proto: bump transcript ID max_len from 128 to 256#2427
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The 128-char cap on conversation_id, turn_id, tool_call_id, model, and user_id has no upstream basis. OTel doesn't constrain gen_ai.conversation.id; chat platforms (Microsoft Teams personal-DM threads, Slack thread IDs, Discord channel IDs) routinely produce IDs that exceed 128 characters. When buf-validate rejects the TranscriptSummary response, the per-agent Transcripts tab is empty even though the spans are visible in the global tracing view. Bump to 256 across the board for consistency with the existing title and TranscriptToolCall.name fields.
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weeco
approved these changes
Apr 28, 2026
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What
Raise the buf-validate
max_lenfrom 128 to 256 on all opaque ID fields intranscript.proto:TranscriptToolCall.tool_call_id,TranscriptTurn.turn_id,TranscriptTurn.model,TranscriptSummary.conversation_id,TranscriptSummary.user_id, andGetTranscriptRequest.conversation_id.Why
128 has no upstream basis. The OTel GenAI semantic conventions don't constrain
gen_ai.conversation.id, and real-world chat platforms produce IDs that exceed it:a:1NXel3V8F74Kb...) run ~150 charactersWhen a conversation slips over 128 chars, server-side response validation rejects the
TranscriptSummary. The per-agent Transcripts tab in console comes back empty whilethe same spans remain visible in the global tracing view (which doesn't run validation).
The mismatch is hard to debug from the UI side.
256 matches the existing limits on
TranscriptSummary.titleandTranscriptToolCall.name,so the contract stays internally consistent.
Implementation details
Six call sites in
proto/redpanda/api/dataplane/v1alpha3/transcript.proto. RegeneratedGo and TypeScript bindings via
task proto:generate. The descriptor varint changesfrom
0x80 0x01(128) to0x80 0x02(256) in the embedded raw descriptor.No code change required — buf-validate runtime reads the cap from the descriptor.
References
None.