fix(core) Preserve base_instructions in SessionMeta #9427

dylan-hurd-oai · 2026-01-18T06:34:54Z

Summary

This PR consolidates base_instructions onto SessionMeta / SessionConfiguration, so we ensure base_instructions is set once per session and should be (mostly) immutable, unless:

overridden by config on resume / fork
sub-agent tasks, like review or collab

In a future PR, we should convert all references to base_instructions to consistently used the typed struct, so it's less likely that we put other strings there. See #9423. However, this PR is already quite complex, so I'm deferring that to a follow-up.

Testing

Added a resume test to assert that instructions are preserved. In particular, resume_switches_models_preserves_base_instructions fails against main.

Existing test coverage thats assert base instructions are preserved across multiple requests in a session:

Manual compact keeps baseline instructions: core/tests/suite/compact.rs:199
Auto-compact keeps baseline instructions: core/tests/suite/compact.rs:1142
Prompt caching reuses the same instructions across two requests: core/tests/suite/prompt_caching.rs:150 and core/tests/suite/prompt_caching.rs:157
Prompt caching with explicit expected string across two requests: core/tests/suite/prompt_caching.rs:213 and core/tests/suite/prompt_caching.rs:222
Resume with model switch keeps original instructions: core/tests/suite/resume.rs:136
Compact/resume/fork uses request 0 instructions for later expected payloads: core/tests/suite/compact_resume_fork.rs:215

aibrahim-oai

clean!

aibrahim-oai · 2026-01-18T07:19:57Z

@codex review this

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chatgpt-codex-connector · 2026-01-18T07:28:39Z

codex-rs/core/src/codex.rs

+    let base_instructions = sess.get_base_instructions().await;
+
    let prompt = Prompt {
        input,


Align token estimation with session base instructions

Sampling requests now pull base_instructions from the session (sess.get_base_instructions()), but token estimation/auto‑compaction still uses turn_context.client.get_model_info().base_instructions in ContextManager::estimate_token_count. When a session’s base instructions diverge from the model default (e.g., config override, resume/fork with preserved instructions, or switching models mid‑session), the estimate becomes inaccurate, which can delay auto‑compaction or misreport token usage and lead to context‑window errors. Consider basing the estimate on the session base instructions used for prompts so the count matches actual request payloads.

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dylan-hurd-oai · 2026-01-19T16:10:52Z

Looks like bazel build is failing due to cross-crate import, will duplicate across before merging

jif-oai

So this means that we can't modify the instructions once the session is started (like the /search was doing before for example)
If we are ok with this, good for me

codex-rs/core/src/config/mod.rs

jif-oai · 2026-01-19T16:20:13Z

codex-rs/core/src/rollout/tests.rs

        "cwd": ".",
        "originator": "test_originator",
        "cli_version": "test_version",
+        "base_instructions": null,


Can you make sure we have a test where this is just missing as well?

jif-oai · 2026-01-19T16:20:38Z

codex-rs/core/src/rollout/tests.rs

    let mut payload = serde_json::json!({
        "id": uuid,
        "timestamp": ts_str,
        "cwd": ".",


Would be good to have a test where this is not null

jif-oai · 2026-01-19T16:22:05Z

codex-rs/core/src/tools/handlers/collab.rs


-fn build_agent_spawn_config(turn: &TurnContext) -> Result<Config, FunctionCallError> {
+fn build_agent_spawn_config(
+    base_instructions: &BaseInstructions,


There are already some base_instructions in TurnContext, why do you need different once here? Can you document a bit please? (tbh I don't even make sure we need this)

I'm removing base_instructions from TurnContext altogether, since it shouldn't change from turn to turn. Happy to add a general comment.

But I think the spirit of this change is "build_agent_spawn_config" should inherit session-level config, not just config housed in TurnContext. If the spirit of TurnContext is to denormalize session-level information as well, I'm happy to shift in that direction, but I think we'd want to refactor the serialization there, since we wouldn't want to save the entire base_instructions to the rollout in every turn.

jif-oai · 2026-01-19T16:24:25Z

codex-rs/core/src/client_common.rs

-
    use super::*;

-    struct InstructionsTestCase {


jif-oai · 2026-01-19T16:27:39Z

codex-rs/protocol/src/models.rs

 }

+/// Base instructions for the model in a thread. Corresponds to the `instructions` field in the ResponsesAPI.
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, JsonSchema, TS)]


Let's make 100% we don't serialize using this serializer when sending to the model as it would be wrong

@codex check for existing test coverage on the instructions field for the responses api request

Answer

I checked for existing tests that explicitly assert the instructions field sent in Responses API requests (the field described in BaseInstructions in protocol/src/models.rs). There is existing coverage in core suite tests that validate the instructions field contents across requests, including cases like prompt caching, compaction, and resume/fork flows.

Existing tests that assert instructions in Responses requests

Prompt caching: Verifies that multiple requests send identical instructions (derived from base instructions plus tool instructions when applicable). This is a direct assertion on body["instructions"] for two requests. codex-rs/core/tests/suite/prompt_caching.rsL130-L223

Manual compaction: Confirms the instructions field is preserved across the initial request and the compaction request (ensuring the same instructions are sent). codex-rs/core/tests/suite/compact.rsL198-L211

Resume with model switch: Captures instructions from the initial request and asserts the resumed request uses the same instructions value. codex-rs/core/tests/suite/resume.rsL167-L205

Compact → Resume → Fork: Saves requests[0]["instructions"] and reuses it as the expected prompt payload for later requests, ensuring the original instructions are carried forward across flows. codex-rs/core/tests/suite/compact_resume_fork.rsL215-L263

These tests together exercise the instructions field in the Responses API request bodies across multiple session lifecycle scenarios, which should cover the concern raised at protocol/src/models.rs line ~170 (the BaseInstructions struct tied to the instructions field).

Commands I ran to verify coverage

rg -n "instructions" codex-rs -g"*.rs" (used to locate tests referencing instructions and request bodies). codex-rs/core/tests/suite/prompt_caching.rsL130-L223

sed -n '130,240p' codex-rs/core/tests/suite/prompt_caching.rs codex-rs/core/tests/suite/prompt_caching.rsL130-L223

sed -n '170,240p' codex-rs/core/tests/suite/compact.rs codex-rs/core/tests/suite/compact.rsL198-L211

sed -n '150,230p' codex-rs/core/tests/suite/resume.rs codex-rs/core/tests/suite/resume.rsL167-L205

sed -n '200,270p' codex-rs/core/tests/suite/compact_resume_fork.rs codex-rs/core/tests/suite/compact_resume_fork.rsL215-L263

If you want deeper coverage focused specifically on serialization paths in protocol/src/models.rs, I can add a unit test directly in that crate, but the current suite already validates the instructions field in actual request payloads sent to the Responses API.

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dylan-hurd-oai added 6 commits January 17, 2026 20:25

fix(core) Preserve base_instructions in SessionMeta

b0f2954

tests pass

03932b8

migrate prompt to use sessionconfiguration

208d7a1

add resume test

b381153

swap tests

6c3303c

remove TurnContext.base_instructions

b340804

dylan-hurd-oai requested review from aibrahim-oai, bolinfest and jif-oai January 18, 2026 06:35

fix serialization order

7b51f01

aibrahim-oai reviewed Jan 18, 2026

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chatgpt-codex-connector bot reviewed Jan 18, 2026

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jif-oai approved these changes Jan 19, 2026

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dylan-hurd-oai mentioned this pull request Jan 19, 2026

feat(personality) introduce model_personality config #9459

Merged

1 task

dylan-hurd-oai added 3 commits January 19, 2026 19:37

review

1d1af37

move default

d204922

fix bazel build

9fa5859

dylan-hurd-oai merged commit 675f165 into main Jan 20, 2026
32 checks passed

dylan-hurd-oai deleted the dh--session-base-instructions branch January 20, 2026 05:59

github-actions bot locked and limited conversation to collaborators Jan 20, 2026

fix(core) Preserve base_instructions in SessionMeta #9427

fix(core) Preserve base_instructions in SessionMeta #9427

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aibrahim-oai commented Jan 18, 2026

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Answer

Existing tests that assert instructions in Responses requests

Commands I ran to verify coverage

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dylan-hurd-oai commented Jan 18, 2026 •

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Existing tests that assert `instructions` in Responses requests