## Why
Manual, pre-turn, and post-turn compaction previously deferred rebuilding initial context until the next turn. Their saved replacement history could omit refreshed instructions and skill catalogs.
## What changed
- Install initial context during local and remote compaction, before the last real user message or summary, keeping the compaction summary last.
- Persist matching full world-state and turn-context baselines with every replacement instead of retaining only partial extension metadata.
- Build replacement context and recompute token usage for the current model even when the previous model performs compaction. Reuse that captured context for eligible current-model retries.
- Capture manual compaction context centrally and propagate preparation errors to the task runner.
## Testing
Update assertions and snapshots for context ordering, refreshed instructions, resume and fork history, current-model checkpoint baselines, and cloud skill catalog retention across compaction and resume.
GitOrigin-RevId: 8572a76c31c6884a3c580b3bbb350d49af876bd1
## Why
After a model switch, compaction with the previous model could fail after exhausting stream retries without falling back to the selected model.
## What changed
Allow compaction to fall back to the current model for all errors except `TurnAborted`, `Interrupted`, and `SessionBudgetExceeded`.
## Testing
Add a regression test that exhausts the previous model's compaction stream retries, then verifies that fallback compaction and turn sampling use the selected model.
GitOrigin-RevId: 9c9b7ccbb206d19f1ae750a32636fc9acaacfb2b
## Why
Remote compaction already uses the normal Responses API, leaving the legacy `/responses/compact` runner unused.
## What changed
- Remove the legacy runner, endpoint client, request types, analytics variant, and obsolete test helpers and snapshots.
- Move tool-output trimming and its metadata tests into `compact_remote_history` for reuse by remote compaction v2.
- Consolidate retained-history filtering in the v2 implementation and remove redundant `RemoteCompactionV2` settings from tests.
## Testing
Extend the retained-history unit test to explicitly check that hook prompts survive compaction.
GitOrigin-RevId: 999bb1391aa22c3c281d6a96f98817d6c9e46ed9
## What changed
- Wrap `CodexErrorDetails` and an optional retry delay in `CodexErr`, allowing any mapped error to preserve server-provided retry timing.
- Generate the payload-free `CodexErrKind` classification alongside the error details and reuse it for analytics.
- Update error handling sites to inspect `CodexErr::details()` while preserving existing display, debug, protocol mapping, and retryability behavior.
## Testing
- Add coverage for legacy debug formatting, error-specific retryability, and retry-delay propagation through API error mapping.
GitOrigin-RevId: d3ab8a305f2a2ee21d0c0a8c8c388b06dda9c59a
## Why
Compacting a resumed conversation can fail when its previous model is no longer
available. Some model-specific failures, such as a model-not-found response, are
not represented as invalid requests and therefore did not trigger the existing
fallback to the currently selected model.
## What changed
- Share a retry predicate between both remote compaction implementations.
- Fall back to the current model for invalid requests, unexpected statuses,
context-window and usage-limit errors, server failures, and exhausted retries.
## Testing
Add an integration test that resumes a conversation whose previous model returns
model-not-found and verifies that compaction and the next turn use the renamed
model.
GitOrigin-RevId: c3857beae2ce79b50589deb13c2e59710ce14725
## Why
Pre-sampling compaction intentionally uses the previous turn's model
when the compaction compatibility hash changes or when switching to a
model with a smaller context window. This keeps compaction aligned with
the settings that produced the history, but it can block the next turn
when a resumed ChatGPT thread still references a model slug that has
since been retired. The Codex backend rejects that compaction request
before the user's currently selected model gets a chance to sample.
This PR lets those threads recover without changing previous-model
compaction behavior for API-key authentication or custom providers. It
is stacked on #31316, which is a behavior-preserving extraction of the
individual remote compaction attempts; this PR contains the fallback
behavior.
## What changed
- For automatic previous-model compaction, capture the selected model's
request context when using ChatGPT authentication with the OpenAI
provider and the selected model differs from the previous model.
- If the previous-model attempt returns an `InvalidRequest`, retry
compaction once with the selected model for both `/responses/compact`
and Responses Compaction V2.
- Complete history processing, lifecycle events, and token accounting
with the context of the model that successfully compacted the thread.
- If the fallback also fails, return the original previous-model error
so the retry does not change the user-visible failure.
- Record fallback attempts with reason, implementation, and outcome
telemetry.
- Leave API-key authentication, custom providers, same-model turns, and
non-`InvalidRequest` failures on their existing paths.
## Testing
- `just test -p codex-core -E 'test(pre_sampling_compact) |
test(model_unavailable_error)'` (10 tests)
- Added integration coverage for a resumed thread whose model was
renamed, a model downshift using Responses Compaction V2, and API-key
authentication with a custom provider.
pakrym-oai