feat(runtime): support Image and Command in PodSet Container

[Raakshass]

What this PR does

Fixes #3177

Populates Image and Command fields in toPodSetContainer from ContainerApplyConfiguration, and adds an InitContainers sync loop in the JobSet Build() method to propagate Image, Command, Env, Ports, and VolumeMounts from PodSet.InitContainers back to the JobSet spec.

Root Cause

Two gaps prevented PodSet from being used for InitContainer customization:

1. toPodSetContainer in runtime.go — Created Container structs but skipped Image and Command, only copying Name, Env, Ports, VolumeMounts. The Container struct already had Image and Command fields, but they were never populated from ContainerApplyConfiguration.

2. Build() in jobset.go — Synced Image, Command, Env, Ports, and VolumeMounts from PodSet.Containers back to the JobSet spec, but had no equivalent sync loop for PodSet.InitContainers.

Changes

File	Change
pkg/runtime/runtime.go	Populate Image and Command in toPodSetContainer from ContainerApplyConfiguration
pkg/runtime/framework/plugins/jobset/jobset.go	Add InitContainers sync loop in Build() mirroring the existing Containers sync
pkg/runtime/runtime_test.go	Update TestNewInfo to set Image/Command on an InitContainer input and assert roundtrip

Context

This unblocks the Flux Framework integration (#3064) from using PodSet for InitContainer customization, as discussed in:

• #3064 (comment)
• #3064 (review discussion)

Testing

• All ./pkg/runtime/... unit tests pass (runtime, framework/core, framework/plugins/jobset, indexer)
• TestNewInfo updated to verify InitContainer Image/Command propagation

Contributor Checklist

• DCO sign-off included (Signed-off-by: Siddhant Jain <siddhantjainofficial26@gmail.com>)
• Unit tests updated and passing
• No unrelated files in diff
• PR title follows Conventional Commits specification
• Changes match master's existing patterns (InitContainers sync mirrors Containers sync)

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[Copilot]

Pull request overview

This PR extends the runtime PodSet container extraction and JobSet template mutation logic so init container image and command are preserved and propagated into the JobSet apply spec.

Changes:

• Populate runtime.Container.Image and runtime.Container.Command when building PodSet containers from PodSpec apply configs.
• Propagate init container image/command (plus env/ports/volumeMounts upserts) from PodSet back into the JobSet apply configuration during JobSet.Build.
• Update runtime unit test expectations to include init container image and command.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
pkg/runtime/runtime.go	Adds Image and Command mapping when converting container apply configs into runtime.Container.
pkg/runtime/runtime_test.go	Updates TestNewInfo expectations to assert init container Image/Command are captured.
pkg/runtime/framework/plugins/jobset/jobset.go	Extends JobSet build-time template sync to include init container command/image and related fields.

[Copilot]

Setting Image via &container.Image takes the address of the range loop variable field, so multiple init containers can end up sharing the same pointer value (often the last iteration’s image); use a per-iteration copy (e.g., img := container.Image) or ptr.To(container.Image) when assigning the *string image field (and consider fixing the same pattern in the main containers loop above).