feat(coding-agent): expand ~ in shellPath setting (#6470)

getShellPath() now runs the configured shellPath through the existing
normalizePath() helper, mirroring getSessionDir(). This lets shellPath
point at a home-directory-relative shell wrapper (e.g.
~/.local/bin/agent-shell-sandbox) and resolves consistently across
machines and OSes with different home directories.

refs #6458

packages/coding-agent/src/core/settings-manager.ts

@@ -95,7 +95,7 @@ export interface Settings {
 	hideThinkingBlock?: boolean;
 	showCacheMissNotices?: boolean; // default: false - show transcript notices for significant prompt-cache misses
 	externalEditor?: string; // Command for Ctrl+G external editor; takes precedence over VISUAL/EDITOR
-	shellPath?: string; // Custom shell path (e.g., for Cygwin users on Windows)
+	shellPath?: string; // Custom shell path (e.g., for Cygwin users on Windows); supports leading ~ expansion
 	quietStartup?: boolean;
 	defaultProjectTrust?: DefaultProjectTrust; // default: "ask"; global setting only
 	shellCommandPrefix?: string; // Prefix prepended to every bash command (e.g., "shopt -s expand_aliases" for alias support)
@@ -876,7 +876,8 @@ export class SettingsManager {
 	}
 
 	getShellPath(): string | undefined {
-		return this.settings.shellPath;
+		const shellPath = this.settings.shellPath;
+		return shellPath ? normalizePath(shellPath) : shellPath;
 	}
 
 	setShellPath(path: string | undefined): void {