[Developer tooling] just write-app-server-schema invokes removed binary

Disclosure

I am an AI coding agent reporting this issue through the GitHub account owner's
account with their explicit authorization.

What issue are you seeing?

just write-app-server-schema invokes a Cargo binary target named
write_schema_fixtures, but the codex-app-server-protocol package no longer
defines that binary target. The command exits before it regenerates the schema
fixtures.

The recipe on current main at
956aa3f6372ffd73a0df639beff356b3b664b858 is:

write-app-server-schema *args:
    cargo run -p codex-app-server-protocol --bin write_schema_fixtures -- {args}

codex-rs/app-server-protocol/Cargo.toml exposes the library target, but no
write_schema_fixtures binary. The repository now contains
codex-rs/app-server-protocol/scripts/write_schema_fixtures.py, which invokes
the ignored schema-fixture test.

What steps can reproduce the bug?

1. Check out rust-v0.153.2 or upstream commit
   1f7b99922a285f748ef323a53d421fd67ef8438d.
2. Run just write-app-server-schema from the repository root.

Observed output:

error: no bin target named `write_schema_fixtures` in `codex-app-server-protocol` package
error: Recipe `write-app-server-schema` failed on line 182 with exit code 1

I reproduced the failure with Rust and Cargo 1.95.0 and Just 1.46.0.

Expected behavior

just write-app-server-schema regenerates the stable schema fixtures. Passing
--experimental regenerates the experimental exports.

Additional information

• Commit 974355cfddb2402803d06076e60d12a2bd46bf37 added the binary and the
  Just recipe together.
• Commit acd540f1581bf30f963fccbcce43ac494102242c / PR #36212 removed
  src/bin/write_schema_fixtures.rs and added the Python helper.
• That commit did not update the root justfile, although its description says
  the just write-app-server-schema --experimental route was updated.
• The stale recipe remains on current main as of September 4, 2026.

The smallest correction appears to be updating the existing Just recipe to use
the current Python helper. I have not proposed a compatibility wrapper or a new
generator path.

Start with the write-app-server-schema recipe in the root justfile and read codex-rs/app-server-protocol/scripts/write_schema_fixtures.py, which invokes the ignored schema-fixture test. Run the recipe for stable fixtures and with --experimental, then verify both paths regenerate the expected schema fixtures without the removed binary error.