[codex] Add Codex slash command support

[StiensWout]

Summary

• Advertise Codex provider slash commands for /review and /compact after the app-server probe succeeds.
• Route standalone /review [instructions] and /compact prompts through Codex app-server RPCs instead of sending them as chat messages.
• Keep this to app-server-backed commands; broader /goal handling remains separate native goal work because Codex exposes dedicated goal RPCs.

Why

Codex slash commands are not a generic text passthrough in T3 Code. /review returns a turn from review/start, while /compact starts through thread/compact/start and reports its turn through turn/started, so the Codex provider runtime needs to own that mapping.

Impact

Codex users see /review and /compact in the composer command menu. Submitting either command starts the matching provider-native turn and preserves the usual T3 turn/session state.

Validation

• PATH="$HOME/.vite-plus/bin:$PATH" vp check
• PATH="$HOME/.vite-plus/bin:$PATH" vp run --filter ./apps/server typecheck
• PATH="$HOME/.vite-plus/bin:$PATH" vp test run apps/server/src/provider/Layers/CodexAdapter.test.ts
• PATH="$HOME/.vite-plus/bin:$PATH" vp run typecheck

Refs #2491

Note

Add /compact and /review slash command support to the Codex provider

• Defines CODEX_APP_SERVER_SLASH_COMMANDS in CodexProvider.ts advertising compact and review slash commands; successful provider probes now include these, while error/disabled states return an empty list.
• Adds parseStandaloneCodexSlashCommand in CodexAdapter.ts to detect single-line /compact or /review [instructions] messages with no attachments, routing them to runSlashCommand instead of a normal sendTurn.
• Implements runSlashCommand in CodexSessionRuntime.ts: /compact calls thread/compact/start and waits for the next turn/started notification; /review calls review/start with optional instructions and inline delivery.
• Serializes all turn starts (both sendTurn and runSlashCommand) with a semaphore, tracking known turn IDs and pending waiters to correctly resolve or fail them on process exit or runtime close.
• Risk: concurrent slash command and sendTurn calls are now serialized, which changes timing behavior for back-to-back turn starts.

^{Macroscope summarized 21bf969.}

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Note

Medium Risk
Changes Codex session turn-start orchestration and async compact turn correlation; failures or missing turn/started events could block or error slash commands without affecting unrelated providers.

Overview
Adds Codex-native slash commands so standalone /review and /compact prompts are not sent as ordinary chat turns.

After a successful app-server probe, the Codex provider snapshot now includes review and compact in slashCommands (empty while disabled or probe fails). In CodexAdapter, parseStandaloneCodexSlashCommand recognizes attachment-free /compact or /review [instructions] input and calls runSlashCommand instead of sendTurn, optionally passing the bound instance’s selected model.

CodexSessionRuntime implements runSlashCommand: review/start with custom instructions or uncommitted changes; thread/compact/start plus a deferred waiter on the next turn/started that ignores already-known turn IDs. Turn starts (slash commands and normal sends) share a semaphore, and known turn IDs are tracked on thread open/read/rollback. Process exit/close fails pending compact waiters.

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Cursor Bugbot has reviewed your changes using high effort and found 2 potential issues.

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[macroscopeapp]

Approvability

Verdict: Needs human review

This PR introduces two new user-facing slash commands (/compact and /review) with significant new runtime logic, async coordination patterns, and API integrations. New feature additions that enable new user-facing workflows warrant human review.

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