docs(release): add 2.8.0 notes

planning/releases/2.8.0.md

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+# modern-di-fastapi 2.8.0 — modern-di 2.21.0 floor + internal cleanups
+
+Maintenance release. **No public API change** — `setup_di`, `FromDI`, `build_di_container`, and the context providers keep their signatures and behavior. It raises the `modern-di` floor and cleans up two internals.
+
+## Internal refactors
+
+- **Connection-kind mapping single-sourced off the context providers.** `build_di_container` no longer re-states each connection type and context key in an `isinstance` ladder; it walks the registered context providers (`_CONNECTION_PROVIDERS`), taking each `context_type` and `scope` from the provider. `setup_di` registers from the same tuple. Adding a connection kind is adding a provider — behavior is unchanged.
+- **Own the lifespan composition.** `setup_di` previously chained its lifespan via the private `fastapi.routing._merge_lifespan_context`. It now uses a small `_compose_lifespan` built on the public `app.router.lifespan_context`, dropping the FastAPI-internals dependency. The original lifespan stays the outer context, its startup/shutdown and yielded state pass through, and the root container still reopens across lifespan cycles.
+
+## Packaging
+
+- **`modern-di` floor raised to `>=2.21.0,<3`** (was `>=2.19.0`). The connection-mapping refactor relies on the public `ContextProvider.context_type` added in modern-di 2.21.0.
+- Enriched PyPI metadata (keywords, classifiers, project URLs).
+
+## Downstream
+
+Requires **`modern-di>=2.21.0`**. There is no API change, so application code that uses `setup_di` / `FromDI` needs no edits — only the `modern-di` floor moves.
+
+## Internals
+
+- 100% line coverage maintained; `ruff`, `ty`, and `eof-fixer` clean.
+- Adopted the portable planning convention (`planning/`) and seeded the `architecture/` truth home; releases are tag-driven.