feat(metrics): per-agent token/cost accounting

Feature 4. claude is now launched with --output-format json; the run-log trailing
result JSON is parsed (defensively, never fatal) for usage + total_cost_usd. New
idempotent ALTERs add input_tokens/output_tokens/cache_read_tokens/cost_usd to
agent_runs; the launcher monitor records usage per run, posts a per-agent finish
comment under that agent bot (e.g. Developer gotov · 45.2k in / 12.1k out · $0.21),
and the deployer posts an end-of-task summary (SUM over agent_runs GROUP BY agent)
on done. New src/usage.py holds parse/format/record/summary helpers; test_usage.py
covers parsing a real CLI JSON blob, NULL-on-garbage, recording, formatting, and the
per-task aggregate.

tests/test_usage.py

@@ -0,0 +1,176 @@
+"""Feature 4: token / cost accounting tests.
+
+Covers:
+  * parse_usage_from_text on a REAL claude --output-format json result blob
+    (captured live from CLI 2.1.142), including a leading text line.
+  * parse on garbage / missing JSON -> None (never raises).
+  * record_usage writes the columns; NULLs when usage is None.
+  * fmt_tokens / fmt_cost formatting.
+  * usage_comment string format.
+  * task_usage_summary / task_summary_comment aggregate over agent_runs.
+
+DB is an isolated temp file; no network or subprocess.
+"""
+
+import os
+import tempfile
+
+os.environ.setdefault("ORCH_PLANE_API_TOKEN", "test-token")
+os.environ.setdefault("ORCH_GITEA_TOKEN", "test-token")
+
+_test_db = os.path.join(tempfile.gettempdir(), "test_orchestrator_usage.db")
+os.environ["ORCH_DB_PATH"] = _test_db
+
+import pytest  # noqa: E402
+
+from src import db as db_module  # noqa: E402
+from src.db import init_db, get_db  # noqa: E402
+from src import usage as U  # noqa: E402
+
+
+# Real claude --output-format json result object (captured from CLI 2.1.142).
+REAL_RESULT_JSON = (
+    '{"type":"result","subtype":"success","is_error":false,"duration_ms":1795,'
+    '"num_turns":1,"result":"Hi!","session_id":"abc",'
+    '"total_cost_usd":0.0560175,'
+    '"usage":{"input_tokens":45231,"cache_creation_input_tokens":7418,'
+    '"cache_read_input_tokens":18500,"output_tokens":12100,'
+    '"service_tier":"standard"},'
+    '"modelUsage":{"claude-opus-4-7":{"inputTokens":6,"outputTokens":7}},'
+    '"permission_denials":[]}'
+)
+
+
+@pytest.fixture(autouse=True)
+def setup_db(monkeypatch):
+    # get_db() reads settings.db_path live; pin it to our isolated DB.
+    monkeypatch.setattr(db_module.settings, "db_path", _test_db, raising=False)
+    if os.path.exists(_test_db):
+        os.unlink(_test_db)
+    init_db()
+    yield
+    if os.path.exists(_test_db):
+        os.unlink(_test_db)
+
+
+# --------------------------------------------------------------------------- #
+# parsing
+# --------------------------------------------------------------------------- #
+def test_parse_real_result_json():
+    u = U.parse_usage_from_text(REAL_RESULT_JSON)
+    assert u is not None
+    assert u["input_tokens"] == 45231
+    assert u["output_tokens"] == 12100
+    assert u["cache_read_tokens"] == 18500
+    assert abs(u["cost_usd"] - 0.0560175) < 1e-9
+
+
+def test_parse_with_leading_text():
+    """The agent may print text before the trailing JSON; we still find it."""
+    text = "some agent stdout line\nanother line\n" + REAL_RESULT_JSON
+    u = U.parse_usage_from_text(text)
+    assert u is not None
+    assert u["input_tokens"] == 45231
+    assert u["output_tokens"] == 12100
+
+
+def test_parse_garbage_returns_none():
+    assert U.parse_usage_from_text("not json at all { broken") is None
+    assert U.parse_usage_from_text("") is None
+    assert U.parse_usage_from_text(None) is None
+
+
+def test_parse_json_without_usage_returns_none():
+    assert U.parse_usage_from_text('{"hello":"world"}') is None
+
+
+def test_parse_from_log_missing_file_returns_none():
+    assert U.parse_usage_from_log("/no/such/file.log") is None
+
+
+# --------------------------------------------------------------------------- #
+# record_usage
+# --------------------------------------------------------------------------- #
+def _new_run(agent="developer", task_id=1):
+    conn = get_db()
+    cur = conn.execute("INSERT INTO agent_runs (task_id, agent) VALUES (?, ?)", (task_id, agent))
+    rid = cur.lastrowid
+    conn.commit()
+    conn.close()
+    return rid
+
+
+def test_record_usage_writes_columns():
+    rid = _new_run()
+    u = U.parse_usage_from_text(REAL_RESULT_JSON)
+    U.record_usage(rid, u)
+    conn = get_db()
+    row = conn.execute(
+        "SELECT input_tokens, output_tokens, cache_read_tokens, cost_usd "
+        "FROM agent_runs WHERE id=?", (rid,)
+    ).fetchone()
+    conn.close()
+    assert row["input_tokens"] == 45231
+    assert row["output_tokens"] == 12100
+    assert row["cache_read_tokens"] == 18500
+    assert abs(row["cost_usd"] - 0.0560175) < 1e-9
+
+
+def test_record_usage_none_writes_nulls():
+    rid = _new_run()
+    U.record_usage(rid, None)  # must not raise
+    conn = get_db()
+    row = conn.execute("SELECT input_tokens, cost_usd FROM agent_runs WHERE id=?", (rid,)).fetchone()
+    conn.close()
+    assert row["input_tokens"] is None
+    assert row["cost_usd"] is None
+
+
+# --------------------------------------------------------------------------- #
+# formatting
+# --------------------------------------------------------------------------- #
+def test_fmt_tokens():
+    assert U.fmt_tokens(6) == "6"
+    assert U.fmt_tokens(1234) == "1.2k"
+    assert U.fmt_tokens(45231) == "45.2k"
+    assert U.fmt_tokens(2_500_000) == "2.5M"
+    assert U.fmt_tokens(None) == "0"
+
+
+def test_fmt_cost():
+    assert U.fmt_cost(0.21) == "$0.21"
+    assert U.fmt_cost(0.0560175) == "$0.06"
+    assert U.fmt_cost(None) == "$0.00"
+
+
+def test_usage_comment_format():
+    u = {"input_tokens": 45231, "output_tokens": 12100, "cost_usd": 0.21}
+    c = U.usage_comment("developer", u)
+    assert "Developer" in c
+    assert "45.2k in" in c
+    assert "12.1k out" in c
+    assert "$0.21" in c
+
+
+# --------------------------------------------------------------------------- #
+# task summary
+# --------------------------------------------------------------------------- #
+def test_task_summary_aggregates_over_agents():
+    # two runs for the same task: developer + tester
+    for agent, ti, to, cost in [("developer", 1000, 200, 0.10), ("tester", 500, 100, 0.05)]:
+        rid = _new_run(agent=agent, task_id=42)
+        U.record_usage(rid, {"input_tokens": ti, "output_tokens": to,
+                             "cache_read_tokens": 0, "cost_usd": cost})
+
+    s = U.task_usage_summary(42)
+    assert s["total_in"] == 1500
+    assert s["total_out"] == 300
+    assert abs(s["total_cost"] - 0.15) < 1e-9
+    agents = {a for a, *_ in s["per_agent"]}
+    assert agents == {"developer", "tester"}
+
+    comment = U.task_summary_comment(42)
+    assert "1.5k" in comment       # total in
+    assert "$0.15" in comment       # total cost
+    assert "Developer" in comment
+    assert "Tester" in comment