[wanda] Add context_owner spec option and include in cache digest

[andrew-anyscale]

Add context_owner field to the wanda Spec, allowing .wanda.yaml files to specify a "uid:gid" override for all files in the build context tar. Wire it through resolveBuildInput to set the tarStream owner, and include it in buildInputCore so changing context_owner invalidates the cache.

Topic: add-context-owner-spec
Relative: add-context-owner-tar

Co-Authored-By: Claude Opus 4.6 (1M context) noreply@anthropic.com
Signed-off-by: andrew andrew@anyscale.com

[andrew-anyscale]

Reviews in this chain:
└#481 [wanda] Add context_owner spec option and include in cache digest

[andrew-anyscale]

#	head	base	diff	date	summary
0	c04891d6	fac3b483	diff	Apr 2 13:44 PM	3 files changed, 16 insertions(+)
1	c438d68c	91254ad6	diff	Apr 2 13:55 PM	2 files changed, 5 insertions(+), 1 deletion(-)
2	917c48ad	08d056c8	diff	Apr 2 19:35 PM	0 files changed
3	0f7f787b	94f6a2f2	diff	Apr 6 8:12 AM	0 files changed

[gemini-code-assist]

Code Review

This pull request introduces a new ContextOwner field to the build specification, allowing users to override the UID and GID for files within the build context tar. The implementation correctly updates the spec structure, the build input core, and the forge logic to parse and apply these ownership settings. I have included a suggestion to ensure the ContextOwner field is processed through expandVar during specification expansion, which enables support for environment variable substitution and ensures proper cache invalidation.

[gemini-code-assist]

The ContextOwner field should be expanded using expandVar to allow the use of environment variables (e.g., context_owner: $UID:$GID) in the specification. Currently, it is copied as a literal string, which prevents variable substitution and will cause parseContextOwner to fail if variables are used. Additionally, it ensures the cache is correctly invalidated when these environment variables change.

Suggested change

	result.ContextOwner = s.ContextOwner
	result.ContextOwner = expandVar(s.ContextOwner, lookup)

[aslonnie]

beautiful!