fix(tui): re-query autocomplete picker on cursor movement

moveCursor() repositioned the cursor but never called updateAutocomplete()
or cancelAutocomplete(), unlike insertCharacter()/handleBackspace(). So an
open autocomplete picker went stale when the cursor moved: e.g. typing
`/cmd ` (argument menu open) then arrowing Left back into the command name
left the argument list showing against a `/cmd` prefix, and a Tab there
concatenated the stale suggestion onto the partial command name
(e.g. `/swarepo`).

Sync the picker at the end of moveCursor(): when a picker is open, re-query
via updateAutocomplete(), which refreshes the list for the new cursor
position or closes it when nothing matches.

Adds a regression test in test/editor.test.ts (verified to fail without the
fix). Fixes earendil-works/pi#5496.

packages/tui/src/components/editor.ts

@@ -1742,6 +1742,18 @@ export class Editor implements Component, Focusable {
 				}
 			}
 		}
+
+		// Keep an open autocomplete picker in sync with the new cursor
+		// position: cursor movement changes the text before the cursor, so a
+		// picker computed for the old position is stale. Re-query so it
+		// refreshes — or closes when the new position yields no suggestions —
+		// mirroring insertCharacter()/handleBackspace(). Without this, arrowing
+		// left from `/cmd ` back into the command name leaves the argument
+		// picker showing against a `/cmd` prefix (and a Tab there would
+		// concatenate the stale suggestion onto the partial command name).
+		if (this.autocompleteState) {
+			this.updateAutocomplete();
+		}
 	}
 
 	/**

packages/tui/test/editor.test.ts

@@ -2250,6 +2250,65 @@ describe("Editor component", () => {
 			assert.strictEqual(editor.isShowingAutocomplete(), true);
 		});
 
+		it("re-queries the autocomplete picker when the cursor moves back into the command name", async () => {
+			// Regression for earendil-works/pi#5496: arrowing left out of a slash
+			// command's argument region must re-query the picker, not leave the
+			// stale argument list showing. Before the fix, moveCursor() never
+			// called updateAutocomplete(), so `/cmd ` (argument menu) + Left kept
+			// displaying the arguments against a `/cmd` prefix — and a Tab there
+			// would concatenate the stale suggestion onto the partial command name.
+			const editor = new Editor(createTestTUI(), defaultEditorTheme);
+
+			const mockProvider: AutocompleteProvider = {
+				getSuggestions: async (lines, _cursorLine, cursorCol) => {
+					const before = (lines[0] || "").slice(0, cursorCol);
+					if (!before.startsWith("/")) return null;
+					// Past the command name (a space before the cursor): offer arguments.
+					if (before.includes(" ")) {
+						return {
+							items: [
+								{ value: "repo", label: "repo" },
+								{ value: "message", label: "message" },
+								{ value: "help", label: "help" },
+							],
+							prefix: before.slice(before.indexOf(" ") + 1),
+						};
+					}
+					// Inside the command name: offer the command name only.
+					return { items: [{ value: "cmd", label: "cmd" }], prefix: before };
+				},
+				applyCompletion,
+			};
+
+			editor.setAutocompleteProvider(mockProvider);
+
+			// Type `/cmd ` so the picker ends up showing the argument list.
+			for (const ch of "/cmd ") {
+				editor.handleInput(ch);
+				await flushAutocomplete();
+			}
+			assert.strictEqual(editor.getText(), "/cmd ");
+			assert.strictEqual(editor.isShowingAutocomplete(), true);
+			const atArg = editor
+				.render(80)
+				.map((l) => stripVTControlCharacters(l))
+				.join("\n");
+			assert.ok(atArg.includes("repo"), "argument menu should be visible at `/cmd `");
+
+			// Arrow Left back into the command name (`/cmd`).
+			editor.handleInput("\x1b[D");
+			await flushAutocomplete();
+
+			// The picker must have re-queried: the stale argument items are gone
+			// (replaced by the command-name suggestion, or the picker closed).
+			const afterMove = editor
+				.render(80)
+				.map((l) => stripVTControlCharacters(l))
+				.join("\n");
+			assert.ok(!afterMove.includes("repo"), "stale argument menu must not survive the cursor move");
+			assert.ok(!afterMove.includes("message"), "stale argument menu must not survive the cursor move");
+		});
+
 		it("debounces # autocomplete while typing", async () => {
 			const editor = new Editor(createTestTUI(), defaultEditorTheme);
 			let suggestionCalls = 0;