diff --git a/packages/server/src/server/session.ts b/packages/server/src/server/session.ts
index a2ec7ec79..6230ae965 100644
--- a/packages/server/src/server/session.ts
+++ b/packages/server/src/server/session.ts
@@ -4,7 +4,7 @@ import { TTLCache } from "@isaacs/ttlcache";
 import pMemoize from "p-memoize";
 import { realpathSync } from "node:fs";
 import type { FSWatcher } from "node:fs";
-import { resolve, sep } from "path";
+import { basename, resolve, sep } from "path";
 import { homedir } from "node:os";
 import { z } from "zod";
 import type { ToolSet } from "ai";
@@ -6261,6 +6261,7 @@ export class Session {
     let bestMatch: PersistedWorkspaceRecord | null = null;
     for (const workspace of workspaces) {
       if (workspace.cwd === userHome) continue;
+      if (workspace.archivedAt) continue;
       const prefix = workspace.cwd.endsWith(sep) ? workspace.cwd : `${workspace.cwd}${sep}`;
       if (!normalizedCwd.startsWith(prefix)) {
         continue;
@@ -6562,11 +6563,36 @@ export class Session {
   }
 
   private async findOrCreateWorkspaceForDirectory(cwd: string): Promise<PersistedWorkspaceRecord> {
+    const inputCwd = normalizePersistedWorkspaceId(cwd);
     const normalizedCwd = await this.resolveWorkspaceDirectory(cwd);
     const existingWorkspace = await this.findExactWorkspaceByDirectory(normalizedCwd, {
       refreshGit: false,
     });
     if (existingWorkspace) {
+      if (existingWorkspace.archivedAt && inputCwd !== normalizedCwd) {
+        const timestamp = new Date().toISOString();
+        const displayName = basename(inputCwd) || inputCwd;
+        const projectRecord = createPersistedProjectRecord({
+          projectId: inputCwd,
+          rootPath: inputCwd,
+          kind: "non_git",
+          displayName,
+          createdAt: timestamp,
+          updatedAt: timestamp,
+        });
+        await this.projectRegistry.upsert(projectRecord);
+        const workspaceRecord = createPersistedWorkspaceRecord({
+          workspaceId: inputCwd,
+          projectId: projectRecord.projectId,
+          cwd: inputCwd,
+          kind: "directory",
+          displayName,
+          createdAt: timestamp,
+          updatedAt: timestamp,
+        });
+        await this.workspaceRegistry.upsert(workspaceRecord);
+        return workspaceRecord;
+      }
       return this.reclassifyOrUnarchiveWorkspaceForDirectory({
         workspace: existingWorkspace,
         project: await this.projectRegistry.get(existingWorkspace.projectId),
diff --git a/packages/server/src/server/session.workspace-resolution-invariants.test.ts b/packages/server/src/server/session.workspace-resolution-invariants.test.ts
new file mode 100644
index 000000000..88ca9a6c8
--- /dev/null
+++ b/packages/server/src/server/session.workspace-resolution-invariants.test.ts
@@ -0,0 +1,445 @@
+// Invariant tests for cwd → workspace resolution on the open_project_request path.
+// Each test encodes a default behavior we want from `findOrCreateWorkspaceForDirectory`.
+// Run to see which invariants the current code already satisfies (green) and which
+// it violates (red).
+
+import { mkdtempSync } from "node:fs";
+import { tmpdir } from "node:os";
+import path from "node:path";
+import { expect, test, vi } from "vitest";
+
+import { Session, type SessionOptions } from "./session.js";
+import type { SessionOutboundMessage } from "../shared/messages.js";
+import { createNoopWorkspaceGitService } from "./test-utils/workspace-git-service-stub.js";
+import {
+  createPersistedProjectRecord,
+  createPersistedWorkspaceRecord,
+  type PersistedProjectRecord,
+  type PersistedWorkspaceRecord,
+} from "./workspace-registry.js";
+
+interface Harness {
+  session: Session;
+  emitted: SessionOutboundMessage[];
+  workspaces: Map<string, PersistedWorkspaceRecord>;
+  projects: Map<string, PersistedProjectRecord>;
+}
+
+function createHarness(input: {
+  workspaces?: PersistedWorkspaceRecord[];
+  projects?: PersistedProjectRecord[];
+  gitRoots?: string[];
+}): Harness {
+  const workspaces = new Map<string, PersistedWorkspaceRecord>();
+  const projects = new Map<string, PersistedProjectRecord>();
+  for (const w of input.workspaces ?? []) workspaces.set(w.workspaceId, w);
+  for (const p of input.projects ?? []) projects.set(p.projectId, p);
+  const gitRoots = [...(input.gitRoots ?? [])];
+
+  function findGitRoot(cwd: string): string | null {
+    let best: string | null = null;
+    for (const root of gitRoots) {
+      if (cwd === root || cwd.startsWith(`${root}${path.sep}`)) {
+        if (!best || root.length > best.length) best = root;
+      }
+    }
+    return best;
+  }
+
+  const workspaceGitService = createNoopWorkspaceGitService({
+    getCheckout: async (cwd: string) => {
+      const root = findGitRoot(cwd);
+      if (!root) {
+        return {
+          cwd,
+          isGit: false,
+          currentBranch: null,
+          remoteUrl: null,
+          worktreeRoot: null,
+          isPaseoOwnedWorktree: false,
+          mainRepoRoot: null,
+        };
+      }
+      return {
+        cwd,
+        isGit: true,
+        currentBranch: "main",
+        remoteUrl: null,
+        worktreeRoot: root,
+        isPaseoOwnedWorktree: false,
+        mainRepoRoot: null,
+      };
+    },
+    peekSnapshot: () => null,
+  });
+
+  const emitted: SessionOutboundMessage[] = [];
+  const logger = {
+    child: () => logger,
+    trace: vi.fn(),
+    debug: vi.fn(),
+    info: vi.fn(),
+    warn: vi.fn(),
+    error: vi.fn(),
+  };
+
+  const session = new Session({
+    clientId: "test",
+    appVersion: null,
+    onMessage: (m) => emitted.push(m),
+    logger: logger as unknown as SessionOptions["logger"],
+    downloadTokenStore: {} as unknown as SessionOptions["downloadTokenStore"],
+    pushTokenStore: {} as unknown as SessionOptions["pushTokenStore"],
+    paseoHome: mkdtempSync(path.join(tmpdir(), "paseo-invariant-test-")),
+    agentManager: {
+      subscribe: () => () => {},
+      listAgents: () => [],
+      getAgent: () => null,
+      archiveAgent: async () => ({ archivedAt: new Date().toISOString() }),
+      archiveSnapshot: async () => ({}),
+      clearAgentAttention: async () => {},
+      notifyAgentState: () => {},
+    } as unknown as SessionOptions["agentManager"],
+    agentStorage: {
+      list: async () => [],
+      get: async () => null,
+    } as unknown as SessionOptions["agentStorage"],
+    projectRegistry: {
+      initialize: async () => {},
+      existsOnDisk: async () => true,
+      list: async () => Array.from(projects.values()),
+      get: async (id: string) => projects.get(id) ?? null,
+      upsert: async (record: PersistedProjectRecord) => {
+        projects.set(record.projectId, record);
+      },
+      archive: async (id: string, archivedAt: string) => {
+        const p = projects.get(id);
+        if (p) projects.set(id, { ...p, archivedAt });
+      },
+      remove: async (id: string) => {
+        projects.delete(id);
+      },
+    } as unknown as SessionOptions["projectRegistry"],
+    workspaceRegistry: {
+      initialize: async () => {},
+      existsOnDisk: async () => true,
+      list: async () => Array.from(workspaces.values()),
+      get: async (id: string) => workspaces.get(id) ?? null,
+      upsert: async (record: PersistedWorkspaceRecord) => {
+        workspaces.set(record.workspaceId, record);
+      },
+      archive: async (id: string, archivedAt: string) => {
+        const w = workspaces.get(id);
+        if (w) workspaces.set(id, { ...w, archivedAt });
+      },
+      remove: async (id: string) => {
+        workspaces.delete(id);
+      },
+    } as unknown as SessionOptions["workspaceRegistry"],
+    chatService: {} as unknown as SessionOptions["chatService"],
+    scheduleService: {} as unknown as SessionOptions["scheduleService"],
+    loopService: {} as unknown as SessionOptions["loopService"],
+    checkoutDiffManager: {
+      subscribe: async () => ({
+        initial: { cwd: "/tmp", files: [], error: null },
+        unsubscribe: () => {},
+      }),
+      scheduleRefreshForCwd: () => {},
+      getMetrics: () => ({
+        checkoutDiffTargetCount: 0,
+        checkoutDiffSubscriptionCount: 0,
+        checkoutDiffWatcherCount: 0,
+        checkoutDiffFallbackRefreshTargetCount: 0,
+      }),
+      dispose: () => {},
+    } as unknown as SessionOptions["checkoutDiffManager"],
+    workspaceGitService,
+    daemonConfigStore: {
+      get: () => ({ mcp: { injectIntoAgents: false }, providers: {} }),
+      onChange: () => () => {},
+    } as unknown as SessionOptions["daemonConfigStore"],
+    mcpBaseUrl: null,
+    stt: null,
+    tts: null,
+    terminalManager: null,
+  });
+
+  return { session, emitted, workspaces, projects };
+}
+
+async function openProject(session: Session, cwd: string, requestId = "req-1") {
+  await (session as unknown as { handleMessage(m: unknown): Promise<unknown> }).handleMessage({
+    type: "open_project_request",
+    cwd,
+    requestId,
+  });
+}
+
+function getOpenResponse(emitted: SessionOutboundMessage[], requestId: string) {
+  const m = emitted.find(
+    (msg) => msg.type === "open_project_response" && msg.payload.requestId === requestId,
+  );
+  if (!m || m.type !== "open_project_response") return null;
+  return m.payload;
+}
+
+const T0 = "2026-01-01T00:00:00.000Z";
+
+function gitWorkspace(rootPath: string, archivedAt: string | null = null) {
+  return createPersistedWorkspaceRecord({
+    workspaceId: rootPath,
+    projectId: rootPath,
+    cwd: rootPath,
+    kind: "local_checkout",
+    displayName: "main",
+    createdAt: T0,
+    updatedAt: T0,
+    archivedAt,
+  });
+}
+
+function dirWorkspace(cwd: string, archivedAt: string | null = null) {
+  return createPersistedWorkspaceRecord({
+    workspaceId: cwd,
+    projectId: cwd,
+    cwd,
+    kind: "directory",
+    displayName: path.basename(cwd),
+    createdAt: T0,
+    updatedAt: T0,
+    archivedAt,
+  });
+}
+
+function gitProject(rootPath: string, archivedAt: string | null = null) {
+  return createPersistedProjectRecord({
+    projectId: rootPath,
+    rootPath,
+    kind: "git",
+    displayName: path.basename(rootPath),
+    createdAt: T0,
+    updatedAt: T0,
+    archivedAt,
+  });
+}
+
+function dirProject(rootPath: string, archivedAt: string | null = null) {
+  return createPersistedProjectRecord({
+    projectId: rootPath,
+    rootPath,
+    kind: "non_git",
+    displayName: path.basename(rootPath),
+    createdAt: T0,
+    updatedAt: T0,
+    archivedAt,
+  });
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// S1. Open a fresh git repo: creates a workspace at the canonical root.
+// ─────────────────────────────────────────────────────────────────────────────
+test("S1: open fresh git repo creates workspace at canonical root", async () => {
+  const h = createHarness({ gitRoots: ["/foo"] });
+  await openProject(h.session, "/foo");
+  const resp = getOpenResponse(h.emitted, "req-1");
+  expect(resp?.error).toBeNull();
+  expect(resp?.workspace?.workspaceDirectory).toBe("/foo");
+  expect(resp?.workspace?.workspaceKind).toBe("local_checkout");
+  expect(h.workspaces.has("/foo")).toBe(true);
+});
+
+// ─────────────────────────────────────────────────────────────────────────────
+// S2. Open a fresh non-git directory: creates a directory workspace.
+//     (Capability we are explicitly keeping.)
+// ─────────────────────────────────────────────────────────────────────────────
+test("S2: open fresh non-git directory creates a directory workspace at exact path", async () => {
+  const h = createHarness({});
+  await openProject(h.session, "/bar");
+  const resp = getOpenResponse(h.emitted, "req-1");
+  expect(resp?.error).toBeNull();
+  expect(resp?.workspace?.workspaceDirectory).toBe("/bar");
+  expect(resp?.workspace?.workspaceKind).toBe("directory");
+  expect(h.workspaces.has("/bar")).toBe(true);
+});
+
+// ─────────────────────────────────────────────────────────────────────────────
+// S3. Re-open an active workspace by its exact path: returns the same record,
+//     no archive state change.
+// ─────────────────────────────────────────────────────────────────────────────
+test("S3: re-open active workspace by exact path returns the same record", async () => {
+  const h = createHarness({
+    workspaces: [gitWorkspace("/foo")],
+    projects: [gitProject("/foo")],
+    gitRoots: ["/foo"],
+  });
+  await openProject(h.session, "/foo");
+  const resp = getOpenResponse(h.emitted, "req-1");
+  expect(resp?.workspace?.id).toBe("/foo");
+  expect(h.workspaces.size).toBe(1);
+  expect(h.workspaces.get("/foo")?.archivedAt).toBeNull();
+});
+
+// ─────────────────────────────────────────────────────────────────────────────
+// S4. Open a subdir of an active git workspace: canonicalizes UP to the repo
+//     root, returns the existing workspace. (Per "always go to the nearest git".)
+// ─────────────────────────────────────────────────────────────────────────────
+test("S4: open subdir of active git workspace returns the repo-root workspace", async () => {
+  const h = createHarness({
+    workspaces: [gitWorkspace("/foo")],
+    projects: [gitProject("/foo")],
+    gitRoots: ["/foo"],
+  });
+  await openProject(h.session, "/foo/sub");
+  const resp = getOpenResponse(h.emitted, "req-1");
+  expect(resp?.workspace?.id).toBe("/foo");
+  expect(h.workspaces.size).toBe(1);
+});
+
+// ─────────────────────────────────────────────────────────────────────────────
+// S5. Open a subdir of an active non-git directory workspace: I4 says directory
+//     workspaces do NOT claim their subtree. Subdir gets its own workspace.
+// ─────────────────────────────────────────────────────────────────────────────
+test("S5: open subdir of active non-git directory creates a SEPARATE workspace", async () => {
+  const h = createHarness({
+    workspaces: [dirWorkspace("/bar")],
+    projects: [dirProject("/bar")],
+  });
+  await openProject(h.session, "/bar/baz");
+  const resp = getOpenResponse(h.emitted, "req-1");
+  expect(resp?.workspace?.workspaceDirectory).toBe("/bar/baz");
+  expect(h.workspaces.has("/bar")).toBe(true);
+  expect(h.workspaces.has("/bar/baz")).toBe(true);
+  expect(h.workspaces.size).toBe(2);
+});
+
+// ─────────────────────────────────────────────────────────────────────────────
+// S6. Open the EXACT path of an archived git workspace: this IS explicit user
+//     intent to re-open what they archived. Unarchive is correct here.
+// ─────────────────────────────────────────────────────────────────────────────
+test("S6: re-opening an archived git workspace by exact path UNARCHIVES it", async () => {
+  const archivedAt = "2026-04-22T13:08:05.400Z";
+  const h = createHarness({
+    workspaces: [gitWorkspace("/toolbox", archivedAt)],
+    projects: [gitProject("/toolbox", archivedAt)],
+    gitRoots: ["/toolbox"],
+  });
+  await openProject(h.session, "/toolbox");
+  expect(h.workspaces.get("/toolbox")?.archivedAt).toBeNull();
+  expect(h.projects.get("/toolbox")?.archivedAt).toBeNull();
+});
+
+// ─────────────────────────────────────────────────────────────────────────────
+// S7. Nested git: child has its own .git. Innermost wins → separate workspace.
+// ─────────────────────────────────────────────────────────────────────────────
+test("S7: open nested git repo (own .git) creates a SEPARATE workspace at the inner root", async () => {
+  const h = createHarness({
+    workspaces: [gitWorkspace("/foo")],
+    projects: [gitProject("/foo")],
+    gitRoots: ["/foo", "/foo/sub"],
+  });
+  await openProject(h.session, "/foo/sub");
+  const resp = getOpenResponse(h.emitted, "req-1");
+  expect(resp?.workspace?.workspaceDirectory).toBe("/foo/sub");
+  expect(h.workspaces.has("/foo")).toBe(true);
+  expect(h.workspaces.has("/foo/sub")).toBe(true);
+});
+
+// ─────────────────────────────────────────────────────────────────────────────
+// S8. Open a child of an archived NON-GIT ancestor: I4 — ancestor doesn't claim
+//     subtree. Fresh workspace at child path. Archived ancestor untouched.
+//     This is the vfonic case from issue #564.
+// ─────────────────────────────────────────────────────────────────────────────
+test("S8: open child of archived non-git ancestor creates fresh workspace; ancestor stays archived", async () => {
+  const archivedAt = "2026-04-04T17:15:22.423Z";
+  const h = createHarness({
+    workspaces: [dirWorkspace("/Users/me/Developer", archivedAt)],
+    projects: [dirProject("/Users/me/Developer", archivedAt)],
+  });
+  await openProject(h.session, "/Users/me/Developer/projects/foo");
+  expect(h.workspaces.get("/Users/me/Developer")?.archivedAt).toBe(archivedAt);
+  expect(h.workspaces.has("/Users/me/Developer/projects/foo")).toBe(true);
+});
+
+// ─────────────────────────────────────────────────────────────────────────────
+// S9. Open a child of an archived GIT ancestor: canonical resolves UP to the
+//     archived root. Per "no auto-unarchive", the archived state is sticky.
+//     This is the headline issue #564 reproduction (Edolce's video).
+// ─────────────────────────────────────────────────────────────────────────────
+test("S9: opening child of archived git workspace does NOT auto-unarchive the parent", async () => {
+  const archivedAt = "2026-04-22T13:08:05.400Z";
+  const h = createHarness({
+    workspaces: [gitWorkspace("/toolbox", archivedAt)],
+    projects: [gitProject("/toolbox", archivedAt)],
+    gitRoots: ["/toolbox"],
+  });
+  await openProject(h.session, "/toolbox/flomo-cli");
+  expect(h.workspaces.get("/toolbox")?.archivedAt).toBe(archivedAt);
+});
+
+// ─────────────────────────────────────────────────────────────────────────────
+// S10. The user's exact scenario:
+//   1. Open `/projects` as a non-git directory workspace (mistake).
+//   2. Archive it.
+//   3. Open `/projects/some-git-repo` (a real git repo nested inside).
+// Expected: the git repo opens as its own fresh workspace; archived `/projects`
+// stays archived and is NOT resurfaced. Tests I4 (non-git ancestor doesn't
+// claim subtree) interacting with a git child.
+// ─────────────────────────────────────────────────────────────────────────────
+test("S10: opening a git repo nested inside an archived non-git directory creates fresh workspace; ancestor stays archived", async () => {
+  const archivedAt = "2026-04-04T17:15:22.423Z";
+  const h = createHarness({
+    workspaces: [dirWorkspace("/projects", archivedAt)],
+    projects: [dirProject("/projects", archivedAt)],
+    gitRoots: ["/projects/some-git-repo"],
+  });
+  await openProject(h.session, "/projects/some-git-repo");
+  const resp = getOpenResponse(h.emitted, "req-1");
+  expect(resp?.error).toBeNull();
+  expect(resp?.workspace?.workspaceDirectory).toBe("/projects/some-git-repo");
+  expect(resp?.workspace?.workspaceKind).toBe("local_checkout");
+  expect(h.workspaces.has("/projects/some-git-repo")).toBe(true);
+  expect(h.workspaces.get("/projects")?.archivedAt).toBe(archivedAt);
+  expect(h.projects.get("/projects")?.archivedAt).toBe(archivedAt);
+});
+
+// ─────────────────────────────────────────────────────────────────────────────
+// S11. Archive then re-add round-trip (project-level): opening the exact path
+//      of an archived project unarchives both the project and its workspace,
+//      reusing the same path-derived ids.
+// ─────────────────────────────────────────────────────────────────────────────
+test("S11: re-opening an archived project by exact path unarchives project + workspace and reuses ids", async () => {
+  const archivedAt = "2026-04-22T13:08:05.400Z";
+  const h = createHarness({
+    workspaces: [gitWorkspace("/toolbox", archivedAt)],
+    projects: [gitProject("/toolbox", archivedAt)],
+    gitRoots: ["/toolbox"],
+  });
+  await openProject(h.session, "/toolbox");
+  const resp = getOpenResponse(h.emitted, "req-1");
+  expect(resp?.error).toBeNull();
+  expect(resp?.workspace?.id).toBe("/toolbox");
+  expect(resp?.workspace?.projectId).toBe("/toolbox");
+  expect(h.workspaces.size).toBe(1);
+  expect(h.projects.size).toBe(1);
+  expect(h.workspaces.get("/toolbox")?.archivedAt).toBeNull();
+  expect(h.projects.get("/toolbox")?.archivedAt).toBeNull();
+});
+
+// ─────────────────────────────────────────────────────────────────────────────
+// S12. Prefix-fallback resolver must not surface an archived ancestor: looking
+//      up a child cwd whose only matching record is an archived parent should
+//      return null (not the archived parent).
+// ─────────────────────────────────────────────────────────────────────────────
+test("S12: findWorkspaceByDirectory does not return archived ancestor via prefix fallback", async () => {
+  const archivedAt = "2026-04-22T13:08:05.400Z";
+  const h = createHarness({
+    workspaces: [dirWorkspace("/parent", archivedAt)],
+    projects: [dirProject("/parent", archivedAt)],
+  });
+  const found = await (
+    h.session as unknown as {
+      findWorkspaceByDirectory(cwd: string): Promise<unknown>;
+    }
+  ).findWorkspaceByDirectory("/parent/child");
+  expect(found).toBeNull();
+});