fix(handlers): keep root session span open across session.idle

[schemaitat]

Description

The opencode.session span and accumulated session totals were ended and deleted on the first session.idle event. Since a session keeps receiving turns after going idle, every subsequent turn's LLM/tool spans had no local session span to nest under and became orphaned root traces, with their token/cost contributions silently dropped from session.total_*.

Keeps the session span and totals alive across session.idle (only snapshotting attributes), and finalizes them in a new handleSessionDeleted handler, on session.error, or on process shutdown.

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Chore (dependency updates, etc.)

Checklist

• I have read the CONTRIBUTING.md document
• My code follows the style guidelines of this project
• bun run lint passes with no errors
• bun run check:jsdoc-coverage passes with no errors
• bun run typecheck passes with no errors
• bun test passes with no errors
• I have added tests that prove my fix is effective or that my feature works
• I have updated the documentation accordingly
• My commits follow the Conventional Commits specification

Related issues

Supersedes #64 and #70 — same fix, rebased as a single commit on current main on a proper feature branch.

Additional context

bun test — 282 pass, 0 fail.

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📥 Commits

Reviewing files that changed from the base of the PR and between c9fee7f and 643ddc4.

📒 Files selected for processing (4)

• src/handlers/session.ts
• src/index.ts
• tests/handlers/session.test.ts
• tests/handlers/spans.test.ts

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[dialupdisaster]

Thanks for the PR. I took another pass on this after merging #74.

My read is:

What #74 did fix:

• It fixes the main orphaned/fragmented later-turn trace problem that this PR is targeting.
• Instead of keeping one root opencode.session span open across multiple session.idle events, fix(tracing): key root runs by user message id #74 changed the model so each user turn gets its own root run span.
• That means later turns no longer depend on the original session span staying open in order for LLM/tool spans to remain connected.

What #74 did not fix:

• It did not preserve the exact long-lived root-session-span behavior proposed here.
• It also did not adopt the same session-wide cumulative totals model across multiple idle boundaries.

So I think #74 supersedes this PR for the tracing/orphan-span bug itself, but not for the separate question of whether session.total_* should represent a truly long-lived multi-turn session aggregate across repeated idle cycles.

From my side, that tracing fix is sufficient, and I would probably close this PR as superseded unless you specifically want to propose a follow-up focused only on session-wide accounting/log semantics across turns.