triage: capture compound/text PK UPDATE tombstone follow-up (TASK-110)

Follow-up from TASK-105 PK UPDATE partial:
- Compound/text PK updates lose tombstones when rowid unchanged
- Repro: bash zig/harness/test-pk-update.sh (currently 11 pass, 5 fail)

Keeps follow-up in triage for next update-tasks phase.

Author: subtleGradient

.tasks/triage/TASK-110-zig-pk-update-compound-text-pk.md

@@ -0,0 +1,65 @@
+# TASK-110: Zig PK UPDATE — Compound/Text PK tombstone fix
+
+## Status
+- [x] Planned
+- [ ] Assigned
+- [ ] In Progress
+- [ ] Blocked (reason: ...)
+- [ ] Complete
+
+## Priority
+medium
+
+## Assigned To
+(unassigned)
+
+## Parent Docs / Cross-links
+- Parent task: `.tasks/done/TASK-105-zig-pk-update-must-emit-tombstone-and-insert.md`
+- Test harness: `zig/harness/test-pk-update.sh`
+- Zig implementation: `zig/src/as_crr.zig`
+
+## Description
+TASK-105 implemented PK UPDATE tombstone semantics for integer PKs, but compound/text PK updates still fail.
+
+### Root Cause
+When rowid doesn't change (compound/text PKs), the new sentinel overwrites the tombstone because:
+- Clock table uses `rowid` as the key
+- For integer PKs, rowid = pk value (changes on update)
+- For compound/text PKs, rowid is auto-assigned (doesn't change on update)
+- When creating tombstone then new entries, they share the same rowid
+
+### Failing Tests (5)
+- Test 1d: Clock table queries for integer PK (test issue — uses blob-encoded pk)
+- Test 2b: Compound PK (a,b) tombstone not created
+- Test 3b: Full compound PK update tombstone not created  
+- Test 4b: Text PK (sku) tombstone not created
+
+### Potential Solutions
+1. **Store pk blob in clock table** instead of rowid
+2. **Use separate tombstone tracking table**
+3. **Create separate pks entries for tombstoned pk blobs**
+
+## Files to Modify
+- `zig/src/as_crr.zig` — trigger generation
+- `zig/src/changes_vtab.zig` — potentially clock table schema
+- `zig/harness/test-pk-update.sh` — may need test fixes
+
+## Acceptance Criteria
+- [ ] All 16 tests in `bash zig/harness/test-pk-update.sh` pass
+- [ ] No regression in `make -C zig test-parity`
+- [ ] Compound PK update creates tombstone for old PK
+- [ ] Text PK update creates tombstone for old PK
+
+## Reproducible Command
+```bash
+cd /Users/tom/Developer/effect-native/cr-sqlite
+bash zig/harness/test-pk-update.sh
+# Current: 11 PASS, 5 FAIL
+# Target: 16 PASS, 0 FAIL
+```
+
+## Progress Log
+### 2025-12-20
+- Task created as follow-up from TASK-105
+
+## Completion Notes