
+`,
+  });
+
+  expect(diagnostics.filter((item) => item.severity === 1)).toEqual([]);
+});
diff --git a/packages/syntax/src/parser.ts b/packages/syntax/src/parser.ts
index 658ef296..2631d2e9 100644
--- a/packages/syntax/src/parser.ts
+++ b/packages/syntax/src/parser.ts
@@ -685,7 +685,7 @@ export function parse(source: string): PageAst {
           }
           if (lx.peek().type === "lbrace") {
             throw new ParseError(
-              `"${rawMode} { … }" data blocks were removed. Declare API calls in a page-level "apis { }" block, and move mode-scoped helpers into "functions { shared function … }".`,
+              `"${rawMode} { … }" data blocks were removed. Declare API calls in a page-level "apis { }" block, and move mode-scoped helpers into "functions { shared function … }" (at offset ${kw.pos}).`,
             );
           }
           throw new ParseError(`Expected a ${rawMode} state block or hydrate assignment`);