DT-3526 describe standalone activity

[rossedfort]

Description & motivation 💭

Implement describe standalone activity page

• On initial load of the page, the UI calls the DescribeActivityExecution API with includeInput: true and includeOutcome: true
• After initial load of the page, if the Activity is Running, the UI will poll the DescribeActivityExecution API with includeInput: false, includeOutcome: true, the runId and longPollToken
• Actions (Pause, Update, and Reset) are intended not to be functional - will do next PR
• The page should look largely similar to the EventCard used on the Pending Activities tab of a workflow execution.

Screenshots (if applicable) 📸

Design Considerations 🎨

Testing 🧪

How was this tested 👻

• Manual testing
• E2E tests added
• Unit tests added

Steps for others to test: 🚶🏽‍♂️🚶🏽‍♀️

Run temporal server from a local build

1. Ensure you have cloned the temporalio/temporal repo
2. Run make bins and make start
3. Running temporal server from a local build does not create the default namespace, run temporal operator namespace create --namespace default
4. Create some search attributes for the default namespace, run temporal operator search-attribute create --namespace default --name MySearchAttribute --type Keyword

Run the UI against a local build of temporal server

1. Checkout the DT-3526-describe-standalone-activity branch in the ui repo
2. cd server/ && make build
3. cd .. && pnpm dev:local-temporal

Run some sample workflows in the samples-go repo

1. cd temporal-fixtures/stuck-workflows/
2. In one terminal window, run go run worker/main.go
3. In another terminal window, run go run starter/main.go

Start a Standalone Activity

1. In the UI, go to http://localhost:3000/namespaces/default/activities/start
2. Generate a random Activity ID or use your own
3. Fill the Task Queue input with stuck-workflows
4. Fill the Activity Type input with StuckWorkflowActivity
5. Fill the Start to Close Timeout field with some long duration, 1 hour for example
6. Click the "Start Standalone Activity" button
7. Go to http://localhost:3000/namespaces/default/activities/<activity_id>/details

To test Activities with Payloads + Codec Server

In the samples-go repo:

1. cd codec-server
2. In one terminal window, run go run ./codec-server -web=http://localhost:3000 -port=8088
3. In a second terminal window, run go run worker/main.go
4. In a third terminal window, run go run starter/main.go

In the UI

1. Set the Data Encoder URL to http://localhost:8088
2. Go to http://localhost:3000/namespaces/default/activities/start
3. Generate a random Activity ID or use your own
4. Fill the Task Queue input with codecserver
5. Fill the Activity Type input with Activity
6. Supply an Input
7. Supply either a Start to Close Timeout or Schedule to Close Timeout
8. Expand the "More Options" section, and supply Search Attribute(s), Summary, and Details
9. Click the "Start Standalone Activity" button
10. Go to http://localhost:3000/namespaces/default/activities/<activity_id>/details and ensure payloads are being decoded.

Checklists

Draft Checklist

Merge Checklist

Issue(s) closed

Docs

Any docs updates needed?

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Project	Deployment	Review	Updated (UTC)
holocene	Ready	Preview, Comment	Jan 16, 2026 9:31pm