chore: import upstream snapshot with attribution

scripts/bench_selfdev_build.sh

@@ -0,0 +1,116 @@
+#!/usr/bin/env bash
+# Repeatable self-dev build benchmark (issue #392, part C).
+#
+# Measures the wall-clock cost of the selfdev build paths that matter day to
+# day, so build-pipeline changes are hill-climbable:
+#
+#   1. warm no-op        - rebuild with zero changes on the same commit
+#   2. leaf touch        - 1-line change in the root `jcode` bin crate
+#   3. tui touch         - 1-line change in jcode-tui (largest UI crate)
+#   4. core touch        - 1-line change in jcode-app-core (mid-stack crate)
+#   5. commit blast      - simulate HEAD moving (JCODE_BUILD_GIT_HASH change),
+#                          which reruns jcode-build-meta's build script and
+#                          recompiles every crate that depends on it
+#                          (base, app-core, tui, setup-hints, telemetry-core, root)
+#
+# Touches are reverted after each run. Requires a clean-enough tree that
+# `scripts/dev_cargo.sh build --profile selfdev -p jcode --bin jcode` succeeds.
+#
+# Usage: scripts/bench_selfdev_build.sh [--skip-warmup]
+
+set -euo pipefail
+
+repo_root="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")/.." && pwd)"
+cd "$repo_root"
+
+build_cmd=(scripts/dev_cargo.sh build --profile selfdev -p jcode --bin jcode)
+
+run_build() {
+    # Per-phase logs survive later phases, so a mid-benchmark failure (often a
+    # concurrent agent breaking the shared tree) stays diagnosable.
+    local label="$1"
+    local log="/tmp/bench_selfdev_build_${label}.log"
+    local start end elapsed
+    start=$(date +%s.%N)
+    if ! "${build_cmd[@]}" >"$log" 2>&1; then
+        echo "  ${label}: BUILD FAILED (see ${log})"
+        return 1
+    fi
+    end=$(date +%s.%N)
+    elapsed=$(echo "$end $start" | awk '{printf "%.1f", $1 - $2}')
+    echo "  ${label}: ${elapsed}s"
+}
+
+touch_file() {
+    # Append and immediately strip a trailing comment marker so the file
+    # content changes (mtime + hash) without altering semantics.
+    local file="$1"
+    printf '\n// bench_selfdev_build touch\n' >> "$file"
+}
+
+revert_file() {
+    local file="$1"
+    # Remove the exact marker we appended (plus its preceding blank line).
+    python3 - "$file" << 'EOF'
+import sys
+path = sys.argv[1]
+with open(path) as fh:
+    content = fh.read()
+marker = "\n// bench_selfdev_build touch\n"
+if content.endswith(marker):
+    content = content[: -len(marker)]
+with open(path, "w") as fh:
+    fh.write(content)
+EOF
+}
+
+echo "selfdev build benchmark ($(git rev-parse --short HEAD), $(nproc) cpus)"
+echo "command: ${build_cmd[*]}"
+echo
+
+if [[ "${1:-}" != "--skip-warmup" ]]; then
+    echo "warmup (populate incremental caches)..."
+    run_build "warmup" || exit 1
+    echo
+fi
+
+echo "1. warm no-op (same commit, no changes):"
+run_build "no-op"
+
+leaf_file="src/main.rs"
+echo "2. leaf touch (${leaf_file}):"
+touch_file "$leaf_file"
+run_build "leaf" || true
+revert_file "$leaf_file"
+
+tui_file="crates/jcode-tui/src/lib.rs"
+echo "3. tui touch (${tui_file}):"
+touch_file "$tui_file"
+run_build "tui" || true
+revert_file "$tui_file"
+
+core_file="crates/jcode-app-core/src/lib.rs"
+echo "4. core touch (${core_file}):"
+touch_file "$core_file"
+run_build "core" || true
+revert_file "$core_file"
+
+echo "5. commit blast radius (simulated HEAD move via JCODE_BUILD_GIT_HASH):"
+fake_hash="bench$(date +%s | tail -c 4)"
+start=$(date +%s.%N)
+if JCODE_BUILD_GIT_HASH="$fake_hash" "${build_cmd[@]}" >/tmp/bench_selfdev_build_commit-blast.log 2>&1; then
+    end=$(date +%s.%N)
+    echo "$end $start" | awk '{printf "  commit-blast: %.1fs\n", $1 - $2}'
+else
+    echo "  commit-blast: BUILD FAILED (see /tmp/bench_selfdev_build_commit-blast.log)"
+fi
+echo "  (restoring real-hash build so the next selfdev build is warm)"
+run_build "restore" || true
+
+echo
+echo "done. Interpretation:"
+echo "  - no-op should be a few seconds (cargo fingerprinting + link check)."
+echo "  - leaf/tui/core touches show per-crate recompile + link cost."
+echo "  - commit-blast shows the cost every commit pays because"
+echo "    jcode-build-meta embeds GIT_HASH via env! and jcode-base/app-core/"
+echo "    tui/setup-hints/telemetry-core all depend on it."