Codex app-server panics on iSH when the aws-lc provider lacks ECDSA P-521

Summary

codex-app-server terminates during startup on an iSH-based ARM64 embedded Linux runtime when the successfully installed aws-lc rustls provider exposes a reduced signature-verification algorithm set that does not contain ECDSA_NISTP521_SHA512.

Environment

• Codex source: rust-v0.147.0
• binary target: aarch64-unknown-linux-musl
• runtime: iSH ARM64 embedded in an iOS app
• device: iPhone

Reproduction

1. Build codex-app-server for aarch64-unknown-linux-musl from rust-v0.147.0.
2. Launch the binary in the iSH ARM64 runtime.
3. Initialize app-server so it installs the process-wide rustls crypto provider.

Actual behavior

Provider installation succeeds, but app-server exits before it can initialize or make a TLS request:

installed rustls crypto provider must support ECDSA_NISTP521_SHA512

Expected behavior

Keep the successfully installed provider and allow app-server to start. If a later TLS connection actually requires an unsupported certificate signature scheme, rustls/WebPKI should reject that connection normally.

Root cause analysis

ensure_rustls_crypto_provider() installs rustls::crypto::aws_lc_rs::default_provider(), then unconditionally asserts that the installed provider advertises ECDSA_NISTP521_SHA512.

That converts a certificate-specific capability into a process-wide startup requirement. It is also stricter than the existing behavior for a provider installed before Codex starts: that provider is preserved without requiring P-521.

Proposed fix

• remove the post-install process-terminating P-521 assertion
• keep the successfully installed platform-provided aws-lc algorithm set
• update the provider integration test to verify that the installed schemes equal the schemes available from that platform's aws-lc provider
• retain fail-closed TLS verification for certificates that use unsupported schemes

Reference implementation:

• commit: https://github.com/jacklv-coder/codex/commit/9bb14f6f57fdb39ce80dd46f85b2ff15168b044a
• branch comparison: https://github.com/openai/codex/compare/main...jacklv-coder:codex/allow-reduced-rustls-provider

Validation

• just fmt
• just test -p codex-utils-rustls-provider — 2 tests passed
• Codex CR completed with no P1/P2 findings
• the same source change was rebuilt for aarch64-unknown-linux-musl and exercised in the iSH ARM64 runtime on iPhone
• patched app-server initialized and completed an HTTPS Responses request; the unmodified release binary reproduced the startup assertion

This does not expand certificate trust: rustls/WebPKI continues to reject certificates whose signature scheme is unsupported by the installed provider.

Start at ensure_rustls_crypto_provider() and the provider integration tests in codex-utils-rustls-provider. Run just test -p codex-utils-rustls-provider after removing the startup requirement for ECDSA_NISTP521_SHA512 and update the test to compare installed schemes with the platform aws-lc provider. Done means reduced providers remain installed, the tests pass, and unsupported certificate schemes still fail during TLS verification.