## Why
JSON schema codegen was silently resolving naming collisions by
appending numeric suffixes (for example `...2`, `...3`). That makes the
generated schema names unstable: removing an earlier colliding type can
cause a later type to be renumbered, which is a breaking change for
consumers that referenced the old generated name.
This PR makes those collisions explicit and reviewable.
Though note that once we remove `v1` from the codegen, we will no longer
support naming collisions. Or rather, naming collisions will have to be
handled explicitly rather than the numeric suffix approach.
## What Changed
- In `codex-rs/app-server-protocol/src/export.rs`, replaced implicit
numeric suffix collision handling for generated variant titles with
explicit special-case maps.
- Added a panic when a collision occurs without an entry in the map, so
new collisions fail loudly instead of silently renaming generated schema
types.
- Added the currently required special cases so existing generated names
remain stable.
- Extended the same approach to numbered `definitions` / `$defs`
collisions (for example `MessagePhase2`-style names) so those are also
explicitly tracked.
## Verification
- Ran targeted generator-path test:
- `cargo test -p codex-app-server-protocol
generate_json_filters_experimental_fields_and_methods -- --nocapture`
---
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* #12408
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