## Why
The generated unnamespaced JSON envelope schemas (`ClientRequest` and
`ServerNotification`) still contained both v1 and v2 variants, which
pulled legacy v1/core types and v2 types into the same `definitions`
graph. That caused `schemars` to produce numeric suffix names (for
example `AskForApproval2`, `ByteRange2`, `MessagePhase2`).
This PR moves JSON codegen toward v2-only output while preserving the
unnamespaced envelope artifacts, and avoids reintroducing numeric-suffix
tolerance by removing the v1/internal-only variants that caused the
collisions in those envelope schemas.
## What Changed
- In `codex-rs/app-server-protocol/src/export.rs`, JSON generation now
excludes v1 schema artifacts (`v1/*`) while continuing to emit
unnamespaced/root JSON schemas and the JSON bundle.
- Added a narrow JSON v1 allowlist (`JSON_V1_ALLOWLIST`) so
`InitializeParams` and `InitializeResponse` are still emitted.
- Added JSON-only post-processing for the mixed envelope schemas before
collision checks run:
- `ClientRequest`: strips v1 request variants from the generated `oneOf`
using the temporary `V1_CLIENT_REQUEST_METHODS` list
- `ServerNotification`: strips v1 notifications plus the internal-only
`rawResponseItem/completed` notification using the temporary
`EXCLUDED_SERVER_NOTIFICATION_METHODS_FOR_JSON` list
- Added a temporary local-definition pruning pass for those envelope
schemas so now-unreferenced v1/core definitions are removed from
`definitions` after method filtering.
- Updated the variant-title naming heuristic for single-property literal
object variants to use the literal value (when available), avoiding
collisions like multiple `state`-only variants all deriving the same
title.
- Collision handling remains fail-fast (no numeric suffix fallback map
in this PR path).
## Verification
- `just write-app-server-schema`
---
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