GPT-5.6 models get no tools in read-only sandbox (codex exec -s read-only says it has no shell/file tools)

What version of Codex is running?

codex-cli 0.144.0 (also reproduced on 0.143.0; pre-5.6 behavior verified on 0.137.0)

What platform is your computer?

macOS (Darwin 25.5.0, arm64)

What steps can reproduce the bug?

With any GPT-5.6 model selected, codex exec -s read-only sessions are provisioned with no tools at all — the model reports it has no shell or file-reading tool and cannot inspect the repo:

$ codex exec -s read-only -m gpt-5.6-sol "Run the shell command \`echo tool-check-ok\` and report its exact output. If you have no shell tool available, say NO-TOOLS."
NO-TOOLS

Reproduction matrix (all from the same machine/auth, same working directory):

| model | sandbox | result |
|---|---|---|
| gpt-5.6-sol | read-only | ❌ NO-TOOLS |
| gpt-5.6-terra | read-only | ❌ NO-TOOLS |
| gpt-5.6-sol | read-only + -c 'sandbox_permissions=["disk-full-read-access"]' | ❌ NO-TOOLS |
| gpt-5.6-sol | workspace-write | ✅ runs echo, returns output |
| gpt-5.5 | read-only | ✅ runs echo, returns output |

CLI version is not the variable: identical results on 0.143.0 and 0.144.0. gpt-5.5 + read-only worked on 0.137.0 earlier the same day and still works on 0.144.0.

In interactive sessions the model describes it as: "This session includes the repo path and filesystem permissions in its context, but no terminal or file-reading tool was actually provisioned to me."

What is the expected behavior?

Read-only sandbox sessions should provision the shell/file tools (with read-only enforcement), as they do for gpt-5.5.

What do you see instead?

GPT-5.6 sessions in read-only sandbox receive no tool bundle at all, so any read-only automation (codex exec -s read-only ..., review flows) silently degrades to a no-tool chat.

Additional information

• Auth: ChatGPT login (Plus/Pro plan), model_provider is the local codex-lb (http://127.0.0.1:2455/backend-api/codex) provided by the ChatGPT desktop app — so this may be backend/rollout-side rather than CLI-side. Filed within hours of the GPT-5.6 GA rollout announcement.
• Workaround: pass -m gpt-5.5 for read-only runs, or use -s workspace-write.