diff --git a/.kiro/specs/admin-config-tool/tasks.md b/.kiro/specs/admin-config-tool/tasks.md
index 7789769..8abde43 100644
--- a/.kiro/specs/admin-config-tool/tasks.md
+++ b/.kiro/specs/admin-config-tool/tasks.md
@@ -57,7 +57,7 @@
   - _Depends: 2.2_
 
 - [ ] 3. Core: xceadmin CLI orchestration
-- [ ] 3.1 (P) Compile a configs directory into a deployable cluster binary
+- [x] 3.1 (P) Compile a configs directory into a deployable cluster binary
   - Running the build command against a directory of YAML files produces a binary output file with a printed checksum
   - A missing individual YAML file is treated as an empty section, not an error
   - Unrecognized-but-valid YAML fields produce a warning, not a failure
@@ -150,3 +150,4 @@
 - **2.2**: The real `controller.capnp` names its reply struct `RequestReply`, not `Reply` as design.md's postcondition states — an inexact design pseudo-type, corrected empirically (verified directly against `src/schema/controller.capnp`, not assumed). pycapnp 2.0.0/capnproto 1.2.0 abort the whole process (uncaught C++ exception, not a Python exception) on a missing cross-file import or malformed `.capnp` content passed to `capnp.load()` — a bare `try/except` cannot catch this. `xcecommon.schema.load_schema()` works around it by pre-validating in an isolated subprocess before ever calling `capnp.load()` in the caller's own process, converting any abort into a clean `SchemaNotFoundError`. Any future code that calls `capnp.load()` directly (bypassing this loader) reintroduces the crash risk — always go through `xcecommon.schema.load_schema()`.
 - **2.3**: `map_all_sections()` (a `SECTION_MAP`-driven orchestrator, not explicitly named in design.md's Service Interface but consistent with its Contracts) is the single call `xceadmin.build` (task 3.1) needs — it treats a missing YAML file identically to a present-but-empty section (byte-for-byte), satisfying Requirement 1.5 structurally. `target.init(field, 0)` and never touching an empty/absent list field produce *different* serialized bytes for the same logical "nothing here" value (verified empirically) — the mapper always picks "never touch" for byte-determinism (9.1). Calling `.to_bytes()` twice on the same capnp builder triggers a spurious "message already written" `UserWarning` even when no field was mutated between calls — capture the bytes once and reuse them rather than calling `.to_bytes()` again.
 - **2.4**: `errors.py`'s exception subclasses (task 1.2) all take `message` as an explicit first constructor argument in addition to their structured fields (e.g. `ConnectionTimeoutError(message, host, port)`, `ReplyDecodeError(message, reason)`) — design.md's abbreviated `Service Interface` type stubs (`class ConnectionTimeoutError(XceAdminError): host: str; port: int`) read as if only the structured fields were needed; always check the real constructor in `errors.py`, not the design doc's shorthand. `xcecommon.wire` is deliberately opcode-agnostic — `send_request`/`send_frame`/`recv_frame` move raw `bytes` only and never import a capnp type; callers own `.to_bytes()`/`.from_bytes()`. Reused `ha/data/xce.crt`/`xce.key` (the repo's existing dev cert pair, same one `deploy-ha.sh` already copies for controller TLS) as the test fixture for both the TLS test server and the client `cert_dir` — no synthetic cert generation needed.
+- **3.1**: Requirement 1.7's "unrecognized-but-schema-valid field" warning is real and fires on essentially every real build using `src/configs/resources.yaml` — `resources.yaml`'s `type` key is *required* by `resources.schema.json` (`required: [name, type]`) but has no `ClusterConfig` destination (per `xcecommon.mapping`'s documented decision not to guess the `valtype`/`ordtype`/`flags` integer encoding), so every valid resource entry triggers a "field 'type' ... ignored" warning unconditionally, not just for unusual input. This is a disclosed spec tradeoff, not a bug — flagged here so a future pass over `xceadmin.build`'s warning UX (e.g. only warning once per field-name per run instead of once per item) knows the noise is expected, not a regression. `xceadmin.build`'s unmapped-field table (`_UNMAPPED_BUT_VALID_ITEM_KEYS`) was derived by cross-referencing `xcecommon.mapping`'s per-item builder functions against the real `src/configs/schema/*.schema.json` property lists directly (not from prose alone) to avoid drift.
diff --git a/src/xceadmin/src/xceadmin/build.py b/src/xceadmin/src/xceadmin/build.py
new file mode 100644
index 0000000..d26dd5b
--- /dev/null
+++ b/src/xceadmin/src/xceadmin/build.py
@@ -0,0 +1,135 @@
+"""``config build`` orchestration for xceadmin (design.md, ``xceadmin.build``;
+Requirements 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.9, 8.3, 8.4).
+
+Pipeline: scan a configs directory for the 7 known YAML files -> validate
+each present file against its bundled schema -> run the cross-file
+business-rule checks -> map validated data to ``ClusterConfig`` -> return
+the serialized bytes. Unrecognized-but-schema-valid fields and undefined
+cross-references are printed to stderr as warnings, never raised (1.7,
+4.4) -- only schema violations, reserved names, and duplicates are hard
+failures (``ValidationError``/``ReservedNameError``/``DuplicateEntryError``,
+all subclassing ``XceAdminError``).
+
+No ``click``/CLI dependency here -- ``xceadmin.cli`` (task 4.1) is a thin
+wrapper around :func:`build_cluster_config`/:func:`write_output` that owns
+argument parsing and the actual "print SHA-256 to stderr" step (1.4); this
+module's job is the pipeline and its warnings only.
+"""
+
+from __future__ import annotations
+
+import hashlib
+import sys
+from pathlib import Path
+
+from xcecommon import mapping, validation
+
+#: Schema-valid YAML fields that intentionally have no ClusterConfig
+#: destination (design.md's ``xcecommon.mapping`` module docstring,
+#: "Deliberately Unmapped Fields") -- cross-checked field-by-field against
+#: the real bundled JSON schemas (``src/configs/schema/*.schema.json``) so
+#: this table can't silently drift from what schema validation actually
+#: allows. Keyed by SECTION_MAP's ``capnp_field`` (not ``yaml_file``,
+#: since ``hosts.yaml`` feeds two fields with two different item shapes).
+_UNMAPPED_BUT_VALID_ITEM_KEYS: dict[str, frozenset[str]] = {
+    "resources": frozenset({"type", "order", "consumable", "release", "resourcemap"}),
+    "queues": frozenset(
+        {
+            "backfill",
+            "cpulimit",
+            "description",
+            "exclusive",
+            "fairshare",
+            "gpu_req",
+            "job_starter",
+            "memlimit",
+            "nice",
+            "preemption",
+            "rerunable",
+            "reservation",
+            "runlimit",
+            "runtimeest",
+        }
+    ),
+    "hostConfigs": frozenset({"description"}),
+    # ugroups, hgroups, hproviders, limits: every schema-valid key is
+    # mapped (mapping.py docstring) -- no entry needed.
+}
+
+#: The 7 known input filenames, derived from SECTION_MAP rather than
+#: hardcoded a second time -- scanning is closed-set, not an open-ended
+#: directory walk (1.1).
+_KNOWN_YAML_FILES: tuple[str, ...] = tuple(
+    dict.fromkeys(spec["yaml_file"] for spec in mapping.SECTION_MAP)
+)
+
+
+def _warn(message: str) -> None:
+    print(f"warning: {message}", file=sys.stderr)
+
+
+def _warn_unrecognized_fields(sections: dict[str, dict]) -> None:
+    """Requirement 1.7: a field that passes JSON Schema validation but has
+    no ``ClusterConfig`` destination is a warning, not a failure.
+    """
+    for spec in mapping.SECTION_MAP:
+        if spec["kind"] != "list":
+            continue
+        unmapped_keys = _UNMAPPED_BUT_VALID_ITEM_KEYS.get(spec["capnp_field"])
+        if not unmapped_keys:
+            continue
+        schema_name = spec["yaml_file"].removesuffix(".yaml")
+        items = (sections.get(schema_name) or {}).get(spec["yaml_key"]) or []
+        for item in items:
+            present = unmapped_keys & item.keys()
+            for key in sorted(present):
+                item_name = item.get("name") or item.get("hostname") or item.get("groupname")
+                _warn(
+                    f"{spec['yaml_file']}: field '{key}' on '{item_name}' is schema-valid "
+                    f"but has no ClusterConfig destination -- ignored"
+                )
+
+
+def _read_sections(configs_dir: str) -> dict[str, dict]:
+    """Read and validate every present known YAML file. A missing file
+    becomes an empty section, not an error (1.5).
+    """
+    configs_path = Path(configs_dir)
+    sections: dict[str, dict] = {}
+    for yaml_file in _KNOWN_YAML_FILES:
+        file_path = configs_path / yaml_file
+        if not file_path.is_file():
+            continue
+        schema_name = yaml_file.removesuffix(".yaml")
+        sections[schema_name] = validation.validate_yaml(str(file_path), schema_name)
+    return sections
+
+
+def build_cluster_config(configs_dir: str) -> bytes:
+    """Full pipeline: validate all present sections, map to ``ClusterConfig``,
+    serialize. Raises ``ValidationError``/``ReservedNameError``/
+    ``DuplicateEntryError`` on hard failures (all subclass ``XceAdminError``).
+    """
+    sections = _read_sections(configs_dir)
+
+    validation.check_reserved_names(sections)
+    validation.check_duplicates(sections)
+    for warning in validation.check_undefined_refs(sections):
+        _warn(warning)
+    _warn_unrecognized_fields(sections)
+
+    target = mapping.new_cluster_config_builder()
+    mapping.map_all_sections(sections, target)
+    return target.to_bytes()
+
+
+def write_output(data: bytes, output_path: str) -> str:
+    """Write ``data`` to ``output_path`` (``"-"`` means stdout). Returns
+    the hex SHA-256 digest of ``data`` -- printing it (1.4) is the CLI
+    layer's job, not this function's.
+    """
+    if output_path == "-":
+        sys.stdout.buffer.write(data)
+    else:
+        Path(output_path).write_bytes(data)
+    return hashlib.sha256(data).hexdigest()
diff --git a/src/xceadmin/tests/test_config_build.py b/src/xceadmin/tests/test_config_build.py
new file mode 100644
index 0000000..93f850a
--- /dev/null
+++ b/src/xceadmin/tests/test_config_build.py
@@ -0,0 +1,261 @@
+"""Golden-file-style build tests for ``xceadmin.build`` (design.md,
+``xceadmin.build``; Requirements 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.9,
+8.3, 8.4).
+"""
+
+from __future__ import annotations
+
+import hashlib
+from pathlib import Path
+
+import pytest
+import yaml
+
+from xcecommon.errors import DuplicateEntryError, ReservedNameError, ValidationError
+from xcecommon.schema import load_schema
+from xceadmin import build
+
+REPO_CONFIGS_DIR = Path(__file__).resolve().parents[2] / "configs"
+
+
+def _write_yaml(path: Path, data: dict) -> None:
+    path.write_text(yaml.safe_dump(data))
+
+
+# ---------------------------------------------------------------------------
+# 1.1 / 1.5: closed-set scan, missing file -> empty section
+# ---------------------------------------------------------------------------
+
+
+def test_build_missing_all_files_still_succeeds(tmp_path):
+    """Observable (task 2.1's bullet, reused here for build): a configs
+    directory with none of the 7 known files present still builds --
+    every section is empty, not an error.
+    """
+    data = build.build_cluster_config(str(tmp_path))
+    mod = load_schema()
+    with mod.ClusterConfig.from_bytes(data) as reader:
+        assert reader.clusterName == ""
+        assert len(reader.queues) == 0
+
+
+def test_build_ignores_unrecognized_extra_files(tmp_path):
+    (tmp_path / "notes.txt").write_text("not a config file")
+    (tmp_path / "schema").mkdir()  # an operator-supplied schema/ dir -- ignored (1.6)
+    (tmp_path / "schema" / "queues.schema.json").write_text("{}")
+
+    data = build.build_cluster_config(str(tmp_path))
+    assert isinstance(data, bytes)
+
+
+def test_build_missing_one_file_matches_present_empty_section(tmp_path):
+    _write_yaml(tmp_path / "xce.yaml", {"cluster_name": "c1", "heartbeat_interval": 5,
+                                         "inactive_heartbeat_count": 2})
+    without_resources = build.build_cluster_config(str(tmp_path))
+
+    _write_yaml(tmp_path / "resources.yaml", {"resources": []})
+    with_empty_resources = build.build_cluster_config(str(tmp_path))
+
+    assert without_resources == with_empty_resources
+
+
+# ---------------------------------------------------------------------------
+# 1.9 / determinism: same input twice -> identical bytes
+# ---------------------------------------------------------------------------
+
+
+def test_build_same_input_twice_is_byte_identical(tmp_path):
+    _write_yaml(tmp_path / "xce.yaml", {"cluster_name": "eda1", "heartbeat_interval": 30,
+                                         "inactive_heartbeat_count": 3})
+    _write_yaml(tmp_path / "queues.yaml", {"queues": [{"name": "normal", "priority": 30}]})
+
+    first = build.build_cluster_config(str(tmp_path))
+    second = build.build_cluster_config(str(tmp_path))
+    assert first == second
+
+
+# ---------------------------------------------------------------------------
+# Hard failures propagate (schema violation, reserved name, duplicates)
+# ---------------------------------------------------------------------------
+
+
+def test_build_raises_validation_error_on_schema_violation(tmp_path):
+    _write_yaml(tmp_path / "queues.yaml", {"queues": [{"priority": 30}]})  # missing "name"
+
+    with pytest.raises(ValidationError):
+        build.build_cluster_config(str(tmp_path))
+
+
+def test_build_raises_reserved_name_error(tmp_path):
+    _write_yaml(tmp_path / "queues.yaml", {"queues": [{"name": "lost_and_found", "priority": 1}]})
+
+    with pytest.raises(ReservedNameError):
+        build.build_cluster_config(str(tmp_path))
+
+
+def test_build_raises_duplicate_entry_error(tmp_path):
+    _write_yaml(
+        tmp_path / "queues.yaml",
+        {"queues": [{"name": "dup", "priority": 1}, {"name": "dup", "priority": 2}]},
+    )
+
+    with pytest.raises(DuplicateEntryError):
+        build.build_cluster_config(str(tmp_path))
+
+
+# ---------------------------------------------------------------------------
+# 1.7: unrecognized-but-schema-valid fields warn, never fail
+# ---------------------------------------------------------------------------
+
+
+def test_build_warns_not_fails_on_schema_valid_unmapped_resource_fields(tmp_path, capsys):
+    _write_yaml(
+        tmp_path / "resources.yaml",
+        {
+            "resources": [
+                {
+                    "name": "gpus",
+                    "type": "numeric",
+                    "order": "increase",
+                    "consumable": True,
+                    "release": False,
+                }
+            ]
+        },
+    )
+
+    data = build.build_cluster_config(str(tmp_path))  # must not raise
+
+    mod = load_schema()
+    with mod.ClusterConfig.from_bytes(data) as reader:
+        assert reader.resources[0].name == "gpus"
+
+    stderr = capsys.readouterr().err
+    assert "resources.yaml" in stderr
+    assert "'type'" in stderr
+    assert "'order'" in stderr
+    assert "'consumable'" in stderr
+    assert "'release'" in stderr
+    assert "gpus" in stderr
+
+
+def test_build_warns_on_schema_valid_unmapped_queue_fields(tmp_path, capsys):
+    _write_yaml(
+        tmp_path / "queues.yaml",
+        {"queues": [{"name": "night", "priority": 30, "nice": 10, "fairshare": [{"user": "u1", "share": 5}]}]},
+    )
+
+    build.build_cluster_config(str(tmp_path))
+
+    stderr = capsys.readouterr().err
+    assert "'nice'" in stderr
+    assert "'fairshare'" in stderr
+    assert "night" in stderr
+
+
+def test_build_warns_on_schema_valid_unmapped_host_description(tmp_path, capsys):
+    _write_yaml(
+        tmp_path / "hosts.yaml",
+        {"hosts": [{"hostname": "h1", "description": "a worker node"}], "hostgroups": []},
+    )
+
+    build.build_cluster_config(str(tmp_path))
+
+    stderr = capsys.readouterr().err
+    assert "'description'" in stderr
+    assert "h1" in stderr
+
+
+def test_build_no_warnings_when_only_mapped_fields_present(tmp_path, capsys):
+    _write_yaml(tmp_path / "scaler.yaml", {"scalers": [{"name": "s1", "type": "script", "script_path": "/x.sh"}]})
+
+    build.build_cluster_config(str(tmp_path))
+
+    assert capsys.readouterr().err == ""
+
+
+# ---------------------------------------------------------------------------
+# 4.4 undefined-ref warnings surface without blocking the build
+# ---------------------------------------------------------------------------
+
+
+def test_build_surfaces_undefined_ref_warnings_without_failing(tmp_path, capsys):
+    _write_yaml(
+        tmp_path / "queues.yaml",
+        {"queues": [{"name": "q1", "priority": 1, "hosts": {"members": ["nonexistent_hg"]}}]},
+    )
+    _write_yaml(tmp_path / "hosts.yaml", {"hosts": [], "hostgroups": []})
+
+    data = build.build_cluster_config(str(tmp_path))  # must not raise
+    assert isinstance(data, bytes)
+
+    stderr = capsys.readouterr().err
+    assert "nonexistent_hg" in stderr
+
+
+# ---------------------------------------------------------------------------
+# Real src/configs/*.yaml fixtures
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.skipif(not REPO_CONFIGS_DIR.is_dir(), reason="src/configs/ fixtures not present")
+def test_build_real_repo_configs_succeeds_and_warns_on_known_gaps(capsys):
+    data = build.build_cluster_config(str(REPO_CONFIGS_DIR))
+
+    mod = load_schema()
+    with mod.ClusterConfig.from_bytes(data) as reader:
+        assert reader.clusterName == "eda1"
+
+    # src/configs/hosts.yaml has 2 pre-existing undefined refs (resource
+    # "mg", host "h3" -- see task 2.1's Implementation Notes) and every
+    # resources.yaml entry has a schema-required "type" field with no
+    # ClusterConfig destination -- both are expected warnings, not errors.
+    stderr = capsys.readouterr().err
+    assert "warning:" in stderr
+
+
+@pytest.mark.skipif(not REPO_CONFIGS_DIR.is_dir(), reason="src/configs/ fixtures not present")
+def test_write_output_real_repo_configs_hash_matches_manual_sha256(tmp_path):
+    data = build.build_cluster_config(str(REPO_CONFIGS_DIR))
+    out_path = tmp_path / "cluster.bin"
+
+    digest = build.write_output(data, str(out_path))
+
+    assert out_path.read_bytes() == data
+    assert digest == hashlib.sha256(data).hexdigest()
+
+
+# ---------------------------------------------------------------------------
+# write_output(): file path, stdout, and hash correctness
+# ---------------------------------------------------------------------------
+
+
+def test_write_output_writes_file_and_returns_correct_hash(tmp_path):
+    data = b"some cluster.bin bytes"
+    out_path = tmp_path / "out.bin"
+
+    digest = build.write_output(data, str(out_path))
+
+    assert out_path.read_bytes() == data
+    assert digest == hashlib.sha256(data).hexdigest()
+
+
+def test_write_output_dash_writes_to_stdout_buffer(capsys):
+    data = b"stdout-bound bytes"
+
+    digest = build.write_output(data, "-")
+
+    captured = capsys.readouterr()
+    assert captured.out.encode() == data
+    assert digest == hashlib.sha256(data).hexdigest()
+
+
+def test_write_output_does_not_print_the_hash_itself(tmp_path, capsys):
+    """1.4's "print SHA-256 to stderr" is the CLI layer's job (task 4.1) --
+    write_output only returns the digest, it never prints anything.
+    """
+    data = b"quiet"
+    build.write_output(data, str(tmp_path / "out.bin"))
+
+    captured = capsys.readouterr()
+    assert captured.err == ""