[Bug]: DAR watch mode doesn't work with UI

[zheli]

Description

Got this error:

❯ dpm localnet dar watch \
  --instance localnet-2 \
  --publish-to http://127.0.0.1:7777
Watching /Users/x/code/canton-localnet-playground/daml-test-2 every 1s — Ctrl-C to stop
watch publish: UI returned 403
watch publish: UI returned 403
Running single package build of daml-test-v2 as no multi-package.yaml was found.

2026-07-13 09:13:32.60 [INFO]  [build]
Compiling daml-test-v2 to a DAR.
File:     daml
Hidden:   no
Range:    1:1-2:1
Source:   Daml-LF typechecker
Severity: DsWarning
Message:
warning while type checking package:
  This package defines templates or interfaces, and depends on daml-script.
  Uploading this package to a ledger will also upload daml-script, which will bloat the package store on your participant.
  It is recommended that scripts/tests are defined in a separate package to your templates, and that
  you remove `335b4b3b7c2247593195954ca5a5f1795fd72e0b6c63af094ba860e86e4f198a (daml-script, 3.5.2)` from the dependencies in your daml.yaml
  Upgrade this warning to an error -Werror=template-interface-depends-on-daml-script
  Disable this warning entirely with -Wno-template-interface-depends-on-daml-script

2026-07-13 09:13:33.72 [INFO]  [build]
Created .daml/dist/daml-test-v2-0.0.1.dar
watch publish: UI returned 403
uploaded: 8f941650f3a26ad5d06f78bc98c67ed1ad0df4e021a1783e76a265485cc8a18a
watch publish: UI returned 403

Steps to reproduce

See my description

Expected behavior

See my description

Actual behavior

See my description

canton-devkit version

v0.15.4

Splice / LocalNet version

0.6.12

Surface

Both

OS / platform

macOS

Instance name

No response

Diagnostic output

Logs / command output