feat(spec-writer): Subagent Spec Writer Pipeline (#76)

- specs/tri/spec_writer.tri: VIBEE spec for spec generation pipeline
- src/tri/tri_spec_writer.zig: extractModuleName, generateSpecContent, writeAndValidate
- 4/4 tests pass, vibee gen + ast-check validated
- Uses Zig 0.15.2 unmanaged ArrayList API (.empty, allocator per method)

Closes #76

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Antigravity Agent

specs/tri/spec_writer.tri

@@ -0,0 +1,156 @@
+# ═══════════════════════════════════════════════════════════════════════════════
+# VIBEE Specification — Spec Writer Pipeline
+# ═══════════════════════════════════════════════════════════════════════════════
+# φ² + 1/φ² = 3 = TRINITY
+# 📝 Generates .tri specs from GitHub issue descriptions
+# Pipeline Link integration: spec_create (Link 6)
+# ═══════════════════════════════════════════════════════════════════════════════
+
+name: spec_writer
+version: "1.0.0"
+language: zig
+module: spec_writer
+
+description: |
+  Spec Writer — generates well-formed .tri specifications from GitHub issues.
+
+  Input: issue number → fetches title, body, labels via gh CLI
+  Output: specs/tri/{module_name}.tri → ready for vibee gen
+
+  Template-based generation:
+  1. Parse issue → extract purpose, types, behaviors
+  2. Fill .tri YAML template
+  3. Write to specs/tri/
+  4. Validate via vibee gen
+  5. If compile fails → log to MU, retry with fixes
+
+# ═══════════════════════════════════════════════════════════════════════════════
+# TYPE SYSTEM
+# ═══════════════════════════════════════════════════════════════════════════════
+
+types:
+  IssueData:
+    fields:
+      number: Int
+      title: String
+      body: String
+      labels: List(String)
+
+  SpecField:
+    fields:
+      name: String
+      field_type: String
+
+  SpecType:
+    fields:
+      name: String
+      kind: String
+      fields: List(SpecField)
+      variants: List(String)
+
+  SpecBehavior:
+    fields:
+      name: String
+      description: String
+      inputs: List(SpecField)
+      output: String
+      steps: List(String)
+
+  GeneratedSpec:
+    fields:
+      module_name: String
+      spec_path: String
+      generated_path: String
+      compile_ok: Bool
+
+  WriteResult:
+    fields:
+      spec: GeneratedSpec
+      errors: List(String)
+
+# ═══════════════════════════════════════════════════════════════════════════════
+# BEHAVIORS
+# ═══════════════════════════════════════════════════════════════════════════════
+
+behaviors:
+  fetch_issue:
+    description: "Fetch GitHub issue data via gh CLI"
+    inputs:
+      - issue_number: Int
+    output: IssueData
+    steps:
+      - Run gh issue view {number} --json title,body,labels
+      - Parse JSON response
+      - Return IssueData struct
+
+  analyze_issue:
+    description: "Extract spec components from issue description"
+    inputs:
+      - issue: IssueData
+    output: List(SpecType)
+    steps:
+      - Parse title for module name
+      - Extract type definitions from body
+      - Identify behavior signatures
+      - Map labels to agent assignments
+
+  generate_spec:
+    description: "Generate .tri spec file from analyzed issue"
+    inputs:
+      - issue: IssueData
+      - types: List(SpecType)
+      - behaviors: List(SpecBehavior)
+    output: GeneratedSpec
+    steps:
+      - Build YAML header (name, version, language, module)
+      - Render types section
+      - Render behaviors section
+      - Write to specs/tri/{module_name}.tri
+
+  validate_spec:
+    description: "Run vibee gen + zig ast-check on generated spec"
+    inputs:
+      - spec: GeneratedSpec
+    output: WriteResult
+    steps:
+      - Run vibee gen {spec_path}
+      - Run zig ast-check {generated_path}
+      - If fail, collect errors
+      - Return WriteResult with compile status
+
+  write_from_issue:
+    description: "Full pipeline: issue → spec → codegen → validate"
+    inputs:
+      - issue_number: Int
+    output: WriteResult
+    steps:
+      - fetch_issue(issue_number)
+      - analyze_issue(issue)
+      - generate_spec(issue, types, behaviors)
+      - validate_spec(spec)
+      - If compile_ok, return success
+      - If fail, log to MU and return errors
+
+# ═══════════════════════════════════════════════════════════════════════════════
+# CONSTRAINTS
+# ═══════════════════════════════════════════════════════════════════════════════
+
+constraints:
+  - All generated specs MUST pass vibee gen without errors
+  - Module names derived from issue title (snake_case)
+  - Generated .zig MUST pass zig ast-check
+  - Maximum 3 retry attempts on compile failure
+  - Each retry logged to MU error patterns
+
+# ═══════════════════════════════════════════════════════════════════════════════
+# TESTS
+# ═══════════════════════════════════════════════════════════════════════════════
+
+tests:
+  - name: "generate spec from mock issue"
+    input: {number: 0, title: "test module", body: "A test", labels: []}
+    expected: {compile_ok: true}
+
+  - name: "snake_case module naming"
+    input: {title: "feat(mu): Agent MU Error Protocol"}
+    expected: {module_name: "agent_mu_error_protocol"}