imbue-mngr-opencode-usage

OpenCode data provider for mngr usage. Single responsibility: install a second in-process TypeScript plugin into each OpenCode agent so each assistant message appends one event to $MNGR_AGENT_STATE_DIR/events/opencode/usage/events.jsonl. The mngr usage CLI walks those events files itself (see imbue-mngr-usage).

How the pieces fit

mngr_opencode_usage's on_after_provisioning hookimpl
  └─→ installs <config_dir>/plugin/mngr_opencode_usage_plugin.ts
        (alongside mngr_opencode's lifecycle plugin; OpenCode auto-loads plugin/*.ts)

OpenCode serve process, on each assistant message.updated
  └─→ mngr_opencode_usage_plugin.ts
        └─→ events/opencode/usage/events.jsonl (append one cost_snapshot event)

mngr usage
  └─→ aggregate_usage_source hookimpl (claims the "opencode" source)
        └─→ aggregate_session_incremental: sum each session's messages

All file I/O goes through host.write_text_file, so provisioning works for local and remote agents.

What gets captured

OpenCode computes cost and tokens per message and exposes them on each assistant message.updated event. The writer emits, per message, a self-contained event carrying:

• cost.total_cost_usd -- OpenCode's own per-message cost (provenance is REPORTED; no estimation needed).
• tokens -- {input, output, cache_read, cache_creation} (reasoning folded into output), for auditability.
• model -- the provider-qualified <providerID>/<modelID>.
• session_id + message_id -- the reader sums per session, keeping the freshest event per message_id so a streaming message's re-fires collapse to its final reading.

Why session-incremental

OpenCode reports each message's own cost, not a session running total. So the writer is stateless -- it appends one self-contained event per message and keeps nothing in memory. The reader (aggregate_session_incremental) recomputes each session's total from the append-only log, which makes it robust across mngr stop/start (a fresh serve process with empty memory loses no history).

cost_mode is API_KEY: OpenCode bills against a real provider key, so the cost is real spend, never an imputed subscription value.