feat(coding-agent): Add sessionDir support in settings.json (#2598)

Users can now set sessionDir in global or project settings.json instead
of passing --session-dir on every invocation. CLI flag takes precedence,
then settings.json, then extension hooks.

Closes #2429

Co-authored-by: Sam Collins <81678+smcllns@users.noreply.github.com>
Co-authored-by: Mario Zechner <badlogicgames@gmail.com>

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

@@ -94,6 +94,7 @@ export interface Settings {
 	autocompleteMaxVisible?: number; // Max visible items in autocomplete dropdown (default: 5)
 	showHardwareCursor?: boolean; // Show terminal cursor while still positioning it for IME
 	markdown?: MarkdownSettings;
+	sessionDir?: string; // Custom session storage directory (same format as --session-dir CLI flag)
 }
 
 /** Deep merge settings: project/overrides take precedence, nested objects merge recursively */
@@ -530,6 +531,10 @@ export class SettingsManager {
 		this.save();
 	}
 
+	getSessionDir(): string | undefined {
+		return this.settings.sessionDir;
+	}
+
 	getDefaultProvider(): string | undefined {
 		return this.settings.defaultProvider;
 	}