fix(opencode): report persisted session cost

[torreyleonard]

Summary

• fetch the completed OpenCode session and propagate its persisted cumulative cost
• report cost for successful, failed, and interrupted turns when session data is available
• preserve zero as a safe fallback when the session endpoint is unavailable
• add regression coverage for non-zero OpenCode cost reporting

Why

The OpenCode harness currently hardcodes total_cost_usd: 0, so OCA reports $0.00 even when OpenCode's session ledger contains a real charge. In a live session, OpenCode persisted $41.5661305 while OCA displayed $0.00.

Verification

• node scripts/run-tests.mjs tests/opencode-harness.test.ts (51 passed)
• pnpm typecheck
• pnpm build
• pnpm check-static-guardrails
• pnpm check-plugin-security

[greptile-apps]

Greptile Summary

This PR reports the persisted cost of completed OpenCode sessions. The main changes are:

• Fetches the session ledger during turn completion.
• Reports cost for completed, failed, and interrupted turns.
• Uses a bounded lookup with zero as the fallback.
• Deduplicates completion work across interruption and failure races.
• Adds tests for cost reporting, timeout fallback, and interruption ordering.

Confidence Score: 5/5

This looks safe to merge.

The optional session lookup has a short timeout, competing completion paths share one session request, and interruption remains authoritative when it races with failure handling.

No blocking issues found in the changed code.

T-Rex Logs

What T-Rex did

• Ran the opencode harness tests with a 120-second timeout; the run completed with exit code 0 in 3889 ms.

_{Ran code and verified through T-Rex}

Important Files Changed

Filename	Overview
src/harness/opencode.ts	Reports validated persisted session cost with a bounded fallback and deduplicated completion handling.
tests/opencode-harness.test.ts	Covers non-zero cost, unavailable session data, interruption ordering, and single-fetch behavior.

_{Reviews (6): Last reviewed commit: "fix(opencode): preserve interrupted outc..." | Re-trigger Greptile}