From f1e8d7147db37d35a1a6dbd14a266d56d32d6c12 Mon Sep 17 00:00:00 2001
From: Frank Midigo <midigofrank@gmail.com>
Date: Fri, 30 Oct 2026 11:05:57 +0300
Subject: [PATCH] Keep target collection ids when deploying to a different
 project

Sandbox merges took the local collections as-is, so every cross-project
deploy sent freshly minted ids for collections the target already had,
and Lightning rejected the update with a 500. Match them to the target's
collections by name, as same-project deploys already do.

Fixes #1606
---
 .changeset/keep-collection-ids.md              |  6 ++++++
 packages/project/src/merge/merge-project.ts    |  2 +-
 .../project/test/merge/merge-project.test.ts   | 18 +++++++++++++-----
 3 files changed, 20 insertions(+), 6 deletions(-)
 create mode 100644 .changeset/keep-collection-ids.md

diff --git a/.changeset/keep-collection-ids.md b/.changeset/keep-collection-ids.md
new file mode 100644
index 000000000..4990cbe62
--- /dev/null
+++ b/.changeset/keep-collection-ids.md
@@ -0,0 +1,6 @@
+---
+'@openfn/project': patch
+'@openfn/cli': patch
+---
+
+Fix deploying to a different project failing once that project has collections
diff --git a/packages/project/src/merge/merge-project.ts b/packages/project/src/merge/merge-project.ts
index 566049bf4..8e1642990 100644
--- a/packages/project/src/merge/merge-project.ts
+++ b/packages/project/src/merge/merge-project.ts
@@ -170,7 +170,7 @@ export function merge(
             source.credentials,
             target.credentials
           ),
-          collections: source.collections,
+          collections: mergeCollections(source.collections, target.collections),
           channels: mergeChannels(source.channels, target.channels),
         }
       : {
diff --git a/packages/project/test/merge/merge-project.test.ts b/packages/project/test/merge/merge-project.test.ts
index 8671afeb1..766494f6a 100644
--- a/packages/project/test/merge/merge-project.test.ts
+++ b/packages/project/test/merge/merge-project.test.ts
@@ -384,7 +384,7 @@ test('replace mode: undefined local collections leave the target collections alo
   t.deepEqual(result.collections, targetCollections);
 });
 
-test('sandbox mode: source collections fully replace target collections', (t) => {
+test('sandbox mode: source collections replace target collections, keeping target uuid on a name match', (t) => {
   const wf = {
     steps: [
       { id: 'x', name: 'X', adaptor: 'common', expression: 'fn(s => s)' },
@@ -395,17 +395,25 @@ test('sandbox mode: source collections fully replace target collections', (t) =>
 
   const targetCollections = [
     { uuid: 'remote-uuid-1', name: 'target-collection' },
+    { uuid: 'remote-uuid-2', name: 'shared-collection' },
+  ];
+  // the source's own uuids belong to a different project
+  const sourceCollections = [
+    { name: 'source-collection' },
+    { uuid: 'source-uuid', name: 'shared-collection' },
   ];
-  const sourceCollections = [{ name: 'source-collection' }];
 
   const target = createProject(wf_a, 'a', { collections: targetCollections });
   const source = createProject(wf_b, 'b', { collections: sourceCollections });
 
   const result = merge(source, target, { mode: SANDBOX_MERGE });
 
-  // b's collections are wholly replaced by a's - sandbox mode does a raw
-  // swap here, unlike replace mode's name-matching mergeCollections
-  t.deepEqual(result.collections, sourceCollections);
+  // a shared collection must keep the target's uuid, or the deploy tries to
+  // create a duplicate and Lightning rejects it
+  t.deepEqual(result.collections, [
+    { name: 'source-collection', uuid: undefined },
+    { name: 'shared-collection', uuid: 'remote-uuid-2' },
+  ]);
 });
 
 test('sandbox mode: target channels are preserved when source has none', (t) => {