Decompose architecture into 28 atomic implementation tasks

Break the @alkdev/taskgraph architecture specs into dependency-ordered
implementation tasks across 8 component directories: setup, schema,
error, graph, analysis, cost-benefit, frontmatter, api, and review.
Each task has clear acceptance criteria referencing specific architecture
docs. Three review tasks serve as quality gates at critical junction
points (schemas-and-errors, graph-complete, complete-library). The
dependency graph is validated acyclic with 9 topological levels enabling
significant parallelism across independent work streams.

tasks/implementation/schema/numeric-methods-and-defaults.md

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+---
+id: schema/numeric-methods-and-defaults
+name: Implement categorical numeric functions and resolveDefaults
+status: pending
+depends_on:
+  - schema/enums
+  - schema/graph-schemas
+scope: narrow
+risk: low
+impact: component
+level: implementation
+---
+
+## Description
+
+Implement the standalone numeric functions that map categorical enum values to their numeric equivalents, plus `resolveDefaults` which fills in defaults for unassessed fields and computes derived numeric values. These live in `src/analysis/defaults.ts` per the project structure.
+
+## Acceptance Criteria
+
+- [ ] `src/analysis/defaults.ts` exports:
+  - `scopeCostEstimate(scope: TaskScope): number` — maps to 1.0–5.0 per table
+  - `scopeTokenEstimate(scope: TaskScope): number` — maps to 500–10000 per table
+  - `riskSuccessProbability(risk: TaskRisk): number` — maps to 0.50–0.98 per table
+  - `riskWeight(risk: TaskRisk): number` — maps to 0.02–0.50 (equals 1 - successProbability)
+  - `impactWeight(impact: TaskImpact): number` — maps to 1.0–3.0 per table
+  - `resolveDefaults(attrs: Partial<TaskGraphNodeAttributes> & Pick<TaskGraphNodeAttributes, 'name'>): ResolvedTaskAttributes`
+- [ ] All numeric mapping tables match [schemas.md](../../../docs/architecture/schemas.md) exactly:
+  - Scope: single=1.0/500, narrow=2.0/1500, moderate=3.0/3000, broad=4.0/6000, system=5.0/10000
+  - Risk: trivial=0.98/0.02, low=0.90/0.10, medium=0.80/0.20, high=0.65/0.35, critical=0.50/0.50
+  - Impact: isolated=1.0, component=1.5, phase=2.0, project=3.0
+- [ ] `resolveDefaults` handles null/undefined categorical fields by falling back to: risk→medium, scope→narrow, impact→isolated
+- [ ] `resolveDefaults` populates derived fields: costEstimate, tokenEstimate, successProbability, riskWeight, impactWeight
+- [ ] Label-only fields (level, priority, status) remain nullable after resolution — no default value assigned
+- [ ] `riskWeight(risk)` equals `1 - riskSuccessProbability(risk)` — guaranteed by implementation
+- [ ] Unit tests covering every enum value's numeric mapping and resolveDefaults with mixed null/present inputs
+
+## References
+
+- docs/architecture/schemas.md — numeric method tables, ResolvedTaskAttributes definition
+- docs/architecture/graph-model.md — categorical field defaults
+
+## Notes
+
+> To be filled by implementation agent
+
+## Summary
+
+> To be filled on completion