bench: add /usr/bin/time -v wrapper and parser

bench/fixtures/time-sample.txt

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+	Command being timed: "sh -c sleep 0.05"
+	User time (seconds): 0.00
+	System time (seconds): 0.00
+	Percent of CPU this job got: 1%
+	Elapsed (wall clock) time (h:mm:ss or m:ss): 0:00.05
+	Average shared text size (kbytes): 0
+	Average unshared data size (kbytes): 0
+	Average stack size (kbytes): 0
+	Average total size (kbytes): 0
+	Maximum resident set size (kbytes): 2944
+	Average resident set size (kbytes): 0
+	Major (requiring I/O) page faults: 0
+	Minor (reclaiming a frame) page faults: 117
+	Voluntary context switches: 5
+	Involuntary context switches: 1
+	Swaps: 0
+	File system inputs: 0
+	File system outputs: 0
+	Socket messages sent: 0
+	Socket messages received: 0
+	Signals delivered: 0
+	Page size (bytes): 4096
+	Exit status: 0

bench/lib/time.sh

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+#!/usr/bin/env bash
+# /usr/bin/time -v wrapper and parser.
+
+time_run() {
+    local out_txt="$1" cmd="$2"
+    /usr/bin/time -v -o "$out_txt" sh -c "$cmd"
+}
+
+# Parse a /usr/bin/time -v output file into a JSON object.
+# Fields that don't appear in the input become null.
+time_parse_v() {
+    local file="$1"
+    awk '
+    BEGIN {
+        keys["peak_rss_kb"] = "null"
+        keys["user_seconds"] = "null"
+        keys["sys_seconds"] = "null"
+        keys["wall_seconds"] = "null"
+        keys["voluntary_ctx_switches"] = "null"
+        keys["involuntary_ctx_switches"] = "null"
+        keys["major_page_faults"] = "null"
+        keys["minor_page_faults"] = "null"
+        keys["fs_inputs"] = "null"
+        keys["fs_outputs"] = "null"
+    }
+    function set(k, v) { keys[k] = v }
+    function wall_to_seconds(s,    parts, n, h, m, sec) {
+        # Accept h:mm:ss(.frac) or m:ss(.frac)
+        n = split(s, parts, ":")
+        if (n == 3)      { return parts[1]*3600 + parts[2]*60 + parts[3] + 0 }
+        else if (n == 2) { return parts[1]*60 + parts[2] + 0 }
+        else             { return s + 0 }
+    }
+    /Maximum resident set size/                   { set("peak_rss_kb", $NF + 0) }
+    /User time/                                   { set("user_seconds", $NF + 0) }
+    /System time/                                 { set("sys_seconds", $NF + 0) }
+    /Elapsed \(wall clock\) time/                 {
+        # Last field is the formatted time
+        v = wall_to_seconds($NF)
+        set("wall_seconds", v)
+    }
+    /Voluntary context switches/                  { set("voluntary_ctx_switches", $NF + 0) }
+    /Involuntary context switches/                { set("involuntary_ctx_switches", $NF + 0) }
+    /Major \(requiring I\/O\) page faults/        { set("major_page_faults", $NF + 0) }
+    /Minor \(reclaiming a frame\) page faults/    { set("minor_page_faults", $NF + 0) }
+    /File system inputs/                          { set("fs_inputs", $NF + 0) }
+    /File system outputs/                         { set("fs_outputs", $NF + 0) }
+    END {
+        # Emit JSON. Numbers are emitted bare (jq -r will keep them as-is),
+        # null literal stays null.
+        printf "{"
+        sep = ""
+        # Stable key order:
+        order = "peak_rss_kb user_seconds sys_seconds wall_seconds " \
+                "voluntary_ctx_switches involuntary_ctx_switches " \
+                "major_page_faults minor_page_faults fs_inputs fs_outputs"
+        n = split(order, ord, " ")
+        for (i = 1; i <= n; i++) {
+            k = ord[i]
+            v = keys[k]
+            if (v == "null") {
+                printf "%s\"%s\":null", sep, k
+            } else {
+                # User/system times are like "0.00"; keep as numeric literal
+                printf "%s\"%s\":%s", sep, k, v
+            }
+            sep = ","
+        }
+        printf "}\n"
+    }
+    ' "$file"
+}

bench/lib/time_test.sh

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+#!/usr/bin/env bash
+set -euo pipefail
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+. "${SCRIPT_DIR}/test_helpers.sh"
+. "${SCRIPT_DIR}/common.sh"
+. "${SCRIPT_DIR}/time.sh"
+
+FIXTURE="${SCRIPT_DIR}/../fixtures/time-sample.txt"
+
+test_parse_peak_rss() {
+    local got
+    got=$(time_parse_v "$FIXTURE" | jq -r '.peak_rss_kb')
+    assert_eq "2944" "$got" "peak_rss_kb"
+}
+
+test_parse_user_seconds() {
+    # jq normalises JSON numbers: 0.00 → 0
+    local got
+    got=$(time_parse_v "$FIXTURE" | jq -r '.user_seconds')
+    assert_eq "0" "$got" "user_seconds"
+}
+
+test_parse_wall_seconds_from_mm_ss() {
+    # 0:00.05 → 0.05 seconds
+    local got
+    got=$(time_parse_v "$FIXTURE" | jq -r '.wall_seconds')
+    assert_eq "0.05" "$got" "wall_seconds"
+}
+
+test_parse_minor_faults() {
+    local got
+    got=$(time_parse_v "$FIXTURE" | jq -r '.minor_page_faults')
+    assert_eq "117" "$got" "minor_page_faults"
+}
+
+test_parse_voluntary_ctx() {
+    local got
+    got=$(time_parse_v "$FIXTURE" | jq -r '.voluntary_ctx_switches')
+    assert_eq "5" "$got" "voluntary_ctx_switches"
+}
+
+test_parse_missing_field_is_null() {
+    local d; d=$(mktempdir)
+    printf '\tMaximum resident set size (kbytes): 1024\n' > "$d/partial.txt"
+    local got
+    got=$(time_parse_v "$d/partial.txt" | jq -r '.user_seconds')
+    assert_eq "null" "$got" "missing field becomes null"
+    rm -rf "$d"
+}
+
+test_time_run_captures_output() {
+    local d; d=$(mktempdir)
+    time_run "$d/out.txt" "true"
+    assert_file_exists "$d/out.txt" "time_run writes output"
+    assert_contains "Maximum resident set size" "$(cat "$d/out.txt")" "verbose output present"
+    rm -rf "$d"
+}
+
+test_parse_peak_rss
+test_parse_user_seconds
+test_parse_wall_seconds_from_mm_ss
+test_parse_minor_faults
+test_parse_voluntary_ctx
+test_parse_missing_field_is_null
+test_time_run_captures_output
+printf 'time_test.sh: ok\n'