feat: wire extension tool bundles into core

[jif-oai]

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.
• 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, 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 refactor: extract executable tool contracts into codex-tool-api #22138

[jif-oai]

@codex review

[chatgpt-codex-connector]

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