diff --git a/packages/pi-tui/src/__tests__/autocomplete.test.ts b/packages/pi-tui/src/__tests__/autocomplete.test.ts
index c3c44ac74..c4a44db76 100644
--- a/packages/pi-tui/src/__tests__/autocomplete.test.ts
+++ b/packages/pi-tui/src/__tests__/autocomplete.test.ts
@@ -119,6 +119,21 @@ describe("CombinedAutocompleteProvider — @ file prefix extraction", () => {
 		const result = provider.getSuggestions(["check @nonexistent_xyz"], 0, 22);
 		assert.ok(result === null || result.items.length >= 0);
 	});
+
+	it("returns null for bare @ with no query to avoid full tree walk (#1824)", () => {
+		const provider = makeProvider([], process.cwd());
+		// A bare "@" produces an empty rawPrefix after stripping the "@".
+		// This must return null to avoid a synchronous full filesystem walk
+		// via the native fuzzyFind addon, which freezes the TUI on large repos.
+		const result = provider.getSuggestions(["@"], 0, 1);
+		assert.equal(result, null, "bare @ should not trigger fuzzy file search");
+	});
+
+	it("returns null for @ after space with no query (#1824)", () => {
+		const provider = makeProvider([], process.cwd());
+		const result = provider.getSuggestions(["look at @"], 0, 9);
+		assert.equal(result, null, "@ after space with no query should not trigger fuzzy file search");
+	});
 });
 
 describe("CombinedAutocompleteProvider — applyCompletion", () => {
diff --git a/packages/pi-tui/src/autocomplete.ts b/packages/pi-tui/src/autocomplete.ts
index 52ea67c25..d0969921f 100644
--- a/packages/pi-tui/src/autocomplete.ts
+++ b/packages/pi-tui/src/autocomplete.ts
@@ -573,9 +573,18 @@ export class CombinedAutocompleteProvider implements AutocompleteProvider {
 	private getFuzzyFileSuggestions(query: string, options: { isQuotedPrefix: boolean }): AutocompleteItem[] {
 		try {
 			const scopedQuery = this.resolveScopedFuzzyQuery(query);
-			const searchPath = scopedQuery?.baseDir ?? this.basePath;
 			const searchQuery = scopedQuery?.query ?? query;
 
+			// Skip the expensive filesystem walk when the query is empty.
+			// An empty query (bare "@" with nothing typed yet) would walk the
+			// entire directory tree via the native fuzzyFind call, blocking
+			// the event loop and freezing the TUI on large repos.
+			if (searchQuery.length === 0 && !scopedQuery) {
+				return [];
+			}
+
+			const searchPath = scopedQuery?.baseDir ?? this.basePath;
+
 			const result = fuzzyFind({
 				query: searchQuery,
 				path: searchPath,
diff --git a/packages/pi-tui/src/components/editor.ts b/packages/pi-tui/src/components/editor.ts
index 0b4b2b525..c9cefb83c 100644
--- a/packages/pi-tui/src/components/editor.ts
+++ b/packages/pi-tui/src/components/editor.ts
@@ -967,13 +967,19 @@ export class Editor implements Component, Focusable {
 				this.tryTriggerAutocomplete();
 			}
 			// Auto-trigger for "@" file reference (fuzzy search)
+			// Debounced: the bare "@" triggers a fuzzyFind call that does a
+			// synchronous filesystem walk via the native addon. Firing it
+			// immediately on the keystroke blocks the event loop and freezes
+			// the TUI on large repos. Debouncing lets subsequent keystrokes
+			// cancel the pending search so the walk only runs once the user
+			// pauses typing.
 			else if (char === "@") {
 				const currentLine = this.state.lines[this.state.cursorLine] || "";
 				const textBeforeCursor = currentLine.slice(0, this.state.cursorCol);
 				// Only trigger if @ is after whitespace or at start of line
 				const charBeforeAt = textBeforeCursor[textBeforeCursor.length - 2];
 				if (textBeforeCursor.length === 1 || charBeforeAt === " " || charBeforeAt === "\t") {
-					this.tryTriggerAutocomplete();
+					this.debouncedTriggerAutocomplete();
 				}
 			}
 			// Also auto-trigger when typing letters in a slash command context
@@ -2116,6 +2122,15 @@ https://github.com/EsotericSoftware/spine-runtimes/actions/runs/19536643416/job/
 	private applyAutocompleteSuggestions(): void {
 		if (!this.autocompleteProvider) return;
 
+		// Deduplicate: skip the (potentially expensive synchronous) lookup
+		// when the prefix hasn't changed since the last call.
+		const currentLine = this.state.lines[this.state.cursorLine] || "";
+		const textBeforeCursor = currentLine.slice(0, this.state.cursorCol);
+		if (this.lastAutocompleteLookupPrefix !== null && this.lastAutocompleteLookupPrefix === textBeforeCursor) {
+			return;
+		}
+		this.lastAutocompleteLookupPrefix = textBeforeCursor;
+
 		const suggestions = this.autocompleteProvider.getSuggestions(
 			this.state.lines,
 			this.state.cursorLine,