diff --git a/openspec/changes/archive/2025-12-24-add-artifact-graph-core/design.md b/openspec/changes/archive/2025-12-24-add-artifact-graph-core/design.md
new file mode 100644
index 00000000..0c1d49a0
--- /dev/null
+++ b/openspec/changes/archive/2025-12-24-add-artifact-graph-core/design.md
@@ -0,0 +1,197 @@
+## Context
+
+This implements "Slice 1: What's Ready?" from the artifact POC analysis. The core insight is using the filesystem as a database - artifact completion is detected by file existence, making the system stateless and version-control friendly.
+
+This module will coexist with the current OpenSpec system as a parallel capability, potentially enabling future migration or integration.
+
+## Goals / Non-Goals
+
+**Goals:**
+- Pure dependency graph logic with no side effects
+- Stateless state detection (rescan filesystem each query)
+- Support glob patterns for multi-file artifacts (e.g., `specs/*.md`)
+- Load artifact definitions from YAML schemas
+- Calculate topological build order
+- Determine "ready" artifacts based on dependency completion
+
+**Non-Goals:**
+- CLI commands (Slice 4)
+- Multi-change management (Slice 2)
+- Template resolution and enrichment (Slice 3)
+- Agent integration or Claude commands
+- Replacing existing OpenSpec functionality
+
+## Decisions
+
+### Decision: Filesystem as Database
+Use file existence for state detection rather than a separate state file.
+
+**Rationale:**
+- Stateless - no state corruption possible
+- Git-friendly - state derived from committed files
+- Simple - no sync issues between state file and actual files
+
+**Alternatives considered:**
+- JSON/SQLite state file: More complex, sync issues, not git-friendly
+- Git metadata: Too coupled to git, complex implementation
+
+### Decision: Kahn's Algorithm for Topological Sort
+Use Kahn's algorithm for computing build order.
+
+**Rationale:**
+- Well-understood, O(V+E) complexity
+- Naturally detects cycles during execution
+- Produces a stable, deterministic order
+
+### Decision: Glob Pattern Support
+Support glob patterns like `specs/*.md` in artifact `generates` field.
+
+**Rationale:**
+- Allows multiple files to satisfy a single artifact requirement
+- Common pattern for spec directories with multiple files
+- Uses standard glob syntax
+
+### Decision: Immutable Completed Set
+Represent completion state as an immutable Set of completed artifact IDs.
+
+**Rationale:**
+- Functional style, easier to reason about
+- State derived fresh each query, no mutation needed
+- Clear separation between graph structure and runtime state
+- Filesystem can only detect binary existence (complete vs not complete)
+
+**Note:** `inProgress` and `failed` states are deferred to future slices. They would require external state tracking (e.g., a status file) since file existence alone cannot distinguish these states.
+
+### Decision: Zod for Schema Validation
+Use Zod for validating YAML schema structure and deriving TypeScript types.
+
+**Rationale:**
+- Already a project dependency (v4.0.17) used in `src/core/schemas/`
+- Type inference via `z.infer<>` - single source of truth for types
+- Runtime validation with detailed error messages
+- Consistent with existing project patterns (`base.schema.ts`, `config-schema.ts`)
+
+**Alternatives considered:**
+- Manual validation: More code, error-prone, no type inference
+- JSON Schema: Would require additional dependency, less TypeScript integration
+- io-ts: Not already in project, steeper learning curve
+
+### Decision: Two-Level Schema Resolution
+Schemas resolve from global user data directory, falling back to package built-ins.
+
+**Resolution order:**
+1. `${XDG_DATA_HOME:-~/.local/share}/openspec/schemas/<name>.yaml` - Global user override
+2. `<package>/schemas/<name>.yaml` - Built-in defaults
+
+**Rationale:**
+- Follows XDG Base Directory Specification (schemas are data, not config)
+- Mirrors existing `getGlobalConfigDir()` pattern in `src/core/global-paths.ts`
+- Built-ins baked into package, never auto-copied
+- Users customize by creating files in global data dir
+- Simple - no project-level overrides (can add later if needed)
+
+**XDG compliance:**
+- Uses `XDG_DATA_HOME` env var when set (all platforms)
+- Unix/macOS fallback: `~/.local/share/openspec/`
+- Windows fallback: `%LOCALAPPDATA%/openspec/`
+
+**Alternatives considered:**
+- Project-level overrides: Added complexity, not needed initially
+- Auto-copy to user space: Creates drift, harder to update defaults
+- Config directory (`XDG_CONFIG_HOME`): Schemas are workflow definitions (data), not user preferences (config)
+
+### Decision: Template Field Parsed But Not Resolved
+The `template` field is required in schema YAML for completeness, but template resolution is deferred to Slice 3.
+
+**Rationale:**
+- Slice 1 focuses on "What's Ready?" - dependency and completion queries only
+- Template paths are validated syntactically (non-empty string) but not resolved
+- Keeps Slice 1 focused and independently testable
+
+### Decision: Cycle Error Format
+Cycle errors list all artifact IDs in the cycle for easy debugging.
+
+**Format:** `"Cyclic dependency detected: A → B → C → A"`
+
+**Rationale:**
+- Shows the full cycle path, not just that a cycle exists
+- Actionable - developer can see exactly which artifacts to fix
+- Consistent with Kahn's algorithm which naturally identifies cycle participants
+
+## Data Structures
+
+**Zod Schemas (source of truth):**
+
+```typescript
+import { z } from 'zod';
+
+// Artifact definition schema
+export const ArtifactSchema = z.object({
+  id: z.string().min(1, 'Artifact ID is required'),
+  generates: z.string().min(1),      // e.g., "proposal.md" or "specs/*.md"
+  description: z.string(),
+  template: z.string(),              // path to template file
+  requires: z.array(z.string()).default([]),
+});
+
+// Full schema YAML structure
+export const SchemaYamlSchema = z.object({
+  name: z.string().min(1, 'Schema name is required'),
+  version: z.number().int().positive(),
+  description: z.string().optional(),
+  artifacts: z.array(ArtifactSchema).min(1, 'At least one artifact required'),
+});
+
+// Derived TypeScript types
+export type Artifact = z.infer<typeof ArtifactSchema>;
+export type SchemaYaml = z.infer<typeof SchemaYamlSchema>;
+```
+
+**Runtime State (not Zod - internal only):**
+
+```typescript
+// Slice 1: Simple completion tracking via filesystem
+type CompletedSet = Set<string>;
+
+// Return type for blocked query
+interface BlockedArtifacts {
+  [artifactId: string]: string[];  // artifact → list of unmet dependencies
+}
+
+interface ArtifactGraphResult {
+  completed: string[];
+  ready: string[];
+  blocked: BlockedArtifacts;
+  buildOrder: string[];
+}
+```
+
+## File Structure
+
+```
+src/core/artifact-graph/
+├── index.ts           # Public exports
+├── types.ts           # Zod schemas and type definitions
+├── graph.ts           # ArtifactGraph class
+├── state.ts           # State detection logic
+├── resolver.ts        # Schema resolution (global → built-in)
+└── schemas/           # Built-in schema definitions (package level)
+    ├── spec-driven.yaml   # Default: proposal → specs → design → tasks
+    └── tdd.yaml           # Alternative: tests → implementation → docs
+```
+
+**Schema Resolution Paths:**
+- Global user override: `${XDG_DATA_HOME:-~/.local/share}/openspec/schemas/<name>.yaml`
+- Package built-in: `src/core/artifact-graph/schemas/<name>.yaml` (bundled with package)
+
+## Risks / Trade-offs
+
+| Risk | Mitigation |
+|------|------------|
+| Glob pattern edge cases | Use well-tested glob library (fast-glob or similar) |
+| Cycle detection | Kahn's algorithm naturally fails on cycles; provide clear error |
+| Schema evolution | Version field in schema, validate on load |
+
+## Open Questions
+
+None - all questions resolved in Decisions section.
diff --git a/openspec/changes/archive/2025-12-24-add-artifact-graph-core/proposal.md b/openspec/changes/archive/2025-12-24-add-artifact-graph-core/proposal.md
new file mode 100644
index 00000000..393d3311
--- /dev/null
+++ b/openspec/changes/archive/2025-12-24-add-artifact-graph-core/proposal.md
@@ -0,0 +1,18 @@
+## Why
+
+The current OpenSpec system relies on conventions and AI inference for artifact ordering. A formal artifact graph with dependency awareness would enable deterministic "what's ready?" queries, making the system more predictable and enabling future features like automated pipeline execution.
+
+## What Changes
+
+- Add `ArtifactGraph` class to model artifacts as a DAG with dependency relationships
+- Add `ArtifactState` type to track completion status (completed, in_progress, failed)
+- Add filesystem-based state detection using file existence and glob patterns
+- Add schema YAML parser to load artifact definitions
+- Implement topological sort (Kahn's algorithm) for build order calculation
+- Add `getNextArtifacts()` to find artifacts ready for creation
+
+## Impact
+
+- Affected specs: New `artifact-graph` capability
+- Affected code: `src/core/artifact-graph/` (new directory)
+- No changes to existing functionality - this is a parallel module
diff --git a/openspec/changes/archive/2025-12-24-add-artifact-graph-core/specs/artifact-graph/spec.md b/openspec/changes/archive/2025-12-24-add-artifact-graph-core/specs/artifact-graph/spec.md
new file mode 100644
index 00000000..bc5898f5
--- /dev/null
+++ b/openspec/changes/archive/2025-12-24-add-artifact-graph-core/specs/artifact-graph/spec.md
@@ -0,0 +1,103 @@
+## ADDED Requirements
+
+### Requirement: Schema Loading
+The system SHALL load artifact graph definitions from YAML schema files.
+
+#### Scenario: Valid schema loaded
+- **WHEN** a valid schema YAML file is provided
+- **THEN** the system returns an ArtifactGraph with all artifacts and dependencies
+
+#### Scenario: Invalid schema rejected
+- **WHEN** a schema YAML file is missing required fields
+- **THEN** the system throws an error with a descriptive message
+
+#### Scenario: Cyclic dependencies detected
+- **WHEN** a schema contains cyclic artifact dependencies
+- **THEN** the system throws an error listing the artifact IDs in the cycle
+
+#### Scenario: Invalid dependency reference
+- **WHEN** an artifact's `requires` array references a non-existent artifact ID
+- **THEN** the system throws an error identifying the invalid reference
+
+#### Scenario: Duplicate artifact IDs rejected
+- **WHEN** a schema contains multiple artifacts with the same ID
+- **THEN** the system throws an error identifying the duplicate
+
+### Requirement: Build Order Calculation
+The system SHALL compute a valid topological build order for artifacts.
+
+#### Scenario: Linear dependency chain
+- **WHEN** artifacts form a linear chain (A → B → C)
+- **THEN** getBuildOrder() returns [A, B, C]
+
+#### Scenario: Diamond dependency
+- **WHEN** artifacts form a diamond (A → B, A → C, B → D, C → D)
+- **THEN** getBuildOrder() returns A before B and C, and D last
+
+#### Scenario: Independent artifacts
+- **WHEN** artifacts have no dependencies
+- **THEN** getBuildOrder() returns them in a stable order
+
+### Requirement: State Detection
+The system SHALL detect artifact completion state by scanning the filesystem.
+
+#### Scenario: Simple file exists
+- **WHEN** an artifact generates "proposal.md" and the file exists
+- **THEN** the artifact is marked as completed
+
+#### Scenario: Simple file missing
+- **WHEN** an artifact generates "proposal.md" and the file does not exist
+- **THEN** the artifact is not marked as completed
+
+#### Scenario: Glob pattern with files
+- **WHEN** an artifact generates "specs/*.md" and the specs/ directory contains .md files
+- **THEN** the artifact is marked as completed
+
+#### Scenario: Glob pattern empty
+- **WHEN** an artifact generates "specs/*.md" and the specs/ directory is empty or missing
+- **THEN** the artifact is not marked as completed
+
+#### Scenario: Missing change directory
+- **WHEN** the change directory does not exist
+- **THEN** all artifacts are marked as not completed (empty state)
+
+### Requirement: Ready Artifact Query
+The system SHALL identify which artifacts are ready to be created based on dependency completion.
+
+#### Scenario: Root artifacts ready initially
+- **WHEN** no artifacts are completed
+- **THEN** getNextArtifacts() returns artifacts with no dependencies
+
+#### Scenario: Dependent artifact becomes ready
+- **WHEN** an artifact's dependencies are all completed
+- **THEN** getNextArtifacts() includes that artifact
+
+#### Scenario: Blocked artifacts excluded
+- **WHEN** an artifact has uncompleted dependencies
+- **THEN** getNextArtifacts() does not include that artifact
+
+### Requirement: Completion Check
+The system SHALL determine when all artifacts in a graph are complete.
+
+#### Scenario: All complete
+- **WHEN** all artifacts in the graph are in the completed set
+- **THEN** isComplete() returns true
+
+#### Scenario: Partially complete
+- **WHEN** some artifacts in the graph are not completed
+- **THEN** isComplete() returns false
+
+### Requirement: Blocked Query
+The system SHALL identify which artifacts are blocked and return all their unmet dependencies.
+
+#### Scenario: Artifact blocked by single dependency
+- **WHEN** artifact B requires artifact A and A is not complete
+- **THEN** getBlocked() returns `{ B: ['A'] }`
+
+#### Scenario: Artifact blocked by multiple dependencies
+- **WHEN** artifact C requires A and B, and only A is complete
+- **THEN** getBlocked() returns `{ C: ['B'] }`
+
+#### Scenario: Artifact blocked by all dependencies
+- **WHEN** artifact C requires A and B, and neither is complete
+- **THEN** getBlocked() returns `{ C: ['A', 'B'] }`
diff --git a/openspec/changes/archive/2025-12-24-add-artifact-graph-core/tasks.md b/openspec/changes/archive/2025-12-24-add-artifact-graph-core/tasks.md
new file mode 100644
index 00000000..125f186c
--- /dev/null
+++ b/openspec/changes/archive/2025-12-24-add-artifact-graph-core/tasks.md
@@ -0,0 +1,61 @@
+## 1. Type Definitions
+- [x] 1.1 Create `src/core/artifact-graph/types.ts` with Zod schemas (`ArtifactSchema`, `SchemaYamlSchema`) and inferred types via `z.infer<>`
+- [x] 1.2 Define `CompletedSet` (Set<string>), `BlockedArtifacts`, and `ArtifactGraphResult` types for runtime state
+
+## 2. Schema Parser
+- [x] 2.1 Create `src/core/artifact-graph/schema.ts` with YAML loading and Zod validation via `.safeParse()`
+- [x] 2.2 Implement dependency reference validation (ensure `requires` references valid artifact IDs)
+- [x] 2.3 Implement duplicate artifact ID detection
+- [x] 2.4 Add cycle detection during schema load (error format: "Cyclic dependency detected: A → B → C → A")
+
+## 3. Artifact Graph Core
+- [x] 3.1 Create `src/core/artifact-graph/graph.ts` with ArtifactGraph class
+- [x] 3.2 Implement `fromYaml(path)` - load graph from schema file
+- [x] 3.3 Implement `getBuildOrder()` - topological sort via Kahn's algorithm
+- [x] 3.4 Implement `getArtifact(id)` - retrieve single artifact definition
+- [x] 3.5 Implement `getAllArtifacts()` - list all artifacts
+
+## 4. State Detection
+- [x] 4.1 Create `src/core/artifact-graph/state.ts` with state detection logic
+- [x] 4.2 Implement file existence checking for simple paths
+- [x] 4.3 Implement glob pattern matching for multi-file artifacts
+- [x] 4.4 Implement `detectCompleted(graph, changeDir)` - scan filesystem and return CompletedSet
+- [x] 4.5 Handle missing changeDir gracefully (return empty CompletedSet)
+
+## 5. Ready Calculation
+- [x] 5.1 Implement `getNextArtifacts(graph, completed)` - find artifacts with all deps completed
+- [x] 5.2 Implement `isComplete(graph, completed)` - check if all artifacts done
+- [x] 5.3 Implement `getBlocked(graph, completed)` - return BlockedArtifacts map (artifact → unmet deps)
+
+## 6. Schema Resolution
+- [x] 6.1 Create `src/core/artifact-graph/resolver.ts` with schema resolution logic
+- [x] 6.2 Add `getGlobalDataDir()` to `src/core/global-config.ts` (XDG_DATA_HOME with platform fallbacks)
+- [x] 6.3 Implement `resolveSchema(name)` - global (`${XDG_DATA_HOME}/openspec/schemas/`) → built-in fallback
+
+## 7. Built-in Schemas
+- [x] 7.1 Create `src/core/artifact-graph/schemas/spec-driven.yaml` (default: proposal → specs → design → tasks)
+- [x] 7.2 Create `src/core/artifact-graph/schemas/tdd.yaml` (alternative: tests → implementation → docs)
+
+## 8. Integration
+- [x] 8.1 Create `src/core/artifact-graph/index.ts` with public exports
+
+## 9. Testing
+- [x] 9.1 Test: Parse valid schema YAML returns correct artifact graph
+- [x] 9.2 Test: Parse invalid schema (missing fields) throws descriptive error
+- [x] 9.3 Test: Duplicate artifact IDs throws error
+- [x] 9.4 Test: Invalid `requires` reference throws error identifying the invalid ID
+- [x] 9.5 Test: Cycle in schema throws error listing cycle path (e.g., "A → B → C → A")
+- [x] 9.6 Test: Compute build order returns correct topological ordering (linear chain)
+- [x] 9.7 Test: Compute build order handles diamond dependencies correctly
+- [x] 9.8 Test: Independent artifacts return in stable order
+- [x] 9.9 Test: Empty/missing changeDir returns empty CompletedSet
+- [x] 9.10 Test: File existence marks artifact as completed
+- [x] 9.11 Test: Glob pattern specs/*.md detected as complete when files exist
+- [x] 9.12 Test: Glob pattern with empty directory not marked complete
+- [x] 9.13 Test: getNextArtifacts returns only root artifacts when nothing completed
+- [x] 9.14 Test: getNextArtifacts includes artifact when all deps completed
+- [x] 9.15 Test: getBlocked returns artifact with all unmet dependencies listed
+- [x] 9.16 Test: isComplete() returns true when all artifacts completed
+- [x] 9.17 Test: isComplete() returns false when some artifacts incomplete
+- [x] 9.18 Test: Schema resolution finds global override before built-in
+- [x] 9.19 Test: Schema resolution falls back to built-in when no global
diff --git a/openspec/specs/artifact-graph/spec.md b/openspec/specs/artifact-graph/spec.md
new file mode 100644
index 00000000..19b0d0bf
--- /dev/null
+++ b/openspec/specs/artifact-graph/spec.md
@@ -0,0 +1,107 @@
+# artifact-graph Specification
+
+## Purpose
+TBD - created by archiving change add-artifact-graph-core. Update Purpose after archive.
+## Requirements
+### Requirement: Schema Loading
+The system SHALL load artifact graph definitions from YAML schema files.
+
+#### Scenario: Valid schema loaded
+- **WHEN** a valid schema YAML file is provided
+- **THEN** the system returns an ArtifactGraph with all artifacts and dependencies
+
+#### Scenario: Invalid schema rejected
+- **WHEN** a schema YAML file is missing required fields
+- **THEN** the system throws an error with a descriptive message
+
+#### Scenario: Cyclic dependencies detected
+- **WHEN** a schema contains cyclic artifact dependencies
+- **THEN** the system throws an error listing the artifact IDs in the cycle
+
+#### Scenario: Invalid dependency reference
+- **WHEN** an artifact's `requires` array references a non-existent artifact ID
+- **THEN** the system throws an error identifying the invalid reference
+
+#### Scenario: Duplicate artifact IDs rejected
+- **WHEN** a schema contains multiple artifacts with the same ID
+- **THEN** the system throws an error identifying the duplicate
+
+### Requirement: Build Order Calculation
+The system SHALL compute a valid topological build order for artifacts.
+
+#### Scenario: Linear dependency chain
+- **WHEN** artifacts form a linear chain (A → B → C)
+- **THEN** getBuildOrder() returns [A, B, C]
+
+#### Scenario: Diamond dependency
+- **WHEN** artifacts form a diamond (A → B, A → C, B → D, C → D)
+- **THEN** getBuildOrder() returns A before B and C, and D last
+
+#### Scenario: Independent artifacts
+- **WHEN** artifacts have no dependencies
+- **THEN** getBuildOrder() returns them in a stable order
+
+### Requirement: State Detection
+The system SHALL detect artifact completion state by scanning the filesystem.
+
+#### Scenario: Simple file exists
+- **WHEN** an artifact generates "proposal.md" and the file exists
+- **THEN** the artifact is marked as completed
+
+#### Scenario: Simple file missing
+- **WHEN** an artifact generates "proposal.md" and the file does not exist
+- **THEN** the artifact is not marked as completed
+
+#### Scenario: Glob pattern with files
+- **WHEN** an artifact generates "specs/*.md" and the specs/ directory contains .md files
+- **THEN** the artifact is marked as completed
+
+#### Scenario: Glob pattern empty
+- **WHEN** an artifact generates "specs/*.md" and the specs/ directory is empty or missing
+- **THEN** the artifact is not marked as completed
+
+#### Scenario: Missing change directory
+- **WHEN** the change directory does not exist
+- **THEN** all artifacts are marked as not completed (empty state)
+
+### Requirement: Ready Artifact Query
+The system SHALL identify which artifacts are ready to be created based on dependency completion.
+
+#### Scenario: Root artifacts ready initially
+- **WHEN** no artifacts are completed
+- **THEN** getNextArtifacts() returns artifacts with no dependencies
+
+#### Scenario: Dependent artifact becomes ready
+- **WHEN** an artifact's dependencies are all completed
+- **THEN** getNextArtifacts() includes that artifact
+
+#### Scenario: Blocked artifacts excluded
+- **WHEN** an artifact has uncompleted dependencies
+- **THEN** getNextArtifacts() does not include that artifact
+
+### Requirement: Completion Check
+The system SHALL determine when all artifacts in a graph are complete.
+
+#### Scenario: All complete
+- **WHEN** all artifacts in the graph are in the completed set
+- **THEN** isComplete() returns true
+
+#### Scenario: Partially complete
+- **WHEN** some artifacts in the graph are not completed
+- **THEN** isComplete() returns false
+
+### Requirement: Blocked Query
+The system SHALL identify which artifacts are blocked and return all their unmet dependencies.
+
+#### Scenario: Artifact blocked by single dependency
+- **WHEN** artifact B requires artifact A and A is not complete
+- **THEN** getBlocked() returns `{ B: ['A'] }`
+
+#### Scenario: Artifact blocked by multiple dependencies
+- **WHEN** artifact C requires A and B, and only A is complete
+- **THEN** getBlocked() returns `{ C: ['B'] }`
+
+#### Scenario: Artifact blocked by all dependencies
+- **WHEN** artifact C requires A and B, and neither is complete
+- **THEN** getBlocked() returns `{ C: ['A', 'B'] }`
+
diff --git a/package.json b/package.json
index 486873d5..0c7c915e 100644
--- a/package.json
+++ b/package.json
@@ -73,7 +73,9 @@
     "@inquirer/prompts": "^7.8.0",
     "chalk": "^5.5.0",
     "commander": "^14.0.0",
+    "fast-glob": "^3.3.3",
     "ora": "^8.2.0",
+    "yaml": "^2.8.2",
     "zod": "^4.0.17"
   }
 }
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 6661eed5..032d0d88 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -20,9 +20,15 @@ importers:
       commander:
         specifier: ^14.0.0
         version: 14.0.0
+      fast-glob:
+        specifier: ^3.3.3
+        version: 3.3.3
       ora:
         specifier: ^8.2.0
         version: 8.2.0
+      yaml:
+        specifier: ^2.8.2
+        version: 2.8.2
       zod:
         specifier: ^4.0.17
         version: 4.0.17
@@ -47,7 +53,7 @@ importers:
         version: 8.50.1(eslint@9.39.2)(typescript@5.9.3)
       vitest:
         specifier: ^3.2.4
-        version: 3.2.4(@types/node@24.2.0)(@vitest/ui@3.2.4)
+        version: 3.2.4(@types/node@24.2.0)(@vitest/ui@3.2.4)(yaml@2.8.2)
 
 packages:
 
@@ -1576,6 +1582,11 @@ packages:
     resolution: {integrity: sha512-r6lPcBGxZXlIcymEu7InxDMhdW0KDxpLgoFLcguasxCaJ/SOIZwINatK9KY/tf+ZrlywOKU0UDj3ATXUBfxJXA==}
     engines: {node: '>=8'}
 
+  yaml@2.8.2:
+    resolution: {integrity: sha512-mplynKqc1C2hTVYxd0PU2xQAc22TI1vShAYGksCCfxbn/dFwnHTNi1bvYsBTkhdUNtGIf5xNOg938rrSSYvS9A==}
+    engines: {node: '>= 14.6'}
+    hasBin: true
+
   yocto-queue@0.1.0:
     resolution: {integrity: sha512-rVksvsnNCdJ/ohGc6xgPwyN8eheCxsiLM8mxuE/t/mOVqJewPuO1miLpTHQiRgTKCLexL4MeAFVagts7HmNZ2Q==}
     engines: {node: '>=10'}
@@ -2202,13 +2213,13 @@ snapshots:
       chai: 5.2.1
       tinyrainbow: 2.0.0
 
-  '@vitest/mocker@3.2.4(vite@7.0.6(@types/node@24.2.0))':
+  '@vitest/mocker@3.2.4(vite@7.0.6(@types/node@24.2.0)(yaml@2.8.2))':
     dependencies:
       '@vitest/spy': 3.2.4
       estree-walker: 3.0.3
       magic-string: 0.30.17
     optionalDependencies:
-      vite: 7.0.6(@types/node@24.2.0)
+      vite: 7.0.6(@types/node@24.2.0)(yaml@2.8.2)
 
   '@vitest/pretty-format@3.2.4':
     dependencies:
@@ -2239,7 +2250,7 @@ snapshots:
       sirv: 3.0.1
       tinyglobby: 0.2.14
       tinyrainbow: 2.0.0
-      vitest: 3.2.4(@types/node@24.2.0)(@vitest/ui@3.2.4)
+      vitest: 3.2.4(@types/node@24.2.0)(@vitest/ui@3.2.4)(yaml@2.8.2)
 
   '@vitest/utils@3.2.4':
     dependencies:
@@ -2987,13 +2998,13 @@ snapshots:
     dependencies:
       punycode: 2.3.1
 
-  vite-node@3.2.4(@types/node@24.2.0):
+  vite-node@3.2.4(@types/node@24.2.0)(yaml@2.8.2):
     dependencies:
       cac: 6.7.14
       debug: 4.4.1
       es-module-lexer: 1.7.0
       pathe: 2.0.3
-      vite: 7.0.6(@types/node@24.2.0)
+      vite: 7.0.6(@types/node@24.2.0)(yaml@2.8.2)
     transitivePeerDependencies:
       - '@types/node'
       - jiti
@@ -3008,7 +3019,7 @@ snapshots:
       - tsx
       - yaml
 
-  vite@7.0.6(@types/node@24.2.0):
+  vite@7.0.6(@types/node@24.2.0)(yaml@2.8.2):
     dependencies:
       esbuild: 0.25.8
       fdir: 6.4.6(picomatch@4.0.3)
@@ -3019,12 +3030,13 @@ snapshots:
     optionalDependencies:
       '@types/node': 24.2.0
       fsevents: 2.3.3
+      yaml: 2.8.2
 
-  vitest@3.2.4(@types/node@24.2.0)(@vitest/ui@3.2.4):
+  vitest@3.2.4(@types/node@24.2.0)(@vitest/ui@3.2.4)(yaml@2.8.2):
     dependencies:
       '@types/chai': 5.2.2
       '@vitest/expect': 3.2.4
-      '@vitest/mocker': 3.2.4(vite@7.0.6(@types/node@24.2.0))
+      '@vitest/mocker': 3.2.4(vite@7.0.6(@types/node@24.2.0)(yaml@2.8.2))
       '@vitest/pretty-format': 3.2.4
       '@vitest/runner': 3.2.4
       '@vitest/snapshot': 3.2.4
@@ -3042,8 +3054,8 @@ snapshots:
       tinyglobby: 0.2.14
       tinypool: 1.1.1
       tinyrainbow: 2.0.0
-      vite: 7.0.6(@types/node@24.2.0)
-      vite-node: 3.2.4(@types/node@24.2.0)
+      vite: 7.0.6(@types/node@24.2.0)(yaml@2.8.2)
+      vite-node: 3.2.4(@types/node@24.2.0)(yaml@2.8.2)
       why-is-node-running: 2.3.0
     optionalDependencies:
       '@types/node': 24.2.0
@@ -3079,6 +3091,8 @@ snapshots:
       string-width: 4.2.3
       strip-ansi: 6.0.1
 
+  yaml@2.8.2: {}
+
   yocto-queue@0.1.0: {}
 
   yoctocolors-cjs@2.1.2: {}
diff --git a/src/core/artifact-graph/builtin-schemas.ts b/src/core/artifact-graph/builtin-schemas.ts
new file mode 100644
index 00000000..bd4fd4c3
--- /dev/null
+++ b/src/core/artifact-graph/builtin-schemas.ts
@@ -0,0 +1,84 @@
+import type { SchemaYaml } from './types.js';
+
+/**
+ * Built-in schema definitions.
+ * These are compiled into the package, avoiding runtime file resolution issues.
+ */
+
+export const SPEC_DRIVEN_SCHEMA: SchemaYaml = {
+  name: 'spec-driven',
+  version: 1,
+  description: 'Default OpenSpec workflow - proposal → specs → design → tasks',
+  artifacts: [
+    {
+      id: 'proposal',
+      generates: 'proposal.md',
+      description: 'Initial proposal document outlining the change',
+      template: 'templates/proposal.md',
+      requires: [],
+    },
+    {
+      id: 'specs',
+      generates: 'specs/*.md',
+      description: 'Detailed specifications for the change',
+      template: 'templates/spec.md',
+      requires: ['proposal'],
+    },
+    {
+      id: 'design',
+      generates: 'design.md',
+      description: 'Technical design document with implementation details',
+      template: 'templates/design.md',
+      requires: ['proposal'],
+    },
+    {
+      id: 'tasks',
+      generates: 'tasks.md',
+      description: 'Implementation tasks derived from specs and design',
+      template: 'templates/tasks.md',
+      requires: ['specs', 'design'],
+    },
+  ],
+};
+
+export const TDD_SCHEMA: SchemaYaml = {
+  name: 'tdd',
+  version: 1,
+  description: 'Test-driven development workflow - tests → implementation → docs',
+  artifacts: [
+    {
+      id: 'spec',
+      generates: 'spec.md',
+      description: 'Feature specification defining requirements',
+      template: 'templates/spec.md',
+      requires: [],
+    },
+    {
+      id: 'tests',
+      generates: 'tests/*.test.ts',
+      description: 'Test files written before implementation',
+      template: 'templates/test.md',
+      requires: ['spec'],
+    },
+    {
+      id: 'implementation',
+      generates: 'src/*.ts',
+      description: 'Implementation code to pass the tests',
+      template: 'templates/implementation.md',
+      requires: ['tests'],
+    },
+    {
+      id: 'docs',
+      generates: 'docs/*.md',
+      description: 'Documentation for the implemented feature',
+      template: 'templates/docs.md',
+      requires: ['implementation'],
+    },
+  ],
+};
+
+/** Map of built-in schema names to their definitions */
+export const BUILTIN_SCHEMAS: Record<string, SchemaYaml> = {
+  'spec-driven': SPEC_DRIVEN_SCHEMA,
+  'tdd': TDD_SCHEMA,
+};
diff --git a/src/core/artifact-graph/graph.ts b/src/core/artifact-graph/graph.ts
new file mode 100644
index 00000000..3f960e60
--- /dev/null
+++ b/src/core/artifact-graph/graph.ts
@@ -0,0 +1,167 @@
+import type { Artifact, SchemaYaml, CompletedSet, BlockedArtifacts } from './types.js';
+import { loadSchema, parseSchema } from './schema.js';
+
+/**
+ * Represents an artifact dependency graph.
+ * Provides methods for querying build order, ready artifacts, and completion status.
+ */
+export class ArtifactGraph {
+  private artifacts: Map<string, Artifact>;
+  private schema: SchemaYaml;
+
+  private constructor(schema: SchemaYaml) {
+    this.schema = schema;
+    this.artifacts = new Map(schema.artifacts.map(a => [a.id, a]));
+  }
+
+  /**
+   * Creates an ArtifactGraph from a YAML file path.
+   */
+  static fromYaml(filePath: string): ArtifactGraph {
+    const schema = loadSchema(filePath);
+    return new ArtifactGraph(schema);
+  }
+
+  /**
+   * Creates an ArtifactGraph from YAML content string.
+   */
+  static fromYamlContent(yamlContent: string): ArtifactGraph {
+    const schema = parseSchema(yamlContent);
+    return new ArtifactGraph(schema);
+  }
+
+  /**
+   * Creates an ArtifactGraph from a pre-validated schema object.
+   */
+  static fromSchema(schema: SchemaYaml): ArtifactGraph {
+    return new ArtifactGraph(schema);
+  }
+
+  /**
+   * Gets a single artifact by ID.
+   */
+  getArtifact(id: string): Artifact | undefined {
+    return this.artifacts.get(id);
+  }
+
+  /**
+   * Gets all artifacts in the graph.
+   */
+  getAllArtifacts(): Artifact[] {
+    return Array.from(this.artifacts.values());
+  }
+
+  /**
+   * Gets the schema name.
+   */
+  getName(): string {
+    return this.schema.name;
+  }
+
+  /**
+   * Gets the schema version.
+   */
+  getVersion(): number {
+    return this.schema.version;
+  }
+
+  /**
+   * Computes the topological build order using Kahn's algorithm.
+   * Returns artifact IDs in the order they should be built.
+   */
+  getBuildOrder(): string[] {
+    const inDegree = new Map<string, number>();
+    const dependents = new Map<string, string[]>();
+
+    // Initialize all artifacts
+    for (const artifact of this.artifacts.values()) {
+      inDegree.set(artifact.id, artifact.requires.length);
+      dependents.set(artifact.id, []);
+    }
+
+    // Build reverse adjacency (who depends on whom)
+    for (const artifact of this.artifacts.values()) {
+      for (const req of artifact.requires) {
+        dependents.get(req)!.push(artifact.id);
+      }
+    }
+
+    // Start with roots (in-degree 0), sorted for determinism
+    const queue = [...this.artifacts.keys()]
+      .filter(id => inDegree.get(id) === 0)
+      .sort();
+
+    const result: string[] = [];
+
+    while (queue.length > 0) {
+      const current = queue.shift()!;
+      result.push(current);
+
+      // Collect newly ready artifacts, then sort before adding
+      const newlyReady: string[] = [];
+      for (const dep of dependents.get(current)!) {
+        const newDegree = inDegree.get(dep)! - 1;
+        inDegree.set(dep, newDegree);
+        if (newDegree === 0) {
+          newlyReady.push(dep);
+        }
+      }
+      queue.push(...newlyReady.sort());
+    }
+
+    return result;
+  }
+
+  /**
+   * Gets artifacts that are ready to be created (all dependencies completed).
+   */
+  getNextArtifacts(completed: CompletedSet): string[] {
+    const ready: string[] = [];
+
+    for (const artifact of this.artifacts.values()) {
+      if (completed.has(artifact.id)) {
+        continue; // Already completed
+      }
+
+      const allDepsCompleted = artifact.requires.every(req => completed.has(req));
+      if (allDepsCompleted) {
+        ready.push(artifact.id);
+      }
+    }
+
+    // Sort for deterministic ordering
+    return ready.sort();
+  }
+
+  /**
+   * Checks if all artifacts in the graph are completed.
+   */
+  isComplete(completed: CompletedSet): boolean {
+    for (const artifact of this.artifacts.values()) {
+      if (!completed.has(artifact.id)) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  /**
+   * Gets blocked artifacts and their unmet dependencies.
+   */
+  getBlocked(completed: CompletedSet): BlockedArtifacts {
+    const blocked: BlockedArtifacts = {};
+
+    for (const artifact of this.artifacts.values()) {
+      if (completed.has(artifact.id)) {
+        continue; // Already completed
+      }
+
+      const unmetDeps = artifact.requires.filter(req => !completed.has(req));
+      if (unmetDeps.length > 0) {
+        blocked[artifact.id] = unmetDeps.sort();
+      }
+    }
+
+    return blocked;
+  }
+}
diff --git a/src/core/artifact-graph/index.ts b/src/core/artifact-graph/index.ts
new file mode 100644
index 00000000..9b78d797
--- /dev/null
+++ b/src/core/artifact-graph/index.ts
@@ -0,0 +1,24 @@
+// Types
+export {
+  ArtifactSchema,
+  SchemaYamlSchema,
+  type Artifact,
+  type SchemaYaml,
+  type CompletedSet,
+  type BlockedArtifacts,
+} from './types.js';
+
+// Schema loading and validation
+export { loadSchema, parseSchema, SchemaValidationError } from './schema.js';
+
+// Graph operations
+export { ArtifactGraph } from './graph.js';
+
+// State detection
+export { detectCompleted } from './state.js';
+
+// Schema resolution
+export { resolveSchema, listSchemas } from './resolver.js';
+
+// Built-in schemas
+export { BUILTIN_SCHEMAS, SPEC_DRIVEN_SCHEMA, TDD_SCHEMA } from './builtin-schemas.js';
diff --git a/src/core/artifact-graph/resolver.ts b/src/core/artifact-graph/resolver.ts
new file mode 100644
index 00000000..1488c7ed
--- /dev/null
+++ b/src/core/artifact-graph/resolver.ts
@@ -0,0 +1,121 @@
+import * as fs from 'node:fs';
+import * as path from 'node:path';
+import { getGlobalDataDir } from '../global-config.js';
+import { BUILTIN_SCHEMAS } from './builtin-schemas.js';
+import { parseSchema, SchemaValidationError } from './schema.js';
+import type { SchemaYaml } from './types.js';
+
+/**
+ * Error thrown when loading a global schema override fails.
+ */
+export class SchemaLoadError extends Error {
+  constructor(
+    message: string,
+    public readonly schemaPath: string,
+    public readonly cause?: Error
+  ) {
+    super(message);
+    this.name = 'SchemaLoadError';
+  }
+}
+
+/**
+ * Resolves a schema name to a SchemaYaml object.
+ *
+ * Resolution order:
+ * 1. Global user override: ${XDG_DATA_HOME}/openspec/schemas/<name>.yaml
+ * 2. Built-in schema
+ *
+ * @param name - Schema name (e.g., "spec-driven")
+ * @returns The resolved schema object
+ * @throws Error if schema is not found in any location
+ */
+export function resolveSchema(name: string): SchemaYaml {
+  // Normalize name (remove .yaml extension if provided)
+  const normalizedName = name.replace(/\.ya?ml$/, '');
+  const builtinNames = Object.keys(BUILTIN_SCHEMAS).join(', ');
+
+  // 1. Check global user override (returns path if found)
+  const globalPath = getGlobalSchemaPath(normalizedName);
+  if (globalPath) {
+    // User override found - load and validate through the same pipeline as other schemas
+    let content: string;
+    try {
+      content = fs.readFileSync(globalPath, 'utf-8');
+    } catch (err) {
+      const ioError = err instanceof Error ? err : new Error(String(err));
+      throw new SchemaLoadError(
+        `Failed to read global schema override at '${globalPath}': ${ioError.message}`,
+        globalPath,
+        ioError
+      );
+    }
+
+    try {
+      return parseSchema(content);
+    } catch (err) {
+      if (err instanceof SchemaValidationError) {
+        // Re-wrap validation errors to include the file path for context
+        throw new SchemaLoadError(
+          `Invalid global schema override at '${globalPath}': ${err.message}`,
+          globalPath,
+          err
+        );
+      }
+      // Handle unexpected parse errors (e.g., YAML syntax errors)
+      const parseError = err instanceof Error ? err : new Error(String(err));
+      throw new SchemaLoadError(
+        `Failed to parse global schema override at '${globalPath}': ${parseError.message}`,
+        globalPath,
+        parseError
+      );
+    }
+  }
+
+  // 2. Check built-in schemas
+  const builtin = BUILTIN_SCHEMAS[normalizedName];
+  if (builtin) {
+    return builtin;
+  }
+
+  throw new Error(
+    `Schema '${normalizedName}' not found. Checked global overrides and built-in schemas. Available built-ins: ${builtinNames}`
+  );
+}
+
+/**
+ * Gets the path to a global user override schema, if it exists.
+ */
+function getGlobalSchemaPath(name: string): string | null {
+  const globalDir = path.join(getGlobalDataDir(), 'schemas');
+
+  // Check both .yaml and .yml extensions
+  for (const ext of ['.yaml', '.yml']) {
+    const schemaPath = path.join(globalDir, `${name}${ext}`);
+    if (fs.existsSync(schemaPath)) {
+      return schemaPath;
+    }
+  }
+
+  return null;
+}
+
+/**
+ * Lists all available schema names.
+ * Combines built-in and user override schemas.
+ */
+export function listSchemas(): string[] {
+  const schemas = new Set<string>(Object.keys(BUILTIN_SCHEMAS));
+
+  // Add user override schemas
+  const globalDir = path.join(getGlobalDataDir(), 'schemas');
+  if (fs.existsSync(globalDir)) {
+    for (const file of fs.readdirSync(globalDir)) {
+      if (file.endsWith('.yaml') || file.endsWith('.yml')) {
+        schemas.add(file.replace(/\.ya?ml$/, ''));
+      }
+    }
+  }
+
+  return Array.from(schemas).sort();
+}
diff --git a/src/core/artifact-graph/schema.ts b/src/core/artifact-graph/schema.ts
new file mode 100644
index 00000000..6371745e
--- /dev/null
+++ b/src/core/artifact-graph/schema.ts
@@ -0,0 +1,124 @@
+import * as fs from 'node:fs';
+import { parse as parseYaml } from 'yaml';
+import { SchemaYamlSchema, type SchemaYaml, type Artifact } from './types.js';
+
+export class SchemaValidationError extends Error {
+  constructor(message: string) {
+    super(message);
+    this.name = 'SchemaValidationError';
+  }
+}
+
+/**
+ * Loads and validates an artifact schema from a YAML file.
+ */
+export function loadSchema(filePath: string): SchemaYaml {
+  const content = fs.readFileSync(filePath, 'utf-8');
+  return parseSchema(content);
+}
+
+/**
+ * Parses and validates an artifact schema from YAML content.
+ */
+export function parseSchema(yamlContent: string): SchemaYaml {
+  const parsed = parseYaml(yamlContent);
+
+  // Validate with Zod
+  const result = SchemaYamlSchema.safeParse(parsed);
+  if (!result.success) {
+    const errors = result.error.issues.map(e => `${e.path.join('.')}: ${e.message}`).join(', ');
+    throw new SchemaValidationError(`Invalid schema: ${errors}`);
+  }
+
+  const schema = result.data;
+
+  // Check for duplicate artifact IDs
+  validateNoDuplicateIds(schema.artifacts);
+
+  // Check that all requires references are valid
+  validateRequiresReferences(schema.artifacts);
+
+  // Check for cycles
+  validateNoCycles(schema.artifacts);
+
+  return schema;
+}
+
+/**
+ * Validates that there are no duplicate artifact IDs.
+ */
+function validateNoDuplicateIds(artifacts: Artifact[]): void {
+  const seen = new Set<string>();
+  for (const artifact of artifacts) {
+    if (seen.has(artifact.id)) {
+      throw new SchemaValidationError(`Duplicate artifact ID: ${artifact.id}`);
+    }
+    seen.add(artifact.id);
+  }
+}
+
+/**
+ * Validates that all `requires` references point to valid artifact IDs.
+ */
+function validateRequiresReferences(artifacts: Artifact[]): void {
+  const validIds = new Set(artifacts.map(a => a.id));
+
+  for (const artifact of artifacts) {
+    for (const req of artifact.requires) {
+      if (!validIds.has(req)) {
+        throw new SchemaValidationError(
+          `Invalid dependency reference in artifact '${artifact.id}': '${req}' does not exist`
+        );
+      }
+    }
+  }
+}
+
+/**
+ * Validates that there are no cyclic dependencies.
+ * Uses DFS to detect cycles and reports the full cycle path.
+ */
+function validateNoCycles(artifacts: Artifact[]): void {
+  const artifactMap = new Map(artifacts.map(a => [a.id, a]));
+  const visited = new Set<string>();
+  const inStack = new Set<string>();
+  const parent = new Map<string, string>();
+
+  function dfs(id: string): string | null {
+    visited.add(id);
+    inStack.add(id);
+
+    const artifact = artifactMap.get(id);
+    if (!artifact) return null;
+
+    for (const dep of artifact.requires) {
+      if (!visited.has(dep)) {
+        parent.set(dep, id);
+        const cycle = dfs(dep);
+        if (cycle) return cycle;
+      } else if (inStack.has(dep)) {
+        // Found a cycle - reconstruct the path
+        const cyclePath = [dep];
+        let current = id;
+        while (current !== dep) {
+          cyclePath.unshift(current);
+          current = parent.get(current)!;
+        }
+        cyclePath.unshift(dep);
+        return cyclePath.join(' → ');
+      }
+    }
+
+    inStack.delete(id);
+    return null;
+  }
+
+  for (const artifact of artifacts) {
+    if (!visited.has(artifact.id)) {
+      const cycle = dfs(artifact.id);
+      if (cycle) {
+        throw new SchemaValidationError(`Cyclic dependency detected: ${cycle}`);
+      }
+    }
+  }
+}
diff --git a/src/core/artifact-graph/state.ts b/src/core/artifact-graph/state.ts
new file mode 100644
index 00000000..449bb723
--- /dev/null
+++ b/src/core/artifact-graph/state.ts
@@ -0,0 +1,61 @@
+import * as fs from 'node:fs';
+import * as path from 'node:path';
+import fg from 'fast-glob';
+import type { CompletedSet } from './types.js';
+import type { ArtifactGraph } from './graph.js';
+
+/**
+ * Detects which artifacts are completed by checking file existence in the change directory.
+ * Returns a Set of completed artifact IDs.
+ *
+ * @param graph - The artifact graph to check
+ * @param changeDir - The change directory to scan for files
+ * @returns Set of artifact IDs whose generated files exist
+ */
+export function detectCompleted(graph: ArtifactGraph, changeDir: string): CompletedSet {
+  const completed = new Set<string>();
+
+  // Handle missing change directory gracefully
+  if (!fs.existsSync(changeDir)) {
+    return completed;
+  }
+
+  for (const artifact of graph.getAllArtifacts()) {
+    if (isArtifactComplete(artifact.generates, changeDir)) {
+      completed.add(artifact.id);
+    }
+  }
+
+  return completed;
+}
+
+/**
+ * Checks if an artifact is complete by checking if its generated file(s) exist.
+ * Supports both simple paths and glob patterns.
+ */
+function isArtifactComplete(generates: string, changeDir: string): boolean {
+  const fullPattern = path.join(changeDir, generates);
+
+  // Check if it's a glob pattern
+  if (isGlobPattern(generates)) {
+    return hasGlobMatches(fullPattern);
+  }
+
+  // Simple file path - check if file exists
+  return fs.existsSync(fullPattern);
+}
+
+/**
+ * Checks if a path contains glob pattern characters.
+ */
+function isGlobPattern(pattern: string): boolean {
+  return pattern.includes('*') || pattern.includes('?') || pattern.includes('[');
+}
+
+/**
+ * Checks if a glob pattern has any matches.
+ */
+function hasGlobMatches(pattern: string): boolean {
+  const matches = fg.sync(pattern, { onlyFiles: true });
+  return matches.length > 0;
+}
diff --git a/src/core/artifact-graph/types.ts b/src/core/artifact-graph/types.ts
new file mode 100644
index 00000000..1758b27e
--- /dev/null
+++ b/src/core/artifact-graph/types.ts
@@ -0,0 +1,33 @@
+import { z } from 'zod';
+
+// Artifact definition schema
+export const ArtifactSchema = z.object({
+  id: z.string().min(1, { error: 'Artifact ID is required' }),
+  generates: z.string().min(1, { error: 'generates field is required' }),
+  description: z.string(),
+  template: z.string().min(1, { error: 'template field is required' }),
+  requires: z.array(z.string()).default([]),
+});
+
+// Full schema YAML structure
+export const SchemaYamlSchema = z.object({
+  name: z.string().min(1, { error: 'Schema name is required' }),
+  version: z.number().int().positive({ error: 'Version must be a positive integer' }),
+  description: z.string().optional(),
+  artifacts: z.array(ArtifactSchema).min(1, { error: 'At least one artifact required' }),
+});
+
+// Derived TypeScript types
+export type Artifact = z.infer<typeof ArtifactSchema>;
+export type SchemaYaml = z.infer<typeof SchemaYamlSchema>;
+
+// Runtime state types (not Zod - internal only)
+
+// Slice 1: Simple completion tracking via filesystem
+export type CompletedSet = Set<string>;
+
+// Return type for blocked query
+export interface BlockedArtifacts {
+  [artifactId: string]: string[];
+}
+
diff --git a/src/core/global-config.ts b/src/core/global-config.ts
index b690113a..271ca5a6 100644
--- a/src/core/global-config.ts
+++ b/src/core/global-config.ts
@@ -5,6 +5,7 @@ import * as os from 'node:os';
 // Constants
 export const GLOBAL_CONFIG_DIR_NAME = 'openspec';
 export const GLOBAL_CONFIG_FILE_NAME = 'config.json';
+export const GLOBAL_DATA_DIR_NAME = 'openspec';
 
 // TypeScript interfaces
 export interface GlobalConfig {
@@ -45,6 +46,37 @@ export function getGlobalConfigDir(): string {
   return path.join(os.homedir(), '.config', GLOBAL_CONFIG_DIR_NAME);
 }
 
+/**
+ * Gets the global data directory path following XDG Base Directory Specification.
+ * Used for user data like schema overrides.
+ *
+ * - All platforms: $XDG_DATA_HOME/openspec/ if XDG_DATA_HOME is set
+ * - Unix/macOS fallback: ~/.local/share/openspec/
+ * - Windows fallback: %LOCALAPPDATA%/openspec/
+ */
+export function getGlobalDataDir(): string {
+  // XDG_DATA_HOME takes precedence on all platforms when explicitly set
+  const xdgDataHome = process.env.XDG_DATA_HOME;
+  if (xdgDataHome) {
+    return path.join(xdgDataHome, GLOBAL_DATA_DIR_NAME);
+  }
+
+  const platform = os.platform();
+
+  if (platform === 'win32') {
+    // Windows: use %LOCALAPPDATA%
+    const localAppData = process.env.LOCALAPPDATA;
+    if (localAppData) {
+      return path.join(localAppData, GLOBAL_DATA_DIR_NAME);
+    }
+    // Fallback for Windows if LOCALAPPDATA is not set
+    return path.join(os.homedir(), 'AppData', 'Local', GLOBAL_DATA_DIR_NAME);
+  }
+
+  // Unix/macOS fallback: ~/.local/share
+  return path.join(os.homedir(), '.local', 'share', GLOBAL_DATA_DIR_NAME);
+}
+
 /**
  * Gets the path to the global config file.
  */
diff --git a/src/core/index.ts b/src/core/index.ts
index 22afd94d..e8677090 100644
--- a/src/core/index.ts
+++ b/src/core/index.ts
@@ -2,9 +2,11 @@
 export {
   GLOBAL_CONFIG_DIR_NAME,
   GLOBAL_CONFIG_FILE_NAME,
+  GLOBAL_DATA_DIR_NAME,
   type GlobalConfig,
   getGlobalConfigDir,
   getGlobalConfigPath,
   getGlobalConfig,
-  saveGlobalConfig
+  saveGlobalConfig,
+  getGlobalDataDir
 } from './global-config.js';
\ No newline at end of file
diff --git a/test/core/artifact-graph/graph.test.ts b/test/core/artifact-graph/graph.test.ts
new file mode 100644
index 00000000..56020754
--- /dev/null
+++ b/test/core/artifact-graph/graph.test.ts
@@ -0,0 +1,268 @@
+import { describe, it, expect } from 'vitest';
+import { ArtifactGraph } from '../../../src/core/artifact-graph/graph.js';
+import type { SchemaYaml } from '../../../src/core/artifact-graph/types.js';
+
+describe('artifact-graph/graph', () => {
+  const createSchema = (artifacts: SchemaYaml['artifacts']): SchemaYaml => ({
+    name: 'test',
+    version: 1,
+    artifacts,
+  });
+
+  describe('fromSchema', () => {
+    it('should create graph from schema object', () => {
+      const schema = createSchema([
+        { id: 'A', generates: 'a.md', description: 'A', template: 't.md', requires: [] },
+      ]);
+
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      expect(graph.getName()).toBe('test');
+      expect(graph.getVersion()).toBe(1);
+    });
+  });
+
+  describe('fromYamlContent', () => {
+    it('should create graph from YAML string', () => {
+      const yaml = `
+name: my-workflow
+version: 2
+artifacts:
+  - id: doc
+    generates: doc.md
+    description: Documentation
+    template: templates/doc.md
+`;
+      const graph = ArtifactGraph.fromYamlContent(yaml);
+
+      expect(graph.getName()).toBe('my-workflow');
+      expect(graph.getVersion()).toBe(2);
+      expect(graph.getArtifact('doc')).toBeDefined();
+    });
+  });
+
+  describe('getArtifact', () => {
+    it('should return artifact by ID', () => {
+      const schema = createSchema([
+        { id: 'proposal', generates: 'proposal.md', description: 'Proposal', template: 't.md', requires: [] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      const artifact = graph.getArtifact('proposal');
+
+      expect(artifact).toBeDefined();
+      expect(artifact?.id).toBe('proposal');
+      expect(artifact?.generates).toBe('proposal.md');
+    });
+
+    it('should return undefined for non-existent ID', () => {
+      const schema = createSchema([
+        { id: 'A', generates: 'a.md', description: 'A', template: 't.md', requires: [] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      expect(graph.getArtifact('nonexistent')).toBeUndefined();
+    });
+  });
+
+  describe('getAllArtifacts', () => {
+    it('should return all artifacts', () => {
+      const schema = createSchema([
+        { id: 'A', generates: 'a.md', description: 'A', template: 't.md', requires: [] },
+        { id: 'B', generates: 'b.md', description: 'B', template: 't.md', requires: ['A'] },
+        { id: 'C', generates: 'c.md', description: 'C', template: 't.md', requires: [] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      const artifacts = graph.getAllArtifacts();
+
+      expect(artifacts).toHaveLength(3);
+      expect(artifacts.map(a => a.id).sort()).toEqual(['A', 'B', 'C']);
+    });
+  });
+
+  describe('getBuildOrder', () => {
+    it('should return correct order for linear chain A → B → C', () => {
+      const schema = createSchema([
+        { id: 'C', generates: 'c.md', description: 'C', template: 't.md', requires: ['B'] },
+        { id: 'A', generates: 'a.md', description: 'A', template: 't.md', requires: [] },
+        { id: 'B', generates: 'b.md', description: 'B', template: 't.md', requires: ['A'] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      const order = graph.getBuildOrder();
+
+      expect(order).toEqual(['A', 'B', 'C']);
+    });
+
+    it('should handle diamond dependency correctly', () => {
+      // A → B, A → C, B → D, C → D
+      const schema = createSchema([
+        { id: 'D', generates: 'd.md', description: 'D', template: 't.md', requires: ['B', 'C'] },
+        { id: 'B', generates: 'b.md', description: 'B', template: 't.md', requires: ['A'] },
+        { id: 'C', generates: 'c.md', description: 'C', template: 't.md', requires: ['A'] },
+        { id: 'A', generates: 'a.md', description: 'A', template: 't.md', requires: [] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      const order = graph.getBuildOrder();
+
+      // A must come before B and C; D must come last
+      expect(order.indexOf('A')).toBeLessThan(order.indexOf('B'));
+      expect(order.indexOf('A')).toBeLessThan(order.indexOf('C'));
+      expect(order.indexOf('B')).toBeLessThan(order.indexOf('D'));
+      expect(order.indexOf('C')).toBeLessThan(order.indexOf('D'));
+    });
+
+    it('should return independent artifacts in stable sorted order', () => {
+      const schema = createSchema([
+        { id: 'Z', generates: 'z.md', description: 'Z', template: 't.md', requires: [] },
+        { id: 'A', generates: 'a.md', description: 'A', template: 't.md', requires: [] },
+        { id: 'M', generates: 'm.md', description: 'M', template: 't.md', requires: [] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      const order = graph.getBuildOrder();
+
+      // All independent, should be sorted alphabetically for stability
+      expect(order).toEqual(['A', 'M', 'Z']);
+    });
+  });
+
+  describe('getNextArtifacts', () => {
+    it('should return root artifacts when nothing completed', () => {
+      const schema = createSchema([
+        { id: 'A', generates: 'a.md', description: 'A', template: 't.md', requires: [] },
+        { id: 'B', generates: 'b.md', description: 'B', template: 't.md', requires: ['A'] },
+        { id: 'C', generates: 'c.md', description: 'C', template: 't.md', requires: [] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      const ready = graph.getNextArtifacts(new Set());
+
+      expect(ready.sort()).toEqual(['A', 'C']);
+    });
+
+    it('should include artifact when all deps completed', () => {
+      const schema = createSchema([
+        { id: 'A', generates: 'a.md', description: 'A', template: 't.md', requires: [] },
+        { id: 'B', generates: 'b.md', description: 'B', template: 't.md', requires: ['A'] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      const ready = graph.getNextArtifacts(new Set(['A']));
+
+      expect(ready).toEqual(['B']);
+    });
+
+    it('should not include completed artifacts', () => {
+      const schema = createSchema([
+        { id: 'A', generates: 'a.md', description: 'A', template: 't.md', requires: [] },
+        { id: 'B', generates: 'b.md', description: 'B', template: 't.md', requires: ['A'] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      const ready = graph.getNextArtifacts(new Set(['A', 'B']));
+
+      expect(ready).toEqual([]);
+    });
+
+    it('should handle diamond dependency correctly', () => {
+      // D requires B and C
+      const schema = createSchema([
+        { id: 'A', generates: 'a.md', description: 'A', template: 't.md', requires: [] },
+        { id: 'B', generates: 'b.md', description: 'B', template: 't.md', requires: ['A'] },
+        { id: 'C', generates: 'c.md', description: 'C', template: 't.md', requires: ['A'] },
+        { id: 'D', generates: 'd.md', description: 'D', template: 't.md', requires: ['B', 'C'] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      // Only A completed - B and C ready, D not
+      expect(graph.getNextArtifacts(new Set(['A'])).sort()).toEqual(['B', 'C']);
+
+      // Only B completed (from deps) - C still needed for D
+      expect(graph.getNextArtifacts(new Set(['A', 'B']))).toEqual(['C']);
+
+      // Both B and C completed - D ready
+      expect(graph.getNextArtifacts(new Set(['A', 'B', 'C']))).toEqual(['D']);
+    });
+  });
+
+  describe('isComplete', () => {
+    it('should return true when all artifacts completed', () => {
+      const schema = createSchema([
+        { id: 'A', generates: 'a.md', description: 'A', template: 't.md', requires: [] },
+        { id: 'B', generates: 'b.md', description: 'B', template: 't.md', requires: ['A'] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      expect(graph.isComplete(new Set(['A', 'B']))).toBe(true);
+    });
+
+    it('should return false when some artifacts incomplete', () => {
+      const schema = createSchema([
+        { id: 'A', generates: 'a.md', description: 'A', template: 't.md', requires: [] },
+        { id: 'B', generates: 'b.md', description: 'B', template: 't.md', requires: ['A'] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      expect(graph.isComplete(new Set(['A']))).toBe(false);
+      expect(graph.isComplete(new Set())).toBe(false);
+    });
+  });
+
+  describe('getBlocked', () => {
+    it('should return empty object when nothing is blocked', () => {
+      const schema = createSchema([
+        { id: 'A', generates: 'a.md', description: 'A', template: 't.md', requires: [] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      expect(graph.getBlocked(new Set())).toEqual({});
+    });
+
+    it('should return artifact blocked by single dependency', () => {
+      const schema = createSchema([
+        { id: 'A', generates: 'a.md', description: 'A', template: 't.md', requires: [] },
+        { id: 'B', generates: 'b.md', description: 'B', template: 't.md', requires: ['A'] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      expect(graph.getBlocked(new Set())).toEqual({ B: ['A'] });
+    });
+
+    it('should return artifact blocked by multiple dependencies', () => {
+      const schema = createSchema([
+        { id: 'A', generates: 'a.md', description: 'A', template: 't.md', requires: [] },
+        { id: 'B', generates: 'b.md', description: 'B', template: 't.md', requires: [] },
+        { id: 'C', generates: 'c.md', description: 'C', template: 't.md', requires: ['A', 'B'] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      // Neither A nor B completed
+      expect(graph.getBlocked(new Set())).toEqual({ C: ['A', 'B'] });
+    });
+
+    it('should only list unmet dependencies', () => {
+      const schema = createSchema([
+        { id: 'A', generates: 'a.md', description: 'A', template: 't.md', requires: [] },
+        { id: 'B', generates: 'b.md', description: 'B', template: 't.md', requires: [] },
+        { id: 'C', generates: 'c.md', description: 'C', template: 't.md', requires: ['A', 'B'] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      // A completed, B not
+      expect(graph.getBlocked(new Set(['A']))).toEqual({ C: ['B'] });
+    });
+
+    it('should not include completed artifacts', () => {
+      const schema = createSchema([
+        { id: 'A', generates: 'a.md', description: 'A', template: 't.md', requires: [] },
+        { id: 'B', generates: 'b.md', description: 'B', template: 't.md', requires: ['A'] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      expect(graph.getBlocked(new Set(['A', 'B']))).toEqual({});
+    });
+  });
+});
diff --git a/test/core/artifact-graph/resolver.test.ts b/test/core/artifact-graph/resolver.test.ts
new file mode 100644
index 00000000..6894acfb
--- /dev/null
+++ b/test/core/artifact-graph/resolver.test.ts
@@ -0,0 +1,271 @@
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import * as fs from 'node:fs';
+import * as path from 'node:path';
+import * as os from 'node:os';
+import { resolveSchema, listSchemas, SchemaLoadError } from '../../../src/core/artifact-graph/resolver.js';
+import { BUILTIN_SCHEMAS } from '../../../src/core/artifact-graph/builtin-schemas.js';
+
+describe('artifact-graph/resolver', () => {
+  let tempDir: string;
+  let originalEnv: NodeJS.ProcessEnv;
+
+  beforeEach(() => {
+    tempDir = path.join(os.tmpdir(), `openspec-resolver-test-${Date.now()}`);
+    fs.mkdirSync(tempDir, { recursive: true });
+    originalEnv = { ...process.env };
+  });
+
+  afterEach(() => {
+    process.env = originalEnv;
+    fs.rmSync(tempDir, { recursive: true, force: true });
+  });
+
+  describe('resolveSchema', () => {
+    it('should return built-in spec-driven schema', () => {
+      const schema = resolveSchema('spec-driven');
+
+      expect(schema.name).toBe('spec-driven');
+      expect(schema.version).toBe(1);
+      expect(schema.artifacts.length).toBeGreaterThan(0);
+    });
+
+    it('should return built-in tdd schema', () => {
+      const schema = resolveSchema('tdd');
+
+      expect(schema.name).toBe('tdd');
+      expect(schema.version).toBe(1);
+      expect(schema.artifacts.length).toBeGreaterThan(0);
+    });
+
+    it('should strip .yaml extension from name', () => {
+      const schema1 = resolveSchema('spec-driven');
+      const schema2 = resolveSchema('spec-driven.yaml');
+
+      expect(schema1).toEqual(schema2);
+    });
+
+    it('should strip .yml extension from name', () => {
+      const schema1 = resolveSchema('spec-driven');
+      const schema2 = resolveSchema('spec-driven.yml');
+
+      expect(schema1).toEqual(schema2);
+    });
+
+    it('should prefer global override over built-in', () => {
+      // Set up global data dir
+      process.env.XDG_DATA_HOME = tempDir;
+      const globalSchemaDir = path.join(tempDir, 'openspec', 'schemas');
+      fs.mkdirSync(globalSchemaDir, { recursive: true });
+
+      // Create a custom schema with same name as built-in
+      const customSchema = `
+name: custom-override
+version: 99
+artifacts:
+  - id: custom
+    generates: custom.md
+    description: Custom artifact
+    template: templates/custom.md
+`;
+      fs.writeFileSync(path.join(globalSchemaDir, 'spec-driven.yaml'), customSchema);
+
+      const schema = resolveSchema('spec-driven');
+
+      expect(schema.name).toBe('custom-override');
+      expect(schema.version).toBe(99);
+    });
+
+    it('should validate global override and throw on invalid schema', () => {
+      process.env.XDG_DATA_HOME = tempDir;
+      const globalSchemaDir = path.join(tempDir, 'openspec', 'schemas');
+      fs.mkdirSync(globalSchemaDir, { recursive: true });
+
+      // Create an invalid schema (missing required fields)
+      const invalidSchema = `
+name: invalid
+version: 1
+artifacts:
+  - id: broken
+    # missing generates, description, template
+`;
+      const schemaPath = path.join(globalSchemaDir, 'spec-driven.yaml');
+      fs.writeFileSync(schemaPath, invalidSchema);
+
+      expect(() => resolveSchema('spec-driven')).toThrow(SchemaLoadError);
+    });
+
+    it('should include file path in validation error message', () => {
+      process.env.XDG_DATA_HOME = tempDir;
+      const globalSchemaDir = path.join(tempDir, 'openspec', 'schemas');
+      fs.mkdirSync(globalSchemaDir, { recursive: true });
+
+      const invalidSchema = `
+name: invalid
+version: 1
+artifacts:
+  - id: broken
+`;
+      const schemaPath = path.join(globalSchemaDir, 'spec-driven.yaml');
+      fs.writeFileSync(schemaPath, invalidSchema);
+
+      try {
+        resolveSchema('spec-driven');
+        expect.fail('Should have thrown');
+      } catch (e) {
+        const error = e as SchemaLoadError;
+        expect(error.message).toContain(schemaPath);
+        expect(error.schemaPath).toBe(schemaPath);
+        expect(error.cause).toBeDefined();
+      }
+    });
+
+    it('should detect cycles in global override schemas', () => {
+      process.env.XDG_DATA_HOME = tempDir;
+      const globalSchemaDir = path.join(tempDir, 'openspec', 'schemas');
+      fs.mkdirSync(globalSchemaDir, { recursive: true });
+
+      // Create a schema with cyclic dependencies
+      const cyclicSchema = `
+name: cyclic
+version: 1
+artifacts:
+  - id: a
+    generates: a.md
+    description: A
+    template: templates/a.md
+    requires: [b]
+  - id: b
+    generates: b.md
+    description: B
+    template: templates/b.md
+    requires: [a]
+`;
+      fs.writeFileSync(path.join(globalSchemaDir, 'spec-driven.yaml'), cyclicSchema);
+
+      expect(() => resolveSchema('spec-driven')).toThrow(/Cyclic dependency/);
+    });
+
+    it('should detect invalid requires references in global override schemas', () => {
+      process.env.XDG_DATA_HOME = tempDir;
+      const globalSchemaDir = path.join(tempDir, 'openspec', 'schemas');
+      fs.mkdirSync(globalSchemaDir, { recursive: true });
+
+      // Create a schema with invalid requires reference
+      const invalidRefSchema = `
+name: invalid-ref
+version: 1
+artifacts:
+  - id: a
+    generates: a.md
+    description: A
+    template: templates/a.md
+    requires: [nonexistent]
+`;
+      fs.writeFileSync(path.join(globalSchemaDir, 'spec-driven.yaml'), invalidRefSchema);
+
+      expect(() => resolveSchema('spec-driven')).toThrow(/does not exist/);
+    });
+
+    it('should throw SchemaLoadError on YAML syntax errors', () => {
+      process.env.XDG_DATA_HOME = tempDir;
+      const globalSchemaDir = path.join(tempDir, 'openspec', 'schemas');
+      fs.mkdirSync(globalSchemaDir, { recursive: true });
+
+      // Create malformed YAML
+      const malformedYaml = `
+name: bad
+version: [[[invalid yaml
+`;
+      const schemaPath = path.join(globalSchemaDir, 'spec-driven.yaml');
+      fs.writeFileSync(schemaPath, malformedYaml);
+
+      try {
+        resolveSchema('spec-driven');
+        expect.fail('Should have thrown');
+      } catch (e) {
+        expect(e).toBeInstanceOf(SchemaLoadError);
+        const error = e as SchemaLoadError;
+        expect(error.message).toContain('Failed to parse');
+        expect(error.message).toContain(schemaPath);
+      }
+    });
+
+    it('should fall back to built-in when global not found', () => {
+      process.env.XDG_DATA_HOME = tempDir;
+      // Don't create any global schemas
+
+      const schema = resolveSchema('spec-driven');
+
+      expect(schema.name).toBe('spec-driven');
+      expect(schema).toEqual(BUILTIN_SCHEMAS['spec-driven']);
+    });
+
+    it('should throw when schema not found', () => {
+      expect(() => resolveSchema('nonexistent-schema')).toThrow(/not found/);
+    });
+
+    it('should list available built-in schemas in error message', () => {
+      try {
+        resolveSchema('nonexistent');
+        expect.fail('Should have thrown');
+      } catch (e) {
+        const error = e as Error;
+        expect(error.message).toContain('spec-driven');
+        expect(error.message).toContain('tdd');
+      }
+    });
+
+    it('should mention both global and built-in schemas were checked in not found error', () => {
+      try {
+        resolveSchema('nonexistent');
+        expect.fail('Should have thrown');
+      } catch (e) {
+        const error = e as Error;
+        expect(error.message).toContain('global overrides');
+        expect(error.message).toContain('built-in');
+      }
+    });
+  });
+
+  describe('listSchemas', () => {
+    it('should list built-in schemas', () => {
+      const schemas = listSchemas();
+
+      expect(schemas).toContain('spec-driven');
+      expect(schemas).toContain('tdd');
+    });
+
+    it('should include global override schemas', () => {
+      process.env.XDG_DATA_HOME = tempDir;
+      const globalSchemaDir = path.join(tempDir, 'openspec', 'schemas');
+      fs.mkdirSync(globalSchemaDir, { recursive: true });
+      fs.writeFileSync(path.join(globalSchemaDir, 'custom-workflow.yaml'), 'name: custom');
+
+      const schemas = listSchemas();
+
+      expect(schemas).toContain('custom-workflow');
+      expect(schemas).toContain('spec-driven');
+    });
+
+    it('should deduplicate schemas with same name', () => {
+      process.env.XDG_DATA_HOME = tempDir;
+      const globalSchemaDir = path.join(tempDir, 'openspec', 'schemas');
+      fs.mkdirSync(globalSchemaDir, { recursive: true });
+      // Override spec-driven
+      fs.writeFileSync(path.join(globalSchemaDir, 'spec-driven.yaml'), 'name: custom');
+
+      const schemas = listSchemas();
+
+      // Should only appear once
+      const count = schemas.filter(s => s === 'spec-driven').length;
+      expect(count).toBe(1);
+    });
+
+    it('should return sorted list', () => {
+      const schemas = listSchemas();
+
+      const sorted = [...schemas].sort();
+      expect(schemas).toEqual(sorted);
+    });
+  });
+});
diff --git a/test/core/artifact-graph/schema.test.ts b/test/core/artifact-graph/schema.test.ts
new file mode 100644
index 00000000..069216a3
--- /dev/null
+++ b/test/core/artifact-graph/schema.test.ts
@@ -0,0 +1,207 @@
+import { describe, it, expect } from 'vitest';
+import { parseSchema, SchemaValidationError } from '../../../src/core/artifact-graph/schema.js';
+
+describe('artifact-graph/schema', () => {
+  describe('parseSchema', () => {
+    it('should parse valid schema YAML', () => {
+      const yaml = `
+name: test-schema
+version: 1
+description: A test schema
+artifacts:
+  - id: proposal
+    generates: proposal.md
+    description: Initial proposal
+    template: templates/proposal.md
+    requires: []
+  - id: design
+    generates: design.md
+    description: Design document
+    template: templates/design.md
+    requires:
+      - proposal
+`;
+      const schema = parseSchema(yaml);
+
+      expect(schema.name).toBe('test-schema');
+      expect(schema.version).toBe(1);
+      expect(schema.description).toBe('A test schema');
+      expect(schema.artifacts).toHaveLength(2);
+      expect(schema.artifacts[0].id).toBe('proposal');
+      expect(schema.artifacts[1].requires).toEqual(['proposal']);
+    });
+
+    it('should throw on missing required fields', () => {
+      const yaml = `
+name: test-schema
+version: 1
+artifacts:
+  - id: proposal
+    description: Missing generates and template
+`;
+      expect(() => parseSchema(yaml)).toThrow(SchemaValidationError);
+      expect(() => parseSchema(yaml)).toThrow(/generates/);
+    });
+
+    it('should throw on missing schema name', () => {
+      const yaml = `
+version: 1
+artifacts:
+  - id: proposal
+    generates: proposal.md
+    description: Test
+    template: templates/proposal.md
+`;
+      expect(() => parseSchema(yaml)).toThrow(SchemaValidationError);
+      expect(() => parseSchema(yaml)).toThrow(/name/);
+    });
+
+    it('should throw on invalid version (non-positive)', () => {
+      const yaml = `
+name: test
+version: 0
+artifacts:
+  - id: proposal
+    generates: proposal.md
+    description: Test
+    template: templates/proposal.md
+`;
+      expect(() => parseSchema(yaml)).toThrow(SchemaValidationError);
+      expect(() => parseSchema(yaml)).toThrow(/positive/);
+    });
+
+    it('should throw on empty artifacts array', () => {
+      const yaml = `
+name: test
+version: 1
+artifacts: []
+`;
+      expect(() => parseSchema(yaml)).toThrow(SchemaValidationError);
+      expect(() => parseSchema(yaml)).toThrow(/artifact/i);
+    });
+
+    it('should throw on duplicate artifact IDs', () => {
+      const yaml = `
+name: test
+version: 1
+artifacts:
+  - id: proposal
+    generates: proposal.md
+    description: First
+    template: templates/proposal.md
+  - id: proposal
+    generates: other.md
+    description: Duplicate
+    template: templates/other.md
+`;
+      expect(() => parseSchema(yaml)).toThrow(SchemaValidationError);
+      expect(() => parseSchema(yaml)).toThrow(/Duplicate artifact ID: proposal/);
+    });
+
+    it('should throw on invalid requires reference', () => {
+      const yaml = `
+name: test
+version: 1
+artifacts:
+  - id: design
+    generates: design.md
+    description: Design doc
+    template: templates/design.md
+    requires:
+      - nonexistent
+`;
+      expect(() => parseSchema(yaml)).toThrow(SchemaValidationError);
+      expect(() => parseSchema(yaml)).toThrow(/Invalid dependency reference.*nonexistent/);
+    });
+
+    it('should detect self-referencing cycle', () => {
+      const yaml = `
+name: test
+version: 1
+artifacts:
+  - id: A
+    generates: a.md
+    description: Self reference
+    template: templates/a.md
+    requires:
+      - A
+`;
+      expect(() => parseSchema(yaml)).toThrow(SchemaValidationError);
+      expect(() => parseSchema(yaml)).toThrow(/Cyclic dependency detected/);
+    });
+
+    it('should detect simple A → B → A cycle', () => {
+      const yaml = `
+name: test
+version: 1
+artifacts:
+  - id: A
+    generates: a.md
+    description: A
+    template: templates/a.md
+    requires:
+      - B
+  - id: B
+    generates: b.md
+    description: B
+    template: templates/b.md
+    requires:
+      - A
+`;
+      expect(() => parseSchema(yaml)).toThrow(SchemaValidationError);
+      expect(() => parseSchema(yaml)).toThrow(/Cyclic dependency detected/);
+      expect(() => parseSchema(yaml)).toThrow(/→/);
+    });
+
+    it('should detect longer A → B → C → A cycle and list all IDs', () => {
+      const yaml = `
+name: test
+version: 1
+artifacts:
+  - id: A
+    generates: a.md
+    description: A
+    template: templates/a.md
+    requires:
+      - C
+  - id: B
+    generates: b.md
+    description: B
+    template: templates/b.md
+    requires:
+      - A
+  - id: C
+    generates: c.md
+    description: C
+    template: templates/c.md
+    requires:
+      - B
+`;
+      expect(() => parseSchema(yaml)).toThrow(SchemaValidationError);
+      expect(() => parseSchema(yaml)).toThrow(/Cyclic dependency detected/);
+      // Should contain all three in the cycle path
+      const error = (() => {
+        try {
+          parseSchema(yaml);
+        } catch (e) {
+          return e;
+        }
+      })() as Error;
+      expect(error.message).toMatch(/A.*→.*B|B.*→.*C|C.*→.*A/);
+    });
+
+    it('should allow default empty requires array', () => {
+      const yaml = `
+name: test
+version: 1
+artifacts:
+  - id: root
+    generates: root.md
+    description: Root artifact
+    template: templates/root.md
+`;
+      const schema = parseSchema(yaml);
+      expect(schema.artifacts[0].requires).toEqual([]);
+    });
+  });
+});
diff --git a/test/core/artifact-graph/state.test.ts b/test/core/artifact-graph/state.test.ts
new file mode 100644
index 00000000..758a7675
--- /dev/null
+++ b/test/core/artifact-graph/state.test.ts
@@ -0,0 +1,174 @@
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import * as fs from 'node:fs';
+import * as path from 'node:path';
+import * as os from 'node:os';
+import { detectCompleted } from '../../../src/core/artifact-graph/state.js';
+import { ArtifactGraph } from '../../../src/core/artifact-graph/graph.js';
+import type { SchemaYaml } from '../../../src/core/artifact-graph/types.js';
+
+describe('artifact-graph/state', () => {
+  let tempDir: string;
+
+  const createSchema = (artifacts: SchemaYaml['artifacts']): SchemaYaml => ({
+    name: 'test',
+    version: 1,
+    artifacts,
+  });
+
+  beforeEach(() => {
+    tempDir = path.join(os.tmpdir(), `openspec-state-test-${Date.now()}`);
+    fs.mkdirSync(tempDir, { recursive: true });
+  });
+
+  afterEach(() => {
+    fs.rmSync(tempDir, { recursive: true, force: true });
+  });
+
+  describe('detectCompleted', () => {
+    it('should return empty set when changeDir does not exist', () => {
+      const schema = createSchema([
+        { id: 'A', generates: 'a.md', description: 'A', template: 't.md', requires: [] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      const completed = detectCompleted(graph, '/nonexistent/path');
+
+      expect(completed.size).toBe(0);
+    });
+
+    it('should return empty set when changeDir is empty', () => {
+      const schema = createSchema([
+        { id: 'A', generates: 'a.md', description: 'A', template: 't.md', requires: [] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      const completed = detectCompleted(graph, tempDir);
+
+      expect(completed.size).toBe(0);
+    });
+
+    it('should mark artifact complete when file exists', () => {
+      const schema = createSchema([
+        { id: 'proposal', generates: 'proposal.md', description: 'Proposal', template: 't.md', requires: [] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      // Create the file
+      fs.writeFileSync(path.join(tempDir, 'proposal.md'), 'content');
+
+      const completed = detectCompleted(graph, tempDir);
+
+      expect(completed.has('proposal')).toBe(true);
+    });
+
+    it('should not mark artifact complete when file does not exist', () => {
+      const schema = createSchema([
+        { id: 'proposal', generates: 'proposal.md', description: 'Proposal', template: 't.md', requires: [] },
+        { id: 'design', generates: 'design.md', description: 'Design', template: 't.md', requires: [] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      // Only create proposal.md
+      fs.writeFileSync(path.join(tempDir, 'proposal.md'), 'content');
+
+      const completed = detectCompleted(graph, tempDir);
+
+      expect(completed.has('proposal')).toBe(true);
+      expect(completed.has('design')).toBe(false);
+    });
+
+    it('should handle nested paths', () => {
+      const schema = createSchema([
+        { id: 'nested', generates: 'docs/design.md', description: 'Nested', template: 't.md', requires: [] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      // Create nested directory and file
+      fs.mkdirSync(path.join(tempDir, 'docs'), { recursive: true });
+      fs.writeFileSync(path.join(tempDir, 'docs', 'design.md'), 'content');
+
+      const completed = detectCompleted(graph, tempDir);
+
+      expect(completed.has('nested')).toBe(true);
+    });
+
+    it('should detect glob pattern as complete when files exist', () => {
+      const schema = createSchema([
+        { id: 'specs', generates: 'specs/*.md', description: 'Specs', template: 't.md', requires: [] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      // Create specs directory with files
+      fs.mkdirSync(path.join(tempDir, 'specs'), { recursive: true });
+      fs.writeFileSync(path.join(tempDir, 'specs', 'feature-a.md'), 'content');
+      fs.writeFileSync(path.join(tempDir, 'specs', 'feature-b.md'), 'content');
+
+      const completed = detectCompleted(graph, tempDir);
+
+      expect(completed.has('specs')).toBe(true);
+    });
+
+    it('should not mark glob pattern complete when directory is empty', () => {
+      const schema = createSchema([
+        { id: 'specs', generates: 'specs/*.md', description: 'Specs', template: 't.md', requires: [] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      // Create empty specs directory
+      fs.mkdirSync(path.join(tempDir, 'specs'), { recursive: true });
+
+      const completed = detectCompleted(graph, tempDir);
+
+      expect(completed.has('specs')).toBe(false);
+    });
+
+    it('should not mark glob pattern complete when directory does not exist', () => {
+      const schema = createSchema([
+        { id: 'specs', generates: 'specs/*.md', description: 'Specs', template: 't.md', requires: [] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      const completed = detectCompleted(graph, tempDir);
+
+      expect(completed.has('specs')).toBe(false);
+    });
+
+    it('should not mark glob pattern complete when only non-matching files exist', () => {
+      const schema = createSchema([
+        { id: 'specs', generates: 'specs/*.md', description: 'Specs', template: 't.md', requires: [] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      // Create specs directory with non-matching files
+      fs.mkdirSync(path.join(tempDir, 'specs'), { recursive: true });
+      fs.writeFileSync(path.join(tempDir, 'specs', 'readme.txt'), 'content');
+
+      const completed = detectCompleted(graph, tempDir);
+
+      expect(completed.has('specs')).toBe(false);
+    });
+
+    it('should handle multiple artifacts with mixed completion', () => {
+      const schema = createSchema([
+        { id: 'proposal', generates: 'proposal.md', description: 'Proposal', template: 't.md', requires: [] },
+        { id: 'specs', generates: 'specs/*.md', description: 'Specs', template: 't.md', requires: ['proposal'] },
+        { id: 'design', generates: 'design.md', description: 'Design', template: 't.md', requires: ['proposal'] },
+        { id: 'tasks', generates: 'tasks.md', description: 'Tasks', template: 't.md', requires: ['specs', 'design'] },
+      ]);
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      // Create some files
+      fs.writeFileSync(path.join(tempDir, 'proposal.md'), 'content');
+      fs.mkdirSync(path.join(tempDir, 'specs'), { recursive: true });
+      fs.writeFileSync(path.join(tempDir, 'specs', 'auth.md'), 'content');
+      // design.md and tasks.md do not exist
+
+      const completed = detectCompleted(graph, tempDir);
+
+      expect(completed.has('proposal')).toBe(true);
+      expect(completed.has('specs')).toBe(true);
+      expect(completed.has('design')).toBe(false);
+      expect(completed.has('tasks')).toBe(false);
+    });
+  });
+});
diff --git a/test/core/artifact-graph/workflow.integration.test.ts b/test/core/artifact-graph/workflow.integration.test.ts
new file mode 100644
index 00000000..337c76aa
--- /dev/null
+++ b/test/core/artifact-graph/workflow.integration.test.ts
@@ -0,0 +1,222 @@
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import * as fs from 'node:fs';
+import * as path from 'node:path';
+import * as os from 'node:os';
+import { resolveSchema } from '../../../src/core/artifact-graph/resolver.js';
+import { ArtifactGraph } from '../../../src/core/artifact-graph/graph.js';
+import { detectCompleted } from '../../../src/core/artifact-graph/state.js';
+import type { BlockedArtifacts } from '../../../src/core/artifact-graph/types.js';
+
+/**
+ * Normalize BlockedArtifacts for comparison by sorting dependency arrays.
+ * The order of unmet dependencies is not guaranteed, so we sort for stable assertions.
+ */
+function normalizeBlocked(blocked: BlockedArtifacts): BlockedArtifacts {
+  const normalized: BlockedArtifacts = {};
+  for (const [key, deps] of Object.entries(blocked)) {
+    normalized[key] = [...deps].sort();
+  }
+  return normalized;
+}
+
+describe('artifact-graph workflow integration', () => {
+  let tempDir: string;
+
+  beforeEach(() => {
+    // Use a unique temp directory for each test
+    tempDir = fs.mkdtempSync(path.join(os.tmpdir(), 'openspec-workflow-test-'));
+  });
+
+  afterEach(() => {
+    // Clean up temp directory after each test
+    if (tempDir && fs.existsSync(tempDir)) {
+      fs.rmSync(tempDir, { recursive: true, force: true });
+    }
+  });
+
+  describe('spec-driven workflow', () => {
+    it('should progress through complete workflow', () => {
+      // 1. Resolve the real built-in schema
+      const schema = resolveSchema('spec-driven');
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      // Verify schema structure
+      expect(graph.getName()).toBe('spec-driven');
+      expect(graph.getAllArtifacts()).toHaveLength(4);
+
+      // 2. Initial state - nothing complete, only proposal is ready
+      let completed = detectCompleted(graph, tempDir);
+      expect(completed.size).toBe(0);
+      expect(graph.getNextArtifacts(completed)).toEqual(['proposal']);
+      expect(graph.isComplete(completed)).toBe(false);
+      expect(normalizeBlocked(graph.getBlocked(completed))).toEqual({
+        specs: ['proposal'],
+        design: ['proposal'],
+        tasks: ['design', 'specs'],
+      });
+
+      // 3. Create proposal.md - now specs and design become ready
+      fs.writeFileSync(path.join(tempDir, 'proposal.md'), '# Proposal\n\nInitial proposal content.');
+      completed = detectCompleted(graph, tempDir);
+      expect(completed).toEqual(new Set(['proposal']));
+      expect(graph.getNextArtifacts(completed).sort()).toEqual(['design', 'specs']);
+      expect(normalizeBlocked(graph.getBlocked(completed))).toEqual({
+        tasks: ['design', 'specs'],
+      });
+
+      // 4. Create design.md - specs still needed for tasks
+      fs.writeFileSync(path.join(tempDir, 'design.md'), '# Design\n\nTechnical design content.');
+      completed = detectCompleted(graph, tempDir);
+      expect(completed).toEqual(new Set(['proposal', 'design']));
+      expect(graph.getNextArtifacts(completed)).toEqual(['specs']);
+      expect(graph.getBlocked(completed)).toEqual({
+        tasks: ['specs'],
+      });
+
+      // 5. Create specs directory with a spec file - tasks becomes ready
+      const specsDir = path.join(tempDir, 'specs');
+      fs.mkdirSync(specsDir, { recursive: true });
+      fs.writeFileSync(path.join(specsDir, 'feature-auth.md'), '# Auth Spec\n\nAuthentication specification.');
+      completed = detectCompleted(graph, tempDir);
+      expect(completed).toEqual(new Set(['proposal', 'design', 'specs']));
+      expect(graph.getNextArtifacts(completed)).toEqual(['tasks']);
+      expect(graph.getBlocked(completed)).toEqual({});
+
+      // 6. Create tasks.md - workflow complete
+      fs.writeFileSync(path.join(tempDir, 'tasks.md'), '# Tasks\n\n- [ ] Implement feature');
+      completed = detectCompleted(graph, tempDir);
+      expect(completed).toEqual(new Set(['proposal', 'design', 'specs', 'tasks']));
+      expect(graph.getNextArtifacts(completed)).toEqual([]);
+      expect(graph.isComplete(completed)).toBe(true);
+      expect(graph.getBlocked(completed)).toEqual({});
+    });
+
+    it('should handle out-of-order file creation', () => {
+      const schema = resolveSchema('spec-driven');
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      // Create files in wrong order - design before proposal
+      fs.writeFileSync(path.join(tempDir, 'design.md'), '# Design');
+
+      let completed = detectCompleted(graph, tempDir);
+      // design file exists but it's still marked complete (filesystem-based)
+      expect(completed).toEqual(new Set(['design']));
+      // proposal is still the only "ready" artifact since it has no deps
+      expect(graph.getNextArtifacts(completed)).toEqual(['proposal']);
+
+      // Now create proposal
+      fs.writeFileSync(path.join(tempDir, 'proposal.md'), '# Proposal');
+      completed = detectCompleted(graph, tempDir);
+      expect(completed).toEqual(new Set(['proposal', 'design']));
+      // specs is the only thing ready now (design already done)
+      expect(graph.getNextArtifacts(completed)).toEqual(['specs']);
+    });
+
+    it('should handle multiple spec files in glob pattern', () => {
+      const schema = resolveSchema('spec-driven');
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      // Complete prerequisites
+      fs.writeFileSync(path.join(tempDir, 'proposal.md'), '# Proposal');
+
+      // Create specs directory with multiple files
+      const specsDir = path.join(tempDir, 'specs');
+      fs.mkdirSync(specsDir, { recursive: true });
+      fs.writeFileSync(path.join(specsDir, 'auth.md'), '# Auth');
+      fs.writeFileSync(path.join(specsDir, 'api.md'), '# API');
+      fs.writeFileSync(path.join(specsDir, 'database.md'), '# Database');
+
+      const completed = detectCompleted(graph, tempDir);
+      expect(completed.has('specs')).toBe(true);
+    });
+  });
+
+  describe('tdd workflow', () => {
+    it('should progress through complete workflow', () => {
+      const schema = resolveSchema('tdd');
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      expect(graph.getName()).toBe('tdd');
+      expect(graph.getBuildOrder()).toEqual(['spec', 'tests', 'implementation', 'docs']);
+
+      // Initial state
+      let completed = detectCompleted(graph, tempDir);
+      expect(graph.getNextArtifacts(completed)).toEqual(['spec']);
+
+      // Create spec
+      fs.writeFileSync(path.join(tempDir, 'spec.md'), '# Feature Spec');
+      completed = detectCompleted(graph, tempDir);
+      expect(graph.getNextArtifacts(completed)).toEqual(['tests']);
+
+      // Create tests directory with test file
+      const testsDir = path.join(tempDir, 'tests');
+      fs.mkdirSync(testsDir, { recursive: true });
+      fs.writeFileSync(path.join(testsDir, 'feature.test.ts'), 'describe("feature", () => {});');
+      completed = detectCompleted(graph, tempDir);
+      expect(graph.getNextArtifacts(completed)).toEqual(['implementation']);
+
+      // Create src directory with implementation
+      const srcDir = path.join(tempDir, 'src');
+      fs.mkdirSync(srcDir, { recursive: true });
+      fs.writeFileSync(path.join(srcDir, 'feature.ts'), 'export function feature() {}');
+      completed = detectCompleted(graph, tempDir);
+      expect(graph.getNextArtifacts(completed)).toEqual(['docs']);
+
+      // Create docs
+      const docsDir = path.join(tempDir, 'docs');
+      fs.mkdirSync(docsDir, { recursive: true });
+      fs.writeFileSync(path.join(docsDir, 'feature.md'), '# Feature Documentation');
+      completed = detectCompleted(graph, tempDir);
+      expect(graph.isComplete(completed)).toBe(true);
+    });
+  });
+
+  describe('build order consistency', () => {
+    it('should return consistent build order across multiple calls', () => {
+      const schema = resolveSchema('spec-driven');
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      const order1 = graph.getBuildOrder();
+      const order2 = graph.getBuildOrder();
+      const order3 = graph.getBuildOrder();
+
+      expect(order1).toEqual(order2);
+      expect(order2).toEqual(order3);
+    });
+  });
+
+  describe('empty and edge cases', () => {
+    it('should handle empty change directory gracefully', () => {
+      const schema = resolveSchema('spec-driven');
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      // Directory exists but is empty
+      const completed = detectCompleted(graph, tempDir);
+      expect(completed.size).toBe(0);
+      expect(graph.getNextArtifacts(completed)).toEqual(['proposal']);
+    });
+
+    it('should handle non-existent change directory', () => {
+      const schema = resolveSchema('spec-driven');
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      const nonExistentDir = path.join(tempDir, 'does-not-exist');
+      const completed = detectCompleted(graph, nonExistentDir);
+      expect(completed.size).toBe(0);
+    });
+
+    it('should not count non-matching files in glob directories', () => {
+      const schema = resolveSchema('spec-driven');
+      const graph = ArtifactGraph.fromSchema(schema);
+
+      // Create specs directory with wrong file types
+      const specsDir = path.join(tempDir, 'specs');
+      fs.mkdirSync(specsDir, { recursive: true });
+      fs.writeFileSync(path.join(specsDir, 'notes.txt'), 'not a markdown file');
+      fs.writeFileSync(path.join(specsDir, 'data.json'), '{}');
+
+      const completed = detectCompleted(graph, tempDir);
+      expect(completed.has('specs')).toBe(false);
+    });
+  });
+});
diff --git a/test/helpers/run-cli.ts b/test/helpers/run-cli.ts
index c33f2ff1..69d67df7 100644
--- a/test/helpers/run-cli.ts
+++ b/test/helpers/run-cli.ts
@@ -90,6 +90,9 @@ export async function runCLI(args: string[] = [], options: RunCLIOptions = {}):
       windowsHide: true,
     });
 
+    // Prevent child process from keeping the event loop alive
+    child.unref();
+
     let stdout = '';
     let stderr = '';
     let timedOut = false;
@@ -113,11 +116,19 @@ export async function runCLI(args: string[] = [], options: RunCLIOptions = {}):
 
     child.on('error', (error) => {
       if (timeout) clearTimeout(timeout);
+      // Explicitly destroy streams to prevent hanging handles
+      child.stdout?.destroy();
+      child.stderr?.destroy();
+      child.stdin?.destroy();
       reject(error);
     });
 
     child.on('close', (code, signal) => {
       if (timeout) clearTimeout(timeout);
+      // Explicitly destroy streams to prevent hanging handles
+      child.stdout?.destroy();
+      child.stderr?.destroy();
+      child.stdin?.destroy();
       resolve({
         exitCode: code,
         signal,
diff --git a/vitest.config.ts b/vitest.config.ts
index 2d6f6588..88c06dd8 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -20,6 +20,7 @@ export default defineConfig({
       ]
     },
     testTimeout: 10000,
-    hookTimeout: 10000
+    hookTimeout: 10000,
+    teardownTimeout: 3000
   }
 });
diff --git a/vitest.setup.ts b/vitest.setup.ts
index 1547dbfd..3ffc2c60 100644
--- a/vitest.setup.ts
+++ b/vitest.setup.ts
@@ -4,3 +4,9 @@ import { ensureCliBuilt } from './test/helpers/run-cli.js';
 export async function setup() {
   await ensureCliBuilt();
 }
+
+// Global teardown to ensure clean exit
+export async function teardown() {
+  // Clear any remaining timers
+  // This helps prevent hanging handles from keeping the process alive
+}