fix(opencode): surface silent provider quota limits (D9)

[paulocorcino]

Problem

An opencode run against a provider whose quota is exhausted could stall for the
full per-issue wall timeout (60m in the observed case) and then be misclassified
as Timeout with saw_error=false — so stop-on-limit never fired and the queue
kept burning budget on subsequent issues.

Root cause: some providers never emit a {type:"error"} event on a quota block.
Z.ai's zai-coding-plan (GLM) treats the AI_APICallError: Usage limit reached
as a retryable stream error and loops on exponential backoff, printing it only
to opencode's own log. The --format json stream stayed silent, so
parse_opencode_limit (a JSON-event scan) saw nothing. Observed live 2026-07-11
(FinCal #71, glm-5.2 — 5-hour cap); an equivalent kimi billing cycle block was
seen earlier.

Fix

• command: pass --print-logs --log-level ERROR so opencode's own logfmt logs
  land on the stderr the headless runner already drains.
• events: add parse_opencode_log_limit, a substring scan over the combined
  stdout+stderr log for the usage limit reached / billing-cycle wording that only
  appears in the logfmt lines (the JSON-event scan structurally can't see it), with
  a text-based reset-hint extractor that handles Z.ai's reset at <ts>.
• lib (execute): fall back to the log scan when the JSON scan finds no limit, so
  the run classifies as Outcome::Limit (stop-on-limit) instead of Timeout.

Fixtures use the exact captured log lines (glm-5.2 5h cap, kimi billing cycle).

Scope / follow-up

This corrects the classification but still waits for the child to exit (the wall
timeout). Killing the child on first detection to reclaim the wasted time is a
deliberate follow-up in the shared headless runner — held back as a separate change
since it touches plumbing used by all adapters. As a zero-code mitigation, a lower
--max-minutes-per-issue bounds the wasted time today.

Verification

cargo fmt --check, cargo clippy -p ralphy-agent-opencode --all-targets -- -D warnings,
and cargo test -p ralphy-agent-opencode (53 passed) all green on the main base.

🤖 Generated with Claude Code