diff --git a/agentex/openapi.yaml b/agentex/openapi.yaml
index 100fb9b8..caa12c7f 100644
--- a/agentex/openapi.yaml
+++ b/agentex/openapi.yaml
@@ -6660,6 +6660,13 @@ components:
             type: object
           - type: 'null'
           title: If provided, replaces task_metadata with this value
+        merge_params:
+          anyOf:
+          - additionalProperties: true
+            type: object
+          - type: 'null'
+          title: Optional shallow-merge patch applied to the task's params column.
+            Top-level keys overwrite; pass full nested objects to change subfields.
       type: object
       title: UpdateTaskRequest
     ValidationError:
diff --git a/agentex/src/api/routes/tasks.py b/agentex/src/api/routes/tasks.py
index a2d30227..a8ae9642 100644
--- a/agentex/src/api/routes/tasks.py
+++ b/agentex/src/api/routes/tasks.py
@@ -193,7 +193,9 @@ async def update_task(
     task_use_case: DTaskUseCase,
 ) -> Task:
     updated_task_entity = await task_use_case.update_mutable_fields_on_task(
-        id=task_id, task_metadata=request.task_metadata
+        id=task_id,
+        task_metadata=request.task_metadata,
+        merge_params=request.merge_params,
     )
     return Task.model_validate(updated_task_entity)
 
diff --git a/agentex/src/api/schemas/tasks.py b/agentex/src/api/schemas/tasks.py
index 9a8a53dd..74c8d83d 100644
--- a/agentex/src/api/schemas/tasks.py
+++ b/agentex/src/api/schemas/tasks.py
@@ -77,6 +77,14 @@ class UpdateTaskRequest(BaseModel):
         None,
         title="If provided, replaces task_metadata with this value",
     )
+    merge_params: dict[str, Any] | None = Field(
+        None,
+        title=(
+            "Optional shallow-merge patch applied to the task's params column. "
+            "Top-level keys overwrite; pass full nested objects to change "
+            "subfields."
+        ),
+    )
 
 
 class TaskStatusReasonRequest(BaseModel):
diff --git a/agentex/src/domain/repositories/task_repository.py b/agentex/src/domain/repositories/task_repository.py
index 231c0e9c..45662015 100644
--- a/agentex/src/domain/repositories/task_repository.py
+++ b/agentex/src/domain/repositories/task_repository.py
@@ -3,7 +3,8 @@
 from typing import Annotated, Literal
 
 from fastapi import Depends
-from sqlalchemy import distinct, func, select, update
+from sqlalchemy import cast, distinct, func, select, update
+from sqlalchemy.dialects.postgresql import JSONB
 from sqlalchemy.orm import selectinload
 from src.adapters.crud_store.adapter_postgres import (
     ColumnPrimitiveValue,
@@ -213,6 +214,46 @@ async def update(self, task: TaskEntity) -> TaskEntity:
             # Return with agents populated
             return TaskEntity.model_validate(modified_orm)
 
+    async def merge_params(self, task_id: str, patch: dict) -> TaskEntity | None:
+        """Atomically shallow-merge ``patch`` into the task's ``params``
+        JSONB column. Returns the updated entity, or ``None`` if no task
+        with that id exists.
+
+        Uses Postgres' ``||`` operator on JSONB so the read-modify-write
+        is collapsed to a single statement (no race with concurrent
+        writers). ``patch`` keys overwrite existing keys at the top
+        level; nested objects are NOT deep-merged — pass the full nested
+        replacement if you need to change a subfield.
+
+        Intended for surfaces that need ``tasks.params`` to reflect the
+        latest agent config after a live edit (see
+        ``TasksUseCase.update_mutable_fields_on_task``); not a
+        general-purpose updater.
+        """
+
+        async with (
+            self.start_async_db_session(True) as session,
+            async_sql_exception_handler(),
+        ):
+            # ``COALESCE(params, '{}'::jsonb)`` so a NULL existing value
+            # doesn't poison the concat to NULL. Both operands cast to
+            # JSONB explicitly so Postgres picks the JSONB ``||`` operator
+            # (not the text concat overload).
+            existing = func.coalesce(TaskORM.params, cast({}, JSONB))
+            merged = existing.op("||", return_type=JSONB)(cast(patch, JSONB))
+            stmt = (
+                update(TaskORM)
+                .where(TaskORM.id == task_id)
+                .values(params=merged)
+                .returning(TaskORM)
+            )
+            result = await session.execute(stmt)
+            row = result.scalar_one_or_none()
+            await session.commit()
+            if row is None:
+                return None
+            return TaskEntity.model_validate(row)
+
     async def transition_status(
         self,
         task_id: str,
diff --git a/agentex/src/domain/services/task_service.py b/agentex/src/domain/services/task_service.py
index 809dd954..299494b8 100644
--- a/agentex/src/domain/services/task_service.py
+++ b/agentex/src/domain/services/task_service.py
@@ -242,6 +242,15 @@ async def update_task(self, task: TaskEntity) -> TaskEntity:
 
         return updated_task
 
+    async def merge_task_params(self, task_id: str, patch: dict) -> TaskEntity | None:
+        """Atomically shallow-merge ``patch`` into ``tasks.params``. Returns
+        the updated entity, or ``None`` if no task with ``task_id`` exists.
+
+        Lets callers update agent config on the task row in place; the agent
+        picks up the new values when it next reads ``task.params``.
+        """
+        return await self.task_repository.merge_params(task_id, patch)
+
     async def delete_task(self, id: str | None = None, name: str | None = None) -> None:
         """
         Delete a task from the repository.
diff --git a/agentex/src/domain/use_cases/tasks_use_case.py b/agentex/src/domain/use_cases/tasks_use_case.py
index 4ad1a61a..dffc6ec3 100644
--- a/agentex/src/domain/use_cases/tasks_use_case.py
+++ b/agentex/src/domain/use_cases/tasks_use_case.py
@@ -94,6 +94,7 @@ async def update_mutable_fields_on_task(
         id: str | None = None,
         name: str | None = None,
         task_metadata: dict[str, Any] | None = None,
+        merge_params: dict[str, Any] | None = None,
     ) -> TaskEntity:
         """Update mutable fields on a task entity. This is used by our API since not all fields should be mutable."""
 
@@ -108,15 +109,28 @@ async def update_mutable_fields_on_task(
             else:
                 raise ItemDoesNotExist(f"Task {name} not found")
 
-        # if no mutations are provided, don't do anything
-        if task_metadata is None:
+        # No-op if neither field was supplied.
+        if task_metadata is None and merge_params is None:
             return task_entity
 
         if task_metadata is not None:
             task_entity.task_metadata = task_metadata
 
-        updated_task_entity = await self.task_service.update_task(task=task_entity)
-        return updated_task_entity
+        # `merge_params` is a separate atomic JSONB shallow-merge so concurrent
+        # callers don't overwrite each other's fields (vs reading→mutating→writing
+        # the whole params dict on task_entity). Falls through to a normal save
+        # only when task_metadata also changed.
+        if merge_params:
+            merged = await self.task_service.merge_task_params(
+                task_entity.id, merge_params
+            )
+            if merged is not None:
+                task_entity = merged
+
+        if task_metadata is not None:
+            task_entity = await self.task_service.update_task(task=task_entity)
+
+        return task_entity
 
     async def _transition_to_terminal(
         self,