Adds an append-only JSONL ledger of every research() call at
~/.marchwarden/costs.jsonl, supplementing (not replacing) the
per-call cost_metadata field returned to callers. The ledger is
the operator-facing source of truth for spend tracking, queryable
via the upcoming `marchwarden costs` command (M2.5.3).
Fields per entry: timestamp, trace_id, question (truncated 200ch),
model_id, tokens_used, tokens_input, tokens_output, iterations_run,
wall_time_sec, tavily_searches, estimated_cost_usd, budget_exhausted,
confidence.
Cost estimation reads ~/.marchwarden/prices.toml, which is
auto-created with seed values for current Anthropic + Tavily rates
on first run. Operators are expected to update prices.toml
manually when upstream rates change — there is no automatic
fetching. Existing files are never overwritten. Unknown models
log a WARN and record estimated_cost_usd: null instead of
crashing.
Each ledger write also emits a structured `cost_recorded` log line
via the M2.5.1 logger, so cost data ships to OpenSearch alongside
the ledger file with no extra plumbing.
Tracking changes in agent.py:
- Track tokens_input / tokens_output split (not just total)
- Count tavily_searches across iterations
- _synthesize now returns (result, synth_in, synth_out) so the
caller can attribute synthesis tokens to the running counters
- Ledger.record() called after research_completed log; failures
are caught and warn-logged so a ledger write can never poison
a successful research call
Tests cover: price table seeding, no-overwrite of existing files,
cost estimation for known/unknown models, tavily-only cost,
ledger appends, question truncation, env var override.
End-to-end verified with a real Anthropic+Tavily call:
9107 input + 1140 output tokens, 1 tavily search, $0.049 estimated.
104/104 tests passing.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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