gHashTag · Oct 17, 2026 · Oct 17, 2026
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+// AU-02 — the Neon audit_event writer and its JSON artifact.
+// Port of gHashTag/trios-railway:crates/trios-railway-audit/src/event.rs
+// (at 8b229e9489ee, 182 lines) — Roadmap Stage 6, goal #4548, target t27c
+// gen-rust.
+//
+// The original writes one audit row into the Neon igla_race_trials table
+// and returns the inserted row id, never silently swallowing errors (R5);
+// the JSON artifact it emits to stdout lets the hourly watchdog parse the
+// result without re-querying Neon. The tokio-postgres connect, the INSERT
+// round-trip and the JSON serialization are plumbing; the decisions the
+// file makes — the Gate-2 contribution rule (this row contributes exactly
+// when bpb < target_bpb, strictly), the image_sha kept-length rule (at
+// most the first eight characters, a shorter sha kept whole), the insert
+// shape (four columns, returning the id), and the Neon env fallback order
+// (RAILWAY_POSTGRES_URL preferred, the legacy NEON_DATABASE_URL accepted)
+// — are ported here as pure functions and tested, including the
+// original's own four artifact tests. The clock is a parameter the caller
+// passes (the original stamps Utc::now inside; the port carries the ts it
+// is given), and the sha truncation is carried as the kept-length
+// decision — the slicing itself is the caller's string plumbing. The
+// audit_event transport keeps its name with an `undefined;` body that no
+// test calls (issue #9790, "Port the decision, not the plumbing").
+
+module port::trios_railway_audit_event;
+
+// ---------------------------------------------------------------------------
+// Original lines 49-67: `pub struct AuditArtifact` — the stdout artifact
+// for the hourly watchdog. Only the facts the decisions read.
+// ---------------------------------------------------------------------------
+
+pub struct AuditArtifact {
+    ts: i64,
+    seed: i32,
+    bpb: f64,
+    step: i32,
+    image_sha: str,
+    row_id: i64,
+    target_bpb: f64,
+    gate2_contribution: bool,
+}
+
+// ---------------------------------------------------------------------------
+// Original lines 69-91: `impl AuditArtifact { pub fn new(...) -> Self }`.
+// The artifact carries the writer's output; the clock is the caller's
+// (Utc::now inside the original becomes the ts parameter), and the
+// image_sha is carried as passed — the kept-length decision below is the
+// truncation rule the caller applies. The Gate-2 contribution is the
+// one computed decision: strictly below the target.
+// ---------------------------------------------------------------------------
+
+pub fn AuditArtifact_new(
+    seed: i32,
+    bpb: f64,
+    step: i32,
+    image_sha: str,
+    row_id: i64,
+    target_bpb: f64,
+    ts: i64,
+) -> AuditArtifact {
+    return AuditArtifact {
+        ts: ts,
+        seed: seed,
+        bpb: bpb,
+        step: step,
+        image_sha: image_sha,
+        row_id: row_id,
+        target_bpb: target_bpb,
+        gate2_contribution: gate2_contributes(bpb, target_bpb),
+    };
+}
+
+// Original line 88: `gate2_contribution: bpb < target_bpb` — this row
+// contributes to Gate-2 PASS exactly when the recorded BPB is strictly
+// below the target.
+pub fn gate2_contributes(bpb: f64, target_bpb: f64) -> bool {
+    if (bpb < target_bpb) {
+        return true;
+    }
+    return false;
+}
+
+// Original line 85: `image_sha[..image_sha.len().min(8)]` — at most the
+// first eight characters; a shorter sha kept whole.
+pub fn image_sha_kept_len(sha_len: usize) -> usize {
+    if (sha_len > 8) {
+        return 8;
+    }
+    return sha_len;
+}
+
+// ---------------------------------------------------------------------------
+// Original lines 109-140: `pub async fn audit_event(...) -> Result<RowId>`.
+// Connects to Neon, inserts one audit row and returns the id. Pure
+// transport — it never silently swallows errors (R5); the insert shape
+// and the env fallback order are its decisions, ported below.
+// ---------------------------------------------------------------------------
+
+pub fn audit_event(seed: i32, bpb: f64, step: i32, image_sha: str, neon_url: str) -> ?i64 {
+    return undefined; // plumbing: Neon connect + INSERT ... RETURNING id (lines 109-140)
+}
+
+// Original lines 129-131: the insert writes four columns — seed, bpb,
+// step, image_sha — and returns the id.
+pub fn insert_column_count() -> usize {
+    return 4;
+}
+
+pub fn insert_returns_id() -> bool {
+    return true;
+}
+
+// Original lines 101-103: the connection string comes from
+// RAILWAY_POSTGRES_URL, the legacy NEON_DATABASE_URL accepted as the
+// fallback (L-NEON-RENAME).
+pub fn preferred_neon_env() -> str {
+    return "RAILWAY_POSTGRES_URL";
+}
+
+pub fn legacy_neon_env() -> str {
+    return "NEON_DATABASE_URL";
+}
+
+pub fn neon_env_var_count() -> usize {
+    return 2;
+}
+
+// ---------------------------------------------------------------------------
+// Tests: every decision above asserted against values read from the
+// original's own tests (lines 146-181). No test calls the audit_event
+// transport.
+// ---------------------------------------------------------------------------
+
+test artifact_gate2_contribution_true_below_target {
+    const a = AuditArtifact_new(100, 1.83, 2000, "abc123de", 42, 1.85, 1700000000);
+    assert(a.gate2_contribution);
+    assert(a.seed == 100);
+    assert(a.row_id == 42);
+}
+
+test artifact_gate2_contribution_false_at_or_above_target {
+    const a = AuditArtifact_new(101, 2.10, 1500, "xyz", 43, 1.85, 1700000000);
+    assert(!a.gate2_contribution);
+    assert(!gate2_contributes(1.85, 1.85));
+}
+
+test image_sha_truncated_to_eight {
+    assert(image_sha_kept_len(16) == 8);
+    assert(image_sha_kept_len(9) == 8);
+    assert(image_sha_kept_len(8) == 8);
+}
+
+test image_sha_short_kept_whole {
+    assert(image_sha_kept_len(3) == 3);
+    assert(image_sha_kept_len(1) == 1);
+}
+
+test artifact_carries_the_writer_output {
+    const a = AuditArtifact_new(100, 1.83, 2000, "deadbeef", 7, 1.85, 1700000000);
+    assert(a.ts == 1700000000);
+    assert(a.bpb == 1.83);
+    assert(a.step == 2000);
+    assert(a.target_bpb == 1.85);
+    assert(a.image_sha == "deadbeef");
+}
+
+test insert_shape_and_env_fallback {
+    assert(insert_column_count() == 4);
+    assert(insert_returns_id());
+    assert(preferred_neon_env() == "RAILWAY_POSTGRES_URL");
+    assert(legacy_neon_env() == "NEON_DATABASE_URL");
+    assert(neon_env_var_count() == 2);
+}