diff --git a/docs/agent-lifecycle.md b/docs/agent-lifecycle.md
index 1d0b29b018..45c54ca18b 100644
--- a/docs/agent-lifecycle.md
+++ b/docs/agent-lifecycle.md
@@ -136,6 +136,12 @@ the marker. Closing a tab sets that client's label to `false`. Any `true` client
 open. Detach clears the parent and every open-tab label. The surviving child therefore becomes a
 normal root agent immediately, and closing its still-open tab archives it.
 
+Agent-scoped workspace creation records the caller's workspace as `parentWorkspaceId`.
+This is informational ancestry for future workspace grouping. It does not change placement,
+visibility, status, or archive behavior. Archiving a parent workspace preserves its children's
+records and parentage. Unscoped creation and existing workspaces have no parent; ancestry is
+never inferred from directories, projects, or Git branches.
+
 Runtime ownership is resolved from explicit workspace ID and caller context, never from `cwd`. Workspace creation is a separate operation with `local | worktree` isolation; agent creation reuses that workspace unless a new workspace is explicitly requested.
 
 Setup belongs to the workspace, including combined workspace-plus-agent creation and the supported agent `worktree` request. Run setup through the workspace workflow before launching configured terminals or scripts. Setup output is read in the Setup panel from per-command snapshots; never produce setup chat timeline rows or concatenate command logs. Legacy agent `git`/`worktreeName` inputs and hidden MCP worktree placement are rejected with workspace-creation guidance. Existing wire schemas retain an empty combined-log string for parsing compatibility.
diff --git a/packages/app/src/runtime/replica-cache/index.test.ts b/packages/app/src/runtime/replica-cache/index.test.ts
index 0ea262f7cb..5c90ffa5e1 100644
--- a/packages/app/src/runtime/replica-cache/index.test.ts
+++ b/packages/app/src/runtime/replica-cache/index.test.ts
@@ -321,6 +321,26 @@ describe("ReplicaCache", () => {
     expect(restored?.range).toBeNull();
   });
 
+  it("preserves workspace parentage and its checkpoint across cache reopen", async () => {
+    const storage = new MemoryStorage();
+    const writer = createCache(storage);
+    const baseline = directory({ workspaces: { generation: "g", afterSeq: 8 } });
+    const workspace = normalizeWorkspaceDescriptor({
+      ...workspacePayload(),
+      parentWorkspaceId: "parent",
+    });
+    baseline.workspaces.set(workspace.id, workspace);
+    commitDirectory(writer, SERVER_ID, baseline);
+    await writer.flush();
+    const reader = createCache(storage);
+    const restored = await reader.readDirectory(SERVER_ID);
+    expect(restored.checkpoint).toEqual(baseline.checkpoint);
+    expect(restored.workspaces.get(workspace.id)?.parentWorkspaceId).toBe("parent");
+    expect((await reader.readWorkspace(SERVER_ID, workspace.id))?.workspace.parentWorkspaceId).toBe(
+      "parent",
+    );
+  });
+
   it("preserves workspace sorting timestamps across cache reopen", async () => {
     const storage = new MemoryStorage();
     const writer = createCache(storage);
diff --git a/packages/app/src/runtime/replica-cache/index.ts b/packages/app/src/runtime/replica-cache/index.ts
index 1032a663bf..91a41e4186 100644
--- a/packages/app/src/runtime/replica-cache/index.ts
+++ b/packages/app/src/runtime/replica-cache/index.ts
@@ -299,6 +299,7 @@ const WorkspaceGitRuntimeSchema = z
   .optional();
 
 const StoredWorkspaceSchema = z.strictObject({
+  parentWorkspaceId: z.string().optional(),
   // Require both keys: a cursor without these values would preserve the wrong sort on reconnect.
   createdAt: IsoDateSchema.nullable(),
   lastUserMessageAt: IsoDateSchema.nullable(),
@@ -707,6 +708,7 @@ function restoreWorkspace(stored: StoredWorkspace): WorkspaceDescriptor {
 
 function serializeWorkspace(workspace: WorkspaceDescriptor): StoredWorkspace {
   return {
+    parentWorkspaceId: workspace.parentWorkspaceId,
     createdAt: workspace.createdAt?.toISOString() ?? null,
     lastUserMessageAt: workspace.lastUserMessageAt?.toISOString() ?? null,
     id: workspace.id,
diff --git a/packages/app/src/stores/session-store.test.ts b/packages/app/src/stores/session-store.test.ts
index fb38605220..1b9052c4c1 100644
--- a/packages/app/src/stores/session-store.test.ts
+++ b/packages/app/src/stores/session-store.test.ts
@@ -557,6 +557,33 @@ describe("normalizeWorkspaceDescriptor", () => {
     expect(blank.workspaceDirectory).toBe("");
   });
 
+  it("preserves informational workspace parentage", () => {
+    const payload = {
+      id: "child",
+      parentWorkspaceId: "parent",
+      projectId: "1",
+      projectDisplayName: "Project 1",
+      projectRootPath: "/repo",
+      workspaceDirectory: "/repo",
+      projectKind: "git",
+      workspaceKind: "checkout",
+      name: "main",
+      archivingAt: null,
+      status: "done",
+      statusEnteredAt: null,
+      activityAt: null,
+      diffStat: null,
+      scripts: [],
+    } as WorkspaceDescriptorPayload;
+
+    const workspace = normalizeWorkspaceDescriptor(payload);
+
+    expect(workspace.parentWorkspaceId).toBe("parent");
+    expect(
+      normalizeWorkspaceDescriptor({ ...payload, parentWorkspaceId: undefined }).parentWorkspaceId,
+    ).toBeUndefined();
+  });
+
   it("defaults missing scripts to an empty array", () => {
     const payload = {
       id: "1",
diff --git a/packages/app/src/stores/session-store.ts b/packages/app/src/stores/session-store.ts
index b1312860a9..0f8a9f2476 100644
--- a/packages/app/src/stores/session-store.ts
+++ b/packages/app/src/stores/session-store.ts
@@ -105,6 +105,7 @@ export interface Agent {
 }
 
 export interface WorkspaceDescriptor {
+  parentWorkspaceId?: string;
   createdAt: Date | null;
   lastUserMessageAt: Date | null;
   id: string;
@@ -162,6 +163,7 @@ export function normalizeWorkspaceDescriptor(
     projectKind: payload.projectKind,
     workspaceKind: payload.workspaceKind,
     background: payload.background ?? false,
+    parentWorkspaceId: payload.parentWorkspaceId,
     name: payload.name,
     title: payload.title ?? null,
     pinnedAt: payload.pinnedAt ?? null,
diff --git a/packages/protocol/src/messages.ts b/packages/protocol/src/messages.ts
index 64f37064e2..5436e1737d 100644
--- a/packages/protocol/src/messages.ts
+++ b/packages/protocol/src/messages.ts
@@ -4189,6 +4189,8 @@ export const WorkspaceGitHubRuntimePayloadSchema = z
 
 export const WorkspaceDescriptorPayloadSchema = z
   .object({
+    // Informational creation ancestry; independent of placement and lifecycle.
+    parentWorkspaceId: z.string().optional(),
     id: z.string(),
     projectId: z.string(),
     projectDisplayName: z.string(),
diff --git a/packages/protocol/src/messages.workspaces.test.ts b/packages/protocol/src/messages.workspaces.test.ts
index 3cb9b0d5bd..8a5bd13224 100644
--- a/packages/protocol/src/messages.workspaces.test.ts
+++ b/packages/protocol/src/messages.workspaces.test.ts
@@ -634,6 +634,26 @@ describe("workspace message schemas", () => {
     ]);
   });
 
+  test("preserves informational workspace parentage in directory updates", () => {
+    const workspace = {
+      id: "child",
+      parentWorkspaceId: "parent",
+      projectId: "project",
+      projectDisplayName: "repo",
+      projectRootPath: "/repo",
+      projectKind: "git",
+      workspaceKind: "worktree",
+      name: "child",
+      status: "done",
+      activityAt: null,
+    };
+    expect(WorkspaceDescriptorPayloadSchema.parse(workspace).parentWorkspaceId).toBe("parent");
+    expect(
+      WorkspaceDescriptorPayloadSchema.parse({ ...workspace, parentWorkspaceId: undefined })
+        .parentWorkspaceId,
+    ).toBeUndefined();
+  });
+
   test("parses legacy workspace descriptors without workspaceDirectory", () => {
     const parsed = SessionOutboundMessageSchema.parse({
       type: "workspace_update",
diff --git a/packages/server/src/server/agent/mcp-parity.e2e.test.ts b/packages/server/src/server/agent/mcp-parity.e2e.test.ts
index 80d6da20a7..d4b1b76af1 100644
--- a/packages/server/src/server/agent/mcp-parity.e2e.test.ts
+++ b/packages/server/src/server/agent/mcp-parity.e2e.test.ts
@@ -1171,7 +1171,7 @@ describe("Suite E: Workspace Tools", () => {
         .callTool({ name: "archive_workspace", args: { workspaceId } })
         .catch(() => undefined);
     }
-  });
+  }, 30_000);
 
   test("agent-scoped workspace creation inherits visibility and permits an explicit false override", async () => {
     const parentWorkspace = await callToolStructured(topLevelClient, "create_workspace", {
@@ -1197,12 +1197,43 @@ describe("Suite E: Workspace Tools", () => {
       });
       ownedWorkspaces.push(str(inherited.workspaceId));
       expect(inherited.background).toBe(true);
+      expect(inherited.parentWorkspaceId).toBe(parentWorkspaceId);
       const visible = await callToolStructured(scoped, "create_workspace", {
         isolation: "local",
         background: false,
       });
       ownedWorkspaces.push(str(visible.workspaceId));
       expect(visible.background).toBe(false);
+      expect(visible.parentWorkspaceId).toBe(parentWorkspaceId);
+      const worktree = await callToolStructured(scoped, "create_workspace", {
+        isolation: "worktree",
+        branchName: "parentage-child",
+        baseBranch: "main",
+        background: false,
+      });
+      ownedWorkspaces.push(str(worktree.workspaceId));
+      expect(worktree.parentWorkspaceId).toBe(parentWorkspaceId);
+      const client = new DaemonClient({ url: `ws://127.0.0.1:${daemonHandle.port}/ws` });
+      try {
+        await client.connect();
+        const created = await client.createWorkspace({
+          source: { kind: "directory", path: worktreeRepoCwd },
+          callerAgentId: str(parent.agentId),
+          background: false,
+        });
+        const workspaceId = str(created.workspace?.id);
+        ownedWorkspaces.push(workspaceId);
+        expect(created.workspace?.parentWorkspaceId).toBe(parentWorkspaceId);
+        const listed = await client.fetchWorkspaces();
+        expect(listed.entries).toContainEqual(
+          expect.objectContaining({
+            id: workspaceId,
+            parentWorkspaceId: parentWorkspaceId,
+          }),
+        );
+      } finally {
+        await client.close();
+      }
     } finally {
       await scoped?.close();
       for (const workspaceId of ownedWorkspaces.toReversed())
@@ -1210,7 +1241,7 @@ describe("Suite E: Workspace Tools", () => {
           .callTool({ name: "archive_workspace", args: { workspaceId } })
           .catch(() => undefined);
     }
-  });
+  }, 30_000);
 
   test("a background agent's children and workspaces are background unless it overrides", async () => {
     const visibleAgentId = await createTopLevelAgent();
diff --git a/packages/server/src/server/agent/tools/paseo-tools.ts b/packages/server/src/server/agent/tools/paseo-tools.ts
index 7b33d2e250..42b6ddec4c 100644
--- a/packages/server/src/server/agent/tools/paseo-tools.ts
+++ b/packages/server/src/server/agent/tools/paseo-tools.ts
@@ -188,6 +188,7 @@ interface ProviderSummary {
 }
 
 const WorkspaceAutomationSummarySchema = z.object({
+  parentWorkspaceId: z.string().optional(),
   workspaceId: z.string(),
   projectId: z.string(),
   cwd: z.string(),
@@ -206,6 +207,7 @@ function toWorkspaceAutomationSummary(workspace: PersistedWorkspaceRecord) {
     kind: workspace.kind,
     title: workspace.title,
     background: workspace.background,
+    parentWorkspaceId: workspace.parentWorkspaceId,
   };
 }
 
diff --git a/packages/server/src/server/session.ts b/packages/server/src/server/session.ts
index 3dec72f45f..339a7c17fb 100644
--- a/packages/server/src/server/session.ts
+++ b/packages/server/src/server/session.ts
@@ -5900,6 +5900,7 @@ export class Session {
       pinnedAt: workspace.pinnedAt,
       ...(workspace.labels && workspace.labels.length > 0 ? { labels: workspace.labels } : {}),
       background: workspace.background,
+      parentWorkspaceId: workspace.parentWorkspaceId,
       archivingAt: null,
       status: "done",
       statusEnteredAt: null,
@@ -5988,6 +5989,7 @@ export class Session {
       projectKind: projectRecord?.kind ?? "git",
       workspaceKind: result.workspace.kind,
       background: result.workspace.background,
+      parentWorkspaceId: result.workspace.parentWorkspaceId,
       name: resolveWorkspaceName({
         title: result.workspace.title,
         derivedDisplayName: result.worktree.branchName || result.workspace.displayName,
diff --git a/packages/server/src/server/session/workspace-provisioning/workspace-provisioning-service.test.ts b/packages/server/src/server/session/workspace-provisioning/workspace-provisioning-service.test.ts
index 012ad0d490..706f199114 100644
--- a/packages/server/src/server/session/workspace-provisioning/workspace-provisioning-service.test.ts
+++ b/packages/server/src/server/session/workspace-provisioning/workspace-provisioning-service.test.ts
@@ -205,6 +205,82 @@ test("fresh non-git directory creates a directory workspace at the exact path",
   expect(workspace.cwd).toBe(dir);
 });
 
+test("workspace parentage survives reload and parent archive without changing placement", async () => {
+  const cwd = path.join(tmpDir, "plain");
+  const parent = await provisioning.createWorkspaceForDirectory(cwd);
+  const child = await provisioning.createWorkspaceForDirectory(cwd, null, undefined, {
+    callerWorkspaceId: parent.workspaceId,
+    background: false,
+  });
+  const grandchild = await provisioning.createWorkspaceForDirectory(
+    path.join(tmpDir, "other"),
+    null,
+    undefined,
+    {
+      callerWorkspaceId: child.workspaceId,
+    },
+  );
+  expect(parent.parentWorkspaceId).toBeUndefined();
+  expect(child).toMatchObject({ parentWorkspaceId: parent.workspaceId, cwd });
+  expect(grandchild).toMatchObject({ parentWorkspaceId: child.workspaceId });
+  await workspaceRegistry.archive(parent.workspaceId, ARCHIVED_AT);
+  const reloaded = new FileBackedWorkspaceRegistry(
+    path.join(tmpDir, "projects", "workspaces.json"),
+    logger,
+  );
+  await reloaded.initialize();
+  expect(await reloaded.get(child.workspaceId)).toMatchObject({
+    parentWorkspaceId: parent.workspaceId,
+    archivedAt: null,
+  });
+  expect(await reloaded.get(grandchild.workspaceId)).toMatchObject({
+    parentWorkspaceId: child.workspaceId,
+    archivedAt: null,
+  });
+});
+
+test("worktree workspace creation records its caller independently of its source project", async () => {
+  const sourceCwd = path.join(tmpDir, "repo");
+  gitRoots.add(sourceCwd);
+  const parent = await provisioning.createWorkspaceForDirectory(path.join(tmpDir, "other"));
+  const child = await provisioning.createWorkspaceForWorktree({
+    sourceCwd,
+    repoRoot: sourceCwd,
+    cwd: path.join(tmpDir, "worktree"),
+    worktreeRoot: path.join(tmpDir, "worktree"),
+    branch: "child",
+    baseBranch: "main",
+    title: null,
+    callerWorkspaceId: parent.workspaceId,
+  });
+  expect(child.parentWorkspaceId).toBe(parent.workspaceId);
+  expect(child.projectId).not.toBe(parent.projectId);
+  expect(await workspaceRegistry.get(child.workspaceId)).toMatchObject({
+    parentWorkspaceId: parent.workspaceId,
+  });
+});
+
+test("workspace creation rejects an unknown caller even with explicit visibility", async () => {
+  await expect(
+    provisioning.createWorkspaceForDirectory(path.join(tmpDir, "plain"), null, undefined, {
+      callerWorkspaceId: "missing",
+      background: false,
+    }),
+  ).rejects.toThrow("Caller workspace missing not found");
+});
+
+test("workspace creation cannot overwrite its caller with a self relationship", async () => {
+  const cwd = path.join(tmpDir, "plain");
+  const parent = await provisioning.createWorkspaceForDirectory(cwd);
+  await expect(
+    provisioning.createWorkspaceForDirectory(cwd, null, undefined, {
+      callerWorkspaceId: parent.workspaceId,
+      workspaceId: parent.workspaceId,
+    }),
+  ).rejects.toThrow("A workspace cannot be its own parent");
+  expect(await workspaceRegistry.get(parent.workspaceId)).toEqual(parent);
+});
+
 test("background workspace creation preserves hooks, inheritance and durable visibility", async () => {
   const dir = path.join(tmpDir, "plain");
   const events: string[] = [];
diff --git a/packages/server/src/server/session/workspace-provisioning/workspace-provisioning-service.ts b/packages/server/src/server/session/workspace-provisioning/workspace-provisioning-service.ts
index 3f2a7b423c..5744c2ddeb 100644
--- a/packages/server/src/server/session/workspace-provisioning/workspace-provisioning-service.ts
+++ b/packages/server/src/server/session/workspace-provisioning/workspace-provisioning-service.ts
@@ -227,15 +227,21 @@ export function createWorkspaceProvisioningService(deps: {
     return project;
   }
 
-  async function resolveBackground(input?: {
+  async function resolveCreationMetadata(input?: {
+    workspaceId?: string;
     background?: boolean;
     callerWorkspaceId?: string;
-  }): Promise<boolean> {
-    if (input?.background !== undefined) return input.background;
-    if (!input?.callerWorkspaceId) return false;
+  }): Promise<{ background: boolean; parentWorkspaceId?: string }> {
+    if (!input?.callerWorkspaceId) return { background: input?.background ?? false };
+    if (input.workspaceId === input.callerWorkspaceId) {
+      throw new Error("A workspace cannot be its own parent");
+    }
     const callerWorkspace = await workspaceRegistry.get(input.callerWorkspaceId);
     if (!callerWorkspace) throw new Error(`Caller workspace ${input.callerWorkspaceId} not found`);
-    return callerWorkspace.background;
+    return {
+      background: input.background ?? callerWorkspace.background,
+      parentWorkspaceId: callerWorkspace.workspaceId,
+    };
   }
 
   async function createWorkspaceForDirectory(
@@ -269,7 +275,7 @@ export function createWorkspaceProvisioningService(deps: {
         title: title?.trim() || null,
         createdAt: timestamp,
         updatedAt: timestamp,
-        background: await resolveBackground(context),
+        ...(await resolveCreationMetadata(context)),
       });
       await workspaceRegistry.upsert(workspace, {
         expectsInitialAgent: context?.expectsInitialAgent,
@@ -310,7 +316,7 @@ export function createWorkspaceProvisioningService(deps: {
       createdAt: timestamp,
       updatedAt: timestamp,
       ...(input.untrustedSource ? { untrustedSource: input.untrustedSource } : {}),
-      background: await resolveBackground(input),
+      ...(await resolveCreationMetadata(input)),
     });
     await workspaceRegistry.upsert(workspace, {
       expectsInitialAgent: input.expectsInitialAgent,
diff --git a/packages/server/src/server/workspace-registry.ts b/packages/server/src/server/workspace-registry.ts
index 351ba043e4..b337543c7e 100644
--- a/packages/server/src/server/workspace-registry.ts
+++ b/packages/server/src/server/workspace-registry.ts
@@ -49,6 +49,7 @@ const PersistedProjectRecordSchema = z.object({
 });
 
 const PersistedWorkspaceRecordSchema = z.object({
+  parentWorkspaceId: z.string().optional(),
   workspaceId: z.string(),
   projectId: z.string(),
   cwd: z.string(),
@@ -679,6 +680,7 @@ export function resolveProjectDisplayName(record: PersistedProjectRecord): strin
 }
 
 export function createPersistedWorkspaceRecord(input: {
+  parentWorkspaceId?: string;
   workspaceId: string;
   projectId: string;
   cwd: string;