Closes task #123 — last piece of #87 cleanup.
Pre-fix: workspace/preflight.py:11 hardcoded a tuple of "supported"
runtime names (claude-code, codex, ollama, langgraph, etc.). Every
new template repo required a code change in molecule-runtime to be
recognized — direct violation of the universal-runtime principle
(#87) where adapters declare themselves and the runtime stays generic.
Post-fix: discovery-based validation via the same ADAPTER_MODULE env
var that production load paths already consult
(workspace/adapters/__init__.py:get_adapter). Distinguished failure
modes so operator messages are concrete:
- ADAPTER_MODULE unset → "no adapter installed; set the env var"
- ADAPTER_MODULE set but module won't import → import error type +
message
- module imports but no Adapter class → "convention violation, add
`Adapter = YourClass`"
- Adapter.name() raises → caught with operator message
- Adapter.name() returns non-string → contract violation message
- Adapter.name() doesn't match config.runtime → drift WARNING (not
fatal; the adapter wins in production, config.yaml is just
documentation)
The drift case is the one behavioral change worth calling out: the
prior static-list path would have hard-failed config.runtime values
not in the allowlist. With discovery, an unknown runtime in
config.yaml is just a documentation drift — the adapter that's
actually installed runs regardless. Operator gets a warning naming
both the configured and installed names so they can fix whichever
is stale.
Tests:
- Replaces the obsolete "static list pass/fail" tests with 6 new
cases covering each distinguished failure mode, plus a positive
test for the adapter-matches-config happy path
- Adds an autouse `_default_langgraph_adapter` fixture that
pre-installs a fake adapter via sys.modules monkey-patching, so
existing tests building default WorkspaceConfig (runtime="langgraph")
inherit a valid adapter without each test setting ADAPTER_MODULE
- Failure-mode tests opt out of the default fixture via
@pytest.mark.no_default_adapter (registered in pytest.ini)
- Sentinel pattern (`_UNSET = object()`) for `name_returns` so None
is a passable test value (otherwise `is not None` would skip the
None branch — exact bug the sentinel avoids)
Verification:
- 22/22 preflight tests pass (was 16; +6 new failure-path tests)
- 1256/1256 workspace pytest pass (was 1251; +5 net)
- No production code path other than preflight changed
Source: 2026-04-27 #87 cleanup audit after PR #2154 (wedge extraction).
This change is independent of the cli_executor.py template moves
(task #122) — completes one of the two remaining cleanup items.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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