# Audit Spine 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:** Build the append-only, immutable audit log — recording who/when/what with field-level before→after diffs — that every later write path will call to satisfy Spectrum "amendment history" (`docs/specs/2026-06-02-mvp-architecture.md` §13).

**Architecture:** Audit value types live in `domain` (pure, no I/O). The `db` crate owns the `audit_log` table (via a schema-bootstrap migration) and a transaction-capable `audit` repository (`record` / `history_for`). Immutability is enforced *in the database* by a trigger that rejects UPDATE/DELETE — infrastructure-enforced, not convention. There is **no `org_id`** column: each deployment's database *is* one organization (§3/§4). No HTTP surface yet — the spine is consumed by future write paths; an audit/history API arrives when entities do.

**Tech Stack:** Rust 2024, sqlx 0.8 (Postgres, +`time` +`json` features), `time` for timestamps, `serde_json` for the JSONB change payload. Tests use `#[sqlx::test]` (auto-applies the migration to a fresh temp DB).

---

## Prerequisites

- A PostgreSQL reachable for tests where the role may CREATE DATABASE. Bring it up with the project compose (`docker compose up -d`) and export `DATABASE_URL`. In a host where 5432 is taken, run an isolated instance, e.g.:
  `docker run -d --name cms-test-pg -e POSTGRES_USER=postgres -e POSTGRES_PASSWORD=postgres -e POSTGRES_DB=cms_dev -p 5433:5432 postgres:17` and use `DATABASE_URL=postgres://postgres:postgres@localhost:5433/cms_dev`.
- Shell env does NOT persist between commands; pass `DATABASE_URL` inline on every test/clippy command.
- Verify crate versions with the cratesio tooling before pinning new ones.

## Design decisions (review these)

1. **Schema bootstrap pre-1.0.** The schema lives as sqlx migration files under **`crates/db/migrations/`** (SQL belongs with the `db` crate). `#[sqlx::test]` auto-applies them to each temp DB; the server applies them on startup via `Db::migrate()` (`sqlx::migrate!()` embeds them at compile time). Per spec §8/D15 we are **not** maintaining forward-only migration history yet — pre-1.0 we **rewrite these files freely and recreate dev databases** (drop & re-apply) rather than writing incremental migrations. At 1.0 we freeze and switch to disciplined migrations. *(This refines the spec's "recreate, don't migrate" into a concrete mechanism — fold it back into the spec.)*
2. **Immutability in the database.** A `BEFORE UPDATE OR DELETE` trigger on `audit_log` raises an exception, so append-only is enforced by Postgres, not by "we only wrote an insert function." Matches the infrastructure-enforced philosophy (§4).
3. **No `org_id`.** Single-tenant database per deployment; the DB is the org boundary.
4. **Actor model.** `AuditActor = User(Uuid) | System`. No `User` entity exists yet, so the user is referenced by raw `Uuid`; auth (Plan 9) will introduce a `UserId` newtype that maps onto this. Auth *events* (login success/failure) are deferred to Plan 9 — this spine covers entity-change events (`created`/`updated`/`deleted`).
5. **Transaction-capable `record`.** `record` takes an `impl sqlx::PgExecutor`, so a future write path can record the audit entry **inside the same transaction** as the entity change (atomic: both commit or both roll back).
6. **`domain` gets wired in.** `db` depends on `domain` for the audit types — this lands the "everything points inward to `domain`" relationship that was aspirational after Plan 0 (issue #4).

## File Structure

```
Cargo.toml                         + time dep; sqlx +time +json features
crates/domain/
  Cargo.toml                       + serde_json, time
  src/lib.rs                       re-export audit types
  src/audit.rs                     AuditAction, AuditActor, FieldChange, NewAuditEvent, AuditEntry (+ unit tests)
crates/db/
  Cargo.toml                       + domain, uuid, time
  migrations/0001_audit_log.sql    audit_log table + immutability trigger + index
  src/lib.rs                       + pub mod audit; + Db::migrate()
  src/audit.rs                     record() + history_for() (transaction-capable)
  tests/migrate.rs                 migrate idempotent + table exists
  tests/audit.rs                   record/read-back, ordering, entity isolation
  tests/audit_immutability.rs      UPDATE/DELETE rejected; rolled-back tx leaves nothing
crates/server/
  src/lib.rs                       run() applies migrations on startup
```

---

## Task 1: `domain` — audit value types

**Files:**
- Modify: `crates/domain/Cargo.toml`
- Create: `crates/domain/src/audit.rs`
- Modify: `crates/domain/src/lib.rs`

- [ ] **Step 1: Add dependencies.** In `Cargo.toml` (workspace root) add to `[workspace.dependencies]` a `time` entry (verify latest 0.3.x):
```toml
time = { version = "0.3", features = ["serde"] }
```
Then in `crates/domain/Cargo.toml`, set `[dependencies]` to:
```toml
[dependencies]
uuid.workspace = true
serde.workspace = true
serde_json.workspace = true
time.workspace = true
```

- [ ] **Step 2: Write the failing test + types.** Create `crates/domain/src/audit.rs`:
```rust
use serde::{Deserialize, Serialize};
use serde_json::Value;
use time::OffsetDateTime;
use uuid::Uuid;

/// What kind of change an audit entry records.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "lowercase")]
pub enum AuditAction {
    Created,
    Updated,
    Deleted,
}

impl AuditAction {
    /// The database/text representation.
    pub fn as_str(&self) -> &'static str {
        match self {
            AuditAction::Created => "created",
            AuditAction::Updated => "updated",
            AuditAction::Deleted => "deleted",
        }
    }

    /// Parse from the database/text representation.
    pub fn from_db(s: &str) -> Option<Self> {
        match s {
            "created" => Some(AuditAction::Created),
            "updated" => Some(AuditAction::Updated),
            "deleted" => Some(AuditAction::Deleted),
            _ => None,
        }
    }
}

/// Who performed the change.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case", tag = "kind", content = "id")]
pub enum AuditActor {
    /// A specific user, referenced by id (a `UserId` newtype arrives with auth).
    User(Uuid),
    /// The system itself (migrations, automated processes).
    System,
}

/// One field's before/after values within a change.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct FieldChange {
    /// Field name (catalogue field key or column name).
    pub field: String,
    /// Value before the change (None when newly set).
    pub before: Option<Value>,
    /// Value after the change (None when cleared).
    pub after: Option<Value>,
}

/// An audit event to be recorded.
#[derive(Debug, Clone, PartialEq)]
pub struct NewAuditEvent {
    pub actor: AuditActor,
    pub action: AuditAction,
    pub entity_type: String,
    pub entity_id: Uuid,
    pub changes: Vec<FieldChange>,
}

/// A recorded audit entry, read back from the log.
#[derive(Debug, Clone, PartialEq)]
pub struct AuditEntry {
    /// Monotonic sequence number (insertion order).
    pub seq: i64,
    /// When it was recorded.
    pub at: OffsetDateTime,
    pub actor: AuditActor,
    pub action: AuditAction,
    pub entity_type: String,
    pub entity_id: Uuid,
    pub changes: Vec<FieldChange>,
}

#[cfg(test)]
mod tests {
    use super::*;
    use serde_json::json;

    #[test]
    fn action_round_trips_via_db_string() {
        for a in [AuditAction::Created, AuditAction::Updated, AuditAction::Deleted] {
            assert_eq!(AuditAction::from_db(a.as_str()), Some(a));
        }
        assert_eq!(AuditAction::from_db("bogus"), None);
    }

    #[test]
    fn field_change_serde_round_trip() {
        let fc = FieldChange {
            field: "name".into(),
            before: Some(json!("Vase")),
            after: Some(json!("Roman Vase")),
        };
        let v = serde_json::to_value(&fc).unwrap();
        assert_eq!(v["field"], "name");
        assert_eq!(v["before"], "Vase");
        assert_eq!(v["after"], "Roman Vase");
        let back: FieldChange = serde_json::from_value(v).unwrap();
        assert_eq!(back, fc);
    }

    #[test]
    fn actor_is_adjacently_tagged() {
        let v = serde_json::to_value(AuditActor::User(Uuid::nil())).unwrap();
        assert_eq!(v["kind"], "user");
        let v2 = serde_json::to_value(AuditActor::System).unwrap();
        assert_eq!(v2["kind"], "system");
    }
}
```
Wire into `crates/domain/src/lib.rs` (keep the existing `mod id; pub use id::OrgId;`), adding:
```rust
mod audit;

pub use audit::{AuditAction, AuditActor, AuditEntry, FieldChange, NewAuditEvent};
```

- [ ] **Step 3: Run the tests to verify they fail, then pass.** First confirm the test file compiles and fails if you stub the types out — but since the types and tests are added together here, run:
`cargo test -p domain`
Expected: PASS — the three new audit tests plus the two existing `id` tests (5 total). If it fails to compile, fix the types until green. (TDD note: the assertions encode the intended behavior — `as_str`/`from_db` inverse, serde shapes — so a regression in those will fail.)

- [ ] **Step 4: Lint + format.** `cargo +nightly fmt` and `cargo clippy -p domain --all-targets -- -D warnings` → clean.

- [ ] **Step 5: Commit.**
```bash
git add Cargo.toml crates/domain
git commit -m "feat(domain): add audit value types"
```

---

## Task 2: Schema bootstrap + `audit_log` table

**Files:**
- Modify: `Cargo.toml` (sqlx features)
- Create: `crates/db/migrations/0001_audit_log.sql`
- Modify: `crates/db/src/lib.rs`
- Modify: `crates/server/src/lib.rs`
- Test: `crates/db/tests/migrate.rs`

- [ ] **Step 1: Enable sqlx `time` + `json` features.** In root `Cargo.toml`, update the sqlx workspace dependency features to include `time` and `json`:
```toml
sqlx = { version = "0.8", features = ["runtime-tokio", "tls-rustls", "postgres", "uuid", "macros", "time", "json"] }
```

- [ ] **Step 2: Write the migration (schema + immutability trigger).** Create `crates/db/migrations/0001_audit_log.sql`:
```sql
-- Append-only audit log. One database == one organization, so there is no org_id.
CREATE TABLE audit_log (
    seq         BIGINT GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
    at          TIMESTAMPTZ NOT NULL DEFAULT now(),
    actor_kind  TEXT  NOT NULL CHECK (actor_kind IN ('user', 'system')),
    actor_id    UUID,
    action      TEXT  NOT NULL CHECK (action IN ('created', 'updated', 'deleted')),
    entity_type TEXT  NOT NULL,
    entity_id   UUID  NOT NULL,
    changes     JSONB NOT NULL DEFAULT '[]'::jsonb,
    CONSTRAINT actor_id_matches_kind CHECK (
        (actor_kind = 'user'   AND actor_id IS NOT NULL) OR
        (actor_kind = 'system' AND actor_id IS NULL)
    )
);

CREATE INDEX audit_log_entity_idx ON audit_log (entity_type, entity_id, seq);

-- Enforce append-only at the database level: reject any UPDATE or DELETE.
CREATE OR REPLACE FUNCTION audit_log_reject_mutation() RETURNS trigger AS $$
BEGIN
    RAISE EXCEPTION 'audit_log is append-only; % is not permitted', TG_OP;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER audit_log_immutable
    BEFORE UPDATE OR DELETE ON audit_log
    FOR EACH ROW EXECUTE FUNCTION audit_log_reject_mutation();
```

- [ ] **Step 3: Add `Db::migrate()`.** In `crates/db/src/lib.rs`, add this method to the `impl Db` block (after `ping`):
```rust
    /// Apply all pending schema migrations (embedded at compile time).
    ///
    /// Pre-1.0 the migration files are rewritten freely and dev databases are
    /// recreated; this is the schema-bootstrap mechanism, not forward-migration
    /// discipline.
    pub async fn migrate(&self) -> Result<(), sqlx::migrate::MigrateError> {
        sqlx::migrate!().run(&self.pool).await
    }
```
(`sqlx::migrate!()` defaults to `./migrations` relative to the `db` crate, i.e. `crates/db/migrations`.)

- [ ] **Step 4: Apply migrations on server startup.** In `crates/server/src/lib.rs`, inside `run`, immediately after the `Db::connect(...)?` line and before building `AppState`, add:
```rust
    db.migrate().await.context("running database migrations")?;
```
(`anyhow::Context` is already imported; `MigrateError` implements `std::error::Error`, so `.context(...)?` works.)

- [ ] **Step 5: Write the migrate test.** Create `crates/db/tests/migrate.rs`:
```rust
use db::Db;
use sqlx::PgPool;

#[sqlx::test]
async fn migrate_is_idempotent_and_creates_audit_log(pool: PgPool) {
    let db = Db::from_pool(pool);

    // sqlx::test already applied migrations to this temp DB; re-running must be a
    // no-op success (idempotent).
    db.migrate().await.expect("re-running migrate is idempotent");

    let regclass: Option<String> =
        sqlx::query_scalar("SELECT to_regclass('public.audit_log')::text")
            .fetch_one(db.pool())
            .await
            .unwrap();
    assert_eq!(regclass.as_deref(), Some("audit_log"));
}
```

- [ ] **Step 6: Run it.** `DATABASE_URL=<url> cargo test -p db --test migrate` → PASS (1 test).

- [ ] **Step 7: Lint + format.** `cargo +nightly fmt` and `DATABASE_URL=<url> cargo clippy -p db -p server --all-targets -- -D warnings` → clean.

- [ ] **Step 8: Commit.**
```bash
git add Cargo.toml crates/db crates/server
git commit -m "feat(db): schema bootstrap with append-only audit_log table"
```

---

## Task 3: `db::audit` repository — record & read history

**Files:**
- Modify: `crates/db/Cargo.toml`
- Create: `crates/db/src/audit.rs`
- Modify: `crates/db/src/lib.rs`
- Test: `crates/db/tests/audit.rs`

- [ ] **Step 1: Add dependencies.** In `crates/db/Cargo.toml`, set:
```toml
[dependencies]
sqlx.workspace = true
thiserror.workspace = true
domain = { path = "../domain" }
uuid.workspace = true
time.workspace = true

[dev-dependencies]
tokio.workspace = true
serde_json.workspace = true
```

- [ ] **Step 2: Write the failing test.** Create `crates/db/tests/audit.rs`:
```rust
use db::Db;
use db::audit;
use domain::{AuditAction, AuditActor, FieldChange, NewAuditEvent};
use serde_json::json;
use sqlx::PgPool;
use uuid::Uuid;

fn created(entity_id: Uuid, name: &str) -> NewAuditEvent {
    NewAuditEvent {
        actor: AuditActor::System,
        action: AuditAction::Created,
        entity_type: "object".into(),
        entity_id,
        changes: vec![FieldChange {
            field: "name".into(),
            before: None,
            after: Some(json!(name)),
        }],
    }
}

#[sqlx::test]
async fn records_and_reads_back_history_in_order(pool: PgPool) {
    let db = Db::from_pool(pool);
    let id = Uuid::new_v4();
    let user = Uuid::new_v4();

    audit::record(db.pool(), &created(id, "Vase")).await.unwrap();
    audit::record(
        db.pool(),
        &NewAuditEvent {
            actor: AuditActor::User(user),
            action: AuditAction::Updated,
            entity_type: "object".into(),
            entity_id: id,
            changes: vec![FieldChange {
                field: "name".into(),
                before: Some(json!("Vase")),
                after: Some(json!("Roman Vase")),
            }],
        },
    )
    .await
    .unwrap();

    let history = audit::history_for(db.pool(), "object", id).await.unwrap();
    assert_eq!(history.len(), 2);
    assert_eq!(history[0].action, AuditAction::Created);
    assert_eq!(history[0].actor, AuditActor::System);
    assert_eq!(history[1].action, AuditAction::Updated);
    assert_eq!(history[1].actor, AuditActor::User(user));
    assert!(history[0].seq < history[1].seq, "ordered by seq");
    assert_eq!(history[1].changes[0].field, "name");
    assert_eq!(history[1].changes[0].after, Some(json!("Roman Vase")));
}

#[sqlx::test]
async fn history_is_scoped_to_one_entity(pool: PgPool) {
    let db = Db::from_pool(pool);
    let a = Uuid::new_v4();
    let b = Uuid::new_v4();
    audit::record(db.pool(), &created(a, "A")).await.unwrap();
    audit::record(db.pool(), &created(b, "B")).await.unwrap();

    let only_a = audit::history_for(db.pool(), "object", a).await.unwrap();
    assert_eq!(only_a.len(), 1);
    assert_eq!(only_a[0].entity_id, a);
}
```

- [ ] **Step 3: Run it to verify it fails.** `DATABASE_URL=<url> cargo test -p db --test audit` → FAIL (`db::audit` / `record` / `history_for` don't exist).

- [ ] **Step 4: Implement the repository.** Create `crates/db/src/audit.rs`:
```rust
//! Append-only audit log access.

use domain::{AuditActor, AuditEntry, FieldChange, NewAuditEvent};
use sqlx::Row;
use uuid::Uuid;

/// Append an audit event. Accepts any executor, so callers can record the event
/// inside the same transaction as the change it describes.
pub async fn record<'e, E>(executor: E, event: &NewAuditEvent) -> Result<(), sqlx::Error>
where
    E: sqlx::PgExecutor<'e>,
{
    let (actor_kind, actor_id) = match event.actor {
        AuditActor::User(id) => ("user", Some(id)),
        AuditActor::System => ("system", None),
    };

    sqlx::query(
        "INSERT INTO audit_log \
         (actor_kind, actor_id, action, entity_type, entity_id, changes) \
         VALUES ($1, $2, $3, $4, $5, $6)",
    )
    .bind(actor_kind)
    .bind(actor_id)
    .bind(event.action.as_str())
    .bind(&event.entity_type)
    .bind(event.entity_id)
    .bind(sqlx::types::Json(&event.changes))
    .execute(executor)
    .await?;

    Ok(())
}

/// Read the full history for one entity, oldest first.
pub async fn history_for<'e, E>(
    executor: E,
    entity_type: &str,
    entity_id: Uuid,
) -> Result<Vec<AuditEntry>, sqlx::Error>
where
    E: sqlx::PgExecutor<'e>,
{
    let rows = sqlx::query(
        "SELECT seq, at, actor_kind, actor_id, action, entity_type, entity_id, changes \
         FROM audit_log \
         WHERE entity_type = $1 AND entity_id = $2 \
         ORDER BY seq",
    )
    .bind(entity_type)
    .bind(entity_id)
    .fetch_all(executor)
    .await?;

    rows.into_iter().map(map_row).collect()
}

fn map_row(row: sqlx::postgres::PgRow) -> Result<AuditEntry, sqlx::Error> {
    let seq: i64 = row.try_get("seq")?;
    let at: time::OffsetDateTime = row.try_get("at")?;
    let actor_kind: String = row.try_get("actor_kind")?;
    let actor_id: Option<Uuid> = row.try_get("actor_id")?;
    let action: String = row.try_get("action")?;
    let entity_type: String = row.try_get("entity_type")?;
    let entity_id: Uuid = row.try_get("entity_id")?;
    let changes: sqlx::types::Json<Vec<FieldChange>> = row.try_get("changes")?;

    let actor = match actor_kind.as_str() {
        "user" => AuditActor::User(
            actor_id.ok_or_else(|| sqlx::Error::Decode("user actor missing actor_id".into()))?,
        ),
        "system" => AuditActor::System,
        other => {
            return Err(sqlx::Error::Decode(
                format!("unknown actor_kind: {other}").into(),
            ));
        }
    };

    let action = domain::AuditAction::from_db(&action)
        .ok_or_else(|| sqlx::Error::Decode(format!("unknown action: {action}").into()))?;

    Ok(AuditEntry {
        seq,
        at,
        actor,
        action,
        entity_type,
        entity_id,
        changes: changes.0,
    })
}
```
Add to `crates/db/src/lib.rs` (top-level, after the module doc comment):
```rust
pub mod audit;
```

- [ ] **Step 5: Run it to verify it passes.** `DATABASE_URL=<url> cargo test -p db --test audit` → PASS (2 tests).

- [ ] **Step 6: Lint + format.** `cargo +nightly fmt` and `DATABASE_URL=<url> cargo clippy -p db --all-targets -- -D warnings` → clean.

- [ ] **Step 7: Commit.**
```bash
git add crates/db
git commit -m "feat(db): add append-only audit repository (record, history_for)"
```

---

## Task 4: Immutability & transactional guarantees

**Files:**
- Test: `crates/db/tests/audit_immutability.rs`

- [ ] **Step 1: Write the tests.** Create `crates/db/tests/audit_immutability.rs`:
```rust
use db::Db;
use db::audit;
use domain::{AuditAction, AuditActor, NewAuditEvent};
use sqlx::PgPool;
use uuid::Uuid;

fn sample() -> NewAuditEvent {
    NewAuditEvent {
        actor: AuditActor::System,
        action: AuditAction::Created,
        entity_type: "object".into(),
        entity_id: Uuid::new_v4(),
        changes: vec![],
    }
}

async fn count(pool: &PgPool) -> i64 {
    sqlx::query_scalar("SELECT count(*) FROM audit_log")
        .fetch_one(pool)
        .await
        .unwrap()
}

#[sqlx::test]
async fn update_and_delete_are_rejected(pool: PgPool) {
    let db = Db::from_pool(pool);
    audit::record(db.pool(), &sample()).await.unwrap();

    let updated = sqlx::query("UPDATE audit_log SET action = 'deleted'")
        .execute(db.pool())
        .await;
    assert!(updated.is_err(), "UPDATE must be rejected by the trigger");

    let deleted = sqlx::query("DELETE FROM audit_log").execute(db.pool()).await;
    assert!(deleted.is_err(), "DELETE must be rejected by the trigger");

    assert_eq!(count(db.pool()).await, 1, "the row is still there");
}

#[sqlx::test]
async fn record_rolls_back_with_caller_transaction(pool: PgPool) {
    let db = Db::from_pool(pool);

    let mut tx = db.pool().begin().await.unwrap();
    audit::record(&mut *tx, &sample()).await.unwrap();
    tx.rollback().await.unwrap();

    assert_eq!(
        count(db.pool()).await,
        0,
        "a rolled-back audit record must not persist"
    );
}

#[sqlx::test]
async fn record_commits_with_caller_transaction(pool: PgPool) {
    let db = Db::from_pool(pool);

    let mut tx = db.pool().begin().await.unwrap();
    audit::record(&mut *tx, &sample()).await.unwrap();
    tx.commit().await.unwrap();

    assert_eq!(count(db.pool()).await, 1, "a committed audit record persists");
}
```

- [ ] **Step 2: Run it.** `DATABASE_URL=<url> cargo test -p db --test audit_immutability` → PASS (3 tests). These exercise the DB-level trigger and the `impl PgExecutor` transaction seam (`&mut *tx`).

- [ ] **Step 3: Full workspace check.** Run:
```bash
cargo +nightly fmt --check
DATABASE_URL=<url> cargo clippy --workspace --all-targets -- -D warnings
DATABASE_URL=<url> cargo test --workspace
```
Expected: all green — domain (5), db (migrate 1 + audit 2 + immutability 3), api (3), server (config 2 + serve 1).

- [ ] **Step 4: Commit.**
```bash
git add crates/db
git commit -m "test(db): enforce audit_log immutability and transactional atomicity"
```

---

## Self-Review (completed)

**Spec coverage (§13 Audit & amendment history):**
- Append-only, immutable → Task 2 trigger + Task 4 negative tests. ✓
- who/when/what with field-level before→after diffs → `AuditActor`, `at`, `AuditAction`, `entity_type`/`entity_id`, `Vec<FieldChange>` (Tasks 1–3). ✓
- Stored in the org DB; no `org_id` (single-tenant) → Task 2 schema. ✓
- Doubles as amendment history (history per entity) → `history_for` (Task 3). ✓
- Covers entity-change events; **auth events deferred to Plan 9** (documented in Design decisions). ✓ (intentional scope boundary, not a gap)
- Transaction-capable so future write paths record atomically → `impl PgExecutor` + Task 4 rollback/commit tests. ✓
- Wires `domain` into `db` (issue #4) → Task 3 dep. ✓

**Placeholder scan:** no TODO/TBD; every step has concrete SQL/Rust/commands. The `<url>` token in commands is the documented `DATABASE_URL` value, not a code placeholder.

**Type consistency:** `NewAuditEvent` / `AuditEntry` / `AuditActor` / `AuditAction` / `FieldChange` field names and signatures are identical across `domain` (Task 1), the `db` repository (Task 3), and all tests (Tasks 3–4). `record(impl PgExecutor, &NewAuditEvent)` and `history_for(impl PgExecutor, &str, Uuid)` signatures match every call site. `Db::migrate()` is defined in Task 2 and used in Task 2's test and `server::run`.

## Notes for follow-on plans

- An audit/amendment-history **HTTP endpoint** lands when entities exist and the admin UI needs it (Plan 8/10), reusing `history_for`.
- **Auth events** (login success/failure) attach to this spine in Plan 9, likely via an `actor`/`action` extension or a sibling table — decide then.
- When the first entity write path lands (Plan 3/4), record its audit entry **inside the entity's transaction** using `record(&mut *tx, …)`.
