`nix/devShell.nix` collected `devShellHook` by scanning every package:
nonNpmHooks = map (p: p.passthru.devShellHook or "") packages;
But `minimal` and `messaging` are `.override` variants of `default`, so
each carries its own `devShellHook` exporting its own HERMES_PYTHON. The
scan therefore concatenated three conflicting exports and forced Nix to
evaluate and realise three separate uv2nix editable venvs on every
`nix develop`.
`attrValues` is alphabetical, so the last hook won (`minimal`) while
`python`/VIRTUAL_ENV came from `default`'s devDeps:
HERMES_PYTHON = ...dimim2... (minimal — no optional deps)
python / VIRTUAL_ENV = ...85r28... (full)
Inside the shell `$HERMES_PYTHON -c "import anthropic"` failed while
`python -c "import anthropic"` succeeded. Worse, `scripts/run_tests.sh`
prefers HERMES_PYTHON, so the suite ran against the minimal venv. Its
guard did not catch this: it only checks that HERMES_PYTHON has pytest,
and minimal's venv does (pytest is in the `dev` group), so the wrong
interpreter was silently accepted.
Tying the hook to `packages.default` — the same package whose `devDeps`
are installed — keeps HERMES_PYTHON, `python`, and VIRTUAL_ENV pointing
at one venv by construction.
editable venvs referenced 3 -> 1
their combined closure 421 MB -> 140 MB
test failures 85 -> 32
The venv mismatch was masking 53 failures; e.g. test_web_tools_config.py
goes 2-failed -> 38-passed. Full suite is now 25369 passed / 32 failed,
and those 32 reproduce identically on a pristine HEAD worktree with no
nix/ changes under the same interpreter (mostly NixOS artifacts — tests
spawning bare `python3` in a scrubbed env exit 127).
7eefb09314