feat(coding-agent): added /fresh to reset provider state while keeping session files

- Added `AgentSession.freshSession()` to rotate provider-facing IDs and prune provider stream state.
- Added `/fresh` command handling in the builtin registry and mode command flow.
- Kept persisted session metadata intact during `/fresh` and cleared transient IDs on session switches.
- Invalidated `appendOnlyContext` and provider caches when refreshing provider state.

packages/coding-agent/src/modes/controllers/command-controller.ts

@@ -802,6 +802,18 @@ export class CommandController {
 		await this.#runNewSessionFlow();
 	}
 
+	async handleFreshCommand(): Promise<void> {
+		const result = this.ctx.session.freshSession();
+		if (!result) {
+			this.ctx.showWarning("Wait for the current response to finish or abort it before refreshing provider state.");
+			return;
+		}
+		const stateLabel = result.closedProviderSessions === 1 ? "provider state" : "provider states";
+		this.ctx.statusLine.invalidate();
+		this.ctx.updateEditorTopBorder();
+		this.ctx.showStatus(`Fresh provider session started (${result.closedProviderSessions} ${stateLabel} pruned).`);
+	}
+
 	async handleDropCommand(): Promise<void> {
 		if (!this.ctx.sessionManager.getSessionFile()) {
 			this.ctx.showError("Nothing to drop (in-memory session)");

packages/coding-agent/src/modes/interactive-mode.ts

@@ -2806,6 +2806,10 @@ export class InteractiveMode implements InteractiveModeContext {
 		return this.#commandController.handleClearCommand();
 	}
 
+	handleFreshCommand(): Promise<void> {
+		return this.#commandController.handleFreshCommand();
+	}
+
 	handleDropCommand(): Promise<void> {
 		this.#prepareSessionSwitch();
 		return this.#commandController.handleDropCommand();

packages/coding-agent/src/modes/types.ts

@@ -247,6 +247,7 @@ export interface InteractiveModeContext {
 	handleDumpCommand(): void;
 	handleDebugTranscriptCommand(): Promise<void>;
 	handleClearCommand(): Promise<void>;
+	handleFreshCommand(): Promise<void>;
 	handleDropCommand(): Promise<void>;
 	handleForkCommand(): Promise<void>;
 	handleBashCommand(command: string, excludeFromContext?: boolean): Promise<void>;