fix: prevent infinite retry loops, surface subagent errors, handle Bedrock undefined messages

- processor.ts: add MAX_RETRIES=10 cap to prevent infinite retry storms (Issue #1)
- processor.ts: preserve metadata on tool-error state updates (Issue #8)
- error.ts: handle Bedrock literal 'undefined' message for overflow detection (Issue #2)
- task.ts: check result.info.error to surface subagent failures to parent (Issue #3)
- test/provider/error.test.ts: 17 tests covering parseAPICallError + parseStreamError
- docs/09-temp/issues.md: full RCA documentation for 9 identified issues

Author: praxstack