diff --git a/openhands-tools/openhands/tools/task/manager.py b/openhands-tools/openhands/tools/task/manager.py
index fc6685ab98..daf6fbec18 100644
--- a/openhands-tools/openhands/tools/task/manager.py
+++ b/openhands-tools/openhands/tools/task/manager.py
@@ -10,6 +10,7 @@
 if the task is resumed for further work later.
 """
 
+import json
 import shutil
 import tempfile
 import threading
@@ -19,7 +20,7 @@
 from pathlib import Path
 from typing import TYPE_CHECKING, Final
 
-from pydantic import BaseModel, ConfigDict, Field
+from pydantic import BaseModel, ConfigDict, Field, ValidationError
 
 from openhands.sdk import Agent
 from openhands.sdk.conversation.impl.local_conversation import LocalConversation
@@ -43,6 +44,7 @@
 logger = get_logger(__name__)
 
 _SUBAGENTS_DIR: Final[str] = "subagents"
+_INDEX_FILENAME: Final[str] = "task_index.json"
 
 
 class TaskStatus(StrEnum):
@@ -134,6 +136,57 @@ def _ensure_parent(self, conversation: LocalConversation) -> None:
                 self._persistence_dir = Path(
                     tempfile.mkdtemp(prefix="openhands_tasks_")
                 )
+            # Rehydrate prior tasks so resume works across a process restart.
+            self._load_index()
+
+    @property
+    def _index_path(self) -> Path | None:
+        """Path to the persisted task index, or None when the parent conversation
+        does not persist (the index would not survive a restart anyway). Derived
+        the same way as close(), so there is no separate state to keep in sync."""
+        parent = self._parent_conversation
+        if self._persistence_dir is None or parent is None:
+            return None
+        if parent.state.persistence_dir is None:
+            return None
+        return self._persistence_dir / _INDEX_FILENAME
+
+    def _save_index(self) -> None:
+        """Persist the task_id -> conversation_id index so resume survives a
+        process restart. No-op when the parent does not persist."""
+        index_path = self._index_path
+        if index_path is None:
+            return
+        with self._tasks_lock:
+            payload = [task.model_dump(mode="json") for task in self._tasks.values()]
+        tmp_path = index_path.parent / f"{index_path.name}.tmp"
+        try:
+            tmp_path.write_text(json.dumps(payload), encoding="utf-8")
+            tmp_path.replace(index_path)  # atomic on the same filesystem
+        except OSError as e:
+            logger.warning(f"Failed to persist task index: {e}")
+
+    def _load_index(self) -> None:
+        """Rehydrate the task index from disk. Conversations are reconstructed
+        lazily on resume; entries load with conversation=None. Tolerates a
+        missing or unreadable index."""
+        index_path = self._index_path
+        if index_path is None or not index_path.exists():
+            return
+        try:
+            payload = json.loads(index_path.read_text(encoding="utf-8"))
+        except (OSError, ValueError) as e:
+            logger.warning(f"Failed to read task index, ignoring: {e}")
+            return
+        with self._tasks_lock:
+            for entry in payload:
+                try:
+                    task = Task.model_validate(entry)
+                except ValidationError as e:
+                    logger.warning(f"Skipping invalid task index entry: {e}")
+                    continue
+                # Do not clobber a live in-memory task with a disk snapshot.
+                self._tasks.setdefault(task.id, task)
 
     @property
     def parent_conversation(self) -> LocalConversation:
@@ -157,6 +210,8 @@ def _evict_task(self, task: Task) -> None:
             task.conversation.close()
         with self._tasks_lock:
             self._tasks[task.id] = task.model_copy(update={"conversation": None})
+        # Persist the final status (completed/error) for cross-process visibility.
+        self._save_index()
 
     def start_task(
         self,
@@ -229,8 +284,10 @@ def _resume_task(self, resume: str, subagent_type: str) -> Task:
                     "status": TaskStatus.RUNNING,
                 }
             )
+            task = self._tasks[resume]
 
-            return self._tasks[resume]
+        self._save_index()
+        return task
 
     def _create_task(
         self,
@@ -269,13 +326,16 @@ def _create_task(
                 factory.definition.get_confirmation_policy(),
             )
 
-            self._tasks[task_id] = Task(
+            task = Task(
                 id=task_id,
                 conversation_id=conversation_id,
                 conversation=sub_conversation,
                 status=TaskStatus.RUNNING,
             )
-            return self._tasks[task_id]
+            self._tasks[task_id] = task
+
+        self._save_index()
+        return task
 
     def _get_conversation(
         self,
diff --git a/tests/tools/task/test_task_manager.py b/tests/tools/task/test_task_manager.py
index 523d80c394..35c4cb851a 100644
--- a/tests/tools/task/test_task_manager.py
+++ b/tests/tools/task/test_task_manager.py
@@ -1,3 +1,4 @@
+import json
 import uuid
 from pathlib import Path
 from unittest.mock import MagicMock, patch
@@ -15,6 +16,7 @@
 from openhands.sdk.subagent.schema import AgentDefinition
 from openhands.tools.preset import register_builtins_agents
 from openhands.tools.task.manager import (
+    _INDEX_FILENAME,
     Task,
     TaskManager,
     TaskStatus,
@@ -942,3 +944,102 @@ def test_with_persistence_subagent_conv_stored_under_subagents(self, tmp_path):
         conv_persistence = conv.state.persistence_dir
         assert conv_persistence is not None
         assert str(conv_persistence).startswith(str(manager._persistence_dir))
+
+
+class TestTaskIndexPersistence:
+    """Cross-process resume: the task_id->conversation_id index is persisted under
+    the parent conversation's dir and rehydrated by a fresh TaskManager."""
+
+    def _parent(self, persist, work, conversation_id):
+        agent = Agent(llm=_make_llm(), tools=[])
+        return LocalConversation(
+            agent=agent,
+            workspace=str(work),
+            visualizer=None,
+            delete_on_close=False,
+            persistence_dir=str(persist),
+            conversation_id=conversation_id,
+        )
+
+    def test_index_written_when_parent_persists(self, tmp_path):
+        register_builtins_agents()
+        persist, work = tmp_path / "p", tmp_path / "w"
+        persist.mkdir()
+        work.mkdir()
+        m = TaskManager()
+        m._ensure_parent(self._parent(persist, work, uuid.uuid4()))
+        task = m._create_task(subagent_type="general-purpose", description=None)
+
+        index_path = m._index_path
+        assert index_path is not None and index_path.name == _INDEX_FILENAME
+        assert index_path.exists()
+        entries = json.loads(index_path.read_text())
+        assert any(e["id"] == task.id for e in entries)
+
+    def test_no_index_when_parent_not_persisting(self, tmp_path):
+        register_builtins_agents()
+        agent = Agent(llm=_make_llm(), tools=[])
+        parent = LocalConversation(
+            agent=agent, workspace=str(tmp_path), visualizer=None, delete_on_close=False
+        )
+        m = TaskManager()
+        m._ensure_parent(parent)
+        m._create_task(subagent_type="general-purpose", description=None)
+        assert m._index_path is None
+
+    def test_resume_across_fresh_manager(self, tmp_path):
+        """A new TaskManager (simulating a process restart) rehydrates the index
+        from the same parent dir and can resume a prior task."""
+        register_builtins_agents()
+        persist, work = tmp_path / "p", tmp_path / "w"
+        persist.mkdir()
+        work.mkdir()
+        pcid = uuid.uuid4()  # parent conversation id is stable across restart
+
+        m1 = TaskManager()
+        m1._ensure_parent(self._parent(persist, work, pcid))
+        task = m1._create_task(subagent_type="general-purpose", description=None)
+        tid, cid = task.id, task.conversation_id
+        m1._evict_task(task)
+
+        m2 = TaskManager()
+        m2._ensure_parent(self._parent(persist, work, pcid))
+        assert tid in m2._tasks  # rehydrated from disk
+        resumed = m2._resume_task(resume=tid, subagent_type="general-purpose")
+        assert resumed.id == tid
+        assert resumed.conversation_id == cid
+        assert resumed.conversation is not None
+        assert resumed.conversation.state.id == cid
+
+    def test_evicted_status_persisted(self, tmp_path):
+        register_builtins_agents()
+        persist, work = tmp_path / "p", tmp_path / "w"
+        persist.mkdir()
+        work.mkdir()
+        m = TaskManager()
+        m._ensure_parent(self._parent(persist, work, uuid.uuid4()))
+        task = m._create_task(subagent_type="general-purpose", description=None)
+        task.set_result("done")
+        m._evict_task(task)
+        index_path = m._index_path
+        assert index_path is not None
+        entries = json.loads(index_path.read_text())
+        entry = next(e for e in entries if e["id"] == task.id)
+        assert entry["status"] == TaskStatus.COMPLETED.value
+
+    def test_load_index_tolerates_corrupt_file(self, tmp_path):
+        register_builtins_agents()
+        persist, work = tmp_path / "p", tmp_path / "w"
+        persist.mkdir()
+        work.mkdir()
+        pcid = uuid.uuid4()
+        m1 = TaskManager()
+        m1._ensure_parent(self._parent(persist, work, pcid))
+        m1._create_task(subagent_type="general-purpose", description=None)
+        # Corrupt the index, then load from a fresh manager — must not raise.
+        index_path = m1._index_path
+        assert index_path is not None
+        index_path.write_text("{not valid json")
+        m2 = TaskManager()
+        m2._ensure_parent(self._parent(persist, work, pcid))  # _load_index runs here
+        assert m2._tasks == {}