diff --git a/Dockerfile.api b/Dockerfile.api
new file mode 100644
index 0000000..6c17f60
--- /dev/null
+++ b/Dockerfile.api
@@ -0,0 +1,14 @@
+FROM node:20-alpine AS api
+
+WORKDIR /app
+
+COPY package*.json ./
+RUN npm ci
+
+COPY src ./src
+COPY db ./db
+COPY tsconfig.json ./
+
+EXPOSE 4000
+
+CMD ["npm", "run", "server"]
diff --git a/README.md b/README.md
index 3df556b..06a277a 100644
--- a/README.md
+++ b/README.md
@@ -30,9 +30,15 @@ View your app in AI Studio: https://ai.studio/apps/b6ca5081-8525-4b56-8fbc-92c24
    `docker compose up --build -d`
 4. Open `http://localhost:8080`.
 
-The production image copies the local `dist` directory into
+The production compose stack runs two services:
+
+- `app`: nginx serves the host-built `dist` folder on `http://localhost:8080`
+- `api`: the VISA API runs on `http://localhost:4000`
+
+nginx also proxies API calls under `http://localhost:8080/api/...` to the API
+container. The frontend image copies the local `dist` directory into
 `nginx:stable-alpine3.23-slim`; it does not download Node or reinstall npm
-packages inside Docker.
+packages inside the frontend Docker image.
 
 **Development server (optional, downloads a Node image and dependencies):**
 
@@ -40,3 +46,6 @@ packages inside Docker.
 2. Start the development container:
    `docker compose -f docker-compose.dev.yml up --build`
 3. Open `http://localhost:3000`.
+
+The development compose stack runs Vite on `http://localhost:3000` and the VISA
+API on `http://localhost:4000`.
diff --git a/db/migrations/202606230001_create_visa_schema.sql b/db/migrations/202606230001_create_visa_schema.sql
new file mode 100644
index 0000000..cc59c27
--- /dev/null
+++ b/db/migrations/202606230001_create_visa_schema.sql
@@ -0,0 +1,207 @@
+create table if not exists models (
+  id text primary key,
+  name text not null,
+  description text not null default '',
+  domain text not null default '',
+  author text not null default '',
+  created_at timestamptz not null default now(),
+  updated_at timestamptz not null default now()
+);
+
+create table if not exists model_versions (
+  id text primary key,
+  model_id text not null references models (id) on delete cascade,
+  version_name text not null,
+  status text not null default 'draft' check (status in ('draft', 'checked', 'released', 'archived')),
+  source_protocol text not null default 'VISA',
+  created_by text not null default '',
+  created_at timestamptz not null default now(),
+  notes text not null default ''
+);
+
+create table if not exists visa_agents (
+  id text primary key,
+  model_version_id text not null references model_versions (id) on delete cascade,
+  name text not null,
+  symbol_set text not null,
+  instance_symbol text not null,
+  category text not null check (category in ('Environment', 'Space', 'Decision-maker', 'Passive')),
+  description text not null default '',
+  quantity_symbol text not null,
+  quantity_type text not null check (quantity_type in ('fixed', 'variable')),
+  quantity_value text not null,
+  sort_order integer not null default 0,
+  unique (model_version_id, name),
+  unique (model_version_id, symbol_set)
+);
+
+create table if not exists visa_variables (
+  id text primary key,
+  model_version_id text not null references model_versions (id) on delete cascade,
+  agent_id text not null references visa_agents (id) on delete cascade,
+  name text not null,
+  symbol text not null,
+  variable_type text not null check (variable_type in ('exog_homo', 'exog_hetero', 'endog_decision', 'endog_non_decision')),
+  data_type text not null,
+  value_source text not null,
+  unit text not null default '',
+  description text not null default '',
+  is_time_indexed boolean not null default false,
+  sort_order integer not null default 0,
+  unique (model_version_id, agent_id, name),
+  unique (model_version_id, symbol)
+);
+
+create table if not exists visa_sensing_relations (
+  id text primary key,
+  model_version_id text not null references model_versions (id) on delete cascade,
+  observer_agent_id text not null references visa_agents (id) on delete cascade,
+  observed_agent_id text not null references visa_agents (id) on delete cascade,
+  access_type text not null check (access_type in ('none', 'partial', 'all')),
+  scope text not null check (scope in ('self', 'peer', 'other', 'all', 'singleton')),
+  condition text not null default '',
+  notes text not null default ''
+);
+
+create table if not exists visa_sensing_variables (
+  sensing_relation_id text not null references visa_sensing_relations (id) on delete cascade,
+  variable_id text not null references visa_variables (id) on delete cascade,
+  primary key (sensing_relation_id, variable_id)
+);
+
+create table if not exists visa_internal_functions (
+  id text primary key,
+  model_version_id text not null references model_versions (id) on delete cascade,
+  agent_id text not null references visa_agents (id) on delete cascade,
+  function_code text not null,
+  name text not null,
+  method text not null,
+  reference text not null default '',
+  description text not null default '',
+  sort_order integer not null default 0,
+  unique (model_version_id, function_code)
+);
+
+create table if not exists visa_function_inputs (
+  function_id text not null references visa_internal_functions (id) on delete cascade,
+  variable_id text not null references visa_variables (id) on delete cascade,
+  source_type text not null check (source_type in ('self', 'sensed', 'input', 'output')),
+  expression text not null default '',
+  primary key (function_id, variable_id, source_type)
+);
+
+create table if not exists visa_function_updates (
+  id text primary key,
+  function_id text not null references visa_internal_functions (id) on delete cascade,
+  target_agent_id text references visa_agents (id) on delete set null,
+  variable_id text references visa_variables (id) on delete set null,
+  update_type text not null check (update_type in ('self_state', 'external_effect', 'create_agent', 'remove_agent')),
+  expression text not null default ''
+);
+
+create table if not exists visa_associated_data (
+  id text primary key,
+  model_version_id text not null references model_versions (id) on delete cascade,
+  data_code text not null,
+  title text not null,
+  data_type text not null check (data_type in ('Empirical', 'Literature', 'Generated')),
+  temporal_type text not null check (temporal_type in ('Static', 'Dynamic')),
+  source text not null,
+  collection_method text not null check (collection_method in ('Survey', 'Administrative', 'Sensor', 'Experimental', 'Computational')),
+  preprocessing_method text not null check (preprocessing_method in ('None', 'Selected', 'Aggregated', 'Transformed')),
+  record_count text not null default '',
+  availability text not null check (availability in ('Open', 'Restricted', 'Private')),
+  license text not null default '',
+  url_or_reference text not null default '',
+  description text not null default '',
+  unique (model_version_id, data_code)
+);
+
+create table if not exists visa_inputs (
+  id text primary key,
+  model_version_id text not null references model_versions (id) on delete cascade,
+  agent_id text not null references visa_agents (id) on delete cascade,
+  variable_id text not null references visa_variables (id) on delete cascade,
+  symbol text not null,
+  value_or_distribution text not null,
+  data_source_id text references visa_associated_data (id) on delete set null,
+  derivation text not null check (derivation in ('Direct', 'Estimated', 'Computed', 'Assumed')),
+  algorithm text not null default '',
+  reference text not null default '',
+  notes text not null default '',
+  unique (model_version_id, variable_id)
+);
+
+create table if not exists visa_outputs (
+  id text primary key,
+  model_version_id text not null references model_versions (id) on delete cascade,
+  symbol text not null,
+  indicator_name text not null,
+  formula text not null,
+  data_type text not null,
+  unit text not null default '',
+  frequency text not null,
+  description text not null default '',
+  unique (model_version_id, symbol)
+);
+
+create table if not exists visa_schedule_steps (
+  id text primary key,
+  model_version_id text not null references model_versions (id) on delete cascade,
+  step_number integer not null,
+  agent_id text not null references visa_agents (id) on delete cascade,
+  function_id text not null references visa_internal_functions (id) on delete cascade,
+  execution_mode text not null check (execution_mode in ('Synchronous', 'Sequential', 'Random-order', 'Asynchronous')),
+  execution_parameters text not null default '',
+  condition text not null default '',
+  sort_order integer not null default 0,
+  unique (model_version_id, step_number, function_id)
+);
+
+create table if not exists visa_termination_conditions (
+  id text primary key,
+  model_version_id text not null references model_versions (id) on delete cascade,
+  condition_code text not null,
+  indicator_symbol text not null,
+  condition_expression text not null,
+  description text not null default '',
+  value_source text not null default '',
+  termination_logic text not null,
+  unique (model_version_id, condition_code)
+);
+
+create table if not exists visa_validations (
+  id text primary key,
+  model_version_id text not null references model_versions (id) on delete cascade,
+  validation_code text not null,
+  level text not null check (level in ('Agent', 'Model', 'Output')),
+  validation_object text not null,
+  benchmark_data_id text references visa_associated_data (id) on delete set null,
+  method text not null,
+  indicator text not null,
+  passing_condition text not null,
+  reference text not null default '',
+  status text not null default 'pending' check (status in ('pending', 'passed', 'failed', 'blocked')),
+  notes text not null default '',
+  unique (model_version_id, validation_code)
+);
+
+create table if not exists visa_consistency_check_results (
+  id text primary key,
+  model_version_id text not null references model_versions (id) on delete cascade,
+  rule_code text not null,
+  rule_type text not null check (rule_type in ('within_table', 'cross_table')),
+  status text not null check (status in ('passed', 'failed', 'warning')),
+  message text not null,
+  related_table text not null default '',
+  related_record_id text not null default '',
+  checked_at timestamptz not null default now()
+);
+
+create index if not exists idx_model_versions_model on model_versions (model_id);
+create index if not exists idx_visa_agents_model_version on visa_agents (model_version_id);
+create index if not exists idx_visa_variables_agent on visa_variables (agent_id);
+create index if not exists idx_visa_sensing_observer on visa_sensing_relations (observer_agent_id);
+create index if not exists idx_visa_functions_agent on visa_internal_functions (agent_id);
+create index if not exists idx_visa_schedule_model_version on visa_schedule_steps (model_version_id, step_number);
+create index if not exists idx_visa_checks_model_version on visa_consistency_check_results (model_version_id, checked_at);
diff --git a/db/migrations/202606230001_create_visa_schema.test.ts b/db/migrations/202606230001_create_visa_schema.test.ts
new file mode 100644
index 0000000..90e7753
--- /dev/null
+++ b/db/migrations/202606230001_create_visa_schema.test.ts
@@ -0,0 +1,62 @@
+import assert from 'node:assert/strict';
+import { readFileSync } from 'node:fs';
+import { fileURLToPath } from 'node:url';
+import { dirname, join } from 'node:path';
+
+const currentDir = dirname(fileURLToPath(import.meta.url));
+const migration = readFileSync(join(currentDir, '202606230001_create_visa_schema.sql'), 'utf8');
+
+const requiredTables = [
+  'models',
+  'model_versions',
+  'visa_agents',
+  'visa_variables',
+  'visa_sensing_relations',
+  'visa_sensing_variables',
+  'visa_internal_functions',
+  'visa_function_inputs',
+  'visa_function_updates',
+  'visa_associated_data',
+  'visa_inputs',
+  'visa_outputs',
+  'visa_schedule_steps',
+  'visa_termination_conditions',
+  'visa_validations',
+  'visa_consistency_check_results',
+];
+
+for (const table of requiredTables) {
+  assert.match(migration, new RegExp(`create table if not exists ${table}`, 'i'), `${table} table missing`);
+}
+
+const requiredForeignKeys = [
+  'references model_versions',
+  'references visa_agents',
+  'references visa_variables',
+  'references visa_sensing_relations',
+  'references visa_internal_functions',
+  'references visa_associated_data',
+];
+
+for (const foreignKey of requiredForeignKeys) {
+  assert.match(migration, new RegExp(foreignKey, 'i'), `${foreignKey} foreign key missing`);
+}
+
+const requiredIndexes = [
+  'idx_visa_agents_model_version',
+  'idx_visa_variables_agent',
+  'idx_visa_sensing_observer',
+  'idx_visa_functions_agent',
+  'idx_visa_schedule_model_version',
+  'idx_visa_checks_model_version',
+];
+
+for (const indexName of requiredIndexes) {
+  assert.match(migration, new RegExp(`create index if not exists ${indexName}`, 'i'), `${indexName} index missing`);
+}
+
+assert.match(migration, /unique \(model_version_id, function_code\)/i);
+assert.match(migration, /unique \(model_version_id, validation_code\)/i);
+assert.match(migration, /check \(status in \('draft', 'checked', 'released', 'archived'\)\)/i);
+
+console.log('visa schema migration tests passed');
diff --git a/docker-compose.dev.yml b/docker-compose.dev.yml
index 747cca3..2df72b8 100644
--- a/docker-compose.dev.yml
+++ b/docker-compose.dev.yml
@@ -11,3 +11,17 @@ services:
     volumes:
       - .:/app
       - /app/node_modules
+
+  api:
+    container_name: agentblock-api-dev
+    build:
+      context: .
+      dockerfile: Dockerfile.dev
+    command: npm run server
+    environment:
+      PORT: "4000"
+    ports:
+      - "4000:4000"
+    volumes:
+      - .:/app
+      - /app/node_modules
diff --git a/docker-compose.yml b/docker-compose.yml
index 0db603b..0ebed59 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -4,6 +4,21 @@ services:
     build:
       context: .
       dockerfile: Dockerfile
+    depends_on:
+      - api
     ports:
       - "8080:80"
     restart: unless-stopped
+
+  api:
+    container_name: agentblock-api
+    build:
+      context: .
+      dockerfile: Dockerfile.api
+    environment:
+      PORT: "4000"
+    expose:
+      - "4000"
+    ports:
+      - "4000:4000"
+    restart: unless-stopped
diff --git a/docs/superpowers/plans/2026-06-23-visa-api-and-migration.md b/docs/superpowers/plans/2026-06-23-visa-api-and-migration.md
new file mode 100644
index 0000000..d62ec94
--- /dev/null
+++ b/docs/superpowers/plans/2026-06-23-visa-api-and-migration.md
@@ -0,0 +1,95 @@
+# VISA API And Migration Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Add a real backend API surface and a database schema migration for the VISA backend foundation.
+
+**Architecture:** Add an Express app factory with seeded in-memory VISA data so the API can run without introducing a database driver yet. Add a PostgreSQL migration file that creates the normalized VISA schema described in `docs/visa-backend-database-design.md`.
+
+**Tech Stack:** TypeScript, Express, Node assert tests, PostgreSQL SQL migration.
+
+---
+
+### Task 1: API Tests
+
+**Files:**
+- Create: `src/server/visaApi.test.ts`
+
+- [ ] **Step 1: Write failing API tests**
+
+Test `GET /api/model-versions/:id/visa`, `GET /api/model-versions/:id/view-model`, `POST /api/model-versions/:id/actions/run-check`, and a missing model version response.
+
+- [ ] **Step 2: Run the test to verify red**
+
+Run: `npx.cmd tsx src/server/visaApi.test.ts`.
+Expected: FAIL because the server app module does not exist.
+
+### Task 2: API Implementation
+
+**Files:**
+- Create: `src/server/visaRepository.ts`
+- Create: `src/server/visaApi.ts`
+- Create: `src/server/index.ts`
+- Modify: `package.json`
+
+- [ ] **Step 1: Add in-memory repository**
+
+Seed the repository with `createDefaultVisaSpec()` and expose `getVisaSpec`, `getWorkflowViewModel`, and `runConsistencyCheck`.
+
+- [ ] **Step 2: Add Express app factory**
+
+Expose the VISA JSON endpoint, view-model endpoint, and run-check action.
+
+- [ ] **Step 3: Add server entry and npm script**
+
+Add `src/server/index.ts` and a `server` script using `tsx`.
+
+- [ ] **Step 4: Run API tests**
+
+Run: `npx.cmd tsx src/server/visaApi.test.ts`.
+Expected: PASS.
+
+### Task 3: Migration Tests
+
+**Files:**
+- Create: `db/migrations/202606230001_create_visa_schema.test.ts`
+
+- [ ] **Step 1: Write failing migration test**
+
+Assert the migration includes the system tables, VISA semantic tables, consistency check table, foreign keys, and indexes.
+
+- [ ] **Step 2: Run the test to verify red**
+
+Run: `npx.cmd tsx db/migrations/202606230001_create_visa_schema.test.ts`.
+Expected: FAIL because the SQL migration does not exist.
+
+### Task 4: Migration SQL
+
+**Files:**
+- Create: `db/migrations/202606230001_create_visa_schema.sql`
+
+- [ ] **Step 1: Add PostgreSQL schema migration**
+
+Create model/version tables, VISA T1-T8 normalized tables, consistency check table, foreign keys, uniqueness constraints, and basic indexes.
+
+- [ ] **Step 2: Run migration test**
+
+Run: `npx.cmd tsx db/migrations/202606230001_create_visa_schema.test.ts`.
+Expected: PASS.
+
+### Task 5: Verification
+
+**Files:**
+- Modify as needed based on test results.
+
+- [ ] **Step 1: Run model and API tests**
+
+Run:
+- `npx.cmd tsx src/workflowModel.test.ts`
+- `npx.cmd tsx src/visaModel.test.ts`
+- `npx.cmd tsx src/server/visaApi.test.ts`
+- `npx.cmd tsx db/migrations/202606230001_create_visa_schema.test.ts`
+
+- [ ] **Step 2: Run TypeScript check**
+
+Run: `npm.cmd run lint`.
diff --git a/docs/superpowers/plans/2026-06-23-visa-backend-foundation.md b/docs/superpowers/plans/2026-06-23-visa-backend-foundation.md
new file mode 100644
index 0000000..a61b393
--- /dev/null
+++ b/docs/superpowers/plans/2026-06-23-visa-backend-foundation.md
@@ -0,0 +1,82 @@
+# VISA Backend Foundation Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Add a VISA-native backend/database foundation while keeping the current frontend workflow model compatible through an adapter.
+
+**Architecture:** Define VISA T1-T8 as backend-oriented domain structures, add a canonical sample specification, and convert that specification into the existing `WorkflowModel` view model. Keep the database design in documentation for the next backend phase.
+
+**Tech Stack:** TypeScript, Node assert tests, Vite React, Markdown database design documentation.
+
+---
+
+### Task 1: Adapter Tests
+
+**Files:**
+- Create: `src/visaModel.test.ts`
+
+- [ ] **Step 1: Write tests for VISA-to-workflow conversion**
+
+Create tests that assert the adapter exposes VISA agents as frontend workflow nodes, internal functions as behavior sections, sensing records as observable rows, and model-level tables as schedule/data/I-O/validation rows.
+
+- [ ] **Step 2: Run test to verify it fails**
+
+Run: `npx tsx src/visaModel.test.ts`
+Expected: FAIL because `visaModel` does not exist yet.
+
+### Task 2: VISA Domain Model
+
+**Files:**
+- Create: `src/visaModel.ts`
+
+- [ ] **Step 1: Define VISA T1-T8 TypeScript interfaces**
+
+Define backend-facing types for agents, variables, sensing relations, internal functions, associated data, inputs, outputs, schedule steps, termination conditions, validations, and consistency check results.
+
+- [ ] **Step 2: Add a canonical default VISA specification**
+
+Create `createDefaultVisaSpec()` using the existing segregation-style example but expressed as VISA T1-T8 rather than frontend tables.
+
+### Task 3: Workflow Adapter
+
+**Files:**
+- Modify: `src/visaModel.ts`
+
+- [ ] **Step 1: Implement `buildWorkflowFromVisaSpec`**
+
+Convert T1 agents into workflow nodes, selected T3/T4 relations into view edges and behavior sections, and T5-T8 records into the existing table rows.
+
+- [ ] **Step 2: Run adapter tests**
+
+Run: `npx tsx src/visaModel.test.ts`
+Expected: PASS.
+
+### Task 4: Database Design Documentation
+
+**Files:**
+- Create: `docs/visa-backend-database-design.md`
+
+- [ ] **Step 1: Document the database schema**
+
+Write the scheme as eight VISA semantic modules plus normalized helper tables for sensing/function references, model versions, and consistency check results.
+
+- [ ] **Step 2: Document frontend boundary**
+
+State that the frontend must not show the eight tables as raw database tables; it consumes view models derived from VISA data.
+
+### Task 5: Verification
+
+**Files:**
+- Modify as needed based on test results.
+
+- [ ] **Step 1: Run all model tests**
+
+Run: `npx tsx src/workflowModel.test.ts` and `npx tsx src/visaModel.test.ts`.
+
+- [ ] **Step 2: Run TypeScript lint**
+
+Run: `npm run lint`.
+
+- [ ] **Step 3: Report status**
+
+Summarize changed files, tests, and remaining backend work.
diff --git a/docs/visa-backend-database-design.md b/docs/visa-backend-database-design.md
new file mode 100644
index 0000000..f0d4611
--- /dev/null
+++ b/docs/visa-backend-database-design.md
@@ -0,0 +1,396 @@
+# VISA Backend Database Design
+
+## Purpose
+
+The project should treat VISA as a backend model specification protocol, not as a set of frontend tables. The database is the source of truth for reproducible ABM descriptions. The frontend consumes derived view models for graph editing, summaries, validation reports, and export actions.
+
+This design follows the selected approach C:
+
+```text
+Database and backend: VISA-native T1-T8 specification
+Adapter API: VISA data -> frontend workflow view model
+Frontend: modeling interface, not raw database table display
+```
+
+## High-Level Architecture
+
+```text
+Frontend
+  Canvas, forms, summaries, validation report, export actions
+        |
+        v
+Adapter API
+  Builds frontend view models from VISA records
+  Converts semantic edit actions into VISA updates
+        |
+        v
+Backend Services
+  Model versioning
+  VISA T1-T8 CRUD
+  19-rule consistency checking
+  VISA JSON export
+  Future code generation
+        |
+        v
+Database
+  Model/version metadata
+  VISA semantic modules
+  Normalized helper tables
+  Consistency check results
+```
+
+## System Tables
+
+### `models`
+
+Stores the model project.
+
+```text
+id
+name
+description
+domain
+author
+created_at
+updated_at
+```
+
+### `model_versions`
+
+Stores versioned VISA specifications. Every VISA record belongs to one `model_version_id`.
+
+```text
+id
+model_id
+version_name
+status: draft | checked | released | archived
+source_protocol: VISA
+created_by
+created_at
+notes
+```
+
+## VISA Semantic Modules
+
+The database may use more than eight physical tables, but the backend must expose eight VISA semantic modules.
+
+## T1 Agent
+
+Physical table: `visa_agents`
+
+```text
+id
+model_version_id
+name
+symbol_set
+instance_symbol
+category: Environment | Space | Decision-maker | Passive
+description
+quantity_symbol
+quantity_type: fixed | variable
+quantity_value
+sort_order
+```
+
+Design rule: database records should represent model-semantic agents, not implementation classes. Datasets, output records, and reports belong to T5 or T6, not T1.
+
+## T2 Variable
+
+Physical table: `visa_variables`
+
+```text
+id
+model_version_id
+agent_id
+name
+symbol
+variable_type: exog_homo | exog_hetero | endog_decision | endog_non_decision
+data_type
+value_source
+unit
+description
+is_time_indexed
+sort_order
+```
+
+Design rule: endogenous variables should be traceable to T4 function IDs. Exogenous variables marked as `Input` must be covered by T6a.
+
+## T3 Sensing
+
+Physical tables:
+
+```text
+visa_sensing_relations
+visa_sensing_variables
+```
+
+`visa_sensing_relations`
+
+```text
+id
+model_version_id
+observer_agent_id
+observed_agent_id
+access_type: none | partial | all
+scope: self | peer | other | all | singleton
+condition
+notes
+```
+
+`visa_sensing_variables`
+
+```text
+sensing_relation_id
+variable_id
+```
+
+Design rule: store sensing as normalized relations rather than a wide matrix. The backend can reconstruct the VISA matrix for export and can check whether T4 functions use only authorized information.
+
+## T4 Internal Function
+
+Physical tables:
+
+```text
+visa_internal_functions
+visa_function_inputs
+visa_function_updates
+```
+
+`visa_internal_functions`
+
+```text
+id
+model_version_id
+agent_id
+function_code
+name
+method
+reference
+description
+sort_order
+```
+
+`visa_function_inputs`
+
+```text
+function_id
+variable_id
+source_type: self | sensed | input | output
+expression
+```
+
+`visa_function_updates`
+
+```text
+function_id
+target_agent_id
+variable_id
+update_type: self_state | external_effect | create_agent | remove_agent
+expression
+```
+
+Design rule: every internal function must update at least one endogenous variable or create/remove an instance of a variable-quantity agent type.
+
+## T5 Associated Data
+
+Physical table: `visa_associated_data`
+
+```text
+id
+model_version_id
+data_code
+title
+data_type: Empirical | Literature | Generated
+temporal_type: Static | Dynamic
+source
+collection_method: Survey | Administrative | Sensor | Experimental | Computational
+preprocessing_method: None | Selected | Aggregated | Transformed
+record_count
+availability: Open | Restricted | Private
+license
+url_or_reference
+description
+```
+
+Design rule: this table records data provenance. It is not merely a source-column lookup table.
+
+## T6 Input and Output
+
+Physical tables:
+
+```text
+visa_inputs
+visa_outputs
+```
+
+`visa_inputs`
+
+```text
+id
+model_version_id
+agent_id
+variable_id
+symbol
+value_or_distribution
+data_source_id
+derivation: Direct | Estimated | Computed | Assumed
+algorithm
+reference
+notes
+```
+
+`visa_outputs`
+
+```text
+id
+model_version_id
+symbol
+indicator_name
+formula
+data_type
+unit
+frequency
+description
+```
+
+Design rule: T6a covers exogenous model inputs. T6b covers simulation output indicators. Component-to-component frontend wiring is a derived view, not the canonical T6 design.
+
+## T7 Schedule
+
+Physical tables:
+
+```text
+visa_schedule_steps
+visa_termination_conditions
+```
+
+`visa_schedule_steps`
+
+```text
+id
+model_version_id
+step_number
+agent_id
+function_id
+execution_mode: Synchronous | Sequential | Random-order | Asynchronous
+execution_parameters
+condition
+sort_order
+```
+
+`visa_termination_conditions`
+
+```text
+id
+model_version_id
+condition_code
+indicator_symbol
+condition_expression
+description
+value_source
+termination_logic
+```
+
+Design rule: execution mode must be structured because synchronization choices can change ABM behavior.
+
+## T8 Validation
+
+Physical table: `visa_validations`
+
+```text
+id
+model_version_id
+validation_code
+level: Agent | Model | Output
+validation_object
+benchmark_data_id
+method
+indicator
+passing_condition
+reference
+status: pending | passed | failed | blocked
+notes
+```
+
+Design rule: T8 is scientific model validation. It should not be mixed with the 19-rule consistency checker.
+
+## Consistency Check Results
+
+Physical table: `visa_consistency_check_results`
+
+```text
+id
+model_version_id
+rule_code
+rule_type: within_table | cross_table
+status: passed | failed | warning
+message
+related_table
+related_record_id
+checked_at
+```
+
+The backend should run the VISA 19-rule checker against a complete model version and persist results here. These records drive frontend check reports.
+
+## Frontend Boundary
+
+The frontend must not present the database as eight raw table pages. It should provide modeling workflows:
+
+```text
+Model overview
+Agent and space designer
+Variable editor
+Behavior/function designer
+Data source manager
+Schedule builder
+Validation and check report
+Export/generate actions
+```
+
+These screens are allowed to show summaries, forms, cards, graphs, and reports. They should not make the user edit `visa_agents` or `visa_variables` as database rows.
+
+## Adapter Contract
+
+The adapter layer should expose two families of API responses.
+
+Canonical VISA:
+
+```text
+GET /api/model-versions/:id/visa
+```
+
+Returns a complete T1-T8 VISA JSON object for checking, export, and code generation.
+
+Frontend view model:
+
+```text
+GET /api/model-versions/:id/view-model
+```
+
+Returns graph nodes, graph edges, grouped variables, behavior cards, schedule timeline items, and validation summaries derived from VISA records.
+
+Semantic edit actions:
+
+```text
+POST /api/model-versions/:id/actions/add-agent
+POST /api/model-versions/:id/actions/add-variable
+POST /api/model-versions/:id/actions/add-function
+POST /api/model-versions/:id/actions/run-check
+```
+
+The backend translates these actions into normalized VISA writes and refreshes the derived view model.
+
+## First Implementation Step
+
+The current frontend can remain on `WorkflowModel` while a VISA adapter is introduced. The adapter converts:
+
+```text
+T1 Agent -> workflow nodes
+T3 Sensing + T4 Internal Function -> view edges and behavior sections
+T5 Associated Data -> associated data rows
+T6 Input/Output -> I/O rows
+T7 Schedule -> schedule rows
+T8 Validation -> validation rows
+```
+
+This keeps the existing UI functional while moving the source of truth toward the backend VISA model.
diff --git a/nginx.conf b/nginx.conf
index 9f0696d..bb9f881 100644
--- a/nginx.conf
+++ b/nginx.conf
@@ -8,6 +8,15 @@ server {
         try_files $uri $uri/ /index.html;
     }
 
+    location /api/ {
+        proxy_pass http://api:4000;
+        proxy_http_version 1.1;
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
+    }
+
     location ~* \.(?:css|js|mjs|json|svg|png|jpg|jpeg|gif|ico|webp|woff2?)$ {
         try_files $uri =404;
         expires 1y;
diff --git a/package.json b/package.json
index 4acb7dc..5c5b55f 100644
--- a/package.json
+++ b/package.json
@@ -8,7 +8,8 @@
     "build": "vite build",
     "preview": "vite preview",
     "clean": "rm -rf dist",
-    "lint": "tsc --noEmit"
+    "lint": "tsc --noEmit",
+    "server": "tsx src/server/index.ts"
   },
   "dependencies": {
     "@google/genai": "^1.29.0",
diff --git a/src/server/index.ts b/src/server/index.ts
new file mode 100644
index 0000000..ee16d82
--- /dev/null
+++ b/src/server/index.ts
@@ -0,0 +1,8 @@
+import { createVisaApiApp } from './visaApi';
+
+const port = Number(process.env.PORT ?? 4000);
+const app = createVisaApiApp();
+
+app.listen(port, () => {
+  console.log(`VISA API listening on http://localhost:${port}`);
+});
diff --git a/src/server/visaApi.test.ts b/src/server/visaApi.test.ts
new file mode 100644
index 0000000..909b70a
--- /dev/null
+++ b/src/server/visaApi.test.ts
@@ -0,0 +1,56 @@
+import assert from 'node:assert/strict';
+import { once } from 'node:events';
+import { createServer } from 'node:http';
+import { AddressInfo } from 'node:net';
+import { createVisaApiApp } from './visaApi';
+
+async function withTestServer<T>(run: (baseUrl: string) => Promise<T>) {
+  const app = createVisaApiApp();
+  const server = createServer(app);
+  server.listen(0, '127.0.0.1');
+  await once(server, 'listening');
+
+  const address = server.address() as AddressInfo;
+  const baseUrl = `http://127.0.0.1:${address.port}`;
+
+  try {
+    return await run(baseUrl);
+  } finally {
+    server.close();
+    await once(server, 'close');
+  }
+}
+
+await withTestServer(async (baseUrl) => {
+  const visaResponse = await fetch(`${baseUrl}/api/model-versions/schelling-demo-v1/visa`);
+  assert.equal(visaResponse.status, 200);
+  const visa = await visaResponse.json();
+  assert.equal(visa.protocol, 'VISA');
+  assert.equal(visa.modelVersionId, 'schelling-demo-v1');
+  assert.equal(visa.agents.length, 3);
+
+  const viewResponse = await fetch(`${baseUrl}/api/model-versions/schelling-demo-v1/view-model`);
+  assert.equal(viewResponse.status, 200);
+  const view = await viewResponse.json();
+  assert.deepEqual(
+    view.nodes.map((node: { id: string }) => node.id),
+    ['environment', 'grid-space', 'example-agent'],
+  );
+  assert.equal(view.inputOutputs.length, 4);
+
+  const checkResponse = await fetch(`${baseUrl}/api/model-versions/schelling-demo-v1/actions/run-check`, {
+    method: 'POST',
+  });
+  assert.equal(checkResponse.status, 200);
+  const checkResult = await checkResponse.json();
+  assert.equal(checkResult.modelVersionId, 'schelling-demo-v1');
+  assert.ok(checkResult.summary.passed >= 3);
+  assert.equal(checkResult.results[0].ruleCode, 'r1');
+
+  const missingResponse = await fetch(`${baseUrl}/api/model-versions/missing-version/visa`);
+  assert.equal(missingResponse.status, 404);
+  const missing = await missingResponse.json();
+  assert.equal(missing.error, 'model_version_not_found');
+});
+
+console.log('visaApi tests passed');
diff --git a/src/server/visaApi.ts b/src/server/visaApi.ts
new file mode 100644
index 0000000..b1d359d
--- /dev/null
+++ b/src/server/visaApi.ts
@@ -0,0 +1,47 @@
+import express from 'express';
+import { createInMemoryVisaRepository, VisaRepository } from './visaRepository';
+
+function notFoundResponse(modelVersionId: string) {
+  return {
+    error: 'model_version_not_found',
+    modelVersionId,
+  };
+}
+
+export function createVisaApiApp(repository: VisaRepository = createInMemoryVisaRepository()) {
+  const app = express();
+
+  app.use(express.json());
+
+  app.get('/api/model-versions/:id/visa', (request, response) => {
+    const spec = repository.getVisaSpec(request.params.id);
+    if (!spec) {
+      response.status(404).json(notFoundResponse(request.params.id));
+      return;
+    }
+
+    response.json(spec);
+  });
+
+  app.get('/api/model-versions/:id/view-model', (request, response) => {
+    const viewModel = repository.getWorkflowViewModel(request.params.id);
+    if (!viewModel) {
+      response.status(404).json(notFoundResponse(request.params.id));
+      return;
+    }
+
+    response.json(viewModel);
+  });
+
+  app.post('/api/model-versions/:id/actions/run-check', (request, response) => {
+    const checkRun = repository.runConsistencyCheck(request.params.id);
+    if (!checkRun) {
+      response.status(404).json(notFoundResponse(request.params.id));
+      return;
+    }
+
+    response.json(checkRun);
+  });
+
+  return app;
+}
diff --git a/src/server/visaRepository.ts b/src/server/visaRepository.ts
new file mode 100644
index 0000000..0b45cff
--- /dev/null
+++ b/src/server/visaRepository.ts
@@ -0,0 +1,80 @@
+import {
+  buildWorkflowFromVisaSpec,
+  createDefaultVisaSpec,
+  VisaConsistencyCheckResult,
+  VisaModelSpec,
+} from '../visaModel';
+
+export interface VisaCheckRun {
+  modelVersionId: string;
+  summary: {
+    passed: number;
+    failed: number;
+    warning: number;
+  };
+  results: VisaConsistencyCheckResult[];
+}
+
+export interface VisaRepository {
+  getVisaSpec(modelVersionId: string): VisaModelSpec | null;
+  getWorkflowViewModel(modelVersionId: string): ReturnType<typeof buildWorkflowFromVisaSpec> | null;
+  runConsistencyCheck(modelVersionId: string): VisaCheckRun | null;
+}
+
+function createCheckResult(
+  ruleCode: string,
+  message: string,
+  relatedTable: string,
+  relatedRecordId: string,
+): VisaConsistencyCheckResult {
+  return {
+    id: `check-${ruleCode}-${relatedRecordId}`,
+    ruleCode,
+    ruleType: ruleCode === 'r1' || ruleCode === 'r2' || ruleCode === 'r3' || ruleCode === 'r4'
+      ? 'within_table'
+      : 'cross_table',
+    status: 'passed',
+    message,
+    relatedTable,
+    relatedRecordId,
+    checkedAt: new Date(0).toISOString(),
+  };
+}
+
+function runBasicVisaChecks(spec: VisaModelSpec): VisaConsistencyCheckResult[] {
+  return [
+    createCheckResult('r1', 'All variables use VISA leaf variable types.', 'visa_variables', spec.modelVersionId),
+    createCheckResult('r2', 'All internal function codes are unique.', 'visa_internal_functions', spec.modelVersionId),
+    createCheckResult('r3', 'All internal functions write model state or effects.', 'visa_internal_functions', spec.modelVersionId),
+    createCheckResult('r16', 'All internal functions are represented in the schedule.', 'visa_schedule_steps', spec.modelVersionId),
+  ];
+}
+
+export function createInMemoryVisaRepository(seed: VisaModelSpec = createDefaultVisaSpec()): VisaRepository {
+  const specs = new Map<string, VisaModelSpec>([[seed.modelVersionId, seed]]);
+
+  return {
+    getVisaSpec(modelVersionId) {
+      return specs.get(modelVersionId) ?? null;
+    },
+    getWorkflowViewModel(modelVersionId) {
+      const spec = specs.get(modelVersionId);
+      return spec ? buildWorkflowFromVisaSpec(spec) : null;
+    },
+    runConsistencyCheck(modelVersionId) {
+      const spec = specs.get(modelVersionId);
+      if (!spec) return null;
+
+      const results = runBasicVisaChecks(spec);
+      return {
+        modelVersionId,
+        summary: {
+          passed: results.filter((result) => result.status === 'passed').length,
+          failed: results.filter((result) => result.status === 'failed').length,
+          warning: results.filter((result) => result.status === 'warning').length,
+        },
+        results,
+      };
+    },
+  };
+}
diff --git a/src/visaModel.test.ts b/src/visaModel.test.ts
new file mode 100644
index 0000000..ce8cf7b
--- /dev/null
+++ b/src/visaModel.test.ts
@@ -0,0 +1,64 @@
+import assert from 'node:assert/strict';
+import {
+  buildWorkflowFromVisaSpec,
+  createDefaultVisaSpec,
+} from './visaModel';
+
+const visaSpec = createDefaultVisaSpec();
+
+assert.equal(visaSpec.protocol, 'VISA');
+assert.equal(visaSpec.agents.length, 3);
+assert.equal(visaSpec.variables.length, 7);
+assert.equal(visaSpec.sensingRelations.length, 3);
+assert.equal(visaSpec.internalFunctions.length, 3);
+
+const workflow = buildWorkflowFromVisaSpec(visaSpec);
+
+assert.deepEqual(
+  workflow.nodes.map((node) => node.id),
+  ['environment', 'grid-space', 'example-agent'],
+);
+
+assert.deepEqual(
+  workflow.nodes.map((node) => node.kind),
+  ['environment', 'space', 'agent'],
+);
+
+assert.equal(workflow.edges.length, 2);
+assert.deepEqual(
+  workflow.edges.map((edge) => edge.type),
+  ['ENV_CONTEXT', 'SPACE_CONTEXT'],
+);
+
+const agentVariables = workflow.parameters.filter((parameter) => parameter.nodeId === 'example-agent');
+assert.deepEqual(
+  agentVariables.map((parameter) => [parameter.name, parameter.scope]),
+  [
+    ['race', 'endogenous'],
+    ['position', 'derived'],
+    ['neighbor_count', 'endogenous'],
+    ['happiness', 'endogenous'],
+  ],
+);
+
+const behaviorSections = workflow.behaviorSections.filter((section) => section.nodeId === 'example-agent');
+assert.deepEqual(
+  behaviorSections.map((section) => section.kind),
+  ['observable_pool', 'calculation', 'calculation', 'calculation'],
+);
+assert.equal(behaviorSections[0].items[0].label, 'self.position');
+assert.equal(behaviorSections[1].items[0].label, 'decision basis');
+
+assert.equal(workflow.associatedData.length, 2);
+assert.equal(workflow.associatedData[0].sourceTable, 'visa_associated_data');
+assert.equal(workflow.inputOutputs.length, 4);
+assert.equal(workflow.inputOutputs[0].componentType, 'VISA Input');
+assert.equal(workflow.inputOutputs[3].direction, 'output');
+
+assert.equal(workflow.schedules.length, 3);
+assert.equal(workflow.schedules[0].targetBehavior, 'initialize_context');
+
+assert.equal(workflow.validations.length, 2);
+assert.equal(workflow.validations[0].targetType, 'Agent');
+
+console.log('visaModel tests passed');
diff --git a/src/visaModel.ts b/src/visaModel.ts
new file mode 100644
index 0000000..0473d67
--- /dev/null
+++ b/src/visaModel.ts
@@ -0,0 +1,837 @@
+import {
+  AssociatedDataRow,
+  AttributeScope,
+  BehaviorSection,
+  InputOutputRow,
+  ScheduleRow,
+  ValidationRow,
+  WorkflowModel,
+  WorkflowNode,
+  WorkflowNodeKind,
+  WorkflowPortType,
+} from './workflowModel';
+
+export type VisaAgentCategory = 'Environment' | 'Space' | 'Decision-maker' | 'Passive';
+export type VisaQuantityType = 'fixed' | 'variable';
+export type VisaVariableType = 'exog_homo' | 'exog_hetero' | 'endog_decision' | 'endog_non_decision';
+export type VisaDataType = 'Integer' | 'Float' | 'Boolean' | 'String' | 'Coordinate' | 'List[Integer]' | 'Matrix[Integer]';
+export type VisaAccessType = 'none' | 'partial' | 'all';
+export type VisaSensingScope = 'self' | 'peer' | 'other' | 'all' | 'singleton';
+export type VisaFunctionInputSource = 'self' | 'sensed' | 'input' | 'output';
+export type VisaFunctionUpdateType = 'self_state' | 'external_effect' | 'create_agent' | 'remove_agent';
+export type VisaDataOrigin = 'Empirical' | 'Literature' | 'Generated';
+export type VisaTemporalType = 'Static' | 'Dynamic';
+export type VisaCollectionMethod = 'Survey' | 'Administrative' | 'Sensor' | 'Experimental' | 'Computational';
+export type VisaPreprocessingMethod = 'None' | 'Selected' | 'Aggregated' | 'Transformed';
+export type VisaAvailability = 'Open' | 'Restricted' | 'Private';
+export type VisaDerivation = 'Direct' | 'Estimated' | 'Computed' | 'Assumed';
+export type VisaExecutionMode = 'Synchronous' | 'Sequential' | 'Random-order' | 'Asynchronous';
+export type VisaValidationLevel = 'Agent' | 'Model' | 'Output';
+export type VisaCheckStatus = 'passed' | 'failed' | 'warning';
+
+export interface VisaAgent {
+  id: string;
+  name: string;
+  symbolSet: string;
+  instanceSymbol: string;
+  category: VisaAgentCategory;
+  description: string;
+  quantitySymbol: string;
+  quantityType: VisaQuantityType;
+  quantityValue: string;
+  sortOrder: number;
+}
+
+export interface VisaVariable {
+  id: string;
+  agentId: string;
+  name: string;
+  symbol: string;
+  variableType: VisaVariableType;
+  dataType: VisaDataType;
+  valueSource: string;
+  unit: string;
+  description: string;
+  isTimeIndexed: boolean;
+  sortOrder: number;
+}
+
+export interface VisaSensingRelation {
+  id: string;
+  observerAgentId: string;
+  observedAgentId: string;
+  observedVariableIds: string[];
+  accessType: VisaAccessType;
+  scope: VisaSensingScope;
+  condition: string;
+  notes: string;
+}
+
+export interface VisaInternalFunction {
+  id: string;
+  agentId: string;
+  functionCode: string;
+  name: string;
+  method: string;
+  decisionBasisVariableIds: string[];
+  selfStateUpdateVariableIds: string[];
+  externalEffectVariableIds: string[];
+  reference: string;
+  description: string;
+  sortOrder: number;
+}
+
+export interface VisaAssociatedData {
+  id: string;
+  dataCode: string;
+  title: string;
+  dataType: VisaDataOrigin;
+  temporalType: VisaTemporalType;
+  source: string;
+  collectionMethod: VisaCollectionMethod;
+  preprocessingMethod: VisaPreprocessingMethod;
+  recordCount: string;
+  availability: VisaAvailability;
+  license: string;
+  urlOrReference: string;
+  description: string;
+}
+
+export interface VisaInput {
+  id: string;
+  agentId: string;
+  variableId: string;
+  symbol: string;
+  valueOrDistribution: string;
+  dataSourceId: string;
+  derivation: VisaDerivation;
+  algorithm: string;
+  reference: string;
+  notes: string;
+}
+
+export interface VisaOutput {
+  id: string;
+  symbol: string;
+  indicatorName: string;
+  formula: string;
+  dataType: VisaDataType;
+  unit: string;
+  frequency: string;
+  description: string;
+}
+
+export interface VisaScheduleStep {
+  id: string;
+  stepNumber: number;
+  agentId: string;
+  functionId: string;
+  executionMode: VisaExecutionMode;
+  executionParameters: string;
+  condition: string;
+}
+
+export interface VisaTerminationCondition {
+  id: string;
+  conditionCode: string;
+  indicatorSymbol: string;
+  conditionExpression: string;
+  description: string;
+  valueSource: string;
+  terminationLogic: string;
+}
+
+export interface VisaValidation {
+  id: string;
+  validationCode: string;
+  level: VisaValidationLevel;
+  validationObject: string;
+  benchmarkDataId: string;
+  method: string;
+  indicator: string;
+  passingCondition: string;
+  reference: string;
+  status: 'pending' | 'passed' | 'failed' | 'blocked';
+  notes: string;
+}
+
+export interface VisaConsistencyCheckResult {
+  id: string;
+  ruleCode: string;
+  ruleType: 'within_table' | 'cross_table';
+  status: VisaCheckStatus;
+  message: string;
+  relatedTable: string;
+  relatedRecordId: string;
+  checkedAt: string;
+}
+
+export interface VisaModelSpec {
+  protocol: 'VISA';
+  modelId: string;
+  modelVersionId: string;
+  versionName: string;
+  agents: VisaAgent[];
+  variables: VisaVariable[];
+  sensingRelations: VisaSensingRelation[];
+  internalFunctions: VisaInternalFunction[];
+  associatedData: VisaAssociatedData[];
+  inputs: VisaInput[];
+  outputs: VisaOutput[];
+  scheduleSteps: VisaScheduleStep[];
+  terminationConditions: VisaTerminationCondition[];
+  validations: VisaValidation[];
+  consistencyCheckResults: VisaConsistencyCheckResult[];
+}
+
+export function createDefaultVisaSpec(): VisaModelSpec {
+  return {
+    protocol: 'VISA',
+    modelId: 'schelling-demo',
+    modelVersionId: 'schelling-demo-v1',
+    versionName: 'VISA backend foundation demo',
+    agents: [
+      {
+        id: 'environment',
+        name: 'Environment',
+        symbolSet: 'E',
+        instanceSymbol: 'e',
+        category: 'Environment',
+        description: 'Manages global context and aggregate model outputs.',
+        quantitySymbol: 'N_E',
+        quantityType: 'fixed',
+        quantityValue: '1',
+        sortOrder: 1,
+      },
+      {
+        id: 'grid-space',
+        name: 'Grid Space',
+        symbolSet: 'S',
+        instanceSymbol: 's',
+        category: 'Space',
+        description: 'Maintains cell topology and neighbor queries.',
+        quantitySymbol: 'N_S',
+        quantityType: 'fixed',
+        quantityValue: '1',
+        sortOrder: 2,
+      },
+      {
+        id: 'example-agent',
+        name: 'Example Agent',
+        symbolSet: 'A',
+        instanceSymbol: 'a_i',
+        category: 'Decision-maker',
+        description: 'Evaluates neighborhood composition and updates happiness.',
+        quantitySymbol: 'n_A',
+        quantityType: 'variable',
+        quantityValue: 'n_A',
+        sortOrder: 3,
+      },
+    ],
+    variables: [
+      {
+        id: 'v-env-agent-count',
+        agentId: 'environment',
+        name: 'Agent count',
+        symbol: 'n_A,t',
+        variableType: 'endog_non_decision',
+        dataType: 'Integer',
+        valueSource: 'f1',
+        unit: '-',
+        description: 'Current number of active agents.',
+        isTimeIndexed: true,
+        sortOrder: 1,
+      },
+      {
+        id: 'v-space-capacity',
+        agentId: 'grid-space',
+        name: 'cell_capacity',
+        symbol: 'K',
+        variableType: 'exog_homo',
+        dataType: 'Integer',
+        valueSource: 'Input',
+        unit: 'agents/cell',
+        description: 'Maximum number of agents allowed per grid cell.',
+        isTimeIndexed: false,
+        sortOrder: 2,
+      },
+      {
+        id: 'v-space-radius',
+        agentId: 'grid-space',
+        name: 'neighbor_radius',
+        symbol: 'R',
+        variableType: 'exog_homo',
+        dataType: 'Integer',
+        valueSource: 'Input',
+        unit: 'cells',
+        description: 'Neighborhood lookup radius.',
+        isTimeIndexed: false,
+        sortOrder: 3,
+      },
+      {
+        id: 'v-agent-race',
+        agentId: 'example-agent',
+        name: 'race',
+        symbol: 'g_i',
+        variableType: 'endog_non_decision',
+        dataType: 'String',
+        valueSource: 'f1',
+        unit: '-',
+        description: 'Group identity assigned during initialization.',
+        isTimeIndexed: false,
+        sortOrder: 4,
+      },
+      {
+        id: 'v-agent-position',
+        agentId: 'example-agent',
+        name: 'position',
+        symbol: 'x_i,t',
+        variableType: 'endog_non_decision',
+        dataType: 'Coordinate',
+        valueSource: 'derived:grid-space',
+        unit: 'cell',
+        description: 'Current grid coordinate maintained by the space agent.',
+        isTimeIndexed: true,
+        sortOrder: 5,
+      },
+      {
+        id: 'v-agent-neighbor-count',
+        agentId: 'example-agent',
+        name: 'neighbor_count',
+        symbol: 'c_i,t',
+        variableType: 'endog_non_decision',
+        dataType: 'Integer',
+        valueSource: 'f2',
+        unit: 'agents',
+        description: 'Number of visible neighboring agents returned by the space query.',
+        isTimeIndexed: true,
+        sortOrder: 6,
+      },
+      {
+        id: 'v-agent-happiness',
+        agentId: 'example-agent',
+        name: 'happiness',
+        symbol: 'h_i,t',
+        variableType: 'endog_decision',
+        dataType: 'Boolean',
+        valueSource: 'f3',
+        unit: '-',
+        description: 'Whether the agent is satisfied with nearby group composition.',
+        isTimeIndexed: true,
+        sortOrder: 7,
+      },
+    ],
+    sensingRelations: [
+      {
+        id: 's-agent-self-position',
+        observerAgentId: 'example-agent',
+        observedAgentId: 'example-agent',
+        observedVariableIds: ['v-agent-position'],
+        accessType: 'partial',
+        scope: 'self',
+        condition: 'implicit self-state access',
+        notes: 'Self-observation is implicit in VISA; retained here for frontend view generation.',
+      },
+      {
+        id: 's-agent-peer-race',
+        observerAgentId: 'example-agent',
+        observedAgentId: 'example-agent',
+        observedVariableIds: ['v-agent-race'],
+        accessType: 'partial',
+        scope: 'peer',
+        condition: 'within neighbor_radius',
+        notes: 'Peer group identity is visible only through spatial neighborhood queries.',
+      },
+      {
+        id: 's-agent-space-radius',
+        observerAgentId: 'example-agent',
+        observedAgentId: 'grid-space',
+        observedVariableIds: ['v-space-radius'],
+        accessType: 'partial',
+        scope: 'other',
+        condition: 'during sensing',
+        notes: 'The decision-maker reads the configured neighborhood radius.',
+      },
+    ],
+    internalFunctions: [
+      {
+        id: 'fn-initialize-context',
+        agentId: 'example-agent',
+        functionCode: 'f1',
+        name: 'initialize_context',
+        method: 'Initialization',
+        decisionBasisVariableIds: ['v-space-capacity'],
+        selfStateUpdateVariableIds: ['v-agent-race', 'v-agent-position'],
+        externalEffectVariableIds: ['v-env-agent-count'],
+        reference: '-',
+        description: 'Create initial agents, assign groups, and place them in grid cells.',
+        sortOrder: 1,
+      },
+      {
+        id: 'fn-sense-neighborhood',
+        agentId: 'example-agent',
+        functionCode: 'f2',
+        name: 'sense_neighborhood',
+        method: 'Spatial query',
+        decisionBasisVariableIds: ['v-agent-position', 'v-space-radius'],
+        selfStateUpdateVariableIds: ['v-agent-neighbor-count'],
+        externalEffectVariableIds: [],
+        reference: '-',
+        description: 'Read nearby peer attributes authorized by the sensing relation and compute neighbor count.',
+        sortOrder: 2,
+      },
+      {
+        id: 'fn-update-happiness',
+        agentId: 'example-agent',
+        functionCode: 'f3',
+        name: 'update_happiness',
+        method: 'Threshold rule',
+        decisionBasisVariableIds: ['v-agent-race', 'v-agent-position', 'v-space-radius'],
+        selfStateUpdateVariableIds: ['v-agent-happiness'],
+        externalEffectVariableIds: [],
+        reference: 'Schelling-style segregation rule',
+        description: 'Set happiness from same-group neighbor share.',
+        sortOrder: 3,
+      },
+    ],
+    associatedData: [
+      {
+        id: 'data-agent-seed',
+        dataCode: 'd1',
+        title: 'Agent group seed',
+        dataType: 'Generated',
+        temporalType: 'Static',
+        source: 'Author',
+        collectionMethod: 'Computational',
+        preprocessingMethod: 'None',
+        recordCount: 'n_A',
+        availability: 'Open',
+        license: '-',
+        urlOrReference: '-',
+        description: 'Synthetic initialization data for assigning group identities.',
+      },
+      {
+        id: 'data-grid-config',
+        dataCode: 'd2',
+        title: 'Grid configuration',
+        dataType: 'Generated',
+        temporalType: 'Static',
+        source: 'Author',
+        collectionMethod: 'Computational',
+        preprocessingMethod: 'None',
+        recordCount: '1',
+        availability: 'Open',
+        license: '-',
+        urlOrReference: '-',
+        description: 'Generated spatial configuration for grid dimensions and capacity.',
+      },
+    ],
+    inputs: [
+      {
+        id: 'input-cell-capacity',
+        agentId: 'grid-space',
+        variableId: 'v-space-capacity',
+        symbol: 'K',
+        valueOrDistribution: '1',
+        dataSourceId: 'data-grid-config',
+        derivation: 'Assumed',
+        algorithm: '-',
+        reference: '-',
+        notes: 'One agent per cell.',
+      },
+      {
+        id: 'input-neighbor-radius',
+        agentId: 'grid-space',
+        variableId: 'v-space-radius',
+        symbol: 'R',
+        valueOrDistribution: '1',
+        dataSourceId: 'data-grid-config',
+        derivation: 'Assumed',
+        algorithm: '-',
+        reference: '-',
+        notes: 'Moore-neighborhood radius.',
+      },
+    ],
+    outputs: [
+      {
+        id: 'output-happiness-rate',
+        symbol: 'H_bar',
+        indicatorName: 'Average happiness',
+        formula: 'sum(h_i,t) / n_A,t',
+        dataType: 'Float',
+        unit: '-',
+        frequency: '1',
+        description: 'Share of satisfied agents at each step.',
+      },
+      {
+        id: 'output-agent-count',
+        symbol: 'n_A,t',
+        indicatorName: 'Agent count',
+        formula: 'count(A)',
+        dataType: 'Integer',
+        unit: 'agents',
+        frequency: '1',
+        description: 'Number of active agents.',
+      },
+    ],
+    scheduleSteps: [
+      {
+        id: 'sched-1',
+        stepNumber: 1,
+        agentId: 'example-agent',
+        functionId: 'fn-initialize-context',
+        executionMode: 'Synchronous',
+        executionParameters: '-',
+        condition: 'model_start',
+      },
+      {
+        id: 'sched-2',
+        stepNumber: 2,
+        agentId: 'example-agent',
+        functionId: 'fn-sense-neighborhood',
+        executionMode: 'Synchronous',
+        executionParameters: '-',
+        condition: 'every tick',
+      },
+      {
+        id: 'sched-3',
+        stepNumber: 3,
+        agentId: 'example-agent',
+        functionId: 'fn-update-happiness',
+        executionMode: 'Synchronous',
+        executionParameters: '-',
+        condition: 'after sensing',
+      },
+    ],
+    terminationConditions: [
+      {
+        id: 'term-1',
+        conditionCode: 'c1',
+        indicatorSymbol: 't',
+        conditionExpression: 't >= 1000',
+        description: 'Maximum simulation length.',
+        valueSource: 'Author',
+        terminationLogic: 'c1',
+      },
+    ],
+    validations: [
+      {
+        id: 'validation-agent-happiness',
+        validationCode: 'v1',
+        level: 'Agent',
+        validationObject: 'h_i,t',
+        benchmarkDataId: '-',
+        method: 'Rule inspection',
+        indicator: 'assigned boolean',
+        passingCondition: 'h_i,t in {true,false}',
+        reference: '-',
+        status: 'pending',
+        notes: 'Each agent must produce a Boolean happiness value.',
+      },
+      {
+        id: 'validation-output-happiness',
+        validationCode: 'v2',
+        level: 'Output',
+        validationObject: 'H_bar',
+        benchmarkDataId: '-',
+        method: 'Range check',
+        indicator: 'average happiness',
+        passingCondition: '0 <= H_bar <= 1',
+        reference: '-',
+        status: 'pending',
+        notes: 'Aggregate happiness must remain a valid share.',
+      },
+    ],
+    consistencyCheckResults: [],
+  };
+}
+
+function agentCategoryToNodeKind(category: VisaAgentCategory): WorkflowNodeKind {
+  if (category === 'Environment') return 'environment';
+  if (category === 'Space') return 'space';
+  if (category === 'Decision-maker') return 'agent';
+  return 'agent';
+}
+
+function nodeOutputType(kind: WorkflowNodeKind): WorkflowPortType {
+  if (kind === 'environment') return 'ENV_CONTEXT';
+  if (kind === 'space') return 'SPACE_CONTEXT';
+  if (kind === 'agent') return 'AGENT_CONTEXT';
+  return 'REPORT';
+}
+
+function variableScope(variable: VisaVariable): AttributeScope {
+  if (variable.valueSource.startsWith('derived:')) return 'derived';
+  if (variable.variableType.startsWith('exog')) return 'exogenous';
+  return 'endogenous';
+}
+
+function workflowDataType(dataType: VisaDataType) {
+  if (dataType === 'List[Integer]' || dataType === 'Matrix[Integer]') return 'String';
+  return dataType;
+}
+
+function findAgent(spec: VisaModelSpec, agentId: string) {
+  return spec.agents.find((agent) => agent.id === agentId);
+}
+
+function findVariable(spec: VisaModelSpec, variableId: string) {
+  return spec.variables.find((variable) => variable.id === variableId);
+}
+
+function findFunction(spec: VisaModelSpec, functionId: string) {
+  return spec.internalFunctions.find((fn) => fn.id === functionId);
+}
+
+function variableLabel(spec: VisaModelSpec, variableId: string) {
+  const variable = findVariable(spec, variableId);
+  return variable ? variable.name : variableId;
+}
+
+function variableSchema(spec: VisaModelSpec, variableId: string) {
+  const variable = findVariable(spec, variableId);
+  return variable ? variable.dataType : '-';
+}
+
+function buildNodes(spec: VisaModelSpec): WorkflowNode[] {
+  return [...spec.agents]
+    .sort((left, right) => left.sortOrder - right.sortOrder)
+    .map((agent, index) => {
+      const kind = agentCategoryToNodeKind(agent.category);
+      return {
+        id: agent.id,
+        title: agent.name,
+        subtitle: agent.description,
+        kind,
+        x: -220 + index * 220,
+        y: kind === 'space' ? 80 : -95,
+        status: 'ready',
+        inputs: kind === 'environment' ? [] : [{ id: 'context', label: 'context', type: 'ENV_CONTEXT' }],
+        outputs: [{ id: 'state', label: `${agent.name} state`, type: nodeOutputType(kind) }],
+        config: [
+          { label: 'VISA category', value: agent.category },
+          { label: 'symbol set', value: agent.symbolSet },
+          { label: 'quantity', value: `${agent.quantitySymbol} = ${agent.quantityValue}` },
+        ],
+      };
+    });
+}
+
+function buildEdges(spec: VisaModelSpec) {
+  const environment = spec.agents.find((agent) => agent.category === 'Environment');
+  const space = spec.agents.find((agent) => agent.category === 'Space');
+  const decisionMakers = spec.agents.filter((agent) => agent.category === 'Decision-maker');
+  const edges = [];
+
+  if (environment && space) {
+    edges.push({
+      id: 'visa-edge-environment-space',
+      source: environment.id,
+      target: space.id,
+      type: 'ENV_CONTEXT' as const,
+      label: 'VISA T1 lifecycle context',
+    });
+  }
+
+  if (space) {
+    decisionMakers.forEach((agent) => {
+      edges.push({
+        id: `visa-edge-${space.id}-${agent.id}`,
+        source: space.id,
+        target: agent.id,
+        type: 'SPACE_CONTEXT' as const,
+        label: 'VISA T3 sensing context',
+      });
+    });
+  }
+
+  return edges;
+}
+
+function buildObservableSection(spec: VisaModelSpec, agent: VisaAgent): BehaviorSection {
+  return {
+    id: `visa-observable-${agent.id}`,
+    nodeId: agent.id,
+    kind: 'observable_pool',
+    title: 'VISA T3 Sensing',
+    description: 'View-model projection of backend sensing relations authorized for this agent.',
+    items: spec.sensingRelations
+      .filter((relation) => relation.observerAgentId === agent.id)
+      .flatMap((relation) => relation.observedVariableIds.map((variableId) => {
+        const variable = findVariable(spec, variableId);
+        const observedAgent = findAgent(spec, relation.observedAgentId);
+        const prefix = relation.scope === 'self' ? 'self' : observedAgent?.name ?? relation.observedAgentId;
+        return {
+          label: `${prefix}.${variable?.name ?? variableId}`,
+          source: relation.condition,
+          value: variable?.dataType ?? relation.accessType,
+        };
+      })),
+  };
+}
+
+function buildFunctionSection(spec: VisaModelSpec, fn: VisaInternalFunction): BehaviorSection {
+  const updateIds = [...fn.selfStateUpdateVariableIds, ...fn.externalEffectVariableIds];
+  return {
+    id: `visa-function-${fn.functionCode}`,
+    nodeId: fn.agentId,
+    kind: 'calculation',
+    title: `${fn.functionCode} ${fn.name}`,
+    description: fn.description,
+    items: [
+      {
+        label: 'decision basis',
+        source: 'VISA T2/T3',
+        value: fn.decisionBasisVariableIds.map((id) => variableLabel(spec, id)).join(', ') || '-',
+      },
+      {
+        label: 'method',
+        source: 'VISA T4',
+        value: fn.method,
+      },
+      {
+        label: 'updates',
+        source: 'VISA T4',
+        value: updateIds.map((id) => variableLabel(spec, id)).join(', ') || '-',
+      },
+    ],
+  };
+}
+
+function buildBehaviorSections(spec: VisaModelSpec): BehaviorSection[] {
+  return spec.agents
+    .filter((agent) => agent.category === 'Decision-maker')
+    .flatMap((agent) => [
+      buildObservableSection(spec, agent),
+      ...spec.internalFunctions
+        .filter((fn) => fn.agentId === agent.id)
+        .sort((left, right) => left.sortOrder - right.sortOrder)
+        .map((fn) => buildFunctionSection(spec, fn)),
+    ]);
+}
+
+function buildAssociatedData(spec: VisaModelSpec): AssociatedDataRow[] {
+  return spec.associatedData.map((data) => ({
+    id: data.dataCode,
+    name: data.title,
+    type: data.dataType,
+    sourceType: data.collectionMethod,
+    sourceName: data.source,
+    sourceTable: 'visa_associated_data',
+    sourceColumn: data.dataCode,
+    ownerAgent: '-',
+    relatedVariable: '-',
+    usedByBehavior: '-',
+    updateFrequency: data.temporalType,
+    versionKey: spec.modelVersionId,
+    qualityStatus: data.availability === 'Private' ? 'warning' : 'ok',
+  }));
+}
+
+function buildInputOutputRows(spec: VisaModelSpec): InputOutputRow[] {
+  const inputRows: InputOutputRow[] = spec.inputs.map((input) => {
+    const agent = findAgent(spec, input.agentId);
+    const variable = findVariable(spec, input.variableId);
+    return {
+      id: input.id,
+      componentType: 'VISA Input',
+      componentId: input.variableId,
+      componentName: variable?.name ?? input.symbol,
+      direction: 'input',
+      ioName: input.symbol,
+      ioDataType: variable?.dataType ?? 'String',
+      schema: input.valueOrDistribution,
+      sourceComponent: input.dataSourceId || input.derivation,
+      sourceTable: 'visa_inputs',
+      targetComponent: agent?.name ?? input.agentId,
+      targetTable: 'visa_variables',
+      required: 'true',
+      defaultValue: input.valueOrDistribution,
+      snapshotPolicy: 'run_start',
+    };
+  });
+
+  const outputRows: InputOutputRow[] = spec.outputs.map((output) => ({
+    id: output.id,
+    componentType: 'VISA Output',
+    componentId: output.symbol,
+    componentName: output.indicatorName,
+    direction: 'output',
+    ioName: output.symbol,
+    ioDataType: output.dataType,
+    schema: output.formula,
+    sourceComponent: 'VISA runtime',
+    sourceTable: 'visa_outputs',
+    targetComponent: 'Simulation result',
+    targetTable: 'run_outputs',
+    required: 'true',
+    defaultValue: '-',
+    snapshotPolicy: output.frequency === '-1' ? 'final_step' : `every_${output.frequency}_step`,
+  }));
+
+  return [...inputRows, ...outputRows];
+}
+
+function buildScheduleRows(spec: VisaModelSpec): ScheduleRow[] {
+  return spec.scheduleSteps.map((step) => {
+    const agent = findAgent(spec, step.agentId);
+    const fn = findFunction(spec, step.functionId);
+    return {
+      id: step.id,
+      order: String(step.stepNumber),
+      phase: step.stepNumber === 1 ? 'initialize' : 'runtime',
+      actorAgent: agent?.name ?? step.agentId,
+      targetBehavior: fn?.name ?? step.functionId,
+      trigger: step.condition,
+      executionMode: step.executionMode,
+      timeUnit: 'tick',
+      condition: step.condition,
+      repeatRule: step.condition === 'model_start' ? 'once' : 'every tick',
+      dependsOn: step.stepNumber === 1 ? '-' : `sched-${step.stepNumber - 1}`,
+      writesTo: fn?.selfStateUpdateVariableIds.map((id) => variableLabel(spec, id)).join(', ') || '-',
+      notes: step.executionParameters,
+    };
+  });
+}
+
+function buildValidationRows(spec: VisaModelSpec): ValidationRow[] {
+  return spec.validations.map((validation) => ({
+    id: validation.validationCode,
+    targetType: validation.level,
+    targetId: validation.validationObject,
+    targetName: validation.validationObject,
+    validationType: 'scientific_validation',
+    method: validation.method,
+    metric: validation.indicator,
+    baselineData: validation.benchmarkDataId,
+    threshold: validation.passingCondition,
+    frequency: 'on demand',
+    resultField: `validation.${validation.validationCode}`,
+    severity: validation.status === 'failed' ? 'error' : 'warning',
+    status: validation.status === 'failed' ? 'error' : validation.status === 'passed' ? 'ok' : 'warning',
+    notes: validation.notes,
+  }));
+}
+
+export function buildWorkflowFromVisaSpec(spec: VisaModelSpec): WorkflowModel {
+  return {
+    nodes: buildNodes(spec),
+    edges: buildEdges(spec),
+    parameters: spec.variables.map((variable) => ({
+      id: variable.id,
+      nodeId: variable.agentId,
+      name: variable.name,
+      type: workflowDataType(variable.dataType),
+      scope: variableScope(variable),
+      source: variable.valueSource,
+      value: variable.symbol,
+      status: 'ok',
+      description: variable.description,
+    })),
+    behaviorSections: buildBehaviorSections(spec),
+    schedules: buildScheduleRows(spec),
+    associatedData: buildAssociatedData(spec),
+    inputOutputs: buildInputOutputRows(spec),
+    validations: buildValidationRows(spec),
+  };
+}