[codex] Generalize service tier slash commands

[aibrahim-oai]

Why

/fast was wired as a one-off slash command even though model metadata now exposes service tiers as catalog data. That meant adding another tier, such as a slower/cheaper tier, would require more hardcoded TUI plumbing instead of letting the model catalog drive the available commands.

This change makes service-tier commands data-driven: each advertised service_tiers entry becomes a /name command using the catalog description, while the request path sends the tier id only when the selected model supports it.

What Changed

• Removed the hardcoded /fast slash-command variant and introduced dynamic service-tier command items in the composer and command popup.
• Added toggle behavior for service-tier commands: invoking /name selects that tier, and invoking it again clears the selection.
• Preserved the existing Fast-mode keybinding/status affordances by resolving the current model tier whose name is fast, while still sending the tier request value such as priority.
• Persisted service-tier selections as raw request strings so non-fast tiers can round-trip through config.
• Updated the Bedrock catalog entry to advertise fast support through service_tiers with id: "priority" and name: "fast".
• Added defensive filtering in core so unsupported selected service tiers are omitted from /responses requests.

Validation

• Added/updated coverage for dynamic service-tier slash command lookup, popup descriptions, composer dispatch, TUI fast toggling, and unsupported-tier omission in core request construction.
• Local tests were not run per request.

[fcoury-oai]

Tested the behavior with gpt-5.5 and gpt-5.4 that advertises service_tiers for fast and it worked as expected.

Code looks good, left one optional nit to address.

Approved! 👍

[fcoury-oai]

nit: we are trying to avoid adding new methods to chatwidget given it's huge size. Do you think we could take this opportunity and extract a new module for service tiers?

[aibrahim-oai]

sounds good