feat(build-time-versioning): xceadmin generates build-info module

xceadmin/meson.build passes the resolved commit_id/build_time meson
options as two new positional args (matching this custom_target's
existing all-positional style) to meson-build.sh, which writes a small
_build_info.py (GIT_COMMIT/BUILD_TIME, independent per-field "unknown"
fallback) into the mirrored source tree's xceadmin package directory,
before the pip install step -- same before-install ordering as the
existing schema-sync step. A file-existence guard checks the exact path
just written and fails loudly rather than silently proceeding with a
missing/wrong module.

Live-verified via a full real build+test+wheel cycle (run independently
twice, once by implementation and once by review): the mirrored tree's
_build_info.py and the packaged wheel both contain real, matching,
non-"unknown" values (commit id matching git rev-parse --short HEAD plus
dirty suffix, real UTC timestamp); full pytest suite passes (258 passed,
3 skipped -- documented live-HA e2e tests, skip-by-design).

Task 5.1/13 of build-time-versioning.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/xceadmin/meson-build.sh

@@ -22,6 +22,21 @@ REPO_ROOT="$3"     # real repo root (contains ha/, src/)
 PYTHON="$4"        # meson's resolved python3 (import('python').find_installation()),
                     # NOT a bare `python3` PATH lookup -- see meson.build's comment
 STAMP_FILE="$5"
+GIT_COMMIT="$6"    # build-time-versioning task 5.1: get_option('commit_id'),
+                    # resolved by xce-build.sh (task 2.1) -- empty if meson was
+                    # invoked without -Dcommit_id= (e.g. a bare `meson setup`)
+BUILD_TIME="$7"    # build-time-versioning task 5.1: get_option('build_time'), same as above
+
+# Requirement 1.4 / 4.2: never hand the mirrored tree a genuinely empty
+# value -- fall back to the literal "unknown", same empty -> "unknown"
+# discipline as src/tools/go_build's XCE_GIT_COMMIT/XCE_BUILD_TIME handling
+# and src/lib/utils.c's xce_version_field().
+if [ -z "$GIT_COMMIT" ]; then
+    GIT_COMMIT=unknown
+fi
+if [ -z "$BUILD_TIME" ]; then
+    BUILD_TIME=unknown
+fi
 
 SRC_DIR="$REPO_ROOT/src"
 
@@ -52,6 +67,33 @@ cp "$SRC_DIR/schema/controller.capnp" "$SCHEMA_DST/controller.capnp"
 cp "$SRC_DIR/schema/c.capnp" "$SCHEMA_DST/c.capnp"
 cp "$SRC_DIR/configs/schema/"*.schema.json "$SCHEMA_DST/json/"
 
+# build-time-versioning task 5.1: generate the build-info module into the
+# MIRRORED tree's xceadmin package dir (src/xceadmin/, containing cli.py) --
+# never the real, checked-in src/xceadmin/src/xceadmin/ tree, which stays a
+# static "unknown"-only fallback stub (task 5.2, separate). Must land before
+# `pip install` below, same before-install ordering as the schema sync just
+# above, so both the pinned dev-venv install and the wheel built later from
+# this same $WORK_DIR package it.
+BUILD_INFO_DST="$WORK_DIR/src/xceadmin/_build_info.py"
+echo "=== xceadmin (meson): writing generated build-info module ==="
+cat > "$BUILD_INFO_DST" <<EOF
+# Generated by meson-build.sh (build-time-versioning task 5.1) -- do not edit.
+# Overwritten on every meson build; never checked in. See
+# src/xceadmin/src/xceadmin/_build_info.py (task 5.2) for the committed,
+# "unknown"-only fallback stub used by \`pip install -e .\` editable installs,
+# which never run this script.
+GIT_COMMIT = "$GIT_COMMIT"
+BUILD_TIME = "$BUILD_TIME"
+EOF
+
+# Requirement 4.2: never silently proceed to pip install/pytest/wheel-build
+# packaging a fallback-shaped-but-actually-missing module -- confirm the
+# write actually landed in the mirrored tree first and fail loudly if not.
+if [ ! -f "$BUILD_INFO_DST" ]; then
+    echo "ERROR: xceadmin (meson): failed to write generated build-info module to $BUILD_INFO_DST -- refusing to proceed to pip install with a missing/wrong build-info module." >&2
+    exit 1
+fi
+
 echo "=== xceadmin (meson): pinned install into build-dir venv (python: $PYTHON) ==="
 rm -rf "$VENV_DIR"
 "$PYTHON" -m venv --system-site-packages "$VENV_DIR"

src/xceadmin/meson.build

@@ -40,6 +40,16 @@ xceadmin_stamp = custom_target('xceadmin',
     meson.current_source_dir() / '..' / '..',  # repo root (contains ha/, src/)
     python3_prog.full_path(),
     '@OUTPUT@',
+    # build-time-versioning task 5.1: same resolved commit_id/build_time
+    # option values src/meson.build:30-31 (C) and apiserver/xcecli's
+    # meson.build (Go, via XCE_GIT_COMMIT/XCE_BUILD_TIME) already thread
+    # through -- passed here as two more positional args, matching this
+    # custom_target's existing positional (not env-var) style. Empty when
+    # unset (meson.options' default); meson-build.sh is responsible for the
+    # empty -> "unknown" fallback, same discipline as go_build's
+    # XCE_GIT_COMMIT/XCE_BUILD_TIME handling.
+    get_option('commit_id'),
+    get_option('build_time'),
   ],
   build_by_default: true,
   build_always_stale: true,