diff --git a/scripts/build_runtime_package.py b/scripts/build_runtime_package.py
index 910ea691..e6977e52 100755
--- a/scripts/build_runtime_package.py
+++ b/scripts/build_runtime_package.py
@@ -78,6 +78,7 @@ TOP_LEVEL_MODULES = {
     "prompt",
     "runtime_wedge",
     "shared_runtime",
+    "smoke_mode",
     "transcript_auth",
     "watcher",
 }
diff --git a/workspace/main.py b/workspace/main.py
index 093860c2..356080f3 100644
--- a/workspace/main.py
+++ b/workspace/main.py
@@ -136,6 +136,20 @@ async def main():  # pragma: no cover
         await adapter.setup(adapter_config)
         executor = await adapter.create_executor(adapter_config)
 
+        # 5a. Boot-smoke short-circuit (issue #2275): if MOLECULE_SMOKE_MODE
+        # is set, exercise the executor's full import tree by calling
+        # execute() once with stub deps + a short timeout. Skips platform
+        # registration + uvicorn entirely. Returns process exit code.
+        from smoke_mode import is_smoke_mode, run_executor_smoke
+        if is_smoke_mode():
+            exit_code = await run_executor_smoke(executor)
+            if hasattr(heartbeat, "stop"):
+                try:
+                    await heartbeat.stop()
+                except Exception:  # noqa: BLE001
+                    pass
+            raise SystemExit(exit_code)
+
         # 5b. Restore from pre-stop snapshot if one exists (GH#1391).
         # The snapshot is scrubbed before being written, so secrets are
         # already redacted — restore_state must not re-expose them.
diff --git a/workspace/smoke_mode.py b/workspace/smoke_mode.py
new file mode 100644
index 00000000..773e0cbe
--- /dev/null
+++ b/workspace/smoke_mode.py
@@ -0,0 +1,140 @@
+"""Boot smoke mode — exercises the executor's full import tree without touching real platforms.
+
+Why this exists (issue #2275): the existing `wheel_smoke.py` only IMPORTS
+`molecule_runtime.main` at module scope. Lazy imports buried inside
+`async def execute(...)` bodies (e.g. `from a2a.types import FilePart`)
+NEVER evaluate at static-import time — they crash at first message
+delivery in production.
+
+The 2026-04-2x v0→v1 a2a-sdk migration shipped 5 such regressions in
+templates that all looked fine at module-load smoke. This module fills
+the gap by actually invoking `executor.execute(stub_ctx, stub_queue)`
+once with a short timeout. If the import-tree is healthy the call
+proceeds far enough to hit a network boundary (LLM call, etc.) and
+times out — that's a *pass*. If a lazy import is broken, the call
+raises `ImportError` / `ModuleNotFoundError` from inside the executor
+body — that's a *fail*.
+
+Activated by setting `MOLECULE_SMOKE_MODE=1` in the env. Wired into
+`main.py` after `executor = await adapter.create_executor(...)` so the
+full adapter setup path runs first; the smoke just adds one more
+exercise step before exit.
+
+CI usage (intended for `molecule-ci/.github/workflows/publish-template-image.yml`):
+  docker run --rm \
+    -e WORKSPACE_ID=fake -e MOLECULE_SMOKE_MODE=1 \
+    "$IMAGE" molecule-runtime
+"""
+from __future__ import annotations
+
+import asyncio
+import logging
+import os
+import sys
+from typing import Any
+
+logger = logging.getLogger(__name__)
+
+
+_SMOKE_TIMEOUT_SECS = float(os.environ.get("MOLECULE_SMOKE_TIMEOUT_SECS", "5.0"))
+
+
+def is_smoke_mode() -> bool:
+    """True iff MOLECULE_SMOKE_MODE is set to a truthy value.
+
+    Recognises the standard truthy strings (`1`, `true`, `yes`,
+    case-insensitive). An unset / empty / `0` env reads as False so
+    the boot path takes the normal branch in production.
+    """
+    raw = os.environ.get("MOLECULE_SMOKE_MODE", "").strip().lower()
+    return raw in ("1", "true", "yes", "on")
+
+
+def _build_stub_context() -> tuple[Any, Any]:
+    """Build a (RequestContext, EventQueue) pair stuffed with a minimal
+    text message ("smoke test"). The Message is enough that
+    `extract_message_text(context)` returns non-empty input, so the
+    executor takes the "real" branch (not the empty-input early-exit)
+    and exercises any lazy imports along that path.
+
+    Imports happen at function scope so smoke_mode.py itself doesn't
+    pull a2a-sdk into every consumer of the runtime — the wheel still
+    boots without smoke mode active.
+    """
+    from a2a.helpers import new_text_message
+    from a2a.server.agent_execution import RequestContext
+    from a2a.server.context import ServerCallContext
+    from a2a.server.events import EventQueue
+    from a2a.types import SendMessageRequest
+
+    message = new_text_message("smoke test")
+    call_ctx = ServerCallContext()
+    request = SendMessageRequest(message=message)
+    context = RequestContext(call_ctx, request=request)
+    queue = EventQueue()
+    return context, queue
+
+
+async def run_executor_smoke(executor: Any) -> int:
+    """Invoke executor.execute() once with stub deps. Return an exit code.
+
+    Returns:
+      0 — import tree healthy. Either execution timed out (the
+          expected outcome — we hit a network boundary like an LLM
+          call) or completed cleanly. Either way, no broken imports.
+      1 — broken lazy import detected. Re-raised as a clear log line
+          so the publish gate's stderr captures the offending symbol.
+
+    The 5-second timeout comes from `MOLECULE_SMOKE_TIMEOUT_SECS` env
+    (default 5.0). Bump it via env if a slow adapter setup overlaps the
+    first execute call. Don't make it too long — the publish workflow
+    multiplies this across N templates.
+    """
+    print(
+        f"[smoke-mode] invoking executor.execute(stub_ctx, stub_queue) "
+        f"with {_SMOKE_TIMEOUT_SECS:.1f}s timeout to exercise lazy imports"
+    )
+
+    try:
+        context, queue = _build_stub_context()
+    except Exception as build_err:  # noqa: BLE001
+        # If we can't even build the stub, the a2a-sdk import path is
+        # broken — that's exactly the regression class this gate exists
+        # for. Treat as a smoke failure.
+        print(
+            f"[smoke-mode] FAIL: stub-context build raised "
+            f"{type(build_err).__name__}: {build_err}",
+            file=sys.stderr,
+        )
+        return 1
+
+    try:
+        await asyncio.wait_for(
+            executor.execute(context, queue),
+            timeout=_SMOKE_TIMEOUT_SECS,
+        )
+    except (asyncio.TimeoutError, asyncio.CancelledError):
+        # Timeout = imports healthy, execution was proceeding and hit
+        # a network boundary or long await. Pass.
+        print("[smoke-mode] PASS: timed out past import-tree (imports healthy)")
+        return 0
+    except (ImportError, ModuleNotFoundError) as imp_err:
+        # The exact regression class issue #2275 exists to catch.
+        print(
+            f"[smoke-mode] FAIL: lazy import broken in execute(): "
+            f"{type(imp_err).__name__}: {imp_err}",
+            file=sys.stderr,
+        )
+        return 1
+    except Exception as other_err:  # noqa: BLE001
+        # Anything else (auth errors, validation errors, runtime bugs)
+        # is downstream of the import gate. Pass — these are caught by
+        # the relevant adapter-level tests, not by this smoke.
+        print(
+            f"[smoke-mode] PASS: execute() raised "
+            f"{type(other_err).__name__} past import-tree (not an import error)"
+        )
+        return 0
+    else:
+        print("[smoke-mode] PASS: execute() completed within timeout (imports + body OK)")
+        return 0
diff --git a/workspace/tests/test_smoke_mode.py b/workspace/tests/test_smoke_mode.py
new file mode 100644
index 00000000..10edbe30
--- /dev/null
+++ b/workspace/tests/test_smoke_mode.py
@@ -0,0 +1,190 @@
+"""Tests for smoke_mode — the executor-stub boot smoke (issue #2275).
+
+These tests exercise the helper module directly. The end-to-end path
+(main.py invoking run_executor_smoke + sys.exit) is not unit-tested
+here because main() is `# pragma: no cover` and integration-shaped;
+that path is covered by the publish-template-image.yml smoke step
+(which is the production gate this helper exists for).
+
+Note on a2a-sdk: conftest.py stubs out a2a.* modules with minimal
+shims that don't include `a2a.server.context.ServerCallContext` or
+`a2a.types.SendMessageRequest` (the real-SDK-only symbols
+_build_stub_context needs). Tests that want to verify the
+`run_executor_smoke` control flow patch _build_stub_context to
+sidestep the real construction; tests that NEED the real SDK
+construction skip when those symbols aren't reachable.
+"""
+from __future__ import annotations
+
+import asyncio
+from unittest.mock import patch
+
+import pytest
+
+import smoke_mode
+
+
+def _real_a2a_sdk_available() -> bool:
+    """True when the real a2a-sdk types needed by _build_stub_context
+    are importable. The conftest's a2a stubs intentionally don't
+    include these — they're only present in the published wheel's
+    runtime env or when a2a-sdk is installed alongside the test."""
+    try:
+        from a2a.server.context import ServerCallContext  # noqa: F401
+        from a2a.types import SendMessageRequest  # noqa: F401
+        return True
+    except (ImportError, AttributeError):
+        return False
+
+
+# ─── is_smoke_mode ─────────────────────────────────────────────────────
+
+
+@pytest.mark.parametrize("env_value", ["1", "true", "yes", "on", "TRUE", "Yes", "ON"])
+def test_is_smoke_mode_truthy_values(env_value: str, monkeypatch: pytest.MonkeyPatch):
+    monkeypatch.setenv("MOLECULE_SMOKE_MODE", env_value)
+    assert smoke_mode.is_smoke_mode() is True
+
+
+@pytest.mark.parametrize("env_value", ["0", "false", "no", "off", "", "  "])
+def test_is_smoke_mode_falsy_values(env_value: str, monkeypatch: pytest.MonkeyPatch):
+    monkeypatch.setenv("MOLECULE_SMOKE_MODE", env_value)
+    assert smoke_mode.is_smoke_mode() is False
+
+
+def test_is_smoke_mode_unset(monkeypatch: pytest.MonkeyPatch):
+    monkeypatch.delenv("MOLECULE_SMOKE_MODE", raising=False)
+    assert smoke_mode.is_smoke_mode() is False
+
+
+# ─── _build_stub_context (real-SDK-only) ───────────────────────────────
+
+
+@pytest.mark.skipif(
+    not _real_a2a_sdk_available(),
+    reason="conftest stubs a2a.* without ServerCallContext / SendMessageRequest; real SDK only",
+)
+def test_build_stub_context_returns_request_context_with_message():
+    """Stub must produce a RequestContext that has a non-empty message
+    payload — otherwise extract_message_text returns empty and the
+    executor takes the early-exit branch instead of exercising the
+    full import tree."""
+    context, _queue = smoke_mode._build_stub_context()
+    assert context.message is not None
+    parts = context.message.parts
+    assert len(parts) == 1
+    assert parts[0].text == "smoke test"
+
+
+@pytest.mark.skipif(
+    not _real_a2a_sdk_available(),
+    reason="conftest stubs a2a.* without ServerCallContext / SendMessageRequest; real SDK only",
+)
+def test_build_stub_context_returns_event_queue():
+    from a2a.server.events import EventQueue
+    _, queue = smoke_mode._build_stub_context()
+    assert isinstance(queue, EventQueue)
+
+
+# ─── run_executor_smoke — control flow with stubbed context ────────────
+#
+# These tests patch _build_stub_context to return sentinel objects, so
+# they don't depend on the real a2a-sdk being present. The executor
+# stubs ignore ctx + queue.
+
+
+class _RaisingExecutor:
+    def __init__(self, exc: Exception):
+        self._exc = exc
+
+    async def execute(self, context, event_queue) -> None:  # noqa: ARG002
+        raise self._exc
+
+
+class _BlockingExecutor:
+    """Simulates an LLM network call that the smoke timeout cuts short."""
+
+    async def execute(self, context, event_queue) -> None:  # noqa: ARG002
+        await asyncio.Event().wait()
+
+
+class _CleanExecutor:
+    async def execute(self, context, event_queue) -> None:  # noqa: ARG002
+        return None
+
+
+@pytest.fixture
+def stub_build():
+    """Replace _build_stub_context with a no-op so execute() gets
+    sentinel ctx/queue. Tests can override this fixture's behavior
+    via monkeypatch when they need a different shape."""
+    sentinel_ctx = object()
+    sentinel_queue = object()
+    with patch.object(
+        smoke_mode, "_build_stub_context",
+        lambda: (sentinel_ctx, sentinel_queue),
+    ):
+        yield
+
+
+@pytest.mark.asyncio
+async def test_smoke_passes_on_timeout(stub_build, monkeypatch: pytest.MonkeyPatch):
+    monkeypatch.setattr(smoke_mode, "_SMOKE_TIMEOUT_SECS", 0.1)
+    code = await smoke_mode.run_executor_smoke(_BlockingExecutor())
+    assert code == 0
+
+
+@pytest.mark.asyncio
+async def test_smoke_passes_on_clean_return(stub_build):
+    code = await smoke_mode.run_executor_smoke(_CleanExecutor())
+    assert code == 0
+
+
+@pytest.mark.asyncio
+async def test_smoke_fails_on_import_error(stub_build):
+    """The exact regression class issue #2275 exists to catch — a lazy
+    import inside execute() that the static smoke missed."""
+    code = await smoke_mode.run_executor_smoke(
+        _RaisingExecutor(ImportError("cannot import name 'FilePart' from 'a2a.types'"))
+    )
+    assert code == 1
+
+
+@pytest.mark.asyncio
+async def test_smoke_fails_on_module_not_found_error(stub_build):
+    code = await smoke_mode.run_executor_smoke(
+        _RaisingExecutor(ModuleNotFoundError("No module named 'temporalio'"))
+    )
+    assert code == 1
+
+
+@pytest.mark.asyncio
+async def test_smoke_passes_on_non_import_runtime_error(stub_build):
+    """Auth errors, validation errors, anything-not-an-import-error
+    pass — those are caught by adapter-level tests, not by this gate."""
+    code = await smoke_mode.run_executor_smoke(
+        _RaisingExecutor(RuntimeError("ANTHROPIC_API_KEY missing"))
+    )
+    assert code == 0
+
+
+@pytest.mark.asyncio
+async def test_smoke_passes_on_value_error(stub_build):
+    code = await smoke_mode.run_executor_smoke(
+        _RaisingExecutor(ValueError("bad config"))
+    )
+    assert code == 0
+
+
+@pytest.mark.asyncio
+async def test_smoke_fails_when_stub_context_build_breaks(monkeypatch: pytest.MonkeyPatch):
+    """If a2a-sdk's own SendMessageRequest / RequestContext can't be
+    constructed (e.g. SDK migration broke the constructor), that's
+    exactly the regression class this gate exists for — fail loud."""
+
+    def _fail_build():
+        raise ImportError("simulated: a2a.types refactored mid-publish")
+
+    monkeypatch.setattr(smoke_mode, "_build_stub_context", _fail_build)
+    code = await smoke_mode.run_executor_smoke(_CleanExecutor())
+    assert code == 1