Phase 1: Cost tracking with budget enforcement for ADF agents

[AlexMikhalev]

Parent Epic

#637

Summary

Add per-agent cost tracking by parsing Claude Code's --output-format stream-json output and enforcing configurable budget limits.

Changes Required

terraphim_spawner

• Add --output-format stream-json to Claude CLI args in config.rs:infer_args()
• Create cost.rs module with CostEvent struct and stream JSON parser
• Parse stdout for Claude stream JSON events: session_id, usage.input_tokens, usage.output_tokens, cost_usd
• Emit CostEvent via broadcast channel alongside OutputEvent

terraphim_orchestrator

• Add budget_monthly_cents: Option<u64> field to AgentDefinition (with #[serde(default)])
• Add CostTracker struct: accumulates per-agent spend, writes to costs.jsonl
• Budget enforcement in reconcile_tick(): warn at 80%, pause agent at 100%
• New AgentStatus field: spent_monthly_cents

Config

[[agents]]
name = "product-development"
budget_monthly_cents = 5000  # $50/month limit

Reference

• Paperclip cost service: server/src/services/costs.ts
• Paperclip Claude parser: packages/adapters/claude-local/src/server/parse.ts
• Claude stream JSON schema: {type: "result", usage: {input_tokens, output_tokens}, cost_usd}

Acceptance Criteria

• Claude agents emit cost events from stream JSON output
• Per-agent costs accumulated and written to costs.jsonl
• Budget enforcement pauses agent when limit reached
• Codex agents gracefully skip cost tracking (no stream JSON available)
• Existing agents work without budget_monthly_cents (default: no limit)
• Unit tests for stream JSON parser and budget enforcement

[AlexMikhalev]

Storage update

Use terraphim_persistence::Persistable trait for CostEvent instead of raw costs.jsonl. See #637 comment for rationale. Key pattern: costs/{agent_name}/{run_id}. Memory backend for fast reads during budget checks, SQLite/redb for durable storage and monthly aggregation queries.