diff --git a/web/workspace/src/lib/workspace/config-source/completion.ts b/web/workspace/src/lib/workspace/config-source/completion.ts
index 8467bdb2..7a4d755c 100644
--- a/web/workspace/src/lib/workspace/config-source/completion.ts
+++ b/web/workspace/src/lib/workspace/config-source/completion.ts
@@ -13,12 +13,11 @@ type ConfigSourceCompletionItem = {
 };
 
 export function toCodeMirrorCompletion(
-  source: string,
   result: ConfigSourceCompletionResult | null,
 ): CompletionResult | null {
   if (!result) return null;
   return {
-    from: utf8ByteOffsetToUtf16(source, result.from),
+    from: result.from,
     options: result.items.map((item) => ({
       label: item.label,
       type: item.kind,
@@ -27,31 +26,3 @@ export function toCodeMirrorCompletion(
     })),
   };
 }
-
-function utf8ByteOffsetToUtf16(source: string, byteOffset: number): number {
-  if (!Number.isSafeInteger(byteOffset) || byteOffset < 0) {
-    throw new RangeError(
-      "completion byte offset must be a non-negative integer",
-    );
-  }
-
-  let bytes = 0;
-  let utf16 = 0;
-  for (const character of source) {
-    if (bytes === byteOffset) return utf16;
-    const codePoint = character.codePointAt(0)!;
-    bytes += codePoint <= 0x7f
-      ? 1
-      : codePoint <= 0x7ff
-      ? 2
-      : codePoint <= 0xffff
-      ? 3
-      : 4;
-    utf16 += character.length;
-    if (bytes > byteOffset) {
-      throw new RangeError("completion byte offset splits a UTF-8 code point");
-    }
-  }
-  if (bytes === byteOffset) return utf16;
-  throw new RangeError("completion byte offset is outside the source");
-}
diff --git a/web/workspace/src/lib/workspace/config-source/toolchain.ts b/web/workspace/src/lib/workspace/config-source/toolchain.ts
index 510b4a00..53969a0f 100644
--- a/web/workspace/src/lib/workspace/config-source/toolchain.ts
+++ b/web/workspace/src/lib/workspace/config-source/toolchain.ts
@@ -79,7 +79,7 @@ export class ConfigSourceToolchain {
       utf16Offset,
       explicit,
     });
-    return toCodeMirrorCompletion(source, result);
+    return toCodeMirrorCompletion(result);
   }
   format(source: string): Promise<string> {
     return this.#request({ kind: "format", source });
diff --git a/web/workspace/src/lib/workspace/config-source/vite-dedupe.ts b/web/workspace/src/lib/workspace/config-source/vite-dedupe.ts
new file mode 100644
index 00000000..c41ab5ba
--- /dev/null
+++ b/web/workspace/src/lib/workspace/config-source/vite-dedupe.ts
@@ -0,0 +1,7 @@
+export const CODEMIRROR_VITE_DEDUPE = [
+  "@codemirror/autocomplete",
+  "@codemirror/language",
+  "@codemirror/state",
+  "@codemirror/view",
+  "@lezer/common",
+];
diff --git a/web/workspace/src/lib/workspace/settings/DecodalSourceEditor.svelte b/web/workspace/src/lib/workspace/settings/DecodalSourceEditor.svelte
index 12623b97..821c8a9e 100644
--- a/web/workspace/src/lib/workspace/settings/DecodalSourceEditor.svelte
+++ b/web/workspace/src/lib/workspace/settings/DecodalSourceEditor.svelte
@@ -1,6 +1,13 @@
 <script lang="ts">
   import { untrack } from 'svelte';
-  import { autocompletion, type CompletionContext, type CompletionResult } from '@codemirror/autocomplete';
+  import {
+    autocompletion,
+    completionKeymap,
+    completionStatus,
+    startCompletion,
+    type CompletionContext,
+    type CompletionResult,
+  } from '@codemirror/autocomplete';
   import { HighlightStyle, syntaxHighlighting } from '@codemirror/language';
   import { Compartment, EditorState } from '@codemirror/state';
   import { EditorView, keymap, lineNumbers, highlightActiveLine, drawSelection } from '@codemirror/view';
@@ -69,6 +76,18 @@
     '.cm-tooltip-autocomplete > ul > li[aria-selected]': { background: 'var(--interactive-selected)', color: 'var(--text-strong)' },
   });
 
+  function scheduleCompletion(editor: EditorView) {
+    queueMicrotask(() => {
+      if (
+        editor.hasFocus &&
+        !editor.state.facet(EditorState.readOnly) &&
+        completionStatus(editor.state) === null
+      ) {
+        startCompletion(editor);
+      }
+    });
+  }
+
   $effect(() => {
     if (!host || untrack(() => view)) return;
     const initialValue = untrack(() => value);
@@ -86,11 +105,16 @@
           highlightActiveLine(),
           decodal({ highlight: false }),
           syntaxHighlighting(syntaxTheme),
-          ...(handleComplete ? [autocompletion({ override: [async (context: CompletionContext) => {
-            const doc = context.state.doc.toString();
-            return await handleComplete(doc, context.pos, context.explicit);
-          }] })] : []),
-          keymap.of([]),
+          autocompletion({
+            override: [
+              async (context: CompletionContext) => {
+                if (!handleComplete) return null;
+                const doc = context.state.doc.toString();
+                return await handleComplete(doc, context.pos, context.explicit);
+              },
+            ],
+          }),
+          keymap.of(completionKeymap),
           fixedSchemaWrapperCompartment.of(
             initialFixedSchemaWrapper ? fixedSchemaWrapperExtension() : [],
           ),
@@ -98,7 +122,16 @@
             EditorState.readOnly.of(initialReadonly),
             EditorView.editable.of(!initialReadonly),
           ]),
+          EditorView.domEventHandlers({
+            focus: (_event, editor) => {
+              scheduleCompletion(editor);
+              return false;
+            },
+          }),
           EditorView.updateListener.of((update) => {
+            if (update.selectionSet && !update.docChanged) {
+              scheduleCompletion(update.view);
+            }
             if (update.docChanged) handleChange(update.state.doc.toString());
           }),
           theme,
@@ -123,6 +156,7 @@
         EditorView.editable.of(!nextReadonly),
       ]),
     });
+    if (!nextReadonly) scheduleCompletion(editor);
   });
 
   $effect(() => {
diff --git a/web/workspace/test/config-source/editor-state.test.ts b/web/workspace/test/config-source/editor-state.test.ts
index 8ce6dda9..3f49e021 100644
--- a/web/workspace/test/config-source/editor-state.test.ts
+++ b/web/workspace/test/config-source/editor-state.test.ts
@@ -1,3 +1,5 @@
+import { CODEMIRROR_VITE_DEDUPE } from "../../src/lib/workspace/config-source/vite-dedupe.ts";
+
 declare const Deno: {
   test(name: string, fn: () => Promise<void> | void): void;
   readTextFile(path: URL): Promise<string>;
@@ -7,6 +9,23 @@ function assert(condition: unknown, message: string): asserts condition {
   if (!condition) throw new Error(message);
 }
 
+Deno.test("Vite deduplicates CodeMirror stateful packages", () => {
+  for (
+    const packageName of [
+      "@codemirror/autocomplete",
+      "@codemirror/language",
+      "@codemirror/state",
+      "@codemirror/view",
+      "@lezer/common",
+    ]
+  ) {
+    assert(
+      CODEMIRROR_VITE_DEDUPE.includes(packageName),
+      `Vite must deduplicate ${packageName}`,
+    );
+  }
+});
+
 Deno.test("config editor snapshots Svelte proxies before cloning baselines", async () => {
   const source = await Deno.readTextFile(
     new URL(
@@ -72,6 +91,13 @@ Deno.test("Decodal editor follows readonly prop changes after mount", async () =
       !source.includes("--border-subtle"),
     "CodeMirror theme must use workspace tokens that actually exist",
   );
+  assert(
+    source.includes("keymap.of(completionKeymap)") &&
+      source.includes("startCompletion(editor)") &&
+      source.includes("update.selectionSet && !update.docChanged") &&
+      source.includes("completionStatus(editor.state) === null"),
+    "completion should be explicitly available and start when an editable cursor moves into an empty schema position",
+  );
   assert(
     source.includes("fixedSchemaWrapperCompartment.reconfigure") &&
       source.includes("fixedSchemaWrapperExtension()") &&
diff --git a/web/workspace/test/config-source/toolchain.test.ts b/web/workspace/test/config-source/toolchain.test.ts
index 2140fb02..28dfbc0c 100644
--- a/web/workspace/test/config-source/toolchain.test.ts
+++ b/web/workspace/test/config-source/toolchain.test.ts
@@ -67,10 +67,9 @@ Deno.test("toolchain converts reactive-like proxies to plain Worker messages", a
   );
 });
 
-Deno.test("toolchain adapts WASM completion items and byte offsets for CodeMirror", () => {
-  const source = "let 名 = tru";
-  const result = toCodeMirrorCompletion(source, {
-    from: new TextEncoder().encode("let 名 = ").length,
+Deno.test("toolchain preserves WASM UTF-16 completion ranges for CodeMirror", () => {
+  const result = toCodeMirrorCompletion({
+    from: "let 名 = ".length,
     items: [
       {
         label: "true",
@@ -84,7 +83,7 @@ Deno.test("toolchain adapts WASM completion items and byte offsets for CodeMirro
   assert(result !== null, "WASM completion should produce a CodeMirror result");
   assert(
     result.from === "let 名 = ".length,
-    "byte offsets should become UTF-16 offsets",
+    "WASM UTF-16 offsets should be preserved for CodeMirror",
   );
   assert(
     result.options.length === 1,
diff --git a/web/workspace/vite.config.ts b/web/workspace/vite.config.ts
index 6598b18c..1f6954b6 100644
--- a/web/workspace/vite.config.ts
+++ b/web/workspace/vite.config.ts
@@ -1,9 +1,14 @@
 import { sveltekit } from "@sveltejs/kit/vite";
 import { defineConfig } from "vite";
+import { CODEMIRROR_VITE_DEDUPE } from "./src/lib/workspace/config-source/vite-dedupe";
 
 export default defineConfig({
   plugins: [sveltekit()],
 
+  resolve: {
+    dedupe: CODEMIRROR_VITE_DEDUPE,
+  },
+
   server: {
     host: "localhost",
     port: 5173,