fix: respect Pi session directories by cwd

src/server/sessiond/sessionProxyRoutes.ts

@@ -24,7 +24,7 @@ export function registerSessionProxyRoutes(app: FastifyInstance, daemon: Session
   app.get(`${prefix}/sessiond/health`, (_request, reply) => proxy({ method: "GET", url: `${prefix}/health` }, reply));
 
   app.get<{ Params: { sessionId: string } }>(`${prefix}/sessions/:sessionId/events`, { websocket: true }, (socket, request) => {
-    bridgeSockets(socket, daemon.connectWebSocket(`/sessions/${request.params.sessionId}/events`));
+    bridgeSockets(socket, daemon.connectWebSocket(stripPrefix(request.url, prefix)));
   });
 
   app.get(`${prefix}/sessions/events`, { websocket: true }, (socket) => {

src/server/sessions/piSessionManagerGateway.test.ts

@@ -0,0 +1,85 @@
+import { mkdir, mkdtemp, rm, writeFile } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { createPiSessionManagerGateway, defaultPiSessionDir, defaultPiSessionsRoot, SessionDirResolver } from "./piSessionManagerGateway.js";
+import type { PiSessionManager } from "./piSessionService.js";
+
+let tempDir: string;
+let agentDir: string;
+let cwd: string;
+
+beforeEach(async () => {
+  tempDir = await mkdtemp(join(tmpdir(), "pi-web-session-gateway-test-"));
+  agentDir = join(tempDir, "agent");
+  cwd = join(tempDir, "workspace");
+  await mkdir(cwd, { recursive: true });
+});
+
+afterEach(async () => {
+  await rm(tempDir, { recursive: true, force: true });
+});
+
+describe("SessionDirResolver", () => {
+  it("uses Pi default session storage when no Pi override is configured", () => {
+    const resolver = new SessionDirResolver({ agentDir, env: {} });
+
+    expect(resolver.resolve(cwd)).toMatchObject({ source: "pi-default", sessionDir: defaultPiSessionDir(cwd, agentDir), usesConfiguredSessionDir: false });
+    expect(defaultPiSessionsRoot(agentDir)).toBe(join(agentDir, "sessions"));
+  });
+
+  it("uses Pi sessionDir settings and resolves relative paths against the session cwd", async () => {
+    await mkdir(agentDir, { recursive: true });
+    await writeFile(join(agentDir, "settings.json"), `${JSON.stringify({ sessionDir: ".pi/sessions" }, null, 2)}\n`, "utf8");
+
+    const resolver = new SessionDirResolver({ agentDir, env: {} });
+
+    expect(resolver.resolve(cwd)).toMatchObject({ source: "settings", sessionDir: join(cwd, ".pi", "sessions"), usesConfiguredSessionDir: true });
+  });
+
+  it("lets project-local Pi sessionDir settings override global Pi settings for that cwd", async () => {
+    await mkdir(agentDir, { recursive: true });
+    await mkdir(join(cwd, ".pi"), { recursive: true });
+    await writeFile(join(agentDir, "settings.json"), `${JSON.stringify({ sessionDir: join(tempDir, "global-sessions") }, null, 2)}\n`, "utf8");
+    await writeFile(join(cwd, ".pi", "settings.json"), `${JSON.stringify({ sessionDir: ".workspace-sessions" }, null, 2)}\n`, "utf8");
+
+    const resolver = new SessionDirResolver({ agentDir, env: {} });
+
+    expect(resolver.resolve(cwd)).toMatchObject({ source: "settings", sessionDir: join(cwd, ".workspace-sessions"), usesConfiguredSessionDir: true });
+  });
+
+  it("lets the Pi sessionDir environment override Pi settings", async () => {
+    const envDir = join(tempDir, "env-sessions");
+    await mkdir(agentDir, { recursive: true });
+    await writeFile(join(agentDir, "settings.json"), `${JSON.stringify({ sessionDir: join(tempDir, "settings-sessions") }, null, 2)}\n`, "utf8");
+
+    const resolver = new SessionDirResolver({ agentDir, env: { PI_CODING_AGENT_SESSION_DIR: envDir } });
+
+    expect(resolver.resolve(cwd)).toMatchObject({ source: "env", sessionDir: envDir, usesConfiguredSessionDir: true });
+  });
+});
+
+describe("Pi session manager gateway", () => {
+  it("lists only sessions for the requested cwd when a custom Pi sessionDir is shared", async () => {
+    const sharedSessionDir = join(tempDir, "shared-sessions");
+    const otherCwd = join(tempDir, "other-workspace");
+    await writeSessionFile(sharedSessionDir, "session-a", cwd);
+    await writeSessionFile(sharedSessionDir, "session-b", otherCwd);
+    const gateway = createPiSessionManagerGateway({ agentDir, env: { PI_CODING_AGENT_SESSION_DIR: sharedSessionDir } });
+
+    await expect(gateway.list(cwd)).resolves.toMatchObject([{ id: "session-a", cwd }]);
+    const created = gateway.create(cwd);
+    expect(hasSessionDir(created)).toBe(true);
+    if (!hasSessionDir(created)) throw new Error("Expected SDK session manager");
+    expect(created.getSessionDir()).toBe(sharedSessionDir);
+  });
+});
+
+function hasSessionDir(manager: PiSessionManager): manager is PiSessionManager & { getSessionDir(): string } {
+  return "getSessionDir" in manager && typeof manager.getSessionDir === "function";
+}
+
+async function writeSessionFile(dir: string, id: string, sessionCwd: string): Promise<void> {
+  await mkdir(dir, { recursive: true });
+  await writeFile(join(dir, `${id}.jsonl`), `${JSON.stringify({ type: "session", version: 3, id, timestamp: "2026-01-01T00:00:00.000Z", cwd: sessionCwd })}\n`, "utf8");
+}

src/server/sessions/piSessionManagerGateway.ts

@@ -0,0 +1,100 @@
+import { homedir } from "node:os";
+import { dirname, isAbsolute, join, resolve } from "node:path";
+import { getAgentDir, SessionManager, SettingsManager } from "@earendil-works/pi-coding-agent";
+import type { PiSessionListEntry, PiSessionManager, PiSessionManagerGateway } from "./piSessionService.js";
+
+export const PI_SESSION_DIR_ENV = "PI_CODING_AGENT_SESSION_DIR";
+
+type SessionDirSource = "env" | "settings" | "pi-default";
+
+export interface SessionDirResolution {
+  source: SessionDirSource;
+  sessionDir: string;
+  usesConfiguredSessionDir: boolean;
+}
+
+export interface SessionDirResolverOptions {
+  agentDir?: string;
+  env?: NodeJS.ProcessEnv;
+}
+
+export class SessionDirResolver {
+  private readonly agentDir: string;
+  private readonly env: NodeJS.ProcessEnv;
+
+  constructor(options: SessionDirResolverOptions = {}) {
+    this.agentDir = options.agentDir ?? getAgentDir();
+    this.env = options.env ?? process.env;
+  }
+
+  resolve(cwd: string): SessionDirResolution {
+    const envSessionDir = this.env[PI_SESSION_DIR_ENV];
+    if (envSessionDir !== undefined && envSessionDir !== "") {
+      return { source: "env", sessionDir: resolveConfiguredPath(envSessionDir, cwd), usesConfiguredSessionDir: true };
+    }
+
+    const settingsSessionDir = SettingsManager.create(cwd, this.agentDir).getSessionDir();
+    if (settingsSessionDir !== undefined && settingsSessionDir !== "") {
+      return { source: "settings", sessionDir: resolveConfiguredPath(settingsSessionDir, cwd), usesConfiguredSessionDir: true };
+    }
+
+    return { source: "pi-default", sessionDir: defaultPiSessionDir(cwd, this.agentDir), usesConfiguredSessionDir: false };
+  }
+}
+
+export type PiSessionManagerGatewayOptions = SessionDirResolverOptions;
+
+export function createPiSessionManagerGateway(options: PiSessionManagerGatewayOptions = {}): PiSessionManagerGateway {
+  return new SettingsAwarePiSessionManagerGateway(new SessionDirResolver(options));
+}
+
+class SettingsAwarePiSessionManagerGateway implements PiSessionManagerGateway {
+  constructor(private readonly resolver: SessionDirResolver) {}
+
+  async list(cwd: string): Promise<PiSessionListEntry[]> {
+    const resolution = this.resolver.resolve(cwd);
+    return filterSessionsForCwd(await listSessionsInDir(resolution.sessionDir), cwd);
+  }
+
+  create(cwd: string): PiSessionManager {
+    const resolution = this.resolver.resolve(cwd);
+    return SessionManager.create(cwd, resolution.sessionDir);
+  }
+
+  open(path: string): PiSessionManager {
+    return SessionManager.open(path, dirname(path));
+  }
+}
+
+export async function listSessionsInDir(sessionDir: string): Promise<PiSessionListEntry[]> {
+  return SessionManager.list("", sessionDir);
+}
+
+export function filterSessionsForCwd(sessions: readonly PiSessionListEntry[], cwd: string): PiSessionListEntry[] {
+  return sessions.filter((session) => session.cwd === cwd);
+}
+
+export function defaultPiSessionsRoot(agentDir = getAgentDir()): string {
+  return join(agentDir, "sessions");
+}
+
+export function defaultPiSessionDir(cwd: string, agentDir = getAgentDir()): string {
+  return sessionDirInDefaultPiStore(defaultPiSessionsRoot(agentDir), cwd);
+}
+
+export function sessionDirInDefaultPiStore(storeRoot: string, cwd: string): string {
+  const safePath = `--${cwd.replace(/^[/\\]/u, "").replace(/[/\\:]/gu, "-")}--`;
+  return join(storeRoot, safePath);
+}
+
+export function resolveConfiguredPath(path: string, cwd: string): string {
+  const expanded = expandTildePath(path);
+  return isAbsolute(expanded) ? expanded : resolve(cwd, expanded);
+}
+
+function expandTildePath(path: string): string {
+  if (path === "~") return homedir();
+  if (path.startsWith("~/")) return join(homedir(), path.slice(2));
+  return path;
+}
+

src/server/sessions/piSessionService.test.ts

@@ -43,6 +43,10 @@ function sessionRecord(id: string, cwd = "/workspace") {
   return { id, path: `/sessions/${id}.jsonl`, cwd, created: new Date("2026-01-01T00:00:00.000Z"), modified: new Date("2026-01-01T00:01:00.000Z"), messageCount: 0, firstMessage: "", allMessagesText: "" };
 }
 
+function sessionRef(id: string, cwd = "/workspace") {
+  return { id, cwd };
+}
+
 function fakeRuntime(sessionId = "session-1", patch: Partial<TestSession> = {}) {
   const promptCalls: { text: string; options: unknown }[] = [];
   const listeners: ((event: unknown) => void)[] = [];
@@ -122,7 +126,6 @@ function sessionGateway(records: ReturnType<typeof sessionRecord>[]): SessionGat
   return {
     create: () => fakeSessionManager(),
     list: () => Promise.resolve(records),
-    listAll: () => Promise.resolve(records),
     open: () => fakeSessionManager(),
   };
 }
@@ -174,7 +177,7 @@ describe("PiSessionService", () => {
         heartbeatIntervalMs: 1_000,
       });
 
-      await service.status("idle-session");
+      await service.status(sessionRef("idle-session"));
       hub.globalEvents.length = 0;
       listener?.({ type: "agent_start" });
 
@@ -209,7 +212,7 @@ describe("PiSessionService", () => {
       heartbeatIntervalMs: 60_000,
     });
 
-    await service.status("completion-session");
+    await service.status(sessionRef("completion-session"));
     hub.globalEvents.length = 0;
     listener?.({ type: "tool_execution_end", toolName: "read", isError: false });
 
@@ -235,7 +238,6 @@ describe("PiSessionService", () => {
           { ...sessionRecord("active"), messageCount: 1, firstMessage: "hello", allMessagesText: "hello" },
           { ...sessionRecord("archived"), messageCount: 2, firstMessage: "bye", allMessagesText: "bye" },
         ]),
-        listAll: () => Promise.resolve([]),
         open: () => fakeSessionManager(),
       },
       heartbeatIntervalMs: 60_000,
@@ -262,7 +264,6 @@ describe("PiSessionService", () => {
       sessionManager: {
         create: () => fakeSessionManager(),
         list: () => Promise.resolve([{ ...sessionRecord("active"), messageCount: 1, firstMessage: "hello", allMessagesText: "hello" }]),
-        listAll: () => Promise.resolve([]),
         open: () => fakeSessionManager(),
       },
       heartbeatIntervalMs: 60_000,
@@ -301,13 +302,12 @@ describe("PiSessionService", () => {
       sessionManager: {
         create: () => fakeSessionManager(),
         list: (cwd) => Promise.resolve(cwd === "/workspace" ? [root, directChild, archivedChild, grandchild] : [otherWorkspaceChild]),
-        listAll: () => Promise.resolve([root, directChild, archivedChild, grandchild, otherWorkspaceChild]),
         open: () => fakeSessionManager(),
       },
       heartbeatIntervalMs: 60_000,
     });
 
-    await expect(service.archiveTree("root")).resolves.toEqual({
+    await expect(service.archiveTree(sessionRef("root"))).resolves.toEqual({
       archived: true,
       sessionIds: ["root", "direct-child", "grandchild"],
       archivedCount: 3,
@@ -331,7 +331,6 @@ describe("PiSessionService", () => {
       sessionManager: {
         create: () => fakeSessionManager(),
         list: () => Promise.resolve([]),
-        listAll: () => Promise.resolve([]),
         open: () => fakeSessionManager(),
       },
       workspaceActivity: {
@@ -360,7 +359,7 @@ describe("PiSessionService", () => {
       heartbeatIntervalMs: 60_000,
     });
 
-    await service.prompt("prompt-session", "Build the thing");
+    await service.prompt(sessionRef("prompt-session"), "Build the thing");
 
     expect(fake.calls.prompt).toEqual([{ text: "Build the thing", options: undefined }]);
     await service.dispose();
@@ -379,7 +378,7 @@ describe("PiSessionService", () => {
       heartbeatIntervalMs: 60_000,
     });
 
-    await expect(service.status("status-session")).resolves.toMatchObject({
+    await expect(service.status(sessionRef("status-session"))).resolves.toMatchObject({
       pendingMessageCount: 2,
       queuedMessages: [{ kind: "steer", text: "adjust this turn" }, { kind: "followUp", text: "then do this" }],
       messageCount: 2,
@@ -399,7 +398,7 @@ describe("PiSessionService", () => {
       heartbeatIntervalMs: 60_000,
     });
 
-    await service.prompt("dedupe-session", "already queued", "followUp");
+    await service.prompt(sessionRef("dedupe-session"), "already queued", "followUp");
 
     expect(fake.calls.prompt).toEqual([]);
     await service.dispose();
@@ -414,7 +413,7 @@ describe("PiSessionService", () => {
       heartbeatIntervalMs: 60_000,
     });
 
-    await service.prompt("queued-session", "Wait for the current turn", "followUp");
+    await service.prompt(sessionRef("queued-session"), "Wait for the current turn", "followUp");
 
     expect(fake.calls.prompt).toEqual([{ text: "Wait for the current turn", options: { streamingBehavior: "followUp" } }]);
     expect(hub.sessionEvents.some(({ event }) => event.type === "message.append")).toBe(false);
@@ -439,12 +438,12 @@ describe("PiSessionService", () => {
       heartbeatIntervalMs: 60_000,
     });
 
-    await service.prompt("compacting-session", "Start task 1", "followUp");
-    await service.prompt("compacting-session", "Then task 2", "followUp");
+    await service.prompt(sessionRef("compacting-session"), "Start task 1", "followUp");
+    await service.prompt(sessionRef("compacting-session"), "Then task 2", "followUp");
 
     expect(fake.calls.prompt).toEqual([]);
     expect(hub.sessionEvents.some(({ event }) => event.type === "message.append")).toBe(false);
-    await expect(service.status("compacting-session")).resolves.toMatchObject({
+    await expect(service.status(sessionRef("compacting-session"))).resolves.toMatchObject({
       pendingMessageCount: 2,
       queuedMessages: [{ kind: "followUp", text: "Start task 1" }, { kind: "followUp", text: "Then task 2" }],
     });
@@ -455,7 +454,7 @@ describe("PiSessionService", () => {
 
     expect(fake.calls.prompt).toEqual([{ text: "Start task 1", options: undefined }]);
     expect(hub.sessionEvents.some(({ event }) => event.type === "message.append" && JSON.stringify(event.message).includes("Start task 1"))).toBe(true);
-    await expect(service.status("compacting-session")).resolves.toMatchObject({
+    await expect(service.status(sessionRef("compacting-session"))).resolves.toMatchObject({
       pendingMessageCount: 1,
       queuedMessages: [{ kind: "followUp", text: "Then task 2" }],
     });
@@ -467,7 +466,7 @@ describe("PiSessionService", () => {
       { text: "Start task 1", options: undefined },
       { text: "Then task 2", options: { streamingBehavior: "followUp" } },
     ]);
-    await expect(service.status("compacting-session")).resolves.toMatchObject({
+    await expect(service.status(sessionRef("compacting-session"))).resolves.toMatchObject({
       pendingMessageCount: 0,
       queuedMessages: [],
     });
@@ -483,8 +482,8 @@ describe("PiSessionService", () => {
       heartbeatIntervalMs: 60_000,
     });
 
-    await service.status("abort-session");
-    await service.abort("abort-session");
+    await service.status(sessionRef("abort-session"));
+    await service.abort(sessionRef("abort-session"));
 
     expect(fake.calls.clearQueue).toBe(1);
     expect(fake.calls.abort).toBe(1);
@@ -499,13 +498,13 @@ describe("PiSessionService", () => {
       heartbeatIntervalMs: 60_000,
     });
 
-    await service.prompt("abort-compaction-session", "Do not deliver after abort", "followUp");
-    await expect(service.status("abort-compaction-session")).resolves.toMatchObject({ pendingMessageCount: 1 });
-    await service.abort("abort-compaction-session");
+    await service.prompt(sessionRef("abort-compaction-session"), "Do not deliver after abort", "followUp");
+    await expect(service.status(sessionRef("abort-compaction-session"))).resolves.toMatchObject({ pendingMessageCount: 1 });
+    await service.abort(sessionRef("abort-compaction-session"));
 
     expect(fake.calls.clearQueue).toBe(1);
     expect(fake.calls.prompt).toEqual([]);
-    await expect(service.status("abort-compaction-session")).resolves.toMatchObject({ pendingMessageCount: 0, queuedMessages: [] });
+    await expect(service.status(sessionRef("abort-compaction-session"))).resolves.toMatchObject({ pendingMessageCount: 0, queuedMessages: [] });
     await service.dispose();
   });
 
@@ -524,7 +523,7 @@ describe("PiSessionService", () => {
       heartbeatIntervalMs: 60_000,
     });
 
-    await service.status("auth-session");
+    await service.status(sessionRef("auth-session"));
     hub.sessionEvents.length = 0;
     hub.globalEvents.length = 0;
 
@@ -553,8 +552,8 @@ describe("PiSessionService", () => {
       heartbeatIntervalMs: 60_000,
     });
 
-    await service.status("stop-session");
-    service.stop("stop-session");
+    await service.status(sessionRef("stop-session"));
+    service.stop(sessionRef("stop-session"));
 
     expect(fake.calls.clearQueue).toBe(1);
     await service.dispose();

src/server/sessions/piSessionService.ts

@@ -13,7 +13,7 @@ import {
   type CreateAgentSessionRuntimeFactory,
   type EditToolDetails,
 } from "@earendil-works/pi-coding-agent";
-import type { ClientArchiveSessionsResponse, ClientCommand, ClientCommandResult, ClientMessagePage, ClientSession, ClientSessionModel, ClientSessionStatus, ClientThinkingLevel, SessionUiEvent } from "../types.js";
+import type { ClientArchiveSessionsResponse, ClientCommand, ClientCommandResult, ClientMessagePage, ClientSession, ClientSessionModel, ClientSessionRef, ClientSessionStatus, ClientThinkingLevel, SessionUiEvent } from "../types.js";
 import { pageMessagesAtSafeBoundary } from "./messagePaging.js";
 import type { SessionEventHub } from "../realtime/sessionEventHub.js";
 import { BUILTIN_COMMANDS } from "./builtinCommands.js";
@@ -24,6 +24,7 @@ import type { ActiveSession } from "./sessionRuntimeStore.js";
 import type { AuthChange } from "./authService.js";
 import { fallbackSessionName, generateShortSessionName } from "./sessionNameGenerator.js";
 import { computeEditPreview, type EditPreviewResult } from "./editPreview.js";
+import { createPiSessionManagerGateway } from "./piSessionManagerGateway.js";
 import type { WorkspaceActivityService } from "../activity/workspaceActivityService.js";
 
 function noop(): void {
@@ -34,6 +35,18 @@ function authLossWarningKey(sessionId: string, provider: string, modelId: string
   return `${sessionId}:${provider}/${modelId}`;
 }
 
+function sessionIdFromLookup(ref: PiSessionLookup): string {
+  return typeof ref === "string" ? ref : ref.id;
+}
+
+function isPiSessionRef(ref: PiSessionLookup): ref is PiSessionRef {
+  return typeof ref !== "string";
+}
+
+function lookupMatchesActiveSession(ref: PiSessionLookup, active: ActiveSession<PiSessionRuntime>): boolean {
+  return !isPiSessionRef(ref) || active.runtime.cwd === ref.cwd;
+}
+
 type QueuedPromptKind = "steer" | "followUp";
 
 interface QueuedPrompt {
@@ -42,7 +55,12 @@ interface QueuedPrompt {
 }
 
 type SessionArchiveRepository = Pick<SessionArchiveStore, "list" | "get" | "archive" | "restore" | "isArchived">;
-interface PiSessionListEntry {
+
+export type PiSessionRef = ClientSessionRef;
+
+type PiSessionLookup = string | PiSessionRef;
+
+export interface PiSessionListEntry {
   id: string;
   path: string;
   cwd: string;
@@ -74,7 +92,6 @@ export interface PiSessionManager {
 export interface PiSessionManagerGateway {
   list(cwd: string): Promise<PiSessionListEntry[]>;
   create(cwd: string): PiSessionManager;
-  listAll(): Promise<PiSessionListEntry[]>;
   open(path: string): PiSessionManager;
 }
 
@@ -201,7 +218,7 @@ export class PiSessionService {
   constructor(private readonly events: SessionEventHub, deps: PiSessionServiceDependencies = {}) {
     this.archiveStore = deps.archiveStore ?? new SessionArchiveStore();
     this.agentDir = deps.agentDir ?? getAgentDir();
-    this.sessionManager = deps.sessionManager ?? SessionManager;
+    this.sessionManager = deps.sessionManager ?? createPiSessionManagerGateway({ agentDir: this.agentDir });
     this.modelRegistry = deps.modelRegistry ?? ModelRegistry.create(AuthStorage.create());
     this.createRuntime = deps.createRuntime ?? createDefaultRuntimeFactory(this.modelRegistry.authStorage, this.modelRegistry);
     this.createAgentRuntime = deps.createAgentRuntime ?? defaultCreateAgentRuntime;
@@ -277,17 +294,17 @@ export class PiSessionService {
     };
   }
 
-  async messages(sessionId: string, page?: { before?: number; limit?: number }): Promise<unknown[] | ClientMessagePage> {
-    const session = await this.getOrOpen(sessionId);
+  async messages(ref: PiSessionLookup, page?: { before?: number; limit?: number }): Promise<unknown[] | ClientMessagePage> {
+    const session = await this.getOrOpen(ref);
     return pageMessagesAtSafeBoundary(historyMessages(session), page);
   }
 
-  async status(sessionId: string): Promise<ClientSessionStatus> {
-    return this.statusFromSession(await this.getOrOpen(sessionId));
+  async status(ref: PiSessionLookup): Promise<ClientSessionStatus> {
+    return this.statusFromSession(await this.getOrOpen(ref));
   }
 
-  async availableModels(sessionId: string): Promise<ClientSessionModel[]> {
-    const session = await this.getOrOpen(sessionId);
+  async availableModels(ref: PiSessionLookup): Promise<ClientSessionModel[]> {
+    const session = await this.getOrOpen(ref);
     session.modelRegistry.refresh();
     const models = session.scopedModels.length > 0
       ? session.scopedModels.map((scoped) => scoped.model)
@@ -295,9 +312,9 @@ export class PiSessionService {
     return models.map(modelToClientModel);
   }
 
-  async setModel(sessionId: string, provider: string, modelId: string): Promise<ClientSessionStatus> {
-    await this.assertWritable(sessionId);
-    const session = await this.getOrOpen(sessionId);
+  async setModel(ref: PiSessionLookup, provider: string, modelId: string): Promise<ClientSessionStatus> {
+    await this.assertWritable(ref);
+    const session = await this.getOrOpen(ref);
     session.modelRegistry.refresh();
     const candidates = session.scopedModels.length > 0
       ? session.scopedModels.map((scoped) => scoped.model)
@@ -311,9 +328,9 @@ export class PiSessionService {
     return this.statusFromSession(session);
   }
 
-  async cycleModel(sessionId: string, direction: "forward" | "backward"): Promise<ClientSessionStatus> {
-    await this.assertWritable(sessionId);
-    const session = await this.getOrOpen(sessionId);
+  async cycleModel(ref: PiSessionLookup, direction: "forward" | "backward"): Promise<ClientSessionStatus> {
+    await this.assertWritable(ref);
+    const session = await this.getOrOpen(ref);
     const result = await session.cycleModel(direction);
     if (result === undefined) throw new Error(session.scopedModels.length > 0 ? "Only one model in scope" : "Only one model available");
     this.publishActivity(session, `model: ${result.model.id}`, "idle", result.model.provider);
@@ -321,23 +338,23 @@ export class PiSessionService {
     return this.statusFromSession(session);
   }
 
-  async availableThinkingLevels(sessionId: string): Promise<ClientThinkingLevel[]> {
-    const session = await this.getOrOpen(sessionId);
+  async availableThinkingLevels(ref: PiSessionLookup): Promise<ClientThinkingLevel[]> {
+    const session = await this.getOrOpen(ref);
     return session.getAvailableThinkingLevels();
   }
 
-  async setThinkingLevel(sessionId: string, level: ClientThinkingLevel): Promise<ClientSessionStatus> {
-    await this.assertWritable(sessionId);
-    const session = await this.getOrOpen(sessionId);
+  async setThinkingLevel(ref: PiSessionLookup, level: ClientThinkingLevel): Promise<ClientSessionStatus> {
+    await this.assertWritable(ref);
+    const session = await this.getOrOpen(ref);
     session.setThinkingLevel(level);
     this.publishActivity(session, `thinking: ${session.thinkingLevel}`, "idle");
     this.publishStatus(session);
     return this.statusFromSession(session);
   }
 
-  async cycleThinkingLevel(sessionId: string): Promise<ClientSessionStatus> {
-    await this.assertWritable(sessionId);
-    const session = await this.getOrOpen(sessionId);
+  async cycleThinkingLevel(ref: PiSessionLookup): Promise<ClientSessionStatus> {
+    await this.assertWritable(ref);
+    const session = await this.getOrOpen(ref);
     const level = session.cycleThinkingLevel();
     if (level === undefined) throw new Error("Current model does not support thinking");
     this.publishActivity(session, `thinking: ${level}`, "idle");
@@ -345,8 +362,8 @@ export class PiSessionService {
     return this.statusFromSession(session);
   }
 
-  async commands(sessionId: string): Promise<ClientCommand[]> {
-    const session = await this.getOrOpen(sessionId);
+  async commands(ref: PiSessionLookup): Promise<ClientCommand[]> {
+    const session = await this.getOrOpen(ref);
     const commands: ClientCommand[] = [...BUILTIN_COMMANDS];
     for (const command of session.extensionRunner.getRegisteredCommands()) {
       commands.push({ name: command.invocationName, ...(command.description === undefined ? {} : { description: command.description }), source: "extension" });
@@ -360,9 +377,9 @@ export class PiSessionService {
     return commands.sort((a, b) => a.name.localeCompare(b.name));
   }
 
-  async prompt(sessionId: string, text: string, streamingBehavior?: "steer" | "followUp"): Promise<void> {
-    await this.assertWritable(sessionId);
-    const session = await this.getOrOpen(sessionId);
+  async prompt(ref: PiSessionLookup, text: string, streamingBehavior?: "steer" | "followUp"): Promise<void> {
+    await this.assertWritable(ref);
+    const session = await this.getOrOpen(ref);
     this.maybeGenerateSessionName(session, text);
     const isQueued = session.isStreaming || session.isCompacting;
     const behavior = isQueued ? streamingBehavior ?? "followUp" : undefined;
@@ -398,9 +415,9 @@ export class PiSessionService {
     this.publishStatus(session);
   }
 
-  async shell(sessionId: string, text: string): Promise<void> {
-    await this.assertWritable(sessionId);
-    const active = await this.getActive(sessionId);
+  async shell(ref: PiSessionLookup, text: string): Promise<void> {
+    await this.assertWritable(ref);
+    const active = await this.getActive(ref);
     const { session } = active.runtime;
     const isExcluded = text.startsWith("!!");
     const command = (isExcluded ? text.slice(2) : text.slice(1)).trim();
@@ -433,26 +450,28 @@ export class PiSessionService {
     });
   }
 
-  async runCommand(sessionId: string, text: string): Promise<ClientCommandResult> {
-    await this.assertWritable(sessionId);
-    return this.commandService.run(sessionId, text);
+  async runCommand(ref: PiSessionLookup, text: string): Promise<ClientCommandResult> {
+    await this.assertWritable(ref);
+    const active = await this.getActive(ref);
+    return this.commandService.run(active.runtime.session.sessionId, text);
   }
 
-  async respondToCommand(sessionId: string, requestId: string, value: string): Promise<ClientCommandResult> {
-    await this.assertWritable(sessionId);
-    return this.commandService.respond(sessionId, requestId, value);
+  async respondToCommand(ref: PiSessionLookup, requestId: string, value: string): Promise<ClientCommandResult> {
+    await this.assertWritable(ref);
+    const active = await this.getActive(ref);
+    return this.commandService.respond(active.runtime.session.sessionId, requestId, value);
   }
 
-  async archive(sessionId: string): Promise<void> {
-    const session = await this.getOrOpen(sessionId);
+  async archive(ref: PiSessionLookup): Promise<void> {
+    const session = await this.getOrOpen(ref);
     if (this.hasActiveWork(session)) throw new Error("Stop current session activity before archiving");
     const archiveInput = await this.archiveInputForSession(session);
     await this.closeActive(session.sessionId);
     await this.archiveStore.archive(archiveInput);
   }
 
-  async archiveTree(sessionId: string): Promise<ClientArchiveSessionsResponse> {
-    const session = await this.getOrOpen(sessionId);
+  async archiveTree(ref: PiSessionLookup): Promise<ClientArchiveSessionsResponse> {
+    const session = await this.getOrOpen(ref);
     const catalog = await this.workspaceArchiveCandidates(session.sessionManager.getCwd());
     const root = findArchiveCandidateByIdOrPrefix(catalog, session.sessionId) ?? archiveCandidateFromActiveSession(session, false);
     const plan = planSessionArchiveTree(root, catalog);
@@ -471,21 +490,24 @@ export class PiSessionService {
     };
   }
 
-  async restore(sessionId: string): Promise<void> {
-    await this.closeActive(sessionId);
-    await this.archiveStore.restore(sessionId);
+  async restore(ref: PiSessionLookup): Promise<void> {
+    const archived = await this.getArchived(ref);
+    if (archived === undefined) throw new Error("Session not found");
+    await this.closeActive(archived.sessionId);
+    await this.archiveStore.restore(archived.sessionId);
   }
 
-  async detachParent(sessionId: string): Promise<void> {
-    const session = await this.getOrOpen(sessionId);
+  async detachParent(ref: PiSessionLookup): Promise<void> {
+    const session = await this.getOrOpen(ref);
     const sessionFile = session.sessionFile;
     if (sessionFile === undefined || sessionFile === "") throw new Error("Session is not persisted");
     await clearParentSession(sessionFile);
   }
 
-  async abort(sessionId: string): Promise<void> {
-    const active = this.active.get(sessionId);
-    if (!active) return;
+  async abort(ref: PiSessionLookup): Promise<void> {
+    const active = this.activeForLookup(ref);
+    if (active === undefined) return;
+    const sessionId = active.runtime.session.sessionId;
     this.clearCompactionPromptQueue(sessionId);
     clearSessionQueue(active.runtime.session);
     await active.runtime.session.abort();
@@ -493,8 +515,10 @@ export class PiSessionService {
     this.publishStatus(active.runtime.session);
   }
 
-  stop(sessionId: string): void {
-    void this.closeActive(sessionId).catch(() => {
+  stop(ref: PiSessionLookup): void {
+    const active = this.activeForLookup(ref);
+    if (active === undefined) return;
+    void this.closeActive(active.runtime.session.sessionId).catch(() => {
       // Best-effort shutdown; callers that need errors await closeActive directly.
     });
   }
@@ -591,26 +615,44 @@ export class PiSessionService {
     }
   }
 
-  private async assertWritable(sessionId: string): Promise<void> {
-    if (await this.archiveStore.isArchived(sessionId)) throw new Error("Archived sessions are read-only. Restore the session to continue.");
+  private async assertWritable(ref: PiSessionLookup): Promise<void> {
+    if (await this.getArchived(ref) !== undefined) throw new Error("Archived sessions are read-only. Restore the session to continue.");
   }
 
-  private async getOrOpen(sessionId: string): Promise<PiAgentSession> {
-    return (await this.getActive(sessionId)).runtime.session;
+  private async getOrOpen(ref: PiSessionLookup): Promise<PiAgentSession> {
+    return (await this.getActive(ref)).runtime.session;
   }
 
-  private async getActive(sessionId: string): Promise<ActiveSession<PiSessionRuntime>> {
-    const active = this.active.get(sessionId);
-    if (active) return active;
+  private async getActive(ref: PiSessionLookup): Promise<ActiveSession<PiSessionRuntime>> {
+    const active = this.activeForLookup(ref);
+    if (active !== undefined) return active;
 
-    const archived = await this.archiveStore.get(sessionId);
+    const archived = await this.getArchived(ref);
     if (archived?.archivePath !== undefined) return this.create(this.sessionManager.open(archived.archivePath), archived.cwd);
 
-    const match = (await this.sessionManager.listAll()).find((s) => s.id === sessionId || s.id.startsWith(sessionId));
+    if (!isPiSessionRef(ref)) throw new Error("Session not found");
+    const match = (await this.sessionManager.list(ref.cwd)).find((s) => s.id === ref.id || s.id.startsWith(ref.id));
     if (!match) throw new Error("Session not found");
     return this.create(this.sessionManager.open(match.path), match.cwd);
   }
 
+  private async getArchived(ref: PiSessionLookup): Promise<ArchivedSessionRecord | undefined> {
+    const archived = await this.archiveStore.get(sessionIdFromLookup(ref));
+    if (archived === undefined) return undefined;
+    if (isPiSessionRef(ref) && archived.cwd !== ref.cwd) return undefined;
+    return archived;
+  }
+
+  private activeForLookup(ref: PiSessionLookup): ActiveSession<PiSessionRuntime> | undefined {
+    const sessionId = sessionIdFromLookup(ref);
+    const exact = this.active.get(sessionId);
+    if (exact !== undefined && lookupMatchesActiveSession(ref, exact)) return exact;
+    for (const [candidateId, active] of this.active.entries()) {
+      if (candidateId.startsWith(sessionId) && lookupMatchesActiveSession(ref, active)) return active;
+    }
+    return undefined;
+  }
+
   private async create(sessionManager: PiSessionManager, cwd: string): Promise<ActiveSession<PiSessionRuntime>> {
     const runtime = await this.createAgentRuntime(this.createRuntime, { cwd, agentDir: this.agentDir, sessionManager });
     const active: ActiveSession<PiSessionRuntime> = { runtime, unsubscribe: noop };

src/server/sessions/sessionRoutes.ts

@@ -1,9 +1,20 @@
 import type { FastifyInstance } from "fastify";
 import type { SessionEventHub } from "../realtime/sessionEventHub.js";
-import type { PiSessionService } from "./piSessionService.js";
+import type { PiSessionRef, PiSessionService } from "./piSessionService.js";
+
+interface SessionQuery {
+  cwd?: string;
+}
+
+interface MessageQuery extends SessionQuery {
+  before?: string;
+  limit?: string;
+}
+
+class SessionRouteValidationError extends Error {}
 
 export function registerSessionRoutes(app: FastifyInstance, sessions: PiSessionService, eventHub: SessionEventHub, prefix = ""): void {
-  app.get<{ Querystring: { cwd?: string } }>(`${prefix}/sessions`, async (request, reply) => {
+  app.get<{ Querystring: SessionQuery }>(`${prefix}/sessions`, async (request, reply) => {
     if (request.query.cwd === undefined || request.query.cwd === "") return reply.code(400).send({ error: "cwd query parameter is required" });
     return sessions.list(request.query.cwd);
   });
@@ -12,164 +23,189 @@ export function registerSessionRoutes(app: FastifyInstance, sessions: PiSessionS
     try {
       return await sessions.start(request.body.cwd);
     } catch (error) {
-      return reply.code(400).send({ error: error instanceof Error ? error.message : String(error) });
+      return reply.code(400).send({ error: errorMessage(error) });
     }
   });
 
-  app.get<{ Params: { sessionId: string }; Querystring: { before?: string; limit?: string } }>(`${prefix}/sessions/:sessionId/messages`, async (request, reply) => {
+  app.get<{ Params: { sessionId: string }; Querystring: MessageQuery }>(`${prefix}/sessions/:sessionId/messages`, async (request, reply) => {
     try {
       const page = { ...optionalField("before", optionalNumber(request.query.before)), ...optionalField("limit", optionalNumber(request.query.limit)) };
-      return await sessions.messages(request.params.sessionId, page);
+      return await sessions.messages(sessionRefFromQuery(request.params.sessionId, request.query), page);
     } catch (error) {
-      return reply.code(404).send({ error: error instanceof Error ? error.message : String(error) });
+      return reply.code(readErrorStatus(error)).send({ error: errorMessage(error) });
     }
   });
 
-  app.get<{ Params: { sessionId: string } }>(`${prefix}/sessions/:sessionId/status`, async (request, reply) => {
+  app.get<{ Params: { sessionId: string }; Querystring: SessionQuery }>(`${prefix}/sessions/:sessionId/status`, async (request, reply) => {
     try {
-      return await sessions.status(request.params.sessionId);
+      return await sessions.status(sessionRefFromQuery(request.params.sessionId, request.query));
     } catch (error) {
-      return reply.code(404).send({ error: error instanceof Error ? error.message : String(error) });
+      return reply.code(readErrorStatus(error)).send({ error: errorMessage(error) });
     }
   });
 
-  app.get<{ Params: { sessionId: string } }>(`${prefix}/sessions/:sessionId/models`, async (request, reply) => {
+  app.get<{ Params: { sessionId: string }; Querystring: SessionQuery }>(`${prefix}/sessions/:sessionId/models`, async (request, reply) => {
     try {
-      return { models: await sessions.availableModels(request.params.sessionId) };
+      return { models: await sessions.availableModels(sessionRefFromQuery(request.params.sessionId, request.query)) };
     } catch (error) {
-      return reply.code(404).send({ error: error instanceof Error ? error.message : String(error) });
+      return reply.code(readErrorStatus(error)).send({ error: errorMessage(error) });
     }
   });
 
-  app.post<{ Params: { sessionId: string }; Body: { provider: string; modelId: string } }>(`${prefix}/sessions/:sessionId/model`, async (request, reply) => {
+  app.post<{ Params: { sessionId: string }; Body: { cwd?: unknown; provider?: unknown; modelId?: unknown } }>(`${prefix}/sessions/:sessionId/model`, async (request, reply) => {
     try {
-      return await sessions.setModel(request.params.sessionId, request.body.provider, request.body.modelId);
+      const body = requireRecord(request.body);
+      return await sessions.setModel(sessionRefFromBody(request.params.sessionId, body), requireString(body, "provider"), requireString(body, "modelId"));
     } catch (error) {
-      return reply.code(400).send({ error: error instanceof Error ? error.message : String(error) });
+      return reply.code(400).send({ error: errorMessage(error) });
     }
   });
 
-  app.post<{ Params: { sessionId: string }; Body: { direction?: "forward" | "backward" } }>(`${prefix}/sessions/:sessionId/model/cycle`, async (request, reply) => {
+  app.post<{ Params: { sessionId: string }; Body: { cwd?: unknown; direction?: "forward" | "backward" } }>(`${prefix}/sessions/:sessionId/model/cycle`, async (request, reply) => {
     try {
-      return await sessions.cycleModel(request.params.sessionId, request.body.direction ?? "forward");
+      const body = requireRecord(request.body);
+      const direction = body["direction"];
+      if (direction !== undefined && direction !== "forward" && direction !== "backward") throw new Error("direction must be forward or backward");
+      return await sessions.cycleModel(sessionRefFromBody(request.params.sessionId, body), direction ?? "forward");
     } catch (error) {
-      return reply.code(400).send({ error: error instanceof Error ? error.message : String(error) });
+      return reply.code(400).send({ error: errorMessage(error) });
     }
   });
 
-  app.get<{ Params: { sessionId: string } }>(`${prefix}/sessions/:sessionId/thinking-levels`, async (request, reply) => {
+  app.get<{ Params: { sessionId: string }; Querystring: SessionQuery }>(`${prefix}/sessions/:sessionId/thinking-levels`, async (request, reply) => {
     try {
-      return { levels: await sessions.availableThinkingLevels(request.params.sessionId) };
+      return { levels: await sessions.availableThinkingLevels(sessionRefFromQuery(request.params.sessionId, request.query)) };
     } catch (error) {
-      return reply.code(404).send({ error: error instanceof Error ? error.message : String(error) });
+      return reply.code(readErrorStatus(error)).send({ error: errorMessage(error) });
     }
   });
 
-  app.post<{ Params: { sessionId: string }; Body: { level: "off" | "minimal" | "low" | "medium" | "high" | "xhigh" } }>(`${prefix}/sessions/:sessionId/thinking-level`, async (request, reply) => {
+  app.post<{ Params: { sessionId: string }; Body: { cwd?: unknown; level?: unknown } }>(`${prefix}/sessions/:sessionId/thinking-level`, async (request, reply) => {
     try {
-      return await sessions.setThinkingLevel(request.params.sessionId, request.body.level);
+      const body = requireRecord(request.body);
+      return await sessions.setThinkingLevel(sessionRefFromBody(request.params.sessionId, body), requireThinkingLevel(body["level"]));
     } catch (error) {
-      return reply.code(400).send({ error: error instanceof Error ? error.message : String(error) });
+      return reply.code(400).send({ error: errorMessage(error) });
     }
   });
 
-  app.post<{ Params: { sessionId: string } }>(`${prefix}/sessions/:sessionId/thinking-level/cycle`, async (request, reply) => {
+  app.post<{ Params: { sessionId: string }; Body: { cwd?: unknown } }>(`${prefix}/sessions/:sessionId/thinking-level/cycle`, async (request, reply) => {
     try {
-      return await sessions.cycleThinkingLevel(request.params.sessionId);
+      const body = requireRecord(request.body);
+      return await sessions.cycleThinkingLevel(sessionRefFromBody(request.params.sessionId, body));
     } catch (error) {
-      return reply.code(400).send({ error: error instanceof Error ? error.message : String(error) });
+      return reply.code(400).send({ error: errorMessage(error) });
     }
   });
 
-  app.get<{ Params: { sessionId: string } }>(`${prefix}/sessions/:sessionId/commands`, async (request, reply) => {
+  app.get<{ Params: { sessionId: string }; Querystring: SessionQuery }>(`${prefix}/sessions/:sessionId/commands`, async (request, reply) => {
     try {
-      return await sessions.commands(request.params.sessionId);
+      return await sessions.commands(sessionRefFromQuery(request.params.sessionId, request.query));
     } catch (error) {
-      return reply.code(404).send({ error: error instanceof Error ? error.message : String(error) });
+      return reply.code(readErrorStatus(error)).send({ error: errorMessage(error) });
     }
   });
 
-  app.post<{ Params: { sessionId: string }; Body: { text: string; streamingBehavior?: "steer" | "followUp" } }>(`${prefix}/sessions/:sessionId/prompt`, async (request, reply) => {
+  app.post<{ Params: { sessionId: string }; Body: { cwd?: unknown; text?: unknown; streamingBehavior?: "steer" | "followUp" } }>(`${prefix}/sessions/:sessionId/prompt`, async (request, reply) => {
     try {
-      await sessions.prompt(request.params.sessionId, request.body.text, request.body.streamingBehavior);
+      const body = requireRecord(request.body);
+      const streamingBehavior = body["streamingBehavior"];
+      if (streamingBehavior !== undefined && streamingBehavior !== "steer" && streamingBehavior !== "followUp") throw new Error("streamingBehavior must be steer or followUp");
+      await sessions.prompt(sessionRefFromBody(request.params.sessionId, body), requireString(body, "text"), streamingBehavior);
       return { accepted: true };
     } catch (error) {
-      return reply.code(400).send({ error: error instanceof Error ? error.message : String(error) });
+      return reply.code(400).send({ error: errorMessage(error) });
     }
   });
 
-  app.post<{ Params: { sessionId: string }; Body: { text: string } }>(`${prefix}/sessions/:sessionId/shell`, async (request, reply) => {
+  app.post<{ Params: { sessionId: string }; Body: { cwd?: unknown; text?: unknown } }>(`${prefix}/sessions/:sessionId/shell`, async (request, reply) => {
     try {
-      await sessions.shell(request.params.sessionId, request.body.text);
+      const body = requireRecord(request.body);
+      await sessions.shell(sessionRefFromBody(request.params.sessionId, body), requireString(body, "text"));
       return { accepted: true };
     } catch (error) {
-      return reply.code(400).send({ error: error instanceof Error ? error.message : String(error) });
+      return reply.code(400).send({ error: errorMessage(error) });
     }
   });
 
-  app.post<{ Params: { sessionId: string }; Body: { text: string } }>(`${prefix}/sessions/:sessionId/commands/run`, async (request, reply) => {
+  app.post<{ Params: { sessionId: string }; Body: { cwd?: unknown; text?: unknown } }>(`${prefix}/sessions/:sessionId/commands/run`, async (request, reply) => {
     try {
-      return await sessions.runCommand(request.params.sessionId, request.body.text);
+      const body = requireRecord(request.body);
+      return await sessions.runCommand(sessionRefFromBody(request.params.sessionId, body), requireString(body, "text"));
     } catch (error) {
-      return reply.code(400).send({ error: error instanceof Error ? error.message : String(error) });
+      return reply.code(400).send({ error: errorMessage(error) });
     }
   });
 
-  app.post<{ Params: { sessionId: string }; Body: { requestId: string; value: string } }>(`${prefix}/sessions/:sessionId/commands/respond`, async (request, reply) => {
+  app.post<{ Params: { sessionId: string }; Body: { cwd?: unknown; requestId?: unknown; value?: unknown } }>(`${prefix}/sessions/:sessionId/commands/respond`, async (request, reply) => {
     try {
-      return await sessions.respondToCommand(request.params.sessionId, request.body.requestId, request.body.value);
+      const body = requireRecord(request.body);
+      return await sessions.respondToCommand(sessionRefFromBody(request.params.sessionId, body), requireString(body, "requestId"), requireString(body, "value"));
     } catch (error) {
-      return reply.code(400).send({ error: error instanceof Error ? error.message : String(error) });
+      return reply.code(400).send({ error: errorMessage(error) });
     }
   });
 
-  app.post<{ Params: { sessionId: string } }>(`${prefix}/sessions/:sessionId/abort`, async (request) => {
-    await sessions.abort(request.params.sessionId);
-    return { aborted: true };
-  });
-
-  app.post<{ Params: { sessionId: string } }>(`${prefix}/sessions/:sessionId/stop`, (request) => {
-    sessions.stop(request.params.sessionId);
-    return { stopped: true };
-  });
-
-  app.post<{ Params: { sessionId: string } }>(`${prefix}/sessions/:sessionId/archive`, async (request, reply) => {
+  app.post<{ Params: { sessionId: string }; Body: { cwd?: unknown } }>(`${prefix}/sessions/:sessionId/abort`, async (request, reply) => {
     try {
-      await sessions.archive(request.params.sessionId);
+      await sessions.abort(sessionRefFromBody(request.params.sessionId, requireRecord(request.body)));
+      return { aborted: true };
+    } catch (error) {
+      return reply.code(400).send({ error: errorMessage(error) });
+    }
+  });
+
+  app.post<{ Params: { sessionId: string }; Body: { cwd?: unknown } }>(`${prefix}/sessions/:sessionId/stop`, (request, reply) => {
+    try {
+      sessions.stop(sessionRefFromBody(request.params.sessionId, requireRecord(request.body)));
+      return { stopped: true };
+    } catch (error) {
+      return reply.code(400).send({ error: errorMessage(error) });
+    }
+  });
+
+  app.post<{ Params: { sessionId: string }; Body: { cwd?: unknown } }>(`${prefix}/sessions/:sessionId/archive`, async (request, reply) => {
+    try {
+      await sessions.archive(sessionRefFromBody(request.params.sessionId, requireRecord(request.body)));
       return { archived: true };
     } catch (error) {
-      return reply.code(400).send({ error: error instanceof Error ? error.message : String(error) });
+      return reply.code(400).send({ error: errorMessage(error) });
     }
   });
 
-  app.post<{ Params: { sessionId: string } }>(`${prefix}/sessions/:sessionId/archive-tree`, async (request, reply) => {
+  app.post<{ Params: { sessionId: string }; Body: { cwd?: unknown } }>(`${prefix}/sessions/:sessionId/archive-tree`, async (request, reply) => {
     try {
-      return await sessions.archiveTree(request.params.sessionId);
+      return await sessions.archiveTree(sessionRefFromBody(request.params.sessionId, requireRecord(request.body)));
     } catch (error) {
-      return reply.code(400).send({ error: error instanceof Error ? error.message : String(error) });
+      return reply.code(400).send({ error: errorMessage(error) });
     }
   });
 
-  app.post<{ Params: { sessionId: string } }>(`${prefix}/sessions/:sessionId/restore`, async (request, reply) => {
+  app.post<{ Params: { sessionId: string }; Body: { cwd?: unknown } }>(`${prefix}/sessions/:sessionId/restore`, async (request, reply) => {
     try {
-      await sessions.restore(request.params.sessionId);
+      await sessions.restore(sessionRefFromBody(request.params.sessionId, requireRecord(request.body)));
       return { restored: true };
     } catch (error) {
-      return reply.code(400).send({ error: error instanceof Error ? error.message : String(error) });
+      return reply.code(400).send({ error: errorMessage(error) });
     }
   });
 
-  app.post<{ Params: { sessionId: string } }>(`${prefix}/sessions/:sessionId/detach-parent`, async (request, reply) => {
+  app.post<{ Params: { sessionId: string }; Body: { cwd?: unknown } }>(`${prefix}/sessions/:sessionId/detach-parent`, async (request, reply) => {
     try {
-      await sessions.detachParent(request.params.sessionId);
+      await sessions.detachParent(sessionRefFromBody(request.params.sessionId, requireRecord(request.body)));
       return { detached: true };
     } catch (error) {
-      return reply.code(400).send({ error: error instanceof Error ? error.message : String(error) });
+      return reply.code(400).send({ error: errorMessage(error) });
     }
   });
 
-  app.get<{ Params: { sessionId: string } }>(`${prefix}/sessions/:sessionId/events`, { websocket: true }, (socket, request) => {
-    eventHub.add(request.params.sessionId, socket);
+  app.get<{ Params: { sessionId: string }; Querystring: SessionQuery }>(`${prefix}/sessions/:sessionId/events`, { websocket: true }, (socket, request) => {
+    try {
+      const ref = sessionRefFromQuery(request.params.sessionId, request.query);
+      eventHub.add(ref.id, socket);
+    } catch {
+      socket.close();
+    }
   });
 
   app.get(`${prefix}/sessions/events`, { websocket: true }, (socket) => {
@@ -181,6 +217,34 @@ export function registerSessionRoutes(app: FastifyInstance, sessions: PiSessionS
   });
 }
 
+function sessionRefFromQuery(id: string, query: SessionQuery): PiSessionRef {
+  const cwd = query.cwd;
+  if (cwd === undefined || cwd === "") throw new SessionRouteValidationError("cwd query parameter is required");
+  return { id, cwd };
+}
+
+function sessionRefFromBody(id: string, body: Record<string, unknown>): PiSessionRef {
+  const cwd = body["cwd"];
+  if (typeof cwd !== "string" || cwd === "") throw new Error("cwd field is required");
+  return { id, cwd };
+}
+
+function requireRecord(value: unknown): Record<string, unknown> {
+  if (!isRecord(value)) throw new Error("request body must be an object");
+  return value;
+}
+
+function requireString(record: Record<string, unknown>, field: string): string {
+  const value = record[field];
+  if (typeof value !== "string") throw new Error(`${field} field must be a string`);
+  return value;
+}
+
+function requireThinkingLevel(value: unknown): "off" | "minimal" | "low" | "medium" | "high" | "xhigh" {
+  if (value === "off" || value === "minimal" || value === "low" || value === "medium" || value === "high" || value === "xhigh") return value;
+  throw new Error("level field is invalid");
+}
+
 function optionalField<T>(key: string, value: T | undefined): Record<string, T> | object {
   return value === undefined ? {} : { [key]: value };
 }
@@ -190,3 +254,15 @@ function optionalNumber(value: string | undefined): number | undefined {
   const parsed = Number(value);
   return Number.isFinite(parsed) ? parsed : undefined;
 }
+
+function errorMessage(error: unknown): string {
+  return error instanceof Error ? error.message : String(error);
+}
+
+function readErrorStatus(error: unknown): 400 | 404 {
+  return error instanceof SessionRouteValidationError ? 400 : 404;
+}
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+  return typeof value === "object" && value !== null && !Array.isArray(value);
+}

src/server/types.ts

@@ -1,6 +1,7 @@
 export type {
   Project,
   Workspace,
+  SessionRef as ClientSessionRef,
   SessionInfo as ClientSession,
   ArchiveSessionsResponse as ClientArchiveSessionsResponse,
   MessagePage as ClientMessagePage,