Merge PR #2950: feat(coding-agent): add copy affordance to completed /btw answers (@wolfiesch)

Adds 'c copy' to the completed /btw panel footer (alongside b branch / Esc
dismiss), copying the sanitized visible answer to the clipboard. The copy
shortcut is guarded by canCopyBtw + main-editor focus + empty editor.

packages/coding-agent/src/modes/components/btw-panel.ts

@@ -16,6 +16,7 @@ export class BtwPanelComponent extends Container {
 	#state: BtwPanelState = "running";
 	#answer = "";
 	#errorMessage: string | undefined;
+	#visibleAnswer = "";
 	#closed = false;
 
 	constructor(options: BtwPanelComponentOptions) {
@@ -28,12 +29,14 @@ export class BtwPanelComponent extends Container {
 	appendText(delta: string): void {
 		if (!delta || this.#closed) return;
 		this.#answer += delta;
+		this.#visibleAnswer = replaceTabs(this.#answer).trim();
 		this.#rebuild();
 	}
 
 	setAnswer(text: string): void {
 		if (this.#closed) return;
 		this.#answer = text;
+		this.#visibleAnswer = replaceTabs(text).trim();
 		this.#rebuild();
 	}
 
@@ -59,7 +62,16 @@ export class BtwPanelComponent extends Container {
 	}
 
 	isBranchable(): boolean {
-		return this.#state === "complete" && this.#answer.trim().length > 0;
+		return this.isCopyable();
+	}
+
+	isCopyable(): boolean {
+		return this.#state === "complete" && this.#visibleAnswer.length > 0;
+	}
+
+	getCopyText(): string | undefined {
+		if (!this.isCopyable()) return undefined;
+		return this.#visibleAnswer;
 	}
 
 	close(): void {
@@ -89,7 +101,7 @@ export class BtwPanelComponent extends Container {
 			case "running":
 				return theme.fg("muted", "Esc cancel /btw");
 			case "complete":
-				return theme.fg("muted", this.isBranchable() ? "b branch · Esc dismiss" : "Esc dismiss");
+				return theme.fg("muted", this.isCopyable() ? "c copy · b branch to chat · Esc dismiss" : "Esc dismiss");
 			case "aborted":
 				return theme.fg("warning", `${theme.status.warning} Cancelled · Esc dismiss`);
 			case "error":
@@ -101,7 +113,7 @@ export class BtwPanelComponent extends Container {
 		if (this.#state === "error") {
 			return new Text(theme.fg("error", replaceTabs(this.#errorMessage ?? "Unknown error")), 1, 0);
 		}
-		const text = replaceTabs(this.#answer).trim();
+		const text = this.#visibleAnswer;
 		if (!text) {
 			const waiting =
 				this.#state === "running" ? `${theme.status.pending} Waiting for response…` : "No text returned.";