perf(stop): cost-tracker builds the subagent type map in two jq calls (#379)

hooks/stop/cost-tracker.sh

@@ -79,21 +79,45 @@ sonnet_rate='{"i":2.0,"o":10.0,"cw":2.50,"cw1h":4.00,"cr":0.20}'
 # on top of the two more full scans emit_rows and emit_codex_invocations did
 # independently. Measured 9.5s/Stop-call against a real 158MB/42,838-line
 # transcript before this fix (docs/research/cost-tracker-single-scan-perf-2026-09-22.md).
+#
+# Two jq calls in all, not 2-3 per file (GH #379: 6.5 s per Stop at 193 subagents). The first
+# reads every meta at once and prints one line per file: its agentType when that is a non-empty
+# one-line string, else "". A "" line (no meta, an unreadable one, any other shape) takes the
+# per-file path below, so every type is the one that path would give. The second builds the map.
+# ponytail: the second call takes 3 args per file (~400 bytes), so macOS ARG_MAX (1 MB) is near
+# 2,000 subagents (the max seen is 193; raw_records' --argjson typemap has the same ceiling). Past
+# it the map falls back to {} (agent_type null); feed the triples on stdin if that ever happens.
 build_type_map() {
-  local parent_map="$1" vmap="$2" out='{}' f meta t tu id; shift 2
+  local parent_map="$1" vmap="$2" f meta t tu id i=0 rf=() fast types=() args=(); shift 2
   for f in "$@"; do
-    id=$(basename "$f" .jsonl); id="${id#agent-}"
     meta="${f%.jsonl}.meta.json"
-    t=$([[ -f "$meta" ]] && jq -r '.agentType // empty' "$meta" 2>/dev/null)
-    if [[ -z "$t" && -f "$meta" ]]; then
-      tu=$(jq -r '.toolUseId // empty' "$meta" 2>/dev/null)
-      [[ -n "$tu" ]] && t=$(printf '%s' "$parent_map" | jq -r --arg k "$tu" '.[$k] // empty' 2>/dev/null)
+    [[ -f "$meta" ]] && rf+=(--rawfile "m$i" "$meta")
+    i=$((i + 1))
+  done
+  fast=$(jq -nr ${rf[@]+"${rf[@]}"} --argjson n "$#" '
+    range(0; $n) as $i | ($ARGS.named["m\($i)"] // null)
+    | if . == null then "" else (try (fromjson | .agentType) catch null)
+      | if type == "string" and . != "" and (test("[\n\u0000]") | not) then . else "" end end' 2>/dev/null) || fast=""
+  while IFS= read -r t; do types+=("$t"); done <<< "$fast"
+  i=0
+  for f in "$@"; do
+    id=${f##*/}; id=${id%.jsonl}; id=${id#agent-}
+    t=${types[$i]:-}
+    if [[ -z "$t" ]]; then
+      meta="${f%.jsonl}.meta.json"
+      t=$([[ -f "$meta" ]] && jq -r '.agentType // empty' "$meta" 2>/dev/null)
+      if [[ -z "$t" && -f "$meta" ]]; then
+        tu=$(jq -r '.toolUseId // empty' "$meta" 2>/dev/null)
+        [[ -n "$tu" ]] && t=$(printf '%s' "$parent_map" | jq -r --arg k "$tu" '.[$k] // empty' 2>/dev/null)
+      fi
+      [[ -z "$t" ]] && t="unknown"
     fi
-    [[ -z "$t" ]] && t="unknown"
-    out=$(printf '%s' "$out" | jq -c --arg f "$f" --arg t "$t" --arg id "$id" --argjson vmap "$vmap" \
-      '. + {($f): {t: $t, v: ($vmap[$id] // [])}}' 2>/dev/null) || out='{}'
+    args+=(--arg "f$i" "$f" --arg "i$i" "$id" --arg "t$i" "$t")
+    i=$((i + 1))
   done
-  printf '%s' "$out"
+  jq -nc ${args[@]+"${args[@]}"} --argjson n "$#" --argjson vmap "$vmap" '$ARGS.named as $a
+    | reduce range(0; $n) as $i ({}; . + {($a["f\($i)"]): {t: $a["t\($i)"], v: ($vmap[$a["i\($i)"]] // [])}})' \
+    2>/dev/null || printf '{}'
 }
 
 # The third handoff cost (docs/research/delegation-criteria-field-survey-2026-09-04.md
@@ -425,7 +449,7 @@ emit_rows() {
 scan_transcript() {
   local _d="${1%.jsonl}/subagents" _f _ids=()
   shopt -s nullglob
-  for _f in "$_d"/agent-*.jsonl; do _f=$(basename "$_f" .jsonl); _ids+=("${_f#agent-}"); done
+  for _f in "$_d"/agent-*.jsonl; do _f=${_f##*/}; _f=${_f%.jsonl}; _ids+=("${_f#agent-}"); done
   shopt -u nullglob
   # ponytail: [inputs|try fromjson] materializes the whole parsed transcript
   # in jq's heap (the original code streamed `inputs` directly through each

tests/hooks/test-cost-tracker.sh

@@ -437,7 +437,57 @@ fi
 trash "$fx" 2>/dev/null || true
 echo "$pass4 passed, $fail4 failed (phase 4)"
 
-pass=$((pass + pass2 + pass3 + pass4))
-fail=$((fail + fail2 + fail3 + fail4))
+# Phase 5 -- build_type_map (GH #379). Failure class: per-file data misattributed
+# by a batched rewrite. Five subagents, one row each: two plain types, a type
+# that starts with "--" (it must reach jq as an option value, never as a
+# positional arg), a meta holding only toolUseId (resolved through the parent's
+# Agent tool_use), and no meta at all ("unknown"). Two return windows (a1, a3)
+# must land on their own file's row, keyed by the id from the file name.
+echo "=== typemap: each subagent row carries its own type and its own return windows ==="
+source "$ROOT/tests/_lib/harness.sh"
+trap _cleanup_trash EXIT
+pass5=0
+fail5=0
+tm_dir=$(fresh_tmpdir)
+tm_home=$(fresh_tmpdir)
+mkdir -p "$tm_dir/s/subagents"
+python3 - "$tm_dir" <<'PY'
+import json, sys
+d = sys.argv[1]
+def use(mid, inp, content=None):
+    m = {"model": "claude-sonnet-5", "id": mid, "usage": {"input_tokens": inp, "output_tokens": 0,
+         "cache_creation_input_tokens": 0, "cache_read_input_tokens": 0}}
+    if content:
+        m["content"] = content
+    return json.dumps({"type": "assistant", "message": m})
+def ret(i):
+    return json.dumps({"type": "user", "message": {"role": "user",
+                       "content": "<task-notification>\n<task-id>%s</task-id>\n</task-notification>" % i}})
+spawn = [{"type": "tool_use", "name": "Agent", "id": "tu1", "input": {"subagent_type": "mh:reviewer"}}]
+with open(d + "/s.jsonl", "w") as f:
+    f.write("\n".join([use("m0", 1, spawn), ret("a1"), use("m1", 100), ret("a3"), use("m2", 40)]) + "\n")
+metas = {"a1": {"agentType": "Explore"}, "a2": {"agentType": "--help"}, "a3": {"toolUseId": "tu1"},
+         "a4": None, "a5": {"agentType": "general-purpose"}}
+for n, (i, meta) in enumerate(metas.items()):
+    with open("%s/s/subagents/agent-%s.jsonl" % (d, i), "w") as f:
+        f.write(use("s" + i, 2 ** n) + "\n")
+    if meta is not None:
+        with open("%s/s/subagents/agent-%s.meta.json" % (d, i), "w") as f:
+            json.dump(meta, f)
+PY
+tm_payload=$(python3 -c 'import json,sys; print(json.dumps({"transcript_path": sys.argv[1], "session_id": "t379"}))' "$tm_dir/s.jsonl")
+printf '%s' "$tm_payload" | HOME="$tm_home" MH_COST_TRACKER_SETTLE_S=0 bash "$SCRIPT" >/dev/null 2>/dev/null
+got=$(jq -r 'select(.stream == "subagent") | [.agent_type, .input_tokens, .returns, (.verify_tokens | tostring)] | @tsv' \
+  "$tm_home/.local/share/kbg/metrics/costs.jsonl" 2>/dev/null | LC_ALL=C sort)
+want=$'--help\t2\t0\tnull\nExplore\t1\t1\t100\ngeneral-purpose\t16\t0\tnull\nmh:reviewer\t4\t1\t40\nunknown\t8\t0\tnull'
+if [[ "$got" == "$want" ]]; then
+  pass5=$((pass5 + 1)); echo "PASS: 5 subagents -> 5 rows, each with its own type (meta, --help, toolUseId, none) and its own return window"
+else
+  fail5=$((fail5 + 1)); echo "FAIL: subagent rows (type, in, returns, verify) were:"$'\n'"$got"$'\n'"expected:"$'\n'"$want" >&2
+fi
+echo "$pass5 passed, $fail5 failed (phase 5)"
+
+pass=$((pass + pass2 + pass3 + pass4 + pass5))
+fail=$((fail + fail2 + fail3 + fail4 + fail5))
 echo "TOTAL: $pass passed, $fail failed"
 [[ "$fail" -eq 0 ]]