docs(quick-001): complete JDK requirement update plan

Tasks completed: 1/1
- Update JDK requirement in research/STACK.md

SUMMARY: .planning/quick/001-update-jdk-requirement-to-21-for-loom-vi/001-SUMMARY.md

.planning/quick/001-update-jdk-requirement-to-21-for-loom-vi/001-SUMMARY.md

@@ -0,0 +1,80 @@
+---
+phase: quick
+plan: 001
+subsystem: infra
+tags: [jdk, loom, virtual-threads, jdbc, quill]
+
+# Dependency graph
+requires: []
+provides:
+  - Updated JDK requirement documentation (21+ for Loom)
+affects: []
+
+# Tech tracking
+tech-stack:
+  added: []
+  patterns: []
+
+key-files:
+  created: []
+  modified:
+    - .planning/research/STACK.md
+
+key-decisions:
+  - "JDK 21+ required for Loom virtual threads benefiting JDBC blocking ops"
+  - "ZIO fibers and JVM virtual threads are complementary, not competing"
+
+patterns-established: []
+
+# Metrics
+duration: 1min
+completed: 2026-02-05
+---
+
+# Quick Task 001: Update JDK Requirement Summary
+
+**JDK requirement updated to 21+ with Loom virtual threads rationale for JDBC blocking operations in Quill**
+
+## Performance
+
+- **Duration:** <1 min
+- **Started:** 2026-02-05T12:07:20Z
+- **Completed:** 2026-02-05T12:07:56Z
+- **Tasks:** 1
+- **Files modified:** 1
+
+## Accomplishments
+- Updated JDK version requirement from 17+ to 21+ in Language & Runtime table
+- Added rationale explaining Loom virtual threads benefit for JDBC blocking operations
+- Clarified that ZIO fibers and JVM virtual threads are complementary, not competing
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Update JDK requirement in research/STACK.md** - `64dcded` (docs)
+
+## Files Created/Modified
+- `.planning/research/STACK.md` - Updated JDK requirement and added Loom rationale note
+
+## Decisions Made
+- JDK 21+ is the new baseline (was 17+) - both are LTS releases
+- Rationale focuses on JDBC blocking operations which benefit from Loom virtual threads
+- Explicitly clarifies that ZIO's fiber system is complementary to JVM virtual threads
+
+## Deviations from Plan
+None - plan executed exactly as written.
+
+## Issues Encountered
+None
+
+## User Setup Required
+None - documentation-only change.
+
+## Next Phase Readiness
+- Stack documentation now accurately reflects JDK 21+ requirement
+- Ready for Phase 2 planning
+
+---
+*Quick Task: 001*
+*Completed: 2026-02-05*