Trace: define cache accounting and prevent token overcounting across providers #3706

Problem

Chainloop Trace reports inflated token usage and estimated cost for a Codex session. Review cache reporting and token accounting across all supported providers. Define and test the rules so this error cannot recur.

Session: 01a1657c-0f4f-7603-96e9-b99f4ee939d7

Evidence digest: sha256:d729cade5c9f2c7eef4ca720290133db119e291445a70e21175ef4901f819391

Download with:

chainloop artifact download --digest sha256:d729cade5c9f2c7eef4ca720290133db119e291445a70e21175ef4901f819391 --output session.json

Verified evidence

The response sums match the final token_usage_record.thread_token_usage counters. Replaying the current parser reproduces the reported numbers exactly, with 147 reset warnings.

The Codex parser consumes two cumulative streams: token_usage_record.thread_token_usage and event_msg.token_count.info.total_token_usage. They diverge after compaction in this transcript. Lower snapshots trigger the reset branch, which adds entire cumulative totals again. The artifact's $900.8926 cost estimate also uses inflated counts. It does not establish billed spend.

Scope and acceptance criteria

• Decide whether cache usage belongs in the reported total, separate metrics, or both. Document the decision and metric names.
• Audit Codex, Claude, Cursor, Pi, and OpenCode. Record whether input includes cache reads or writes, and whether output includes reasoning tokens.
• Encode each provider's semantics in parsing and normalization. Count cache and reasoning subsets only once.
• Define how to handle duplicate events, multiple usage streams, cumulative counters, per-response usage, compaction, resets, and resumed sessions.
• Add regression fixtures and assertions for those cases. The supplied artifact must produce the response totals above, without false reset warnings.
• Verify cost calculations use the same normalized counts and each provider's cache semantics.
• Document any required evidence-schema or display changes, including the treatment of existing inflated records.

Starting points

• app/cli/internal/trace/codex/parse.go: consumeUsage
• app/cli/internal/trace/codex/pricing.go
• Provider parsers under app/cli/internal/trace/{claude,cursor,pi,opencode}/