fix(agents): filter unrelated OpenCode session errors

[kunchenguid]

Summary

• Filter payload-wrapped OpenCode stream errors by matching sessionID so errors from other sessions do not fail the current run.
• Preserve handling for top-level provider errors without a session id, including overload reporting.
• Add OpenCode unit coverage and an e2e mock-server scenario for provider overload/error handling.

Risk Assessment

✅ Low: The changes are narrowly scoped to OpenCode SSE output/error handling and add targeted unit/e2e coverage for the altered behavior, with the prior session-filtering issue addressed.

Testing

• Summary: Exercised the OpenCode agent stream parsing changes and the targeted provider-overload e2e path; all focused tests passed.
• npx vitest run "src/core/agents/opencode.test.ts"
• npm run build
• npx vitest run "e2e/e2e.test.ts" -t "reports an OpenCode provider overload"
• Outcome: ✅ passed across 1 run (35.6s)

Pipeline

Updates from git push no-mistakes

✅ **Rebase** - passed

Round 1 - passed ✅

🔧 **Review** - 1 issue found → auto-fixed

Round 1 - found 1 warning

• ⚠️ src/core/agents/opencode.ts:847 - Payload-wrapped stream errors can include properties.sessionID, but this now extracts and records the error before the existing session filter. Because /global/event is a global stream, a session.error for another session could fail the current run; accept payload-wrapped errors only when their sessionID matches, while still allowing top-level provider errors that have no session id.

Round 2 (auto-fix) - passed ✅

✅ **Test** - passed

Round 1 - passed ✅

• npx vitest run "src/core/agents/opencode.test.ts"
• npm run build
• npx vitest run "e2e/e2e.test.ts" -t "reports an OpenCode provider overload"

✅ **Document** - passed

Round 1 - passed ✅

🔧 **Lint** - 1 issue found → auto-fixed

Round 1 - found 1 warning

• ⚠️ e2e/e2e.test.ts:386 - Prettier reported a formatting issue in the changed file; auto-formatted the assertion wrapping with npx prettier --write e2e/e2e.test.ts.

Round 2 (auto-fix) - passed ✅

✅ **Push** - passed

Round 1 - passed ✅