Currently, running agents with viv requires a --branch parameter. For example:

viv run ai_rd_triton_cumsum/main@531602ae79cec6f24bcc9936e9989eb94038cb09
 --yes --low_priority --name='example-runset'  --repo 'modular-public' --branch 'main' --commit '58ad4fb08809da0c70858e84d81668c8c5eb9fac' --agent_settings_pack 't_context_and_usage_awarep_claude_legacy_1xc3ogd_always_savea'

Returns the error 'agentCommitId is set but agentBranch is not'.

Our current YAML file plan for specs does not require branch, but since it's required in viv, our options are:

1. Require users to specify branch on their agent implementations in the YAML file that specifies a measurement.
2. Remove the requirement that agentBranch must be set if agentCommitId is set. The relevant code is here

In practice, the agent is uniquely identified by the commit. So it feels pretty reasonable me to relax this requirement. Lucas in his comment here is fine with either solution, but would prefer dropping branch as a requirement.

Making the change in input validation is pretty easy (it's just deleting code), but I'm wondering if the invariant that "branch exists if commit id exists" is relied on in other parts of the codebase, for some reason. Guidance here would be helpful, or happy to dig in more and investigate this question if it's helpful.