docs(adr): compress to 1 record in the domain-modeling format

docs/adr/0001-expose-installs-into-modules-only.md

@@ -1,30 +1,12 @@
-# `expose` installs into modules only; no `FixtureSet` install seam
-
-**Decision:** `expose()` installs fixtures into modules only; we will not introduce a `FixtureSet`
-(or equivalent installer) seam.
-
-`expose()` does two things: it **decides** which providers become fixtures (discovery, the
-skip-non-Provider rule, cross-group collision detection) and it **installs** the resulting fixtures
-onto a module. The decision half was extracted into the private, pure `_collect_fixtures`, which
-captured the durable value — the rules became testable through a return value, and the test suite
-collapsed accordingly.
-
-The recurring follow-up is to extract the *install* half too: wrap the `name -> provider` mapping in
-a `FixtureSet` exposing `.install(into=...)`, turning the install target into a seam.
-
-The architectural test for introducing a seam is **one adapter = hypothetical seam, two = real
-one**. The install targets that actually exist are the caller's module (default, located via
-`inspect.stack()`) and an explicit module passed as `module=`. Both are `types.ModuleType` — the
-*same* adapter type exercised with two instances, not two adapters. There is no concrete non-module
-install target — a pytest class namespace, a programmatic consumer, an ecosystem integration —
-now or clearly coming. The library is, and is expected to remain, a conftest-level adapter that
-installs fixtures into modules.
-
-So a `FixtureSet` would fail the deletion test: delete it and no complexity reappears, because the
-`setattr` loop simply inlines back into `expose()`. It would add an interface without adding
-behaviour. The install step stays a plain `setattr` loop over the mapping `_collect_fixtures`
-returns, and the public surface stays at two symbols.
-
-**Revisit trigger:** a real second install target appears — two genuinely different adapters at the
-install point, such as installing onto a pytest test-class namespace, or handing the mapping to a
-programmatic consumer. At that moment the seam becomes real and a `FixtureSet` earns its keep.
+# `expose` installs into modules only
+
+`expose()` both decides which providers become fixtures, by collecting each group's named providers,
+rejecting an empty call and raising on a name two groups both claim, and installs them onto a
+module. The decision half already lives in the private, pure `_collect_fixtures`; the recurring
+proposal is to extract the install half too, wrapping the `name -> provider` mapping in a
+`FixtureSet` exposing `.install(into=...)`. We will not, because a seam needs two adapters and the
+only install targets are the caller's module, located via `inspect.stack()`, and an explicit
+`module=`, both `types.ModuleType` - one adapter exercised with two instances. Deleting a
+`FixtureSet` would bring back no complexity, since its `setattr` loop simply inlines, so the install
+step stays that loop and the public surface stays at `expose` and `modern_di_fixture`. A genuinely
+different install target, such as a pytest class namespace, is what would make the seam real.