When using locked sigs in auto.conf with a line like:
    require ../locked-sigs.inc

an attempt to build the eSDK (invoked with bitbake -k core-image-sato:do_populate_sdk_ext) fails with the following:

ERROR: core-image-sato-1.0-r0 do_populate_sdk_ext: Failed to generate filtered task list for extensible SDK:

### Shell environment set up for builds. ###

You can now run 'bitbake <target>'

Common targets are:
    core-image-minimal
    core-image-sato
    meta-toolchain
    meta-ide-support

You can also run generated qemu images with a command like 'runqemu qemux86'
ERROR: bitbake failed:
ERROR: ParseError at /srv/autobuilder/yocto-autobuilder/yocto-worker/nightly-qa-extras/build/build/newtmp/work/qemux86_64-poky-linux/core-image-sato/1.0-r0/sdk-ext/image/tmp-renamed-sdk/conf/local.conf:23: Could not include required file ../locked-sigs.inc
ERROR: core-image-sato-1.0-r0 do_populate_sdk_ext: Function failed: copy_buildsystem
ERROR: Logfile of failure stored in: /srv/autobuilder/yocto-autobuilder/yocto-worker/nightly-qa-extras/build/build/newtmp/work/qemux86_64-poky-linux/core-image-sato/1.0-r0/temp/log.do_populate_sdk_ext.49644
NOTE: recipe core-image-sato-1.0-r0: task do_populate_sdk_ext: Failed
ERROR: Task (/srv/autobuilder/yocto-autobuilder/yocto-worker/nightly-qa-extras/build/meta/recipes-sato/images/core-image-sato.bb:do_populate_sdk_ext) failed with exit code '1'
NOTE: Tasks Summary: Attempted 7344 tasks of which 6862 didn't need to be rerun and 1 failed.

This may be because the locked-sigs.inc isn't available at the relative path when bitbake is invoked within the simulated eSDK environment during eSDK generation?

If that's the case one possible solution may be to ensure that any required file is available and that the path is correct within the eSDK generation code?