fix: defer Workspace Build output channel creation until first write

Constructing TerminalOutputChannel previously called
createOutputChannel and show(true) immediately, which forced the
Output panel open even on reconnects to an already-running workspace
where no build logs would ever be written. The empty channel was
disposed shortly after, but the Output panel itself stayed visible.

Defer both calls to the first write, so reconnects to a running
workspace never create the channel and never pop the panel.

Author: EhabY

CHANGELOG.md

@@ -5,6 +5,13 @@
      from published versions since it shows up in the VS Code extension changelog
      tab and is confusing to users. Add it back between releases if needed. -->
 
+## Unreleased
+
+### Fixed
+
+- The **Coder: Workspace Build** output channel is no longer created when reconnecting to an
+  already-running workspace, so the Output panel doesn't pop open empty.
+
 ## [v1.14.4-pre](https://github.com/coder/vscode-coder/releases/tag/v1.14.4-pre) 2026-04-20
 
 ### Added

src/remote/terminalOutputChannel.ts

@@ -1,20 +1,25 @@
 import stripAnsi from "strip-ansi";
 import * as vscode from "vscode";
 
-/** Adapts terminal-style output for a VS Code OutputChannel. Strips ANSI escape sequences and carriage returns. */
+/**
+ * Adapts terminal-style output for a VS Code OutputChannel.
+ * Strips ANSI escape sequences and carriage returns;
+ * creates the underlying channel lazily on first write.
+ */
 export class TerminalOutputChannel implements vscode.Disposable {
-	private readonly channel: vscode.OutputChannel;
+	private channel: vscode.OutputChannel | undefined;
 
-	constructor(name: string) {
-		this.channel = vscode.window.createOutputChannel(name);
-		this.channel.show(true);
-	}
+	constructor(private readonly name: string) {}
 
 	write(data: string): void {
+		if (!this.channel) {
+			this.channel = vscode.window.createOutputChannel(this.name);
+			this.channel.show(true);
+		}
 		this.channel.append(stripAnsi(data).replace(/\r/g, ""));
 	}
 
 	dispose(): void {
-		this.channel.dispose();
+		this.channel?.dispose();
 	}
 }

test/unit/remote/terminalOutputChannel.test.ts

@@ -27,4 +27,13 @@ describe("TerminalOutputChannel", () => {
 	])("%s", (_label, input, expected) => {
 		expect(setup(input).content.join("")).toBe(expected);
 	});
+
+	it("does not create the channel until first write", () => {
+		vi.mocked(vscode.window.createOutputChannel).mockClear();
+		const channel = new TerminalOutputChannel("test");
+		expect(vscode.window.createOutputChannel).not.toHaveBeenCalled();
+
+		channel.write("hello");
+		expect(vscode.window.createOutputChannel).toHaveBeenCalledOnce();
+	});
 });