feat: 3 feature-gaps vs other coding agents (consolidated request)

Summary

Three feature gaps observed while running Codex CLI alongside Claude Code, OpenCode, and Cursor on the same repos. Filing consolidated per your triage preference; happy to split if you'd rather.

Gaps

| # | Gap | Codex today | Seen in |
|---|---|---|---|
| 1 | Adaptive reasoning with always-thinking floor | model_reasoning_effort static per-request | Claude Code (alwaysThinkingEnabled + adaptive) |
| 2 | Rich @-mention namespaces beyond @file | @file shipped (#18551, #2952, #22888, #22903); @docs/@web/@git/@definitions absent | Cursor |
| 3 | Zero-ceremony custom tools as file drops | codex plugin exists but requires marketplace registration | OpenCode (.opencode/plugins/*.ts hot-loaded) |

Rough impl hints

1. Add reasoning_floor + reasoning_adaptive config keys. Enforce a minimum reasoning-token count per turn while letting depth scale on complexity signals. Prevents zero-think regressions of the kind seen in Claude Code Feb 2026.
2. Extend mentions_v2 with resolvers for @docs, @web, @git, @definitions (already have @file, @chrome, @Mac-app). TUI typeahead as with existing @ handler. Baseline: #18551 confirms @file shipped; this issue is scoped to the missing namespaces only, not re-litigating file mentions.
3. Support .codex/plugins/*.ts (or .js) exporting tool({description, args, execute}) with Zod-style arg schemas. Hot-load on session start. No npm publish, no marketplace round-trip, no MCP-server boilerplate — matches OpenCode's file-drop UX.

Alternatives considered

• Reasoning floor: setting model_reasoning_effort=high globally — over-spends on trivial turns; adaptive+floor is the balanced position.
• Rich mentions: MCP resource servers — works but shifts context assembly out of the CLI and loses TUI typeahead affordance.
• File-drop plugins: MCP servers cover the capability, but the boilerplate (server process, stdio wiring, registration) is a 10x-longer path than a .ts file export for the common 10-line-tool case. Marketplace plugins solve distribution, not authoring friction.

Thanks for the excellent Codex CLI — happy to open individual issues per gap if preferred.