V2: event audit tracker #35021

Summary

Mega tracker for the V2 event/schema audit from the Discord gang-grill session.

Source discussion: https://discord.com/channels/1391832426048651334/1522263729318658181
V2 TODO post: https://discord.com/channels/1391832426048651334/1520962938733723720/1522327808465043566

The goal is to make the V2 event contract beta-ready: domain-shaped, replayable, deterministic, and pleasant for SDK/UI consumers.

Child issues

• V2: clean up session event schema names and payloads before beta #35014
  V2 session event schema names/payloads
• V2: make session log replay/tail deterministic and replication-safe #35015
  Session log replay/tail
• V2: redesign execution, retry, and error events #35016
  Execution/retry/error events
• V2: add structured guidance/context update summaries #35017
  Guidance/context update summaries
• V2: align session shell events with Shell service #35018
  Shell events + Shell service
• V2: simplify assistant content fragment IDs and provider state #35019
  Assistant fragments + provider state
• V2: follow-up cleanup from event schema gang grill #35020
  Misc cleanup: tool settlement ordering, compaction template, synthetic shape

Big decisions to preserve

• Drop session.next.*; next was migration scaffolding.
• Put event creation time on the event envelope as created instead of payload timestamp.
• Remove projection-only messageID fields where projected IDs can be derived from event IDs.
• Keep domain IDs only where they are real correlation facts, e.g. callID, shell IDs, fork from.
• Replace session.status with explicit execution lifecycle events.
• Retry should reduce into current assistant retry state, not become message spam.
• Event errors need a closed structured union with dot-cased type discriminators.
• Rename provider continuation payloads from providerMetadata to state.
• Keep metadata only for actual app/plugin extension metadata, e.g. synthetic messages.
• Session shell should reuse Shell.Info and Shell.Output.
• Durable log replay should use a fixed replay watermark, paged reads, and log.synced.

Acceptance themes

• Reconnect/replay consumers can reconstruct durable state without timing races.
• UI can render terminal states, retries, blocked provider content, guidance changes, and shell output without parsing hidden model text.
• Provider finish: "content-filter" never looks like an empty successful assistant response.
• Generated schema/client/plugin APIs reflect the cleaned event contract.

Notes

This tracker is intentionally broad. Use the child issues for implementation-sized work and close this when the event audit is complete or intentionally split into a later cleanup milestone.