Support workflow variable binding for the Send Email action's Attachments field

[josephj]

Scope & Context

We use the Send Email workflow action for stage-change emails and need to attach a document that lives on the triggering record (e.g. a contract file stored on an Opportunity), so each email carries that record's own file. This ticket covers the Send Email node's Attachments field only.

Current behavior

In the Send Email workflow action, the Attachments field (WorkflowSendEmailAttachments) only allows static file uploads. It has no VariablePicker, unlike the To / Subject / Body fields in the same node, which already accept workflow variables. So the same fixed file is attached on every run; you cannot attach a file that lives on the triggering record.

[screenshot of the Attachments field with no variable option]

Expected behavior

The Attachments field should accept a workflow variable (e.g. a record Files field), alongside static uploads, so the per-record file(s) are attached at runtime.

Note: the backend already supports this end to end, only the UI can't express it:

• ToolBackedWorkflowAction.execute() runs resolveInput(input, context) over the whole input, including files.
• The tool input schema accepts files (EmailToolInputZodSchema).
• Setting files to a variable via the API / workflow:push already works; only the node editor can't bind one.

Technical inputs

• Add VariablePicker support to the attachments input in WorkflowEditActionEmailBase.tsx (the WorkflowSendEmailAttachments usage), and extend WorkflowSendEmailAttachments.tsx to allow a variable as an alternative to a static upload.
• The resolved value must conform to workflowFileSchema ({ id, name, size, type, createdAt }) so existing backend validation passes.
• Verify: bind Attachments to a record Files field variable -> email sends with that record's file(s); empty field -> email sends with no attachment and no error; static upload still works.