Add field selection and NDJSON streaming for list commands

[vdemeester]

Summary

AI agents pay per token and lose reasoning capacity with irrelevant output. List commands should support field selection and streaming to minimize context window usage.

Proposal

Field Selection

# Only return specific fields
tkn pipelinerun list --fields name,status,startTime --output json

NDJSON Streaming

# One JSON object per line, streamable
tkn pipelinerun list --output ndjson

This allows agents to process results incrementally without buffering large arrays, and to request only the fields they need.

Acceptance Criteria

• --fields flag on list commands to select output fields
• --output ndjson for newline-delimited JSON (one object per line)
• Works with all resource list commands

/kind feature

[vdemeester]

Closing for now — Kubernetes API doesn't support server-side field selection, so this would be client-side filtering only. --limit already exists for list size. NDJSON can be revisited if there's demand.

[vdemeester]

Reopening — while this is client-side filtering only (K8s API doesn't support server-side field projection), it still directly reduces token consumption in agent context windows, which is the primary goal. Cheap to implement, meaningful impact for agents.

NDJSON streaming can be scoped separately if needed.