[stawan15]

Cost and tokens were counted in memory and nowhere else: e.cost was added up per response and shown in the sidebar, then lost when the app exited. Nothing outside a running teveus could report what a session cost, so a menu bar monitor, a script or a spreadsheet had nothing to read.

Each billed response now appends one JSON line to ~/.config/teveus/usage.jsonl:

{"time":"2026-11-01T05:04:17.798825Z","id":"20261101050417.798825000-api-abc","session":"api-abc","provider":"anthropic","model":"claude-sonnet-5","project":"app","cwd":"/Users/me/app","input":12,"output":340,"cacheRead":29570,"cacheWrite":9140,"cost":0.0342,"subagent":false}

• Append-only, so a reader can follow it live without re-reading a whole file.
• In the config directory, so TEVEUS_CONFIG moves it with everything else.
• Write errors are swallowed on purpose: the ledger is for reporting, and a read-only config directory must not fail a conversation.
• History compaction is recorded too. It is a billed request like any other and was previously counted in e.cost but invisible everywhere else.

UsageRecord in internal/agent/usage.go is a contract now that another program reads it, so usage_test.go pins the field names and the shape rather than only the arithmetic.

Why this shape

Field names are lowerCamelCase to match what JSON consumers expect, and model keeps teveus's provider/model-id form while provider is split out beside it. A consumer that needs a bare model id can take the last path segment; one that wants the router can read provider.

Verification

• go build ./..., go vet, gofmt clean; full go test ./... passes.
• Round-tripped end to end: generated a real ledger from the engine and parsed it back.

The reader side is the claude-monitor menu bar app, which shipped this in Claude-Usage-Monitor v0.1.2. It shows nothing for older teveus, which writes no ledger.