Part 1 of guardian as extension. This bind all the logic to spawn
another agent from an extension and it adds `ThreadId` in the start
thread collaborator
## Why
This is the next narrow step toward moving concrete tool families out of
core. After #22138 introduced `codex-tool-api`, we still needed a real
end-to-end seam that lets an extension own an executable tool definition
once and have core install it without the temporary `extension-api`
wrapper or a dependency on `codex-tools`.
`codex-tool-api` is the small extension-facing execution contract, while
`codex-tools` still has a different job: host-side shared tool metadata
and planning logic that is not “run this contributed tool”, like spec
shaping, namespaces, discovery, code-mode augmentation, and
MCP/dynamic-to-Responses API conversion
## What changed
- Moved the shared leaf tool-spec and JSON Schema types into
`codex-tool-api`, so the executable contract now lives with
[`ToolBundle`](c538758095/codex-rs/tool-api/src/bundle.rs (L19-L70)).
- Replaced the temporary extension-side tool wrapper with direct
`ToolBundle` use in `codex-extension-api`.
- Taught core to collect contributed bundles, include them in spec
planning, register them through
[`ToolRegistryBuilder::register_tool_bundle`](c538758095/codex-rs/core/src/tools/registry.rs (L653-L667)),
and dispatch them through the existing router/runtime path.
- Added focused coverage for contributed tools becoming model-visible
and dispatchable, plus spec-planning coverage for contributed function
and freeform tools.
## Verification
- Added `extension_tool_bundles_are_model_visible_and_dispatchable` in
`core/src/tools/router_tests.rs`.
- Added spec-plan coverage in `core/src/tools/spec_plan_tests.rs` for
contributed extension bundles.
## Related
- Follow-up to #22138
## Why
Git commit attribution is prompt policy, not session orchestration.
After #21737 adds the extension-registry seam, this moves that
prompt-only behavior out of `codex-core` so `Session` can consume
extension-contributed prompt fragments instead of owning a one-off
policy path itself.
Before this PR, `Session` injected the trailer instruction directly from
`codex-core` ([session
assembly](a57a747eb6/codex-rs/core/src/session/mod.rs (L2733-L2739)),
[helper
module](a57a747eb6/codex-rs/core/src/commit_attribution.rs (L1-L33))).
This branch moves that same responsibility into
[`codex-git-attribution`](b5029a6736/codex-rs/ext/git-attribution/src/lib.rs (L14-L100)).
## What changed
- Added the `codex-git-attribution` extension crate.
- Snapshot `CodexGitCommit` plus `commit_attribution` at thread start,
then contribute the developer-policy fragment through the extension
registry.
- Register the extension in app-server thread extensions.
- Remove the old `codex-core` helper module and direct `Session`
injection path.
This keeps the existing behavior intact: the prompt is only contributed
when `CodexGitCommit` is enabled, blank attribution still disables the
trailer, and the default remains `Codex <noreply@openai.com>`.
## Stack
- Stacked on #21737.
## Why
`codex-core` still owns a growing amount of product-specific behavior.
This PR starts the extraction path by introducing a small, typed
first-party extension seam: features can install the contribution
families they actually own, while the host keeps lifecycle and state
ownership instead of pushing a broad service locator into the API.
See the `examples/` for illustration
## Known limitations
* Tool contract definition will be shared with core
* Fragments must be extracted
* Missing some contributors
