#521 fix(codex): suppress inherited forked subagent usage

Summary

• Suppresses inherited parent records in Codex forked child JSONL files until the child's first turn_context.
• Tracks the skipped inherited token baseline so the repeated post-turn_context snapshot is not counted as child-local usage.
• Preserves forked child provider, agent, and workspace metadata, and bumps the source-message cache schema for the updated Codex incremental state.

Why

Codex native subagent logs can include copied parent session history before the child session records its own turn_context. Those inherited token_count rows are parent work, not child-local work. Counting them inside every forked child can multiply the parent usage and produce large artificial spikes.

Fixes #520.

Test plan

• cargo test -p tokscale-core sessions::codex::tests::test_forked_child (2 passed)
• cargo test -p tokscale-core codex (61 passed)
• cargo test -p tokscale-core (661 passed, 1 ignored)
• cargo test --workspace --all-features (passed)
• cargo clippy -p tokscale-core --all-features -- -D warnings (passed)
• cargo fmt --all --check (passed)
• git diff --check (passed)

---

Summary by cubic

Suppress inherited parent records in Codex forked child logs until the child’s first turn_context so token usage reflects only child-local work. This prevents double-counting by tracking the inherited baseline and keeps provider/agent/workspace metadata intact (fixes #520).

• Bug Fixes

  • Ignore copied parent token_count rows before the child’s first turn_context.
  • Compare the first post-turn_context snapshot to the inherited baseline to avoid recounting.
  • Parse total_tokens in usage payloads and preserve child provider/agent/workspace attribution.

• Migration

  • Bump source-message cache schema to v12 to store the forked-child suppression baseline in incremental state.