Improve test coverage for cmd/bd/doctor/fix (23.9% → 50%)

The doctor/fix package has only 23.9% test coverage. The doctor fix functionality is important for troubleshooting.

Current coverage: 23.9%
Target coverage: 50%


Optimize GetReadyWork performance - 752ms on 10K database (target: <50ms)

# Performance Analysis (10K Issue Database)

Analyzed using CPU profiles from benchmark suite on Apple M2 Pro.

## Operation Performance

| Operation                        | Time    | Allocations | Memory |
|----------------------------------|---------|-------------|--------|
| bd ready (GetReadyWork)          | ~752ms  | 167,466     | 16MB   |
| bd list (SearchIssues no filter) | ~11.6ms | 89,214      | 5.8MB  |
| bd list (SearchIssues filtered)  | ~9.2ms  | 62,365      | 3.5MB  |
| bd create (CreateIssue)          | ~2.6ms  | 146         | 8.6KB  |
| bd update (UpdateIssue)          | ~0.32ms | 364         | 15KB   |
| bd close (UpdateIssue)           | ~0.32ms | 364         | 15KB   |

**Target: <50ms for all operations on 10K database**

**Current issue: GetReadyWork is 15x over target (752ms vs 50ms)**

## Root Cause

GetReadyWork (internal/storage/sqlite/ready.go:90-128) uses recursive CTE to propagate blocking:
- 65x slower than SearchIssues
- Recalculates entire blocked issue tree on every call
- Algorithm:
  1. Find directly blocked issues via 'blocks' dependencies
  2. Recursively propagate blockage to descendants (max depth: 50)
  3. Exclude all blocked issues from results

## CPU Profile Analysis

- Database syscalls (pthread_cond_signal, syscall6): ~75%
- SQLite engine overhead: inherent to recursive CTE
- Application code (query construction): <1%

**Bottleneck is the recursive CTE query execution, not application code.**

## Optimization Recommendations

### High Impact (Likely to achieve <50ms target)

1. **Cache blocked issue calculation**
   - Add `blocked_issues` table updated on dependency changes
   - Trade write complexity for read speed (ready called >> dependency changes)
   - Eliminates recursive CTE on every read

2. **Add/verify database indexes**
   ```sql
   CREATE INDEX IF NOT EXISTS idx_dependencies_blocked
     ON dependencies(issue_id, type, depends_on_id);
   CREATE INDEX IF NOT EXISTS idx_issues_status
     ON issues(status);
   ```

### Medium Impact

3. **Reduce allocations** (167K allocations for GetReadyWork)
   - Profile `scanIssues()` for object pooling opportunities
   - Reuse slice capacity for repeated calls

### Low Impact (Not recommended)
- Query optimization for CRUD operations (already <3ms)
- Connection pooling tuning (not showing in profiles)

## Verification

Run benchmarks to validate optimization:
```bash
make bench-quick
go tool pprof -http=:8080 internal/storage/sqlite/bench-cpu-*.prof
```

Profile files automatically generated in `internal/storage/sqlite/`.


Add warning when staleness check errors

## Problem

When ensureDatabaseFresh() calls CheckStaleness() and it errors (corrupted metadata, permission issues, etc.), we silently proceed with potentially stale data.

**Location:** cmd/bd/staleness.go:27-32

**Scenarios:**
- Corrupted metadata table
- Database locked by another process
- Permission issues reading JSONL file
- Invalid last_import_time format in DB

## Current Code

```go
isStale, err := autoimport.CheckStaleness(ctx, store, dbPath)
if err \!= nil {
    // If we can't determine staleness, allow operation to proceed
    // (better to show potentially stale data than block user)
    return nil
}
```

## Fix

```go
isStale, err := autoimport.CheckStaleness(ctx, store, dbPath)
if err \!= nil {
    fmt.Fprintf(os.Stderr, "Warning: Could not verify database freshness: %v\n", err)
    fmt.Fprintf(os.Stderr, "Proceeding anyway. Data may be stale.\n\n")
    return nil
}
```

## Impact
Medium - users should know when staleness check fails

## Effort
Easy - 5 minutes


bd validate - Comprehensive health check

Run all validation checks in one command.

Checks:
- Duplicates
- Orphaned dependencies
- Test pollution
- Git conflicts

Supports --fix-all for auto-repair.

Depends on bd-cbed9619.1, bd-0dcea000, bd-31aab707, bd-9826b69a.

Files: cmd/bd/validate.go (new)


CRDT-based architecture for guaranteed convergence (v2.0)

## Vision
Redesign beads around Conflict-Free Replicated Data Types (CRDTs) to provide mathematical guarantees for N-way collision resolution at arbitrary scale.

## Current Limitations
- Content-hash based collision resolution fails at 5+ clones
- Non-deterministic convergence in multi-round scenarios
- UNIQUE constraint violations during rename operations
- No formal proof of convergence properties

## CRDT Benefits
- Provably convergent (Strong Eventual Consistency)
- Commutative/Associative/Idempotent operations
- No coordination required between clones
- Scales to 100+ concurrent workers
- Well-understood mathematical foundations

## Proposed Architecture

### 1. UUID-Based IDs
Replace sequential IDs with UUIDs:
- Current: bd-1c63eb84, bd-9063acda, bd-4d80b7b1
- CRDT: bd-a1b2c3d4-e5f6-7890-abcd-ef1234567890
- Human aliases maintained separately: #42 maps to UUID

### 2. Last-Write-Wins (LWW) Elements
Each field becomes an LWW register:
- title: (timestamp, clone_id, value)
- status: (timestamp, clone_id, value)
- Deterministic conflict resolution via Lamport timestamp + clone_id tiebreaker

### 3. Operation Log
Track all operations as CRDT ops:
- CREATE(uuid, timestamp, clone_id, fields)
- UPDATE(uuid, field, timestamp, clone_id, value)
- DELETE(uuid, timestamp, clone_id) - tombstone, not hard delete

### 4. Sync as Merge
Syncing becomes merging two CRDT states:
- No merge conflicts possible
- Deterministic merge function
- Guaranteed convergence

## Implementation Phases

### Phase 1: Research & Design (4 weeks)
- Study existing CRDT implementations (Automerge, Yjs, Loro)
- Design schema for CRDT-based issue tracking
- Prototype LWW-based Issue CRDT
- Benchmark performance vs current system

### Phase 2: Parallel Implementation (6 weeks)
- Implement CRDT storage layer alongside SQLite
- Build conversion tools: SQLite ↔ CRDT
- Maintain backward compatibility with v1.x format
- Migration path for existing databases

### Phase 3: Testing & Validation (4 weeks)
- Formal verification of convergence properties
- Stress testing with 100+ clone scenario
- Performance profiling and optimization
- Documentation and examples

### Phase 4: Migration & Rollout (4 weeks)
- Release v2.0-beta with CRDT backend
- Gradual migration from v1.x
- Monitoring and bug fixes
- Final v2.0 release

## Risks & Mitigations

**Risk 1: Performance overhead**
- Mitigation: Benchmark early, optimize hot paths
- CRDTs can be slower than append-only logs
- May need compaction strategy

**Risk 2: Storage bloat**
- Mitigation: Implement operation log compaction
- Tombstone garbage collection for deleted issues
- Periodic snapshots to reduce log size

**Risk 3: Breaking changes**
- Mitigation: Maintain v1.x compatibility layer
- Gradual migration tools
- Dual-mode operation during transition

**Risk 4: Complexity**
- Mitigation: Use battle-tested CRDT libraries
- Comprehensive documentation
- Clear migration guide

## Success Criteria
- 100-clone collision test passes without failures
- Formal proof of convergence properties
- Performance within 2x of current system
- Zero manual conflict resolution required
- Backward compatible with v1.x databases

## Timeline
18-20 weeks total (4-5 months)

## References
- Automerge: https://automerge.org
- Yjs: https://docs.yjs.dev
- Loro: https://loro.dev
- CRDT theory: Shapiro et al, A comprehensive study of CRDTs
- Related issues: bd-0dcea000, bd-4d7fca8a, bd-6221bdcd


Improve test coverage for internal/syncbranch (33.0% → 70%)

The syncbranch package has only 33.0% test coverage. This package handles git sync operations and is critical for data integrity.

Current coverage: 33.0%
Target coverage: 70%


AI-supervised database migrations for safer schema evolution

## Problem

Database migrations can lose user data through edge cases that are hard to anticipate (e.g., GH #201 where bd migrate failed to set issue_prefix, or bd-d355a07d false positive data loss warnings). Since beads is designed to be run by AI agents, we should leverage AI to make migrations safer.

## Current State

Migrations run blindly with:
- No pre-flight validation
- No data integrity verification
- No rollback on failure
- Limited post-migration testing

Recent issues:
- GH #201: Migration didn't set issue_prefix config, breaking commands
- bd-d355a07d: False positive "data loss" warnings on collision resolution
- Users reported migration data loss (fixed but broader problem remains)

## Proposal: AI-Supervised Migration Framework

Use AI to supervise migrations through structured verification:

### 1. Pre-Migration Analysis
- AI reads migration code and current schema
- Identifies potential data loss scenarios
- Generates validation queries to verify assumptions
- Creates snapshot queries for before/after comparison

### 2. Migration Execution
- Take database backup/snapshot
- Run validation queries (pre-state)
- Execute migration in transaction
- Run validation queries (post-state)

### 3. Post-Migration Verification
- AI compares pre/post snapshots
- Verifies data integrity invariants
- Checks for unexpected data loss
- Validates config completeness (like issue_prefix)

### 4. Rollback on Anomalies
- If AI detects data loss, rollback transaction
- Present human-readable error report
- Suggest fix before retrying

## Example Flow

```
$ bd migrate

→ Analyzing migration plan...
→ AI identified 3 potential data loss scenarios
→ Generating validation queries...
→ Creating pre-migration snapshot...
→ Running migration in transaction...
→ Verifying post-migration state...
✓ All 247 issues accounted for
✓ Config table complete (issue_prefix: "mcp")
✓ Dependencies intact (342 relationships verified)
→ Migration successful!
```

If something goes wrong:
```
$ bd migrate

→ Analyzing migration plan...
→ AI identified issue: Missing issue_prefix config after migration
→ Recommendation: Add prefix detection step
→ Aborting migration - database unchanged
```

## Implementation Ideas

### A. Migration Validator Tool
Create `bd migrate --validate` that:
- Simulates migration on copy of database
- Uses AI to verify data integrity
- Reports potential issues before real migration

### B. Migration Test Generator
AI generates test cases for migrations:
- Edge cases (empty DB, large DB, missing config)
- Data integrity checks
- Regression tests

### C. Migration Invariants
Define invariants that AI checks:
- Issue count should not decrease (unless collision resolution)
- All required config keys present
- Foreign key relationships intact
- No orphaned dependencies

### D. Self-Healing Migrations
AI detects incomplete migrations and suggests fixes:
- Missing config values (like GH #201)
- Orphaned data
- Index inconsistencies

## Benefits

1. **Catch edge cases**: AI explores scenarios humans miss
2. **Self-documenting**: AI explains what migration does
3. **Agent-friendly**: Agents can run migrations confidently
4. **Fewer rollbacks**: Detect issues before committing
5. **Better testing**: AI generates comprehensive test suites

## Open Questions

1. Which AI model? (Fast: Haiku, Thorough: Sonnet/GPT-4)
2. How to balance safety vs migration speed?
3. Should AI validation be required or optional?
4. How to handle offline scenarios (no API access)?
5. What invariants should always be checked?

## Related Work

- bd-b245: Migration registry (makes migrations introspectable)
- GH #201: issue_prefix migration bug (motivating example)
- bd-d355a07d: False positive data loss warnings

## Progress

### ✅ Phase 1: Migration Invariants (COMPLETED)

**Implemented:**
- Created internal/storage/sqlite/migration_invariants.go with 3 invariants
- Updated RunMigrations() to verify invariants after migrations
- All tests pass ✓

### ✅ Phase 2: Inspection Tools (COMPLETED & PUSHED)

**Commit:** 1abe4e7 - "Add migration inspection tools for AI agents (bd-627d Phase 2)"

**Implemented:**
1. ✅ bd migrate --inspect --json - Shows migration plan
2. ✅ bd info --schema --json - Returns schema details
3. ✅ Migration warnings system
4. ✅ Documentation updated in AGENTS.md
5. ✅ All tests pass

### ✅ Phase 3: MCP Tools (COMPLETED & PUSHED)

**Commit:** 2493693 - "Add MCP tools for migration inspection (bd-627d Phase 3)"

**Implemented:**
1. ✅ inspect_migration(workspace_root) tool in beads-mcp
2. ✅ get_schema_info(workspace_root) tool in beads-mcp
3. ✅ Abstract methods in BdClientBase
4. ✅ CLI client implementations
5. ✅ All tests pass

**All phases complete!** Migration inspection fully integrated into MCP server.


Test parent issue


Design tombstone merge semantics

Define how tombstones participate in 3-way merge. Key question: does tombstone always win over live issue (like current deletion-wins rule), or should we use updated_at comparison? Consider: tombstone with older timestamp vs live issue with newer edits. Recommendation: tombstone wins unless expired, matching current behavior but with longer TTL window.


Implement postinstall script for binary download

Create npm/scripts/postinstall.js that downloads platform-specific binaries:

## Platform detection
- Detect os.platform() and os.arch()
- Map to GitHub release asset names:
  - linux-amd64 → bd-linux-amd64
  - linux-arm64 → bd-linux-arm64
  - darwin-amd64 → bd-darwin-amd64
  - darwin-arm64 → bd-darwin-arm64
  - win32-x64 → bd-windows-amd64.exe

## Download logic
- Fetch from GitHub releases: https://github.com/steveyegge/beads/releases/latest/download/${asset}
- Save to npm/bin/bd (or bd.exe on Windows)
- Set executable permissions (chmod +x)
- Handle errors gracefully with helpful messages

## Error handling
- Check for unsupported platforms
- Retry on network failures
- Provide manual download instructions if automated fails
- Skip download if binary already exists (for local development)


Implement backup functionality for reset

Add backup capability that can be used by reset command.

## Functionality
- Copy .beads/ to .beads-backup-{timestamp}/
- Timestamp format: YYYYMMDD-HHMMSS
- Preserve file permissions
- Return backup path for user feedback

## Location
`internal/reset/backup.go` - keep with reset package for now (YAGNI)

## Interface
```go
func CreateBackup(beadsDir string) (backupPath string, err error)
```

## Notes
- Simple recursive file copy, no compression needed
- Error if backup dir already exists (unlikely with timestamp)
- Backup directories SHOULD be gitignored
- Add `.beads-backup-*/` pattern to .beads/.gitignore template in doctor package
- Consider: ListBackups() for future `bd backup list` command (not for this PR)