Keep extracting memories out of core and moving the write trigger in the
app-server
This is temporary and it should move at the client level as a follow-up
This makes core fully independant from `codex-memories-write`
---------
Co-authored-by: Codex <noreply@openai.com>
## Why
MultiAgentV2 children should not receive an extra model-visible
developer fragment just because they were spawned. The parent/configured
developer instructions should carry through normally, but the dedicated
`<spawned_agent_context>` block is no longer desired.
## What changed
- Removed the `SpawnAgentInstructions` context fragment and its
`<spawned_agent_context>` wrapper.
- Stopped appending spawned-agent instructions in
`codex-rs/core/src/tools/handlers/multi_agents_v2/spawn.rs`.
- Updated subagent notification coverage to assert inherited parent
developer instructions without expecting the spawned-agent wrapper.
## Verification
- `cargo test -p codex-core --test all
spawned_multi_agent_v2_child_inherits_parent_developer_context --
--nocapture`
- `cargo test -p codex-core --test all
skills_toggle_skips_instructions_for_parent_and_spawned_child --
--nocapture`
- `cargo test -p codex-core --test all subagent_notifications --
--nocapture`
