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codex/codex-rs
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Michael Bolin 01f89c8c59 core: persist initial context window metadata (#29519)
## Why

PR #29494 made context-window IDs visible to the model by wrapping the
token-budget window payload in `<context_window>`, but rollout JSONL
consumers still could not see the initial window identity by tailing the
session file. Compacted rollout items carry window IDs only after
compaction has happened, so a session with no compaction had no durable
JSONL record for window 0.

This change gives tailing consumers a stable initial-window record at
session creation time.

## What Changed

- Added `session_meta.context_window.window_id` for the initial
context-window identity.
- `CreateThreadParams` now requires `initial_window_id: String`, so
thread-store callers cannot accidentally create new threads without
window-0 metadata.
- Live thread creation derives the persisted initial window ID from the
same `AutoCompactWindowIds` used to initialize `SessionState`, keeping
runtime state and JSONL metadata aligned.
- Rollout reconstruction uses `session_meta.context_window.window_id` as
the initial-window fallback and derives `window_number = 0`,
`first_window_id = window_id`, and `previous_window_id = None`
internally.
- Fork reconstruction intentionally uses the same rollout reconstruction
path; consumers that need to distinguish copied initial-window metadata
can use the rollout `thread_id`.
- Legacy compactions without `window_number` still use compaction-count
fallback accounting instead of being reset to window 0 by the
initial-window fallback.
- Compacted rollout metadata still takes precedence once compaction
records exist, preserving the richer chain fields there.

## JSONL Shape

Real rollout JSONL is one object per line. This example is expanded for
readability, but shows the new initial `session_meta.context_window`
record followed by the existing compacted rollout item shape that also
carries window IDs:

```jsonl
{
  "timestamp": "2026-06-22T12:00:00.000Z",
  "type": "session_meta",
  "payload": {
    "session_id": "<THREAD_ID>",
    "id": "<THREAD_ID>",
    "timestamp": "2026-06-22T12:00:00.000Z",
    "cwd": "/repo",
    "originator": "codex",
    "cli_version": "0.0.0",
    "source": "cli",
    "model_provider": "<MODEL_PROVIDER>",
    "context_window": {
      "window_id": "<INITIAL_WINDOW_ID>"
    }
  }
}
...
{
  "timestamp": "2026-06-22T12:34:56.000Z",
  "type": "compacted",
  "payload": {
    "message": "<COMPACTION_SUMMARY>",
    "replacement_history": [
      "..."
    ],
    "window_number": 1,
    "first_window_id": "<INITIAL_WINDOW_ID>",
    "previous_window_id": "<INITIAL_WINDOW_ID>",
    "window_id": "<NEXT_WINDOW_ID>"
  }
}
```

The nested `context_window` object is intentional: it gives rollout
consumers a stable namespace for context-window metadata while only
writing the non-derivable initial `window_id`. For the initial window,
`window_number`, `first_window_id`, and `previous_window_id` are derived
internally instead of being written to the rollout.

## Verification

- `just test -p codex-protocol`
- `just test -p codex-rollout
recorder_materializes_on_flush_with_pending_items`
- `just test -p codex-core reconstruct_history`
- `just test -p codex-core
record_initial_history_reconstructs_forked_transcript`
- `just test -p codex-thread-store`
- `just test -p codex-state`
- `just test -p codex-app-server
thread_read_returns_summary_without_turns`
- `just test -p codex-rollout persistence_metrics`
01f89c8c59 · 2026-06-23 21:50:50 +00:00
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2026-06-23 15:25:28 +01:00
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