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Owen Lin 812cd2bb57 ensure thread.history_mode is immutable (#30261)
## Description

This PR makes `thread.history_mode` immutable after the thread's
canonical first `SessionMeta` has been written. Later same-thread
`SessionMeta` lines are compatibility metadata writes, not a new thread
definition.

Without this, an older binary could append a `SessionMeta` that omits
`history_mode`; when a newer binary replays it, serde defaults that
missing field to `legacy` and SQLite could downgrade a paginated thread.

## Why

`history_mode` is the persisted thread storage contract.
Paginated-thread fail-closed behavior and SQLite memory filtering depend
on it staying aligned with canonical rollout metadata, especially when
multiple Codex binary versions can touch the same local rollout.

## What changed

- Stop generic rollout metadata replay from overwriting `history_mode`
from later `SessionMeta` items.
- Remove `history_mode` from `ThreadMetadataPatch`, so mutable metadata
sync and app-server metadata updates cannot rewrite it.
- When local metadata sync has to recreate a missing SQLite row, recover
`history_mode` from the rollout's canonical first `SessionMeta` instead
of from a mutable patch.
- Keep the in-memory thread store using the created thread's canonical
`history_mode` instead of metadata patches.
- Fill the one remaining core test `CreateThreadParams` initializer with
the new `history_mode` field; Bazel CI caught this after the parent
history-mode PR landed.

## Validation

- `just fmt`
- `just test -p codex-thread-store`
- `just test -p codex-state
session_meta_does_not_set_model_or_reasoning_effort`
812cd2bb57 ยท 2026-06-26 12:32:31 -07:00
History
..
2026-04-14 13:51:00 -07:00

Thread Store

codex-thread-store is the storage boundary for Codex threads. It defines the ThreadStore trait plus local and in-memory implementations. Other storage implementations may live outside this repository.

Responsibilities

  • ThreadStore::append_items is the raw canonical history append API. It does not infer metadata from item contents.
  • ThreadStore::update_thread_metadata is the only thread metadata write API. It accepts a single literal metadata patch shape, regardless of whether the caller is applying a user/API mutation or facts derived above the store from appended history.
  • LiveThread is the preferred API for active session persistence. It owns a per-thread metadata sync helper, applies the rollout persistence policy, appends canonical history, and then sends metadata patches through ThreadStore::update_thread_metadata.
  • ThreadManager routes metadata mutations for loaded and cold threads through one entrypoint. Loaded threads use their LiveThread; cold threads go directly to the store.
  • LocalThreadStore persists history through codex-rollout JSONL files and persists queryable metadata through the SQLite state database when available. Local explicit metadata mutations also maintain JSONL/name-index compatibility so reading old or SQLite-less local storage keeps working.
  • RolloutRecorder is the local JSONL writer. It writes already-canonical items for ThreadStore::append_items; it no longer decides metadata updates for live thread-store appends.
  • core/session creates or resumes LiveThread handles and does not need to know whether persistence is backed by local files or another store.

Direction

New metadata observation semantics should live above ThreadStore. Stores persist explicit metadata fields, but raw history appends remain history-only.