Follow up to: #3582504 **Description:** Before RC1, the selector should expose stable extension points so contrib modules do not couple directly to `AiContextSelector` internals. This will make future selector refactors safer while allowing modules to filter, boost, inspect, or alter selection behavior through events. **Scope:** - Add selection pipeline event classes, for example pre-select, post-filter, post-select, and post-render. - Dispatch events from stable points in `AiContextSelector`. - Ensure events expose useful data without leaking mutable internals unnecessarily. - Document the events for developers. - Add tests proving subscribers can observe and alter supported pipeline data. **Acceptance criteria:** - Contrib can subscribe to documented selector events. - No behavior changes occur when no subscribers are registered. - Event dispatch order is deterministic. - Tests cover at least one subscriber altering/filtering selection and one subscriber observing rendered output. **Implementation notes (RC1):** This issue implements two selector pipeline events for RC1: `ai_context.selection.post_select` and `ai_context.selection.post_render` (`AiContextPostSelectEvent`, `AiContextPostRenderEvent`, constants on `AiContextSelectionEvents`). `pre_select` and `post_filter` are intentionally deferred to avoid locking candidate filtering/scoring internals before there are concrete contrib requirements. The `ai_context.selection.*` prefix is reserved for future pipeline events. See `docs/developers/events.md`. All acceptance criteria are met. Additional behavior: view access checks on `setSelectedItems()`, read-only truncated item IDs on post-render, merge-only cache metadata via `addCacheableDependency()`, post-event `tokensUsed` recalculation, and warning logs when subscribers exceed configured `max_items` / `max_tokens`. Tests: `tests/src/Kernel/AiContextSelectorEventsTest.php`. **AI usage disclosure:** - [x] AI Assisted Issue - [x] AI Generated Code