feat(tui): support autocomplete trigger characters

closes #4703

packages/coding-agent/CHANGELOG.md

@@ -4,12 +4,10 @@
 
 ### Added
 
-<<<<<<< Updated upstream
 - Added `areExperimentalFeaturesEnabled` feature guard to allow users to opt-in to early features.
 - Added `ctx.isProjectTrusted()` for extensions to observe the effective project trust decision, including temporary trust decisions ([#5523](https://github.com/earendil-works/pi/issues/5523)).
-=======
 - Added a global `defaultProjectTrust` setting to choose whether unresolved project trust asks, always trusts, or never trusts by default.
->>>>>>> Stashed changes
+- Added extension autocomplete trigger character support for `ctx.ui.addAutocompleteProvider()` wrappers ([#4703](https://github.com/earendil-works/pi/issues/4703)).
 
 ### Fixed
 

packages/coding-agent/docs/extensions.md

@@ -2281,6 +2281,7 @@ ctx.ui.pasteToEditor("pasted content");
 
 // Stack custom autocomplete behavior on top of the built-in provider
 ctx.ui.addAutocompleteProvider((current) => ({
+  triggerCharacters: ["#"],
   async getSuggestions(lines, line, col, options) {
     const beforeCursor = (lines[line] ?? "").slice(0, col);
     const match = beforeCursor.match(/(?:^|[ \t])#([^\s#]*)$/);
@@ -2329,7 +2330,7 @@ Custom working-indicator frames are rendered verbatim. If you want colors, add t
 
 ### Autocomplete Providers
 
-Use `ctx.ui.addAutocompleteProvider()` to stack custom autocomplete logic on top of the built-in slash-command and path provider.
+Use `ctx.ui.addAutocompleteProvider()` to stack custom autocomplete logic on top of the built-in slash-command and path provider. Set `triggerCharacters` for custom natural triggers such as `$`.
 
 Typical pattern:
 
@@ -2341,6 +2342,7 @@ Typical pattern:
 ```typescript
 pi.on("session_start", (_event, ctx) => {
   ctx.ui.addAutocompleteProvider((current) => ({
+    triggerCharacters: ["#"],
     async getSuggestions(lines, cursorLine, cursorCol, options) {
       const line = lines[cursorLine] ?? "";
       const beforeCursor = line.slice(0, cursorCol);

packages/coding-agent/src/modes/interactive/interactive-mode.ts

@@ -555,8 +555,13 @@ export class InteractiveMode {
 
 	private setupAutocompleteProvider(): void {
 		let provider = this.createBaseAutocompleteProvider();
+		const triggerCharacters: string[] = [];
 		for (const wrapProvider of this.autocompleteProviderWrappers) {
 			provider = wrapProvider(provider);
+			triggerCharacters.push(...(provider.triggerCharacters ?? []));
+		}
+		if (triggerCharacters.length > 0) {
+			provider.triggerCharacters = [...new Set(triggerCharacters)];
 		}
 
 		this.autocompleteProvider = provider;

packages/coding-agent/test/interactive-mode-status.test.ts

@@ -324,6 +324,36 @@ describe("InteractiveMode.setupAutocompleteProvider", () => {
 		expect(provider.shouldTriggerFileCompletion?.(["foo"], 0, 3)).toBe(true);
 		expect(calls).toEqual(["shouldTrigger:wrap2", "shouldTrigger:wrap1"]);
 	});
+
+	test("merges triggerCharacters from wrapper factories", () => {
+		const defaultEditor = { setAutocompleteProvider: vi.fn() };
+		const customEditor = { setAutocompleteProvider: vi.fn() };
+		const passThrough =
+			(triggerCharacters: string[]): AutocompleteProviderFactory =>
+			(current) => ({
+				triggerCharacters,
+				getSuggestions: (lines, cursorLine, cursorCol, options) =>
+					current.getSuggestions(lines, cursorLine, cursorCol, options),
+				applyCompletion: (lines, cursorLine, cursorCol, item, prefix) =>
+					current.applyCompletion(lines, cursorLine, cursorCol, item, prefix),
+			});
+
+		const fakeThis = {
+			createBaseAutocompleteProvider: () => new CombinedAutocompleteProvider([], "/tmp/project", undefined),
+			defaultEditor,
+			editor: customEditor,
+			autocompleteProviderWrappers: [passThrough(["$"]), passThrough(["!"])],
+		};
+
+		(
+			InteractiveMode as unknown as {
+				prototype: { setupAutocompleteProvider: (this: typeof fakeThis) => void };
+			}
+		).prototype.setupAutocompleteProvider.call(fakeThis);
+
+		const provider = defaultEditor.setAutocompleteProvider.mock.calls[0]?.[0] as AutocompleteProvider;
+		expect(provider.triggerCharacters).toEqual(["$", "!"]);
+	});
 });
 
 describe("InteractiveMode.showLoadedResources", () => {