[FEATURE]: pass sessionID into tool.definition hooks

[ian-pascoe]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

tool.definition hooks should always receive the active sessionID when tool definitions are built.

Right now that session context is not available consistently across tool listing paths, which makes it hard for plugins to customize tool descriptions or schemas per session. The need is the same across prompt resolution, batch execution, debug tool listing, and /experimental/tool, so those entry points should use one session-aware contract instead of each path behaving differently.

This would also keep the plugin hook contract and generated SDK types aligned with the API behavior.

[github-actions]

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