Fault-tolerant delivery system

migrations/20250901135528_create_idempotency_table.sql

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+CREATE TYPE header_pair AS (
+    name TEXT,
+    value BYTEA
+);
+
+CREATE TABLE idempotency (
+    user_id UUID NOT NULL REFERENCES users (user_id),
+    idempotency_key TEXT NOT NULL,
+    response_status_code SMALLINT NOT NULL,
+    response_headers header_pair[] NOT NULL,
+    response_body BYTEA NOT NULL,
+    created_at TIMESTAMPTZ NOT NULL,
+    PRIMARY KEY (user_id, idempotency_key)
+);

migrations/20250903130815_relax_null_checks_on_idempotency.sql

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+ALTER TABLE idempotency ALTER COLUMN response_status_code DROP NOT NULL;
+ALTER TABLE idempotency ALTER COLUMN response_body DROP NOT NULL;
+ALTER TABLE idempotency ALTER COLUMN response_headers DROP NOT NULL;

migrations/20250903151350_create_newsletter_issues_table.sql

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+CREATE TABLE newsletter_issues (
+    newsletter_issue_id UUID NOT NULL,
+    title TEXT NOT NULL,
+    text_content TEXT NOT NULL,
+    html_content TEXT NOT NULL,
+    published_at TIMESTAMPTZ NOT NULL,
+    PRIMARY KEY (newsletter_issue_id)
+);

migrations/20250903153225_create_issue_delivery_queue_table.sql

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+CREATE TABLE issue_delivery_queue (
+    newsletter_issue_id UUID NOT NULL
+        REFERENCES newsletter_issues (newsletter_issue_id),
+    subscriber_email TEXT NOT NULL,
+    PRIMARY KEY (newsletter_issue_id, subscriber_email)
+);