fix(net): preserve cached history for late relay subscribers

[kixelated]

Problem

A second subscriber requesting group 0 could lose a relay's cached finished group when the newer live group's stream arrived first. TRACK_INFO churn parked the copy with no declared start, so SUBSCRIBE_START used arrival order and permanently raised the reader's floor past the older group.

Approach

Declare the earliest visible group retained by a warm copy as its start. Add a deterministic relay regression that reverses upstream stream arrival and keeps the first subscriber alive while the second joins. It reads known frame counts rather than waiting for the open live group's FIN, avoiding paused-time linger artifacts. Remove the completed quest and references.

Impact

• No public API or wire-format changes. Existing SUBSCRIBE_START now preserves the cached history floor.

Alternatives

Changing splice cursors or ordering all cached deliveries is unnecessary: the lost start metadata belongs to the warm copy itself.

Validation

• New regression fails before the fix and passes afterward.
• nix develop --command just check: passed, including 4,616 tests (8 skipped), lint, docs, feature builds, and Markdown/shell checks.
• nix develop --command quest check: 462 documents valid.

Follow-ups

No new decisions. The existing splice-edges and resume-latest quests remain separate.

(Written by GPT-6)

[kixelated]

Implemented and locally verified. The late-joiner regression fails before the fix and passes afterward; just check passes with 4,616 tests, and quest check passes. No public API or wire-format changes and no unresolved decisions.

Left as a draft for the batch coordinator. Recommend /quest-merge after review and CI; the existing splice-edges and resume-latest quests can proceed separately.

(Written by GPT-6)

[coderabbitai]

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📥 Commits

Reviewing files that changed from the base of the PR and between 7eebe7c and fe8ecc7.

📒 Files selected for processing (5)

• quest/m1/README.md
• quest/m1/relay-late-joiner-history.md
• quest/m1/track-tail-interop.md
• rs/moq-net/src/model/origin.rs
• rs/moq-net/tests/history_groups.rs

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[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-29T13:23:46.867704Z	fe8ecc7	Draft marked ready

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