F042: Decision Dependency Graph

Status: Proposed Priority: Medium Inspired by: Beads (steveyegge/beads) - graph links with relates_to, duplicates, supersedes, blocks

Problem

CSTP's related_to field is flat - it lists similar decisions found during query but doesn't capture semantic relationships. There's no way to express:

• "Decision B was blocked until Decision A resolved"
• "Decision C supersedes Decision B (we changed our mind)"
• "Decision D duplicates Decision E (same choice, different context)"

This limits the decision history to a searchable list rather than a navigable knowledge graph.

Solution

Add typed dependency links between decisions, enabling graph traversal and relationship-aware queries.

Link Types

Type	Meaning	Example
blocks	A must resolve before B can proceed	"Choose DB" blocks "Design schema"
supersedes	B replaces A (A is now obsolete)	"Use HTMX" supersedes "Use React"
duplicates	Same decision in different context	Two agents independently chose the same approach
relates_to	Loosely connected (existing)	Topically similar decisions
contradicts	B conflicts with A	Opposing approaches in different subsystems
refines	B narrows/improves A	"Use PostgreSQL" refines "Use SQL database"

Data Model

class DecisionLink:
    source_id: str
    target_id: str
    link_type: LinkType
    created_at: datetime
    created_by: str        # Agent that created the link
    context: str | None    # Why this link exists

API

cstp.linkDecisions    - Create typed link between decisions
cstp.getGraph         - Get decision graph (optional: depth, link_types)
cstp.findBlocked      - Decisions blocked by unresolved dependencies
cstp.getChain         - Follow supersedes chain to current decision
cstp.findContradictions - Detect conflicting active decisions

Graph Queries

# "What's the current active decision for database choice?"
cstp.getChain("dec-001")  # Follows supersedes links to latest

# "Are there any contradictions in my architecture decisions?"
cstp.findContradictions(category="architecture")

# "What decisions are blocked right now?"
cstp.findBlocked(status="pending")

Phases

1. P1: Link CRUD + basic graph storage
2. P2: Supersedes chains + contradiction detection
3. P3: Blocking/unblocking with notifications
4. P4: Graph visualization in dashboard (F011)

Integration Points

• F024 (Bridge Definitions): Links informed by bridge similarity
• F027 (Decision Quality): Link density as quality signal
• F030 (Circuit Breakers): Contradiction count as breaker trigger
• F040 (Task Graph): Tasks inherit decision dependencies