fix(build): make setup fail when the environment doesn't actually work

pip install exiting 0 is not evidence the venv is usable (D-24) - the
2026-08-09 core-api incident was exactly this shape: a venv that
"installed fine" but was missing sqlalchemy, surfacing as 11 collection
errors that read like broken imports rather than an environment
problem.

setup now ends with `pytest --collect-only`, scoped like `make test`
(excludes e2e/integration/contracts) and run with --no-cov. Collection
imports every test module without running the suite, so a missing or
mismatched dependency fails setup itself instead of showing up later
as a confusing test failure.

Workspace T-47.

CHANGELOG.md

@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+
+- `make setup` now ends with a `pytest --collect-only` pass so a broken environment
+  (missing or mismatched dependency) fails the target itself instead of exiting 0
+  and surfacing later as a confusing test failure (T-47)
+
 ## [2.4.3] - 2026-08-08
 
 ### Fixed

Makefile

@@ -18,6 +18,17 @@ setup: ## Create venv and install all dependencies
 	python3 -m venv $(VENV)
 	$(PIP) install --upgrade pip
 	$(PIP) install -e ".[dev]"
+	# Exit 0 from pip install is not evidence the environment works (D-24) - the
+	# 2026-08-09 core-api incident was exactly this: a venv that "installed fine"
+	# but was missing a declared dependency, surfacing as 11 collection errors
+	# that read like broken imports rather than an environment problem. Collection
+	# is the right cheap check here for that same reason: it imports every test
+	# module (and everything they import) without running the suite, so a missing
+	# or mismatched dependency fails setup itself instead of showing up later as a
+	# mysterious test failure. Scoped like `make test` (excludes e2e/integration/
+	# contracts, which need external services) and --no-cov since coverage
+	# instrumentation is irrelevant to "does this collect".
+	$(PYTEST) --collect-only -q --ignore=tests/e2e --ignore=tests/integration --ignore=tests/contracts --no-cov
 
 run: ## Start the development server on port 8777
 	@mkdir -p build/logs