diff --git a/src/buildcompiler/api/__init__.py b/src/buildcompiler/api/__init__.py
index 3eb0c63..fc04f2b 100644
--- a/src/buildcompiler/api/__init__.py
+++ b/src/buildcompiler/api/__init__.py
@@ -1,5 +1,6 @@
-"""Public API contracts and options for BuildCompiler."""
+"""Public API contracts, options, and compiler facade for BuildCompiler."""
 
+from .compiler import BuildCompiler, full_build
 from .options import (
     ApprovalOptions,
     BuildOptions,
@@ -16,6 +17,7 @@
 )
 
 __all__ = [
+    "BuildCompiler",
     "ApprovalOptions",
     "BuildOptions",
     "CombinatorialOptions",
@@ -28,4 +30,5 @@
     "ReagentOptions",
     "ReportingOptions",
     "SelectionOptions",
+    "full_build",
 ]
diff --git a/src/buildcompiler/api/compiler.py b/src/buildcompiler/api/compiler.py
new file mode 100644
index 0000000..2823293
--- /dev/null
+++ b/src/buildcompiler/api/compiler.py
@@ -0,0 +1,115 @@
+"""Public BuildCompiler API skeleton."""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import Any
+
+from .options import BuildOptions
+
+
+@dataclass
+class BuildCompiler:
+    """Lightweight dependency-injected compiler facade."""
+
+    inventory: Any = None
+    sbol_document: Any = None
+    planner: Any = None
+    executor: Any = None
+    adapters: Any = None
+    options: BuildOptions = field(default_factory=BuildOptions)
+
+    @classmethod
+    def from_synbiohub(
+        cls,
+        *,
+        collections: list[str] | None = None,
+        sbh_registry: str | None = None,
+        auth_token: str | None = None,
+        sbol_doc: Any = None,
+        options: BuildOptions | None = None,
+        **kwargs: Any,
+    ) -> "BuildCompiler":
+        """Factory boundary reserved for future SynBioHub loading/indexing."""
+        if collections:
+            raise NotImplementedError(
+                "Automatic SynBioHub collection loading/indexing is not implemented yet. "
+                "Inject inventory dependencies directly for now."
+            )
+
+        return cls(
+            sbol_document=sbol_doc,
+            options=options or BuildOptions(),
+            **kwargs,
+        )
+
+    def plan(self, abstract_designs: Any, options: BuildOptions | None = None) -> Any:
+        """Plan a build request via injected planner (placeholder in skeleton)."""
+        if self.planner is None:
+            raise NotImplementedError(
+                "Build planning is not implemented in the API skeleton. "
+                "Inject a planner dependency to use BuildCompiler.plan()."
+            )
+
+        effective_options = options or self.options
+        return self.planner.plan(abstract_designs, options=effective_options)
+
+    def execute(self, plan: Any, options: BuildOptions | None = None) -> Any:
+        """Execute a build plan via injected executor (placeholder in skeleton)."""
+        if self.executor is None:
+            raise NotImplementedError(
+                "Build execution is not implemented in the API skeleton. "
+                "Inject an executor dependency to use BuildCompiler.execute()."
+            )
+
+        effective_options = options or self.options
+        return self.executor.execute(plan, options=effective_options)
+
+    def full_build(self, abstract_designs: Any, options: BuildOptions | None = None) -> Any:
+        """Convenience skeleton method: plan then execute."""
+        plan = self.plan(abstract_designs, options=options)
+        return self.execute(plan, options=options)
+
+
+def full_build(
+    abstract_designs: Any,
+    *,
+    inventory: Any = None,
+    sbol_document: Any = None,
+    planner: Any = None,
+    executor: Any = None,
+    adapters: Any = None,
+    options: BuildOptions | None = None,
+    collections: list[str] | None = None,
+    sbh_registry: str | None = None,
+    auth_token: str | None = None,
+    sbol_doc: Any = None,
+    **kwargs: Any,
+) -> Any:
+    """Module-level full-build entry point for the public API skeleton."""
+    compiler_options = options or BuildOptions()
+
+    if collections is not None or sbh_registry is not None or auth_token is not None or sbol_doc is not None:
+        compiler = BuildCompiler.from_synbiohub(
+            collections=collections,
+            sbh_registry=sbh_registry,
+            auth_token=auth_token,
+            sbol_doc=sbol_doc,
+            options=compiler_options,
+            inventory=inventory,
+            planner=planner,
+            executor=executor,
+            adapters=adapters,
+            **kwargs,
+        )
+    else:
+        compiler = BuildCompiler(
+            inventory=inventory,
+            planner=planner,
+            executor=executor,
+            adapters=adapters,
+            options=compiler_options,
+            **kwargs,
+        )
+
+    return compiler.full_build(abstract_designs, options=compiler_options)
diff --git a/tests/unit/api/test_compiler_api.py b/tests/unit/api/test_compiler_api.py
new file mode 100644
index 0000000..23a34d6
--- /dev/null
+++ b/tests/unit/api/test_compiler_api.py
@@ -0,0 +1,132 @@
+import sys
+
+import pytest
+
+from buildcompiler.api import BuildCompiler, BuildOptions, full_build
+
+
+class FakePlanner:
+    def __init__(self):
+        self.calls = []
+
+    def plan(self, abstract_designs, *, options):
+        self.calls.append((abstract_designs, options))
+        return {"plan": abstract_designs, "options": options}
+
+
+class FakeExecutor:
+    def __init__(self):
+        self.calls = []
+
+    def execute(self, plan, *, options):
+        self.calls.append((plan, options))
+        return {"result": plan, "options": options}
+
+
+def test_import_smoke():
+    assert BuildCompiler is not None
+    assert full_build is not None
+    assert BuildOptions is not None
+
+
+def test_constructor_defaults_and_injected_dependencies():
+    compiler = BuildCompiler()
+    assert compiler.inventory is None
+    assert compiler.sbol_document is None
+    assert compiler.planner is None
+    assert compiler.executor is None
+    assert compiler.adapters is None
+    assert isinstance(compiler.options, BuildOptions)
+
+    inventory = object()
+    sbol_document = object()
+    planner = object()
+    executor = object()
+    adapters = object()
+
+    injected = BuildCompiler(
+        inventory=inventory,
+        sbol_document=sbol_document,
+        planner=planner,
+        executor=executor,
+        adapters=adapters,
+    )
+
+    assert injected.inventory is inventory
+    assert injected.sbol_document is sbol_document
+    assert injected.planner is planner
+    assert injected.executor is executor
+    assert injected.adapters is adapters
+
+
+def test_api_import_does_not_load_optional_automation_modules():
+    assert "pudupy" not in sys.modules
+    assert "opentrons" not in sys.modules
+    assert "SBOLInventory" not in sys.modules
+
+
+def test_from_synbiohub_placeholder_without_collection_loading():
+    compiler = BuildCompiler.from_synbiohub(
+        collections=[],
+        sbh_registry=None,
+        auth_token=None,
+        sbol_doc=None,
+    )
+    assert isinstance(compiler, BuildCompiler)
+
+
+def test_from_synbiohub_raises_when_collection_loading_is_requested():
+    with pytest.raises(NotImplementedError, match="collection loading/indexing"):
+        BuildCompiler.from_synbiohub(collections=["https://example.org/collection"])
+
+
+def test_plan_execute_raise_without_injected_dependencies():
+    compiler = BuildCompiler()
+    with pytest.raises(NotImplementedError, match="planning"):
+        compiler.plan({"x": 1})
+
+    with pytest.raises(NotImplementedError, match="execution"):
+        compiler.execute({"plan": 1})
+
+
+def test_plan_execute_full_build_delegate_to_injected_dependencies():
+    planner = FakePlanner()
+    executor = FakeExecutor()
+    options = BuildOptions()
+    compiler = BuildCompiler(planner=planner, executor=executor, options=options)
+
+    plan = compiler.plan("design")
+    result = compiler.execute(plan)
+    full = compiler.full_build("design")
+
+    assert plan["plan"] == "design"
+    assert result["result"]["plan"] == "design"
+    assert full["result"]["plan"] == "design"
+    assert planner.calls
+    assert executor.calls
+
+
+def test_module_level_full_build_uses_lightweight_constructor_path():
+    planner = FakePlanner()
+    executor = FakeExecutor()
+
+    result = full_build("design", planner=planner, executor=executor)
+
+    assert result["result"]["plan"] == "design"
+
+
+def test_module_level_full_build_uses_synbiohub_factory_path_when_requested():
+    planner = FakePlanner()
+    executor = FakeExecutor()
+
+    result = full_build(
+        "design",
+        planner=planner,
+        executor=executor,
+        collections=[],
+        sbh_registry=None,
+        auth_token=None,
+        sbol_doc=None,
+    )
+
+    assert result["result"]["plan"] == "design"