Summary

Sets status: 'PENDING' in the deploys reducer on both DEPLOY_PREVIEW_REQUEST and DEPLOY_PREVIEW_FAILURE, preventing stale production URLs from appearing and ensuring the "Check for Preview" button remains visible during polling. Adds unit tests for the deploys reducer (none existed before).

Problem

When a user opens an existing published entry, getDeploy stores { status: "SUCCESS", url: "https://production-url/..." } in Redux. If the user then saves (creating an editorial workflow branch), getDeployPreview polls for commit statuses. Two issues:

1. Stale production URL: If no commit status exists yet, the old SUCCESS state and production URL persisted, causing "View Preview" to link to the production URL instead of the deploy preview.
2. Disappearing controls: Clearing status to undefined caused the deploy preview controls to disappear entirely — renderDeployPreviewControls has a guard clause if (!status) return — leaving editors with no way to manually check for a preview.

Fix

     case DEPLOY_PREVIEW_REQUEST: {
       const { collection, slug } = action.payload;
       const key = `${collection}.${slug}`;
-      state[key] = state[key] || {};
-      state[key].isFetching = true;
+      state[key] = { isFetching: true, status: 'PENDING' };
       break;
     }
     ...
     case DEPLOY_PREVIEW_FAILURE: {
       const { collection, slug } = action.payload;
-      state[`${collection}.${slug}`].isFetching = false;
+      const key = `${collection}.${slug}`;
+      state[key].isFetching = false;
+      state[key].url = undefined;
+      state[key].status = 'PENDING';
       break;
     }

• DEPLOY_PREVIEW_REQUEST: Resets the entry to { isFetching: true, status: 'PENDING' }, clearing stale url/status while keeping the "Check for Preview" button visible.
• DEPLOY_PREVIEW_FAILURE: Clears url and sets status: 'PENDING' so the button stays visible and clickable for manual retries.

Tests

Added packages/decap-cms-core/src/reducers/__tests__/deploys.spec.ts. Covers:

• All three action types (REQUEST, SUCCESS, FAILURE)
• REQUEST clears stale url and sets status to PENDING
• FAILURE clears url and sets status to PENDING
• selectDeployPreview selector

Fixes #7755