Added code for backend glue

backend/migrations/init.sql

@@ -0,0 +1,66 @@
+SET sql_mode = 'STRICT_ALL_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION';
+
+-- USERS
+CREATE TABLE IF NOT EXISTS users (
+  id            BIGINT PRIMARY KEY AUTO_INCREMENT,
+  email         VARCHAR(255) NOT NULL UNIQUE,
+  pass_bcrypt   VARBINARY(60) NOT NULL,
+  created_at    TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
+) ENGINE=InnoDB;
+
+-- CONVERSATIONS (one tree-ish DAG per conversation)
+CREATE TABLE IF NOT EXISTS conversations (
+  id            BIGINT PRIMARY KEY AUTO_INCREMENT,
+  owner_id      BIGINT NOT NULL,
+  title         VARCHAR(255),
+  created_at    TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  CONSTRAINT fk_conversations_owner
+    FOREIGN KEY (owner_id) REFERENCES users(id)
+      ON DELETE CASCADE
+) ENGINE=InnoDB;
+
+-- NODES = commits (plain numeric IDs). author_kind for display only.
+CREATE TABLE IF NOT EXISTS nodes (
+  id                BIGINT PRIMARY KEY AUTO_INCREMENT,
+  conversation_id   BIGINT NOT NULL,
+  author_kind       ENUM('user','assistant') NOT NULL,
+  content           MEDIUMTEXT NOT NULL,
+  created_at        TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  CONSTRAINT fk_nodes_conversation
+    FOREIGN KEY (conversation_id) REFERENCES conversations(id)
+      ON DELETE CASCADE
+) ENGINE=InnoDB;
+
+-- EDGES (parent -> child). Acyclic enforced in application.
+CREATE TABLE IF NOT EXISTS edges (
+  parent_id   BIGINT NOT NULL,
+  child_id    BIGINT NOT NULL,
+  PRIMARY KEY (parent_id, child_id),
+  CONSTRAINT fk_edges_parent
+    FOREIGN KEY (parent_id) REFERENCES nodes(id)
+      ON DELETE CASCADE,
+  CONSTRAINT fk_edges_child
+    FOREIGN KEY (child_id)  REFERENCES nodes(id)
+      ON DELETE CASCADE
+) ENGINE=InnoDB;
+
+-- BRANCHES (named pointers to any node within a conversation)
+CREATE TABLE IF NOT EXISTS branches (
+  id                BIGINT PRIMARY KEY AUTO_INCREMENT,
+  conversation_id   BIGINT NOT NULL,
+  name              VARCHAR(128) NOT NULL,
+  head_node_id      BIGINT NOT NULL,
+  created_at        TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  UNIQUE KEY uq_branch_name (conversation_id, name),
+  CONSTRAINT fk_branches_conversation
+    FOREIGN KEY (conversation_id) REFERENCES conversations(id)
+      ON DELETE CASCADE,
+  CONSTRAINT fk_branches_head
+    FOREIGN KEY (head_node_id) REFERENCES nodes(id)
+      ON DELETE CASCADE
+) ENGINE=InnoDB;
+
+CREATE INDEX idx_nodes_conv_created ON nodes (conversation_id, created_at, id);
+CREATE INDEX idx_edges_child ON edges (child_id);
+CREATE INDEX idx_edges_parent ON edges (parent_id);
+CREATE INDEX idx_branches_conv_head ON branches (conversation_id, head_node_id);