diff --git a/packages/app-ai-native/src/pages/multica/open-session-by-id.test.ts b/packages/app-ai-native/src/pages/multica/open-session-by-id.test.ts
index 18dd62b20..b295bdbb2 100644
--- a/packages/app-ai-native/src/pages/multica/open-session-by-id.test.ts
+++ b/packages/app-ai-native/src/pages/multica/open-session-by-id.test.ts
@@ -1,5 +1,5 @@
 import { describe, expect, test } from "bun:test"
-import { deriveWorkspaceName, findWorkspaceForDevice, openSessionById } from "./open-session-by-id"
+import { deriveWorkspaceName, findWorkspaceForSession, openSessionById } from "./open-session-by-id"
 import type { OpenSessionDeps } from "./open-session-by-id"
 import type { Device, Workspace } from "@/pages/workspace/types"
 
@@ -30,6 +30,15 @@ function workspace(id: string, opts: Partial<Workspace> = {}): Workspace {
   }
 }
 
+/** Shorthand for a workspace bound to a device with one registered directory. */
+function workspaceWithDir(id: string, deviceUniqueId: string, path: string): Workspace {
+  return workspace(id, {
+    deviceUniqueId,
+    // Only `path` matters for directory matching; cast to keep the fixture small.
+    directories: [{ path } as any],
+  })
+}
+
 // Collects the effects of openSessionById for assertions.
 function harness(over: Partial<OpenSessionDeps> = {}) {
   const calls = {
@@ -56,20 +65,43 @@ function harness(over: Partial<OpenSessionDeps> = {}) {
   return { calls, deps }
 }
 
-describe("findWorkspaceForDevice", () => {
-  test("matches on deviceUniqueId (routing id)", () => {
-    const ws = [workspace("w1", { deviceUniqueId: "dev-uniq" })]
-    expect(findWorkspaceForDevice(ws, device("db-1", "dev-uniq"))).toBe("w1")
+describe("findWorkspaceForSession", () => {
+  test("matches the workspace whose directory contains the session dir", () => {
+    const ws = [workspaceWithDir("w1", "dev-uniq", "/p")]
+    expect(findWorkspaceForSession(ws, device("db-1", "dev-uniq"), "/p/workdir")).toBe("w1")
+  })
+
+  test("matches on deviceId (db id) when deviceUniqueId is absent", () => {
+    const ws = [workspace("w1", { deviceId: "db-1", directories: [{ path: "/p" } as any] })]
+    expect(findWorkspaceForSession(ws, device("db-1", "dev-uniq"), "/p/workdir")).toBe("w1")
+  })
+
+  test("prefers the most specific (longest) containing directory", () => {
+    const ws = [
+      workspaceWithDir("w-root", "dev-uniq", "/p"),
+      workspaceWithDir("w-nested", "dev-uniq", "/p/workdir"),
+    ]
+    expect(findWorkspaceForSession(ws, device("db-1", "dev-uniq"), "/p/workdir/task")).toBe("w-nested")
+  })
+
+  test("does not match a same-device workspace with a different directory", () => {
+    const ws = [workspaceWithDir("w1", "dev-uniq", "/other/project")]
+    expect(findWorkspaceForSession(ws, device("db-1", "dev-uniq"), "/p/workdir")).toBeUndefined()
   })
 
-  test("matches on deviceId (db id) as fallback", () => {
-    const ws = [workspace("w1", { deviceId: "db-1" })]
-    expect(findWorkspaceForDevice(ws, device("db-1", "dev-uniq"))).toBe("w1")
+  test("does not match a containing directory on another device", () => {
+    const ws = [workspaceWithDir("w1", "other-device", "/p")]
+    expect(findWorkspaceForSession(ws, device("db-1", "dev-uniq"), "/p/workdir")).toBeUndefined()
   })
 
-  test("returns undefined when no workspace is on the device", () => {
-    const ws = [workspace("w1", { deviceUniqueId: "other" })]
-    expect(findWorkspaceForDevice(ws, device("db-1", "dev-uniq"))).toBeUndefined()
+  test("a path prefix without a separator boundary is not containment", () => {
+    const ws = [workspaceWithDir("w1", "dev-uniq", "/p/work")]
+    expect(findWorkspaceForSession(ws, device("db-1", "dev-uniq"), "/p/workdir")).toBeUndefined()
+  })
+
+  test("returns undefined for an empty session directory", () => {
+    const ws = [workspaceWithDir("w1", "dev-uniq", "/p")]
+    expect(findWorkspaceForSession(ws, device("db-1", "dev-uniq"), "")).toBeUndefined()
   })
 })
 
@@ -86,11 +118,11 @@ describe("deriveWorkspaceName", () => {
 })
 
 describe("openSessionById", () => {
-  test("navigates to an existing workspace on the owning device", async () => {
+  test("navigates to the workspace containing the session directory", async () => {
     const { calls, deps } = harness({
       listDevices: async () => [device("db-1", "dev-1"), device("db-2", "dev-2")],
       probeSession: async (d) => (d.id === "db-2" ? { directory: "/p/workdir" } : null),
-      listWorkspaces: async () => [workspace("w2", { deviceUniqueId: "dev-2" })],
+      listWorkspaces: async () => [workspaceWithDir("w2", "dev-2", "/p")],
     })
     await openSessionById("sess-1", deps)
     expect(calls.navigated).toEqual({ workspaceId: "w2", sessionId: "sess-1" })
@@ -113,6 +145,24 @@ describe("openSessionById", () => {
     expect(calls.navigated).toEqual({ workspaceId: "ws-new", sessionId: "sess-1" })
   })
 
+  test("creates a new workspace when the device only has mismatched-directory workspaces", async () => {
+    // Regression: reusing a same-device workspace that points at another
+    // directory rendered the session in the wrong project tree and dropped it
+    // from the directory-scoped session list (lost on refresh).
+    const { calls, deps } = harness({
+      listDevices: async () => [device("db-1", "dev-1")],
+      probeSession: async () => ({ directory: "/p/multica_workspaces/x/workdir" }),
+      listWorkspaces: async () => [workspaceWithDir("w-other", "dev-1", "/Users/x/project")],
+    })
+    await openSessionById("sess-1", deps)
+    expect(calls.created).toEqual({
+      name: "workdir",
+      deviceId: "db-1",
+      directory: "/p/multica_workspaces/x/workdir",
+    })
+    expect(calls.navigated).toEqual({ workspaceId: "ws-new", sessionId: "sess-1" })
+  })
+
   test("skips offline devices when probing", async () => {
     const probed: string[] = []
     const { calls, deps } = harness({
@@ -121,7 +171,7 @@ describe("openSessionById", () => {
         probed.push(d.id)
         return d.id === "db-2" ? { directory: "/p/workdir" } : null
       },
-      listWorkspaces: async () => [workspace("w2", { deviceUniqueId: "dev-2" })],
+      listWorkspaces: async () => [workspaceWithDir("w2", "dev-2", "/p")],
     })
     await openSessionById("sess-1", deps)
     expect(probed).toEqual(["db-2"])
@@ -145,7 +195,7 @@ describe("openSessionById", () => {
         if (d.id === "db-1") throw new Error("proxy down")
         return { directory: "/p/workdir" }
       },
-      listWorkspaces: async () => [workspace("w2", { deviceUniqueId: "dev-2" })],
+      listWorkspaces: async () => [workspaceWithDir("w2", "dev-2", "/p")],
     })
     await openSessionById("sess-1", deps)
     expect(calls.navigated?.workspaceId).toBe("w2")
diff --git a/packages/app-ai-native/src/pages/multica/open-session-by-id.ts b/packages/app-ai-native/src/pages/multica/open-session-by-id.ts
index a1c3adde3..4eff4d86f 100644
--- a/packages/app-ai-native/src/pages/multica/open-session-by-id.ts
+++ b/packages/app-ai-native/src/pages/multica/open-session-by-id.ts
@@ -9,8 +9,11 @@ import type { Device, Workspace } from "@/pages/workspace/types"
  *   1. enumerate the user's devices,
  *   2. probe each ONLINE device for the session id (lookup is directory-
  *      independent on the device side),
- *   3. once found, reuse an existing workspace on that device, or create one
- *      on demand for the session's directory,
+ *   3. once found, reuse the workspace on that device whose registered
+ *      directories CONTAIN the session's directory — never a workspace that
+ *      points elsewhere, or the session would render inside the wrong project
+ *      tree and fall out of the directory-scoped session list — or create a
+ *      workspace on demand for the session's directory,
  *   4. navigate to /workspace/<id>?session=<sessionId>.
  *
  * All I/O is injected so the orchestration is unit-testable.
@@ -50,7 +53,7 @@ export async function openSessionById(sessionId: string, deps: OpenSessionDeps):
     }
 
     const workspaces = await deps.listWorkspaces()
-    const existing = findWorkspaceForDevice(workspaces, hit.device)
+    const existing = findWorkspaceForSession(workspaces, hit.device, hit.directory)
     if (existing) {
       deps.navigateToSession(existing, sessionId)
       return
@@ -68,17 +71,42 @@ export async function openSessionById(sessionId: string, deps: OpenSessionDeps):
 }
 
 /**
- * Find an existing workspace bound to the given device. Matches on the routing
- * id (`Workspace.deviceUniqueId` === `Device.deviceId`) first, then the DB id
- * (`Workspace.deviceId` === `Device.id`).
+ * Find the workspace that owns the session's directory. Only workspaces on the
+ * given device are considered, and a workspace matches only when one of its
+ * registered directories CONTAINS the session's working directory — reusing a
+ * workspace that points at a different directory would render the session
+ * inside the wrong project tree and drop it from the directory-scoped session
+ * list. When several nested directories match, the longest (most specific)
+ * path wins. Returns undefined when nothing contains the directory, so the
+ * caller creates a workspace for the session's own directory instead.
  */
-export function findWorkspaceForDevice(workspaces: Workspace[], device: Device): string | undefined {
-  const match = workspaces.find(
-    (w) =>
+export function findWorkspaceForSession(
+  workspaces: Workspace[],
+  device: Device,
+  directory: string,
+): string | undefined {
+  const dir = normalizePath(directory)
+  if (!dir) return undefined
+  let best: { id: string; len: number } | undefined
+  for (const w of workspaces) {
+    const onDevice =
       (!!w.deviceUniqueId && w.deviceUniqueId === device.deviceId) ||
-      (!!w.deviceId && w.deviceId === device.id),
-  )
-  return match?.id
+      (!!w.deviceId && w.deviceId === device.id)
+    if (!onDevice) continue
+    for (const d of w.directories ?? []) {
+      const p = normalizePath(d.path)
+      if (!p) continue
+      if (dir === p || dir.startsWith(p + "/") || dir.startsWith(p + "\\")) {
+        if (!best || p.length > best.len) best = { id: w.id, len: p.length }
+      }
+    }
+  }
+  return best?.id
+}
+
+/** Strip trailing slashes so directory containment checks compare cleanly. */
+function normalizePath(p: string): string {
+  return (p ?? "").replace(/[/\\]+$/, "")
 }
 
 /** Last path segment of the session's directory, used to name an auto-created workspace. */